Gondwana Research 41 (2017) 9–28

Contents lists available at ScienceDirect

Gondwana Research

j ourna l homepage: www.e lsev ie r .com/ locate /gr

Post-collisional potassic magmatism in the eastern Lhasa terrane, SouthTibet: Products of partial melting of mélanges in a continentalsubduction channel

Lihong Zhang a,b, Zhengfu Guo a,⁎, Maoliang Zhang a,b, Zhihui Cheng a,b, Yutao Sun a,b

a Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, Chinab University of Chinese Academy of Sciences, Beijing 100049, China

⁎ Corresponding author at: No. 19, BeituchengWestern100029, China. Tel.: +86 10 82998393; fax: +86 10 6201

E-mail address: zfguo@mail.iggcas.ac.cn (Z. Guo).

http://dx.doi.org/10.1016/j.gr.2015.11.0071342-937X/© 2015 International Association for Gondwa

a b s t r a c t

a r t i c l e i n f o

Article history:Received 29 May 2015Received in revised form 18 October 2015Accepted 3 November 2015Available online 23 December 2015

Post-collisional, potassic magmatic rocks widely distributed in the eastern Lhasa terrane provide significantinformation for comprehensive understanding of geodynamic processes of northward subduction of the Indianlithosphere and uplift of the Tibetan Plateau. A combined dataset of whole-rock major and trace elements,Sr–Nd–Pb isotopes, and in situ zircon U–Pb dating and Hf–O isotopic analyses are presented for the Yangyingpotassic volcanic rocks (YPVR) in the eastern part of the Lhasa terrane, South Tibet. These volcanic rocks consistof trachytes, which are characterized by high K2O (5.46–9.30 wt.%), SiO2 (61.34–68.62 wt.%) and Al2O3 (15.06–17.36 wt.%), and relatively low MgO (0.47–2.80 wt.%) and FeOt (1.70–4.90 wt.%). Chondrite-normalized rareearth elements (REE) patterns display clearly negative Eu anomalies. Primitive mantle-normalized incompatibletrace elements diagrams exhibit strong enrichment in large ion lithophile elements (LILE) relative to high fieldstrength elements (HFSE) and display significantly negative Nb–Ta–Ti anomalies. Initial isotopic compositionsindicate relatively radiogenic Sr [(87Sr/86Sr)i = 0.711978–0.712090)] and unradiogenic Nd [(143Nd/144Nd)i =0.512121–0.512148]. Combined with their Pb isotopic compositions [(206Pb/204Pb)i = 18.615–18.774,(207Pb/204Pb)i = 15.708–15.793, (208Pb/204Pb)i = 39.274–39.355)], these data are consistent with the involve-ment of component from subducted continental crustal sediment in their source region. The whole-rock Sr–Nd–Pb isotopic compositions exhibit linear trends betweenenrichedmantle-derivedmafic ultrapotassicmagmasand relatively depleted crustal contaminants from the Lhasa terrane. The enrichment of the upper mantle belowSouth Tibet is considered to result from the addition of components derived from subducted Indian continentalcrust to depleted MORB-source mantle during northward underthrusting of the Indian continental lithospherebeneath the Lhasa terrane since India–Asia collision at ~55 Ma. Secondary Ion Mass Spectrometry (SIMS) U–Pbzircon analyses yield the eruptive ages of 10.61 ± 0.10 Ma and 10.70 ± 0.18 Ma (weighted mean ages). ZirconHf isotope compositions [ƐHf(t) = −4.79 to −0.17], combined with zircon O isotope ratios (5.51–7.22‰),imply an addition of crustal material in their petrogenesis. Clinopyroxene-liquid thermobarometer reveals pres-sure (2.5–4.1 kbar) and temperature (1029.4–1082.9 °C) of clinopyroxene crystallization, suggesting that depthof the magma chamber was 11.6–16.4 km. Energy-constrained assimilation and fractional crystallization (EC–AFC) model calculation indicates depth of assimilation and fractional crystallization in the region of 14.40–18.75 km underneath the Lhasa terrane, which is in consistent with depth of the magma chamber as suggestedby clinopyroxene-liquid thermobarometer. Based on the whole-rock major and trace elements and Sr–Nd–Pbisotope compositions, combined with EC–AFC modeling simulations and zircon Hf–O isotope data, we proposethat the YPVR resulted from assimilation and fractional crystallization (AFC) process of the K-richmafic primitivemagmas, which were caused by partial melting of the Indian continental subduction-induced mélange rocks.

© 2015 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Keywords:Post-collisional potassic magmatismZircon U–Pb datingAssimilation and fractional crystallization (AFC)Indian mélangesSouth Tibet

1. Introduction

During India–Asia collision and subsequent northward subductionof the Indian continental lithosphere, multi-stage magmatism andcrust–mantle interaction took place in the Lhasa terrane, South Tibet(e.g., Miller et al., 1999; Ding et al., 2003, 2006; Mo et al., 2003, 2006a,

Road, ChaoyangDistrict, Beijing0846.

na Research. Published by Elsevier B.

2006b; Zhao et al., 2006, 2009; Gao et al., 2007a, 2007b, 2009, 2010;Guo et al., 2007, 2013, 2015; Wang et al., 2008, 2014, 2015; J.L. Chenet al., 2010; Chen et al., 2011, 2012; Guo and Wilson, 2012; Hou et al.,2013; Zhu et al., 2013; Jiang et al., 2014; Ma et al., 2014; Liu et al.,2015). The magmatism in continental collision settings recordsrecycling of subducted crustal components at continental subductionzone and uplift process of the Tibetan Plateau (e.g., Chung et al., 2003,2005, 2009; Ding et al., 2003; Hou et al., 2006, 2013; Guo et al., 2007,2013, 2015; Zhao et al., 2009; Guo and Wilson, 2012). Post-collisional,K-rich (including ultrapotassic and potassic) magmatic rocks (25–

V. All rights reserved.

10 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

8 Ma) in the Lhasa terrane are thought to link to partial melting eventsassociated with deep geodynamic processes in the Himalaya–Tibetcontinent orogenic zone, such as northward subduction of the Indiancontinental lithosphere (Ding et al., 2003; Hou et al., 2006; Guo et al.,2013, 2015) and convective thinning of over-thickened Tibetan conti-nental lithosphere (e.g., Turner et al., 1996; Miller et al., 1999; Chunget al., 2003, 2005, 2009; Sun et al., 2007; Zhao et al., 2009; C.Z. Liuet al., 2011, 2014; D. Liu et al., 2014; Liu et al., 2015; Tian et al., 2012;Wang et al., 2014) and break-off of a northward subducted slab of theIndian continental lithosphere (e.g., Mahéo et al., 2002; Replumazet al., 2010, 2013, 2014). Intense controversies still remain in spite ofmany previous studies, which proposed that ultrapotassic and potassicmagmas are derived from: (1) asthenospheric mantle enriched bymaterials from subducted Indian continental lithosphere (e.g., Arnaudet al., 1992; Guo et al., 2013, 2015); and (2) enriched metasomatizedlithospheric mantle and/or mafic lower crust (e.g., Turner et al., 1996;

Fig. 1. (a) Simplified map showing distribution of the Cenozoic magmatic rocks in the Lhasa tYangying potassic volcanic field (modified from Li et al., 1992; Zhou et al., 2010).

Miller et al., 1999; Ding et al., 2003; Nomade et al., 2004; Zhao et al.,2009; J.L. Chen et al., 2010; Chen et al., 2012; Zhou et al., 2010; C.Z. Liuet al., 2011, 2014; D. Liu et al., 2011, 2014; Liu et al., 2015; Wang et al.,2014). Because these previous studies simply presented whole-rock major element, trace element and Sr–Nd–Pb isotopic data of thepotassic rocks in South Tibet, lack of detailed zircon Hf–O isotopic dataand comprehensive mineralogical and petrological data has precludedfurther understanding of the origin and evolution of these potassicmagmas.

We focus on the Yangying potassic volcanic rocks (YPVR) (Fig. 1),which have been thought to exhibit many typical outcrops ofthe post-collisional potassium-rich magmatic rocks in South Tibet (Liet al., 1992). In this study, we report new systematic dataset of whole-rock major, trace elements and Sr–Nd–Pb isotopes, in situ zircon U–Pbage and Hf–O isotopes of the YPVR, South Tibet. These data, combinedwith previously published geochemical and geophysical data, allow us

errane, South Tibet (modified from Guo et al., 2015). (b) Simplified geological map of the

Table 1Phenocryst and groundmass mineral assemblages of the Yangying potassic volcanic rocks.

Sample no. Rock type Phenocrysts Groundmass

YY-01 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-02 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-03 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-04 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-05 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-06 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-07 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-08 Trachyte Sani + Pl + Phl Sani + Pl + Ap + Fe–TiYY-09 Trachyte Sani + Phl Sani + Pl + ApYY-10 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-11 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-12 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-13 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–TiYY-14 Trachyte Cpx + Sani + Pl + Phl Cpx + Sani + Pl + Ap + Fe–Ti

Abbreviations are as follows: Ap, apatite; Cpx, clinopyroxene; Fe–Ti, Fe–Ti oxides; Phl,phlogopite; Pl, plagioclase; Sani, sanidine.

11L. Zhang et al. / Gondwana Research 41 (2017) 9–28

to develop a more robust petrogenetic model for the YPVR in SouthTibet.

2. Geological setting

Tibetan Plateau is composed of the Kunlun-Qaidam, Songpan-Ganzi,Qiangtang and Lhasa terranes fromnorth to south,whichwere integratedtogether during closure of the Tethys Oceans since the Paleozoic times(Yin and Harrison, 2000). The Lhasa and Qiangtang terranes areseparated by the Jurassic-Cretaceous Bangong-Nujiang suture (BNS),whereas the Indus-Tsangpo suture (ITS) marks the boundary betweenthe Lhasa terrane and the Himalayas (Fig. 1a; Kapp et al., 2003, 2007).Precambrian basement has been only discovered in the central andnorthern Lhasa terrane, as represented by metamorphic rocks to thewest of the Nam Lake (~750 Ma; Hu et al., 2005) and the Amdo gneiss(852Ma; Guynn et al., 2006). Paleozoic to Mesozoic sedimentary strataand Jurassic to Cretaceous volcanic rocks comprise sedimentary cover ofthe Lhasa terrane (Zhu et al., 2008).

The onset of Indian and Asian continent collision was still a contro-versial issue; estimates vary from as early as the late Cretaceous (70–65 Ma; Gnos et al., 1997; Yin and Harrison, 2000; Mo et al., 2007; Xiaet al., 2011) to the Paleocene (65–55 Ma, e.g., Ding et al., 2005; Huet al., 2012; X. Hu et al., 2015; Chung et al., 2009; J. Chen et al., 2010;Yi et al., 2011; Jiang et al., 2014; F.Y. Wu et al., 2014) or even later(55–50 Ma, e.g., Patriat and Achache, 1984; Tapponnier et al., 2001;Royden et al., 2008; Najman et al., 2010; Aitchison et al., 2011;Shellnutt et al., 2014). The India–Asia continent collision has led to exten-sivemagmatism in the Lhasa terrane, generatingwidespreadCenozoic ig-neous rocks (Fig. 1a) which are mainly classified as Gangdese batholith(e.g., Jiang et al., 1999; Dong et al., 2005, 2008; Mo et al., 2005; Wenet al., 2008; Zhu et al., 2008, 2009, 2011, 2013; Ji et al., 2009a, 2009b,2012, 2014), Linzizong volcanic rocks (e.g., Mo et al., 2005, 2006a,2006b; Lee et al., 2007, 2009, 2012), adakitic rocks (e.g., Chung et al.,2003, 2009; Hou et al., 2004, 2013; Gao et al., 2007a, 2010; Guo et al.,2007; King et al., 2007; Xu et al., 2010; Chen et al., 2011; Guan et al.,2012; Hébert et al., 2014; Jiang et al., 2014; Ma et al., 2014; L.Y. Zhanget al., 2014; Zeng et al., 2017; S. Wu et al., 2014; Y. Hu et al., 2015) andK-rich magmatic rocks (e.g., Miller et al., 1999; Williams et al., 2001,2004; Ding et al., 2003, 2006; Nomade et al., 2004; Zhao et al., 2009; J.L.Chen et al., 2010; Chen et al., 2012; Zhou et al., 2010; Guo et al., 2013,2015; C.Z. Liu et al., 2011, 2014; D. Liu et al., 2011, 2014; Liu et al., 2013,2015; Wang et al., 2008, 2014; Huang et al., 2015). Ultrapotassic and po-tassic magmatic rocks in South Tibet are found as lavas, plugs and dikeswith small volumes, which mainly crop out in near NS trending rifts tothe west of longitude 87°E while potassic lavas have only been discov-ered in two volcanic fields (Majiang and Yangying) to the east of longi-tude 87°E (Fig. 1a).

Yangying volcanic field is located at central segment of the NE–SWtrending Yadong-Gulu rift, about 80 km west of Lhasa (Fig. 1b). YPVRmainly consist of trachytes which cover an area less than 10 km2.These lavas are controlled by NS trending high-angle normal faultsand crop out as the lava flow and domewhich are cut by PujiemuValley,Nangzeng Valley and Qialagai Valley from south to north (Fig. 1b; Liet al., 1992, 1994). High-temperature hydrothermal activities (e.g., hotsprings, soil microseepage) are pervasive around the Yangying volcanicfield (Li et al., 1994). Volatiles and volcanic gases from high-temperature hydrothermal systems in the Yangying volcanic fieldmight be related with shallow magmatic heat source, similar to thosefrom Yangbajing geothermal field ~30 km north of Yangying (Zhaoet al., 1993; Brown et al., 1996; Nelson et al., 1996; Liao and Zhao,1999;Wei et al., 2001). Recent studies show that total soilmicroseepageCO2 flux (~4.43 × 104 t a−1; Guo et al., 2014b) of the Yangying volcanicfield is comparable to that (~8.59 × 104 t a−1; L.H. Zhang et al., 2014) ofthe Yangbajing geothermal field with well-developed geothermal ener-gy, suggesting considerable potentiality for geothermal power genera-tion in the Yangying volcanic field, South Tibet.

3. Petrography

Fourteen samples were collected for analyses from the Yangyingvolcanic field (Fig. 1b). The analyzed samples have porphyritic texturesand most phenocrysts with size ranging from 1 to 5 mm. Phenocrystminerals consist of clinopyroxene, alkali feldspar, plagioclase and phlog-opite scattered in the groundmass composed of feldspar, clinopyroxene,apatite and Fe–Ti oxides (Table 1 and Fig. 2). The clinopyroxene crystalsare mostly euhedral (Fig. 2a). Almost all the plagioclase phenocrystshave reaction rims of alkali feldspars (Fig. 2). Phlogopite phenocrystsare characterized by altered and oxidized dark rims of Fe–Ti oxides(Fig. 2e and f).

4. Analytical methods

4.1. Whole-rock elemental and Sr–Nd–Pb isotopic analyses

All samples from Yangying potassic volcanic field (Fig. 1b) wereanalyzed for their major and trace elements and Sr–Nd–Pb isotopiccompositions at Beijing Research Institute of Uranium Geology (BRIUG).FeO concentrations were obtained by KMnO4 titration. Sample powdersfor trace elements analyses were digested with mixed HNO3 + HF acidin steel-bomb coated Teflon beakers to assure the complete dissolutionof refractory minerals. The trace elements were measured using aFinnigan Element II ICP–MS at the BRIUG following the proceduresdescribed by Li (1997). The analytical precisions for trace elementswere between 5% and 10% depending on the concentration level ofa specific element. The major and trace element analytical data arepresented in Table S1 in the Supplementary data.

Sr–Nd–Pb isotopes were determined by an Isoprobe-T thermal ioni-zationmass spectrometry (TIMS) at the BRIUG following the proceduresof GB/T17672-1999. Powder samples were mixed for isotope dilutionand dissolved using HF + HNO3 + HClO4 in sealed Teflon capsules ona hot plate for 24 h. After the separation of the Rb, Sr and light REE ina cation-exchange column, the Sm and Nd were further purified usinga cation-exchange column, conditioned and eluted with dilute HCl.The isotopic mass fractions were normalized to 143Nd/144Nd = 0.7219and 87Sr/86Sr = 0.1194, respectively. Repeated analyses of the86Sr/88Sr ratio of the standard NBS987 and 146Nd/144Nd ratio of thestandard SHINESTU gave 0.710250 ± 0.000007 (2σ) and 0.512118 ±0.000003 (2σ), respectively. Total chemical blanks were b200 pgfor strontium and b50 pg for neodymium (X. Zhao et al., 2014). Theanalytical precision for Rb/Sr and Sm/Nd ratios were below 1%. For Pbisotope measurements, Pb was separated from the silicate matrix andpurified using AG1 × 8 anionic ion-exchange columns with dilute HBras eluant. During the period of analyses repeat analyses of the interna-tional standard NBS981 yielded 204Pb/206Pb = 0.0591107 ± 0.000002;

Fig. 2. Representativemicrophotographs of the YPVR (cross-polarized). (a) Euhedral clinopyroxene phenocrysts. (b) Euhedral plagioclase and sanidine phenocrysts. (c) Sanidine showingthin reaction rim of alkali feldspar. (d) Plagioclase showing thin rim of alkali feldspar. (e) Altered phlogopite phenocrysts. (f) Corroded sanidine and phlogopite phenocrysts. Abbreviationsare as follows: Ap, apatite; Cpx, clinopyroxene; Phl, phlogopite; Pl, plagioclase; Sani, sanidine.

12 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

207Pb/206Pb = 0.914338 ± 0.00007; 208Pb/206Pb = 2.164940 ±0.000015. Pb isotope fractionations were corrected using correctionfactors from the certified values of the international standard NBS981.The analytical precision for Pb isotopic ratios was below 0.05%. The Sr,Nd and Pb isotopic data are presented in Table S2 in the Supplementarydata.

4.2. Zircon U–Pb dating

Zircon U–Pb dating, together with pre-analytical prepared work,was achieved at the Institute of Geology and Geophysics, ChineseAcademy of Sciences (IGGCAS), Beijing. The pre-analytical preparationscontain the following two parts: (1) zircon grains were separated usingheavy-liquid and magnetic techniques and then they were mounted inepoxy resin and polished for analyses; (2) transmitted, reflected lightimages and cathodoluminescence (CL) images of the zircon wereobtained. Cathodoluminescence images were used to check the internalstructures of individual zircon grains and to select positions for analyses(Fig. 6a and b).

U and Pb isotopes were measured using Cameca IMS-1280 SIMS.The O2− primary ion beamwas accelerated at ~13 kV, with an intensityof ca. 10 nA and the ellipsoidal spot is about 20 μm × 30 μm. Positivesecondary ions use a 60 eV energy window and a mass resolution of~5400. Each measurement consists of 40 cycles, and the total analyticaltime is 12 min. Analytical procedures are described in details (Li et al.,2009, 2012; Balintoni et al., 2011; Dan et al., 2012, 2016; Eyal et al.,2014; Wang et al., 2015). Zircon U–Pb isotopic data are presented inTable S3 in the Supplementary data.

4.3. Zircon Hf–O isotopic analyses

Zircon oxygen isotopes were measured using Cameca IMS-1280 atthe IGGCAS. The Cs+ primary ion beam was accelerated at 10 kV withintensity of ca. 2 nA and rastered over a 10 μmareawith a spot diameterof 20 μm. Oxygen isotopes were measured in multi-collector modeusing two off axis Faraday cups. The internal precision of single analyseswas generally better than 0.2 ‰ for 18O/16O ratio. The instrumentalmass fractionation factor (IMF) was corrected using 91,500 zircon

13L. Zhang et al. / Gondwana Research 41 (2017) 9–28

standard with (δ18O)VSMOW = 9.9‰ (Wiedenbeck et al., 2004). Mea-sured 18O/16O was normalized by using VSMOW (Vienna StandardMean Ocean Water) compositions, and then corrected for the instru-mentalmass fractionation factor. The working conditions and analyticalprocedures have been described in details (Li et al., 2009; Su et al., 2011;

Table 2Zircon Hf–O isotope data of the Yangying potassic volcanic rocks.

Sample t (Ma) 176Yb/177Hf 176Lu/177Hf 176Hf/177Hf ± 2σ

YY-08-01 10.0 0.005357 0.000203 0.282705 0.000015YY-08-02 62.9 0.040641 0.001667 0.282900 0.000016YY-08-03 10.6 0.007239 0.000272 0.282730 0.000017YY-08-04 10.9 0.005083 0.000194 0.282699 0.000016YY-08-05 10.9 0.007185 0.000263 0.282729 0.000022YY-08-06 63.5 0.072463 0.002993 0.282896 0.000026YY-08-07 10.3YY-08-08 10.4 0.009920 0.000394 0.282681 0.000014YY-08-09 10.5 0.014747 0.000526 0.282711 0.000020YY-08-10 10.3YY-08-11 10.3 0.028974 0.001027 0.282681 0.000018YY-08-12 10.6 0.025624 0.000929 0.282704 0.000017YY-08-13 10.5 0.032422 0.001144 0.282695 0.000019YY-08-14 59.2 0.048940 0.001882 0.282922 0.000021YY-08-15 10.9YY-08-16 10.5 0.011925 0.000489 0.282698 0.000014YY-08-17 10.9 0.008937 0.000325 0.282707 0.000015YY-08-18 10.3 0.016233 0.000594 0.282702 0.000018YY-08-19 65.4YY-08-20 62.9 0.066980 0.002635 0.282871 0.000017YY-08-21 10.1 0.008673 0.000324 0.282754 0.000025YY-08-22 9.9 0.013494 0.000490 0.282687 0.000018YY-08-23 10.9 0.019257 0.000676 0.282647 0.000015YY-08-24 11.0 0.006092 0.000226 0.282686 0.000018YY-08-25 67.0 0.040666 0.001570 0.282974 0.000304YY-08-26 10.2 0.011021 0.000405 0.282752 0.000021YY-08-27 10.8 0.015357 0.000569 0.282735 0.000019YY-08-28 10.2 0.013133 0.000483 0.282704 0.000017YY-08-29 10.5 0.009313 0.000351 0.282702 0.000015YY-12-01 10.9 0.017196 0.000618 0.282694 0.000019YY-12-02 10.8 0.004635 0.000177 0.282710 0.000016YY-12-03 61.1 0.076558 0.003048 0.282944 0.000018YY-12-04 10.6 0.049378 0.001679 0.282704 0.000017YY-12-05 10.5YY-12-06 37.5 0.059471 0.002473 0.282951 0.000016YY-12-07 63.2 0.026749 0.001078 0.282850 0.000014YY-12-08 10.5 0.008267 0.000305 0.282692 0.000015YY-12-09 63.3 0.035398 0.001460 0.282905 0.000013YY-12-10 9.6 0.016490 0.000595 0.282698 0.000018YY-12-11 10.7 0.051714 0.001778 0.282680 0.000017YY-12-12 10.5 0.037633 0.001318 0.282774 0.000022YY-12-13 10.7 0.019032 0.000681 0.282673 0.000022YY-12-14 58.7 0.034657 0.001429 0.282933 0.000015YY-12-15 10.2 0.009032 0.000328 0.282700 0.000022YY-12-16 10.2 0.011190 0.000417 0.282643 0.000016

Initial 176Lu/177Hf and 176Hf/177Hf ratios and εHf(t) (the parts in 104 deviation of initial Hf isotowith the reference to the chondritic uniform reservoir (CHUR) at the time of zircon growth froThe ratios of (176Lu/177Hf)CHUR= 0.0336 and (176Hf/177Hf)CHUR= 0.282785 (Bouvier et al., 200mantle model ages (TDM) were calculated with reference to depleted mantle at a present-day 1

hafnium isotopic “crustal”model ages (TDM C)were also calculated for each zircon grain by assum176Lu/177Hf = 0.015, that originated from the depleted mantle source (Griffin et al., 2002). The

εHf 0ð Þ ¼

176Hf

.177Hf Þ

� �Sample

176Hf.

177Hf Þ

� �CHUR

−1

26664

37775� 104; εHf tð Þ ¼

176Hf

.177Hf Þ

� �Sample

− 176Lu

.177Hf Þ

� �

176Hf.

177Hf Þ

� �CHUR

− 176 Lu�

177Hf Þ� �

C

26664

TDM ¼ 1�λ � ln 1þ

176Hf

.177Hf Þ

� �Sample

− 176Lu

.177Hf Þ

� �DM

176Hf.

177Hf Þ

� �Sample

− 176 Lu�

177Hf Þ� �

DM

8>>><>>>:

9>>>=>>>;; TC

DM ¼ TDM− TDM−tð Þ � f

f Sample ¼176Lu

.177Hf Þ

� �Sample

176 Lu�

177Hf Þ� �

CHUR

−1; f MC ¼176Lu

.177Hf Þ

� �MC

176 Lu�

177Hf Þ� �

CHUR

−1; f DM ¼176Lu

.177Hf Þ

� �DM

176 Lu�

177Hf Þ� �

CHUR

−1

t, crystallization time of zircon; 206Pb/238U ages were used for zircons younger than 1000 Ma.

Dan et al., 2012, 2016; Wang et al., 2015). Zircon oxygen isotopic dataare listed in Table 2.

Lu–Hf isotopes were measured using laser-ablation multi-collectorinductively coupled plasma mass spectrometry (LA–ICP–MS) at theIGGCAS. Lu–Hf isotopic analyseswere obtained on the same zircon grains

ƐHf(t) ƐHf(0) TDM(Ma) TDMC (Ma) fSample δ18O (‰)

−2.59 −2.81 758 1231 −0.99 6.475.41 4.08 507 761 −0.95 6.35

−1.72 −1.95 726 1176 −0.99 6.13−2.79 −3.03 767 1245 −0.99 6.19−1.76 −1.99 727 1179 −0.99 6.69

5.21 3.92 533 774 −0.91 5.656.86

−3.45 −3.68 796 1287 −0.99 7.16−2.39 −2.62 757 1219 −0.98 6.75

6.67−3.45 −3.67 809 1286 −0.97 6.51−2.63 −2.85 774 1234 −0.97 6.63−2.95 −3.17 792 1254 −0.97 6.41

6.07 4.83 480 715 −0.94 5.606.21

−2.85 −3.08 775 1248 −0.99 5.51−2.54 −2.78 759 1228 −0.99 6.61−2.73 −2.95 771 1240 −0.98 6.62

5.664.31 3.03 565 831 −0.92 5.62

−0.88 −1.10 693 1122 −0.99 6.50−3.27 −3.48 790 1274 −0.99 6.54−4.64 −4.87 849 1362 −0.98 6.66−3.26 −3.51 786 1275 −0.99 7.22

8.11 6.69 399 590 −0.95 5.82−0.94 −1.16 697 1126 −0.99 6.32−1.52 −1.76 724 1163 −0.98 6.19−2.65 −2.87 766 1235 −0.99 6.27−2.71 −2.94 766 1239 −0.99 6.18−3.00 −3.23 783 1258 −0.98 6.02−2.42 −2.65 751 1221 −0.99 6.13

6.86 5.62 462 666 −0.91 5.71−2.65 −2.87 791 1235 −0.95 5.96

6.446.65 5.87 444 661 −0.93 5.533.65 2.29 571 873 −0.97 6.27

−3.05 −3.28 779 1261 −0.99 6.595.59 4.24 498 749 −0.96 5.76

−2.85 −3.06 776 1248 −0.98 6.53−3.47 −3.70 827 1288 −0.95 6.34−0.17 −0.39 683 1077 −0.96 6.60−3.73 −3.96 813 1304 −0.98 6.15

6.47 5.23 458 689 −0.96 5.77−2.77 −2.99 768 1243 −0.99 6.41−4.79 −5.01 849 1371 −0.99 6.46

pe ratios between the zircon sample and the chondritic reservoir) values were calculatedm magmas. The 176Lu decay constant was 1.867 × 10−11 year−1 (Söderlund et al., 2004).8), (176Lu/177Hf)DM= 0.0384 (Griffin et al., 2000) were also shown. And then the depleted76Hf/177Hf ratio of 0.28325 similar to that of the average MORB (Nowell et al., 1998). Theing its parentalmagma tohave been derived fromanaverage continental crust (MC),withcalculation formulas used in Table 2 are presented below.

Sample� eλt−1� �

HUR� eλt−1ð Þ

−1

37775� 104;

MC− f Sample

f MC− f DM

;

Fig. 3. (a) K2O+Na2O (wt.%) vs. SiO2 (wt.%) for the YPVR and other K-rich volcanic rocksof the Lhasa terrane. All data plotted have been recalculated to 100 wt.% on a volatile-freebasis. Classification boundaries are from Le Bas et al. (1986) and Le Maitre et al. (1989).Filled and open symbols represent, respectively, data from this study and the publishedliteratures of Miller et al. (1999); Williams et al. (2001, 2004); Ding et al. (2003, 2006);Jiang (2003); Jiang et al. (2003); Gao et al. (2007a, 2009); Sun et al. (2007); Wang et al.(2008, 2014); Zhao et al. (2009); Chen et al. (2012); J.L. Chen et al. (2010); Tian et al.(2012); Guo et al. (2013); D. Liu et al. (2011, 2014) and reference therein. Rock typesshown by letters are as follows: S2, basaltic trachyandesite; S3, trachyandesite; T,trachyte; R, rhyolite; U3, tephriphonolite; Ph, phonolite; O1, basaltic andesite; O2,andesite; O3, dacite. (b) K2O (wt.%) vs. SiO2 (wt.%) diagram for same samples as plottedin (a). The dividing lines show the classification boundaries from Rickwood (1989).

14 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

thatwere previously analyzed forU–Pb andO isotopes,with ablation pitsof 40–80 μmindiameter, ablation time of 26 s and repetition rate of 8Hz.The detailed analytical procedures are described in Li et al. (2010) andWang et al. (2015). Zircon Hf isotopic data are presented in Table 2.

4.4. Mineral compositional analyses

The compositions of phenocryst minerals of the YPVR weredetermined using a JEOL JXA-8100 electron microprobe at the IGGCAS.Analytical conditions include an accelerating voltage of 15 kV, beamcurrent of 2 × 10−8 A, a spot diameter of 5 μm for clinopyroxene, phlog-opite and feldspar. The analytical procedures are described in details(Cheng and Kusky, 2007; Tam et al., 2011; H. Xu et al., 2015). The bulkcompositions of phenocryst minerals are presented in Tables S4, S5and S6 in the Supplementary data.

5. Results

5.1. Whole-rock major, trace elements and Sr–Nd–Pb isotopes

Samples of the YPVR are all plotted in the field of trachyte (Fig. 3a),which have relatively high SiO2 (61.34–68.62 wt.%), K2O (5.46–9.30 wt.%), Al2O3 (15.06–17.36 wt.%), low MgO (0.47–2.80 wt.%) andFeOt (1.70–4.90 wt.%) contents (Table S1 in the Supplementary data).These trachytes are potassic (K2O/Na2O N 1) according to the criteriaproposed by Nelson (1992) and mainly lie in the shoshonitic series(Fig. 3b) with the exception of sample YY-09 which might be alteredin the hydrothermal field (Li et al., 1992). MgO, FeOt, CaO decreasewith increasing SiO2 in Harker diagrams (not shown), indicatingfractional crystallization of clinopyroxene and plagioclase. Negativecorrelation between SiO2 and TiO2 (or P2O5) might be interpreted asthe fractional crystallization of Fe–Ti oxides and apatite. Al2O3 firstlyincreases and then decreases with increasing SiO2, implying removalof feldspar from magma during low-pressure fractional crystallization.

The chondrite-normalized rare earth elements (REE) patterns of theYPVR are characterized by enrichment of LREE and distinctive negativeEu anomalies (δEu = 0.55–0.68; Table S1 in the Supplementary dataand Fig. 4a), which can be explained by fractional crystallization ofplagioclase. Primitive mantle-normalized incompatible trace elementsdiagrams of the studied rocks show positive anomalies for large ionlithosphile element (LILE, e.g., K, Ba and Rb; Fig. 4b) and significantlynegative anomalies for high field strength elements (HFSE, e.g., Nb, Taand Ti; Fig. 4b).

The studied YPVR have relatively radiogenic initial Sr isotopic com-position [(87Sr/86Sr)i = (0.711978–0.712090)] and unradiogenic initialNd isotopic composition [(143Nd/144Nd)i = (0.512121–0.512148)](Table S2 in the Supplementary data), which differs from Sr–Nd isotopiccompositions of theGangdese batholith, adakites and Linzizong volcanicrocks (Fig. 5a). The YPVR are characterized by fairly radiogenic Pb isotopicsignatures [(206Pb/204Pb)i = (18.615–18.774), (207Pb/204Pb)i = (15.708–15.793), (208Pb/204Pb)i = (39.274–39.355)](Table S2 in the Supple-mentary data), which are plotted above the North HemisphereReference Line (NHRL; Hart, 1984) as shown in Fig. 5b–e, suggestingenriched source for the Yangying potassic magma.

5.2. Zircon U–Pb geochronology

As shown in cathodoluminescence (CL) images (Fig. 6a and b),zircons for U–Pb dating from samples YY-08 and YY-12 are mostlyeuhedral and display long to short prismatic shapes with crystal lengthsof about 50–250 μm,which could bedivided into twogroups: (1)Group1is composed of magmatic zircons exhibiting weak oscillatory zoning anduniform internal texture (Corfu et al., 2003; Hoskin and Schaltegger,2003). Most of these zircons have Th/U ratios higher than 1 (1.1–4.3;Table S3 in the Supplementary data), in consistent with those of mag-matic zircons (N0.5; Hoskin and Schaltegger, 2003); and (2) Group 2

represents zircon xenocrysts or inherited core with lower Th/U ratios(0.23–0.83) that were captured during evolution of the Yangyingpotassic magma, suggesting potential crustal materials involved in theYangying magma generation. In situ zircon U–Pb age of the Group 1zircons could be interpreted as crystallization age of the YPVR (Wuet al., 2007; Chiu et al., 2009).

Magmatic zircons from sample YY-08 are coeval and yield a lowerintercept age of 10.62 ± 0.10 Ma (MSWD = 0.88) and a weightedmean 206Pb/238U age of 10.61 ± 0.10 Ma (MSWD = 0.88) in the Tera-Wasserburg U–Pb concordia diagram (Fig. 6c). Five zircon grains with

Fig. 4. (a) Chondrite-normalized rare earth element diagram of the YPVR. (b) Primitivemantle-normalized incompatible trace element patterns of the YPVR. Normalizationfactors are from Sun and McDonough (1989). Data for the average composition ofsubduction channel mélange rocks are from Marschall and Schumacher (2012) andreferences therein. Data sources of the potassic and ultrapotassic rocks in the Lhasaterrane are as in Fig. 3.

15L. Zhang et al. / Gondwana Research 41 (2017) 9–28

U–Pb ages ranging from 63 to 67.4 Ma are interpreted as xenocrysticcrystals which represent contaminants added to the Yangyingmagmas.Eleven analyses of magmatic zircons from sample YY-12 yields a lowerintercept age of 10.72 ± 0.14 Ma (MSWD= 1.3) and a weighted mean206Pb/238U age of 10.70 ± 0.18 Ma (MSWD = 1.3) (Fig. 6d), in consis-tent with crystallization age of sample YY-08. U–Pb ages of zirconxenocrysts range from 58.7 to 67 Ma (Table S3 in the Supplementarydata). In situ zircon U–Pb ages for the YPVR in this study are consistentwith previously published age data using K–Ar and Ar–Ar datingmethods (10.83 ± 0.27 Ma, 10.84 ± 0.17 Ma; Li et al., 1992; Zhouet al., 2010). Furthermore, potassicmagmatism in the Yangying volcanicfield is coeval with the late stage of the ultrapotassic magmatism in thewestern Lhasa terrane (25–8Ma; e.g., Miller et al., 1999;Williams et al.,2001, 2004; Ding et al., 2003; Zhao et al., 2009; J.L. Chen et al., 2010;Chen et al., 2012; Guo et al., 2013).

5.3. Zircon Hf–O isotopes

In situ zircon Hf–O isotopic data were analyzed for 45 zircongrains (samples YY-08 and YY-12) that have been previously dated bySIMS. Magmatic zircons exhibit relatively uniform 176Hf/177Hf ratios(0.282647–0.282774) and negative ƐHf(t) values (−4.79 to −0.17). Incontrast, xenocrystic zircons have relatively variable 176Hf/177Hf ratios(0.282850–0.282996) and positive ƐHf(t) values (3.65–8.11). The δ18Ovalues of the magmatic zircons range from 5.51‰ to 7.22‰ andxenocrystic zircons have similar δ18O value (5.62–6.57‰), which are

slightly higher than those of mantle zircons (δ18O = 5.3 ± 0.3‰;Valley, 2003).

5.4. Mineral chemistry

Clinopyroxene is ubiquitous and the most abundant phase occurredboth as phenocryst and groundmass in the YPVR (Fig. 2a), and plottedin the fields of augite and endiopside (Fig. 7a). These clinopyroxenephenocrysts are characterized by relatively low AlVI/AlIV (0.5–4), Ti/Al(0.091–0.25) ratios, and lowAl (b0.2 apfu) andNa (b0.05 apfu) contents(Table S6 in the Supplementary data), suggesting the crystallization ofthe clinopyroxene occurring at low pressure situation (b10 × 103 bar;Dobosi and Fodor, 1992; Haase et al., 1996; Seyler and Bonatti, 1994;McCarthy and PatiÑO Douce, 1998). Meanwhile, the AlVI/AlIV ratioshave relatively broad ranges, suggesting the AlVI of clinopyroxenecrystallizing much deeper than that of AlVI beneath the Lhasa terranecrust and the changing depth of clinopyroxene crystallization.

Alkali feldspar and plagioclase are themost commonminerals in theYPVR (Fig. 2). The plagioclases (An30–39) are plotted within the fields ofandesine and K-andesine in An–Ab–Or diagram (Fig. 7b), while all thealkali feldspars have relatively uniform end-member values (Or38–54Ab45–59 An3–10) (Fig. 7b), including euhedral alkali feldspar phenocrysts(Fig. 2b and f), cores and rims of overgrowth alkali feldspars (Fig. 2a, c–e).

Phlogopite phenocrysts are very common in the South Tibetanpotassic and ultrapotassic magmatic rocks. All analyzed phlogopites inthe YPVR are plotted within the field of ultrapotassic magmatic rocksin the Lhasa terrane (Fig. 7c). Moreover, the analyzed phlogopitephenocrysts are characterized by high-Ti (TiO2 = 5.55–7.93 wt.%), lowMgO (15.46–18.60 wt.%) and low K2O (7.52–8.44 wt.%) (Table S4 inthe Supplementary data), which resemble cores of phlogopite inultrapotassic rocks in the Lhasa terrane (Miller et al., 1999; Gao et al.,2007b), suggesting a genetic relation between the YPVR andultrapotassicmagmas in South Tibet.

6. Discussion

6.1. Origin of YPVR and the relationships between the ultrapotassic andpotassic magmas in the Lhasa terrane

The YPVR have different geochemical characteristics (i.e., whole-rock major elements, trace elements and Sr–Nd–Pb isotope ratios)from those of Miocene mantle-derived ultrapotassic magmatic rocksin the Lhasa terrane (e.g., Miller et al., 1999; Zhao et al., 2009; Guoet al., 2013, 2015; D. Liu et al., 2014; Liu et al., 2015) and of Mioceneadakitic rocks derived by partial melting of thickened lower crust inSouth Tibet (e.g., Chung et al., 2003, 2009; Gao et al., 2007a; Guo et al.,2007; Chen et al., 2011; Li et al., 2011; Hou et al., 2013) (Figs. 3–5).The YPVR are mainly characterized by high SiO2 (61.34–64.48 wt.%),low MgO (0.84–2.80 wt.%), FeOt (3.70–4.91 wt.%) and low contents ofCr (53.1–79.2 ppm) and Ni (27.2–36.4 ppm) and other compatibleelements (Table S1 in the Supplementary data), implying that theymight result from either partial melting of the mafic lower crust orassimilation and fractional crystallization (AFC) of mantle-derivedprimitive melts.

The negative Eu anomalies (δEu = 0.55–0.68) in Chondrite-normalized REE patterns of the YPVR (Fig. 4a) indicate fractionalcrystallization of plagioclase, which differs from lower crust-derivedadakitic rocks with positive or no Eu anomalies in the Lhasa terrane(e.g., Guo et al., 2007; Chen et al., 2011). Furthermore, the YPVR arecharacterized by relatively higher (87Sr/86Sr)i, (207Pb/204Pb)i, (208Pb/204Pb)i, (206Pb/204Pb)i and lower (143Nd/144Nd)i relative to those ofadakitic rocks in the Lhasa terrane (Fig. 5), indicating different magmasources for potassic and adakitic rocks which questions the hypothesisthat potassic magma of the Lhasa terrane originated from the maficlower crust (e.g., J.L. Chen et al., 2010; D. Liu et al., 2014).

Fig. 5. (a) (143Nd/144Nd)i vs. (87Sr/86Sr)i. (b) (87Sr/86Sr)i vs. (206Pb/204Pb)i. (c) (143Nd/144Nd)i vs. (206Pb/204Pb)i. (d) (207Pb/204Pb)i vs. (206Pb/204Pb)i. (e) (208Pb/204Pb)i vs. (206Pb/204Pb)i.Lower continental crust (LCC) and upper continental crust (UCC) are from Zartman and Haines (1988). Data for the average composition of subduction channel mélange rocks arecalculated from Bulle et al. (2010). The GLOSS (Global Subducting Sediment; Plank and Langmuir, 1998), NHRL (Northern Hemisphere Reference Line; Hart, 1984), EMI and EMII(enriched mantle end-members; Zindler and Hart, 1986; Hofmann, 1997; Zou et al., 2000), and MORB and OIB fields (Wilson, 1989; Hofmann, 1997) are shown for comparison. Thepotassic and ultrapotassic rocks from North Tibet are from Turner et al. (1993, 1996), Deng (1998); Liu (1999); Ding et al. (2003, 2007), Guo et al. (2006) and references therein. Datafor the Higher Himalayan Crystalline Sequence (HHCS) are from Allègre and Ben Othman (1980); Vidal et al. (1982, 1984); Deniel et al. (1987); Inger and Harris (1993); Parrish andHodges (1996); Harrison et al. (1999); Whittington et al. (1999); Ahmad et al. (2000); Robinson et al. (2001); Richards et al. (2005); Guo and Wilson (2012) and references therein.Compositions of the Gangdese batholith in the Lhasa terrane are from Jiang et al. (1999); Dong et al. (2008); and Z.D. Zhao et al. (2011). Linzizong volcanic rocks in Lhasa terrane arefrom Dong (2002) and Zhang (1996) and Lee et al. (2007, 2009, 2012). Adakitic rocks in Lhasa terrane are from Guo et al. (2007); Chen et al. (2011); Hou et al. (2004, 2013) andreferences therein. Lower crust in South Tibet is from Miller et al. (1999). Data sources of the potassic and ultrapotassic rocks in the Lhasa terrane are as in Fig. 3.

16 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

Compared with ultrapotassic magmatic rocks with MgO ≥ 6 wt.%from the Lhasa terrane, the bulk potassic magmatic rocks (includingthe YPVR) display slightly lower (87Sr/86Sr)i and higher (143Nd/144Nd)iratios, and moreover the potassic rocks plot in linear trends betweenmantle-derived mafic ultrapotassic magmas and relatively depletedcrustal contaminants from the Lhasa terrane (Fig. 5), suggesting closelinks with ultrapotassic magmas and the relatively depleted crustal

contaminants. The YPVR have lower contents of LILE (e.g., Rb, Ba, Sr)and LREE than those of the ultrapotassic rocks in the Lhasa terrane(Fig. 4), indicating that only fractional crystallization of the ultrapotassicmagmas could not account for geochemical characteristics of the YPVRand crustal contaminant must be involved. Additionally, the maficultrapotassic rocks (MgO ≥ 6 wt.%) in the Lhasa terrane have extremelyhigh (87Sr/86Sr)i (0.7117–0.7393), (206Pb/204Pb)i (18.284–18.965),

17L. Zhang et al. / Gondwana Research 41 (2017) 9–28

(207Pb/204Pb)i (15.660–15.839) and (208Pb/204Pb)i (39.092–40.025)ratios and low (143Nd/144Nd)i (0.5117–0.5212) ratios (e.g., Milleret al., 1999; Williams et al., 2001, 2004; Liao et al., 2002; Jiang, 2003;Gao et al., 2007b; Zhao et al., 2009; Ding et al., 2006; Chen et al., 2012;Tian et al., 2012; Guo et al., 2013), further enriched relative to thewhole-rock continental crust (Fig. 5; Zartman and Haines, 1988).Hence, ultrapotassic and potassic magmatic rocks including the YPVRdisplay a positive correlation between (143Nd/144Nd)i and SiO2

Fig. 6.Cathodoluminescence (CL) images of zircons of theYPVR samples YY08 (a) andYY12 (b).zircons. Solid circles and dashed ellipses indicate the locations of in situ U–Pb dating (yellow–da(yellow number), Hf isotopic values (green number) and O isotopic values (white number) anspot. Tera-Wasserburg diagrams (lower intercept age) and weighted-mean age diagrams (2

(e) Zircon δ18O vs. ƐHf(t) for the YPVR. (f) Zircon ƐHf(t) vs. U–Pb age for the YPVR, GangdeseHf isotope and U–Pb ages of Gangdese batholith, adakitic rocks and Linzizong volcanic rock(2009b, 2012) and Hou et al. (2013).

(Fig. 8a), whichmight be interpreted as assimilation of the ultrapotassicmagma by crustal materials during fractional crystallization.

Albeit with broader ranges of (87Sr/86Sr)i and SiO2 for ultrapotassicand potassic magmatic rocks (Fig. 8b), their correlations might beexplained by AFC processes of ultrapotassic magma involving variablecrustal contaminants (from an enriched one to a depleted one)(DePaolo, 1981; Handley et al., 2010), giving rise to potassic magmawith higher SiO2 (51.41–76.30 wt.%) and broad (87Sr/86Sr)i (0.710749–

Cathodoluminescence (CL) images are taken for inspecting internal structures of individualshed ellipses) andHf–O isotope analyses (green—solid circles), respectively. TheU–Pb agesd the grain numbers for measured zircon (blue number) are also shown for each analyses06Pb/238U age) of zircons from the YPVR are shown for samples YY08 (c) and YY12 (d).batholith, adakitic rocks and Linzizong volcanic rocks from the Lhasa terrane. The Zircons from Lhasa terrane are from Lee et al. (2007, 2009, 2012); Wen et al. (2008); Ji et al.

Fig. 6 (continued).

18 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

0.737638). Therefore, we suggest that the YPVRmight result from assim-ilation and fractional crystallization of the mantle-derived ultrapotassicmagma involving depleted crustal contaminant with lower (87Sr/86Sr)iand higher (143Nd/144Nd)i in the Lhasa terrane. The processes responsi-ble for evolution of the Yangying potassic magmas will be discussed indetail below based on energy-constrained assimilation and fractionalcrystallization (EC–AFC) model.

6.2. Petrogenesis of the ultrapotassic magmatic rocks in the Lhasa terrane

Convective thinning of the over-thickened Tibetan lithosphere(e.g., Miller et al., 1999; Williams et al., 2001; Zhao et al., 2009; D. Liuet al., 2014) has been proposed to explain the genesis of the post-collisional K-rich magmatic rocks in South Tibet. However, this modelmight be ineffective to account for E–W trending linear distribution ofultrapotassic and potassic rocks in the Lhasa terrane and youngingtrend of the K-rich magmatism from north to south (Ding et al., 2003;Nomade et al., 2004; Guo et al., 2013). Although break-off of the north-ward subducted Indian continental lithosphere (e.g., Mahéo et al., 2002;Replumaz et al., 2010, 2013, 2014) can explain the E–W trending K-richmagmatic belt in the Lhasa terrane, it is inconsistentwith the southwardyounging trend and systematic variations onproportions ofmetasomaticcomponents added to the mantle source of the K-rich magmatic rocksfrom Xuruco lake–Dangre Yongcuo lake rift in the central Lhasa terrane(Guo et al., 2013). Considering the temporal, spatial and compositionalvariations of the post-collisional K-rich magmas in the Lhasa terrane,rollback and breakoff of northward subducted Indian slab mightbe reasonable geodynamic mechanism responsible for the post-collisional K-rich volcanism (Guo et al., 2013, 2015), which is supportedby Cenozoic plate motion reconstruction of Indian and Asian plates and

geodynamic modeling for subduction kinetics (Lee and Lawver, 1995;Mahéo et al., 2002; Husson et al., 2012). Partial melting of previouslyenriched mantle wedge induced by decompression and hot astheno-spheric corner flow during rollback of northward subducted Indianslab would gave rise to formation of the post-collisional K-richmagmas(Guo et al., 2013). However, the nature of enriched component added tomantle source of the K-rich magmas remains a matter of heated debate(Miller et al., 1999; Gao et al., 2007b; Guo et al., 2013).

Previous studies (e.g., Gao et al., 2007b) have focused on the role ofsubducted sediments from the Neo-Tethyan oceanic lithosphere inenrichment of the mantle source. However, the low (207Pb/204Pb)i and(208Pb/204Pb)i ratios of the Neo-Tethyan oceanic subducted sedimentscannot account for the extremely high (87Sr/86Sr)i, (206Pb/204Pb)i,(207Pb/204Pb)i and (208Pb/204Pb)i ratios and low (143Nd/144Nd)i ratiosof the ultrapotassic rocks in South Tibet (Fig. 5; Zhao et al., 2009).Whole-rock Sr–Nd–Pb isotopic compositions exhibit linear trendsbetween depleted MORB-sourcemantle (DMM) and Indian continentalcrust (Fig. 5). Enrichment of mantle source for the post-collisionalK-rich magmas might have close affinity with subducted Indian conti-nental crust added to depleted MORB-source mantle during northwardunderthrusting of the Indian continental lithosphere beneath the Lhasaterrane (Mahéo et al., 2002). Using Sr–Nd–Pb–O isotopes and traceelements ratios from Higher Himalayan Crystalline Sequence (HHCS),many previous studies (e.g., Ding et al., 2003; Zhao et al., 2006, 2009;Guo et al., 2013, 2015) have pointed out that the ultrapotassic lavascan be well explained by underthrusting of the Himalayan continentalmaterials into the mantle source beneath the southern Tibet. In Figs. 5and 10, the ultrapotassic samples lie along a clear linear trend betweendepleted MORB-source mantle (DMM; Workman and Hart, 2005) andthe Indian continental margin sediments (HHCS; e.g., Najman et al.,

Fig. 7.Mineral compositions of major phenocrysts in the YPVR. (a) Pyroxenes plotted on the enstatite–ferrosilite–diopside–hedenbergite quadrilateral diagram after Morimoto (1988).(b) Feldspars plotted on ternary diagram after Smith (1974). (c) Micas plotted on the Al–Mg–Fe diagram after Sheppard and Taylor (1992). Data for phlogopite of the ultrapotassicrocks in the Lhasa terrane are from Miller et al. (1999); Zhao et al. (2009); Gao et al. (2007a) and C.Z. Liu et al. (2011). Data for the Sailipu mantle xenolith are from C.Z. Liu et al.(2011). Data for kamafugite of the West Qinling are from Yu (1994).

19L. Zhang et al. / Gondwana Research 41 (2017) 9–28

2010; Robinson et al., 2001; Harris et al., 2004; Zhao et al., 2009; Guoand Wilson, 2012; Guo et al., 2013 and references therein), implyingthe involvement of the Indian plate-derivedmaterials due to northwardsubduction of the Indian lithosphere beneath the Tibetan Plateau.Therefore, we propose a two-component mixing model to accountfor the enrichment of asthenospheric mantle source of the maficultrapotassic magmas beneath the Lhasa terrane (Fig. 9b). As shownin Fig. 9b, Sr–Nd isotopic compositions of the mantle-derivedultrapotassic magmas could be explained by a simple two-componentmixing between DMM and HHCS. The HHCS are represented by themetamorphic rocks in the Higher Himalaya (e.g., Najman et al., 2010;Robinson et al., 2001; Harris et al., 2004; Richards et al., 2005; Guoand Wilson, 2012), while the composition of the DMM is taken from

Fig. 8. (a) (143Nd/144 Nd)i vs. SiO2 and (b) (87Sr/86Sr)i vs. SiO2. Data sources and the sy

Workman and Hart (2005). In addition, modeling curves 1 and 2 inFig. 9b represent upper and lower limitation of the simulation curvesbetween HHCS and DMM (Table 3).

Previous studies (e.g., Johnson and Plank, 1999; Woodhead et al.,2001) demonstrated that ratios of fluid/melt-mobile trace elements tofluid/melt-immobile trace elements can effectively reflect the impor-tance of subduction-induced fluids/melts in the mantle source ofsubduction-related magmas, and particularly these elements ratios areinsignificantly fractionated during partial melting (Class et al., 2000).The combination of incompatible element and Sr–Nd isotopic ratioshas been effectively used as a fingerprint in identifying metasomaticcomponents in the mantle source of the subduction-related magmas(e.g., Hawkesworth et al., 1997; Turner and Hawkesworth, 1997; Class

mbols of the potassic and ultrapotassic rocks in the Lhasa terrane are as in Fig. 3.

Fig. 9. (a) (87Sr/86Sr)i vs. Sr and (b) (143Nd/144Nd) vs. (87Sr/86Sr)i plots for the potassic andultrapotassic rocks in the Lhasa terrane, showing two-component mixing line of HigherHimalayan Crystalline Sequence (HHCS) and depleted MORB-source Mantle (DMM) andthe AFC and EC–AFC processes. For two-component mixing trends with the F = 10%increment. The AFC trends are displayed as green curves with 5% increment in F = Mm/M0 (Mm, present mass of magma; M0, initial mass of magma). EC–AFC trends (redcurve) for equilibration temperatures (Teq) of 900 °C are shown. Abbreviations are asfollows: A, crustal assimilant; P, primitive magma.

Table 3Sr and Nd concentration (ppm) and initial (87Sr/86Sr)i and (144Nd/143Nd)i of the HighHimalayan Crystalline Sequence (HHCS) and depleted MORB-source mantle (DMM).

End-member parameterHHCS

DMMMin Max

Sr (ppm) 2 253.5 7.66(87Sr/86Sr)i 0.705442 1.198001 0.702626Nd (ppm) 1.1 1847 0.58(144Nd/143Nd)i 0.511591 0.512571 0.513106

Sr and Nd concentration and their initial isotopic ratios of the HHCS are taken from Vidalet al. (1982), Deniel et al. (1987), France-Lanord et al. (1993), Inger and Harris (1993),Parrish and Hodges (1996), Whittington et al. (1999), Ahmad et al. (2000); Najman et al.(2010); Robinson et al. (2001); Harris et al. (2004), Richards et al. (2005), Guo andWilson(2012). Compositions of depleted MORB-source mantle wedge (DMM) are taken fromWorkman and Hart (2005). The HHCS and DMM are age-corrected to 10 Ma based on theage of the Yangying potassic volcanic rocks.

20 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

et al., 2000; Guo et al., 2005, 2006, 2013, 2014a, 2015). Therefore, weuse Ba/La, Ba/Th and Th/Nd ratios to constrain the involvement of fluidsand melts in generation of the ultrapotassic magmas. High Ba/La, Ba/Thand Th/Nd ratios in the ultrapotassic rocks in the Lhasa terrane reflectpresence of the slab-derived fluids and melts in the mantle source re-gion (Fig. 10).

Recently, subduction-derived mélange rocks, mixture of hydrousfluids and melts derived from subducted slab and mantle peridotiteformed at the slab–mantle interface, have been introduced to illustratethe physico-chemical process responsible for recycling of crustal com-ponent to the mantle-source region of arc volcanic rocks (Marschalland Schumacher, 2012; Guo et al., 2014a). The ultrapotassic magmaticrocks in the Lhasa terrane and the mélange rocks both display enrich-ment in LILE, LREE and depletion in HFSE, e.g., positive Pb anomalyand negative Nb, Ta and Ti anomalies (Fig. 4), suggesting that the mé-lange rocks might be potential source rocks for the mantle-derivedultrapotassic magmatic rocks. This inference is in good agreementwith comparable Nb/La and Ce/Pb ratios between ultrapotassic igneousrocks and mélange rocks (Fig. 11a).

Positively-correlated Ba/Th and (La/Sm)N ratios of the ultrapotassicmagmatic rocks in the Lhasa terrane suggest involvement ofsubduction-related fluids and melts in magma generation (Fig. 11b),which could be well explained by characteristics of the mélange rocks(Marschall and Schumacher, 2012; Guo et al., 2014a). Th/La and Sm/Laratios of ultrapotassic magmatic rocks in the Lhasa terrane show a pos-itive correlation (Fig. 12a), suggesting that Th and Sm enrichmentscould be linked to the involvement of the subducted Indian mélangeswhich might contain zoisite/epidote and lawsonite (Guo et al., 2014a,2015). Ultrapotassic magmatic rocks in the Lhasa terrane are character-ized by lower Dy/Dy* than those of magmas derived from oceanic platesubduction and oceanic island basalts (Fig. 12b; Davidson et al., 2013),implying the addition of the Indian continental subducted sedimentsto themantle source and the different evolution trend ofmagma at con-tinental and oceanic seduction zones.

6.3. Shallow crustal magma chamber processes

Clinopyroxene-liquid thermobarometers are key tools in under-standing processes of storage, cooling, and fractionation of magmas(Putirka et al., 1996, 2003; Putirka, 2008). There are several steps thatshould be followed before calculating temperature and pressure usingthe clinopyroxene-liquid thermobarometers.

First, choose the suitable melts which are in equilibrium withclinopyroxenes. Themost commonly usedmelts are represented by com-positions of whole rock, groundmass and glass (e.g., Shaw and Klügel,2002; Putirka and Condit, 2003; Putirka et al., 2003; Dahren et al.,2012). Considering that clinopyroxene crystallizes at the early stage dur-ingmagma evolution, whole rock components of the YPVR are chosen tobe liquid composition (Putirka et al., 1996, 2003; Putirka, 2008).

Second, check whether the clinopyroxene grains are in equilibriumwith the host melt. Clinopyroxenes of the YPVR (Fig. 2) are commonlyeuhedral, exhibiting no clear petrographic indications of disequilibriumwith their host melt (e.g., reaction rim texture, corrosion structure).Based on major elements of the clinopyroxene analyses (Table S6 inthe Supplementary data), we use the Fe–Mg exchange coefficientsKD(Fe–Mg)cpx-liq to test for the clinopyroxene-melt equilibrium(Putirka et al., 2003), as is shown by the equation below:

KD Fe−Mgð Þcpx−liq ¼ Mgliq Fecpx

Mgcpx Feliq¼ 0:27� 0:03

Third, estimate H2O content of the magma before eruption. H2Ocontent is a very influential parameter for the clinopyroxene-liquid thermobarometers (e.g., Putirka, 2008; Dahren et al., 2012).Based on the thermal model proposed by Melekhova et al. (2013), thecompositional distribution of derivative magma varies as a function

Fig. 10. (a) Ba/Th vs. Th/Nd. (b) Ba/La vs. Th/Nd. (c) (87Sr/86Sr)i vs. Ba/La. (d) (87Sr/86Sr)i vs. Th/Nd. (e) (143Nd/144Nd)i vs. Ba/La and (f) (143Nd/144Nd)i vs. Th/Nd. The ultrapotassic rocks(MgO ≥ 6%, filled circle) in the Lhasa terrane form linear arrays, suggesting binary mixing (brown dashed-line with double-sided arrows) between DMM and HHCS-derived componentswith higher Ba/La (fluids) and Th/Nd (melts) ratios relative to the bulk HHCS (Fig. 10c–f). Data sources and symbols of the K-rich rocks are as in Figs. 3 and 5.

21L. Zhang et al. / Gondwana Research 41 (2017) 9–28

of water content of themagmatic system, which is related with the fluxand duration of magma input. In order to minimize the effect of H2Ocontent, we use a new equation of clinopyroxene-liquidthermobarometers proposed by Masotta et al. (2013) for alkalinedifferentiated magmas. The pre-eruptive H2O content we used inclinopyroxene-liquid thermobarometer is estimated at 3%.

Based on the above analyses, we calculated pressure (P) andtemperature (T) conditions under which clinopyroxenes crystallize inthe magma chamber beneath the Yangying volcanic field in SouthTibet. The results of the clinopyroxene-liquid thermobarometersdisplay a relatively concentrated pressure (P = 2.5–4.1 kbar) and tem-perature (T= 1029.4–1082.9 °C) range (Table S6 in the Supplementary

data). Using the equation D (km)=4.02+ 3.03 × P (kbar) proposed byAve Lallemant et al. (1980), we calculated storage depth of the magmachamber which ranges from 11.60 km to 16.44 km, consistent withthe changing depth of the clinopyroxene crystallization due to broadrange of AlVI/AlIV ratios. Previous studies have demonstrated that pres-ence of a low-velocity anomaly zone with depth of ~15 km beneaththe Yadong-Gulu rift which was interpreted as partiallymolten middle crust (Nelson et al., 1996; Brown et al., 1996; Weiet al., 2001). Our estimations are consistent with the depth of theMiocene Yangying magma chamber, implying that the low-velocityanomaly zone might be remnant of the Late Miocene potassic magmassince eruption.

Fig. 11. (a) Ce/Pb vs. Na/La plot for the potassic and ultrapotassic rocks in the Lhasa terrane. (b) Ba/Th vs. (La/Sm)N plot for the potassic and ultrapotassic rocks in the Lhasa terrane. Data forthe average composition of subduction channelmélange rocks are fromMarschall and Schumacher (2012) and references therein. TheGlobal Subducting Sediment (GLOSS) data are fromPlank and Langmuir (1998). Upper continental crust (UCC) data are fromZartman andHaines (1988).MORB andOIB data are from Sun andMcDonough (1989). Data sources and symbolsof the K-rich rocks are as in Figs. 3 and 5.

22 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

6.4. Energy-constrained assimilation and fractional crystallization (EC–AFC) modeling

Crustal contamination and fractional crystallization are consideredas important processes contributing to magmatic differentiation of theevolved magma (DePaolo, 1981; Foland et al., 1993; Douce, 1999;Spera and Bohrson, 2001, 2004; Barnes et al., 2005; Guo et al., 2006;Farahat et al., 2007). Based on the available geochemical data of themafic ultrapotassic (MgO ≥ 6 wt.%) and potassic rocks in the Lhasaterrane, we present EC–AFC model to quantitatively illustrate physicaland chemical characteristics of the magma–country rock interactionsin YPVR, which could provide rigorous constraints on evolution of themantle-derived ultrapotassic magma in crustal magma chamberbeneath the Yangying volcanic field. Reasonable ranges of initialthermal and compositional parameters used in the EC–AFC model arefrom Bohrson and Spera (2007) as shown in Table 4.

Potential crustal materials involved in petrogenesis of the YPVRare characterized by low (87Sr/86Sr)i and high (143Nd/144Nd)i ratios(Figs. 5 and 8), similar to those of relatively depleted crustal materialsfrom the Lhasa terrane, e.g., adakitic rocks, Linzizong volcanic rocksand Gangdese batholith (Fig. 5a). Moreover, the best-fit lithology forcrustal contamination of the mafic ultrapotassic magmas must also be

Fig. 12. (a) Sm/La vs. Th/La plot for the YPVR and thepotassic and ultrapotassic rocks in Lhasa terPlank and Langmuir, 1998) are reported as proxies of crustal recycled components. MORB and Othe potassic–ultrapotassic rocks in Lhasa terrane. Fields forMORB and OIB and continent crust adepleted mantle (DM) is from Salters and Stracke (2004). GLOSS average are calculated from P

consistent with ƐHf(t) (3.65–8.11) and ages (67–59 Ma) of xenocrysticzircons in the YPVR. Following these considerations, the adakitic rocksshould be ruled out because their extrusive/intrusive ages (26–8 Ma;e.g., Hou et al., 2004, 2013; Guo et al., 2007) postdate the U–Pb ages(67–59 Ma) of these xenocrystic zircons (Fig. 6f). Hence, the Gangdesebatholith and/or Linzizong volcanic rocks might be the most appropri-ate crustal material mixed to mantle-derived ultrapotassic melts inthe middle crust, because (1) they have the proper Sr–Nd–Pb isotoperatios required for assimilation of the mantle-derived ultrapotassicmelts to generate YPVR magmas (Fig. 5; Zhang, 1996; Jiang et al.,1999; Dong, 2002; Guo et al., 2007; Lee et al., 2007, 2009, 2012; Donget al., 2008; Z.D. Zhao et al., 2011); (2) they have consistent intrusiveages and zircon Hf isotopic ratios (Fig. 6f) with the studied xenocrysticzircons from YPVR (Lee et al., 2007, 2009, 2012; Wen et al., 2008; Jiet al., 2009b, 2012); (3) Guo et al. (2007) have indicated that theLinzizong magmas underplate the lower crust of the Lhasa terrane,and result in the lower crustal thickening. The middle crust of Lhasaterrane also might be affected by the underplating of the Linzizongmagmas, suggesting the component of the Lhasa terrane middle crustconsistent with the Linzizong magmas. Furthermore, Mo et al. (2003)have provided evidence to demonstrate that the composition of theLinzizong magmas could be regarded as the component of middle-

rane. Continental Crust (Rudnick andGao, 2003) andGlobal Subducting Sediment (GLOSS;IB data are from Sun andMcDonough (1989). (b) Dy/Yb vs. Dy/Dy* plot for the YPVR and

re fromDavidson et al. (2013). Primitivemantle (PM) is from Sun andMcDonough (1989);lank and Langmuir (1998). Data sources and symbols of the K-rich rocks are as in Fig. 3.

Table 4Assumed parameters and best-fit calculation results of the EC-AFC model calculations.

Modeling processesYangying potassicvolcanic fields

Thermal parametersMagma liquidus temperature (Tl,q, °C) 1200Magma initial temperature (Tm°, °C) 1200Assimilant liquidus temperature (Tl,a, °C) 1000Assimilant initial temperature (Ta°, °C) 230–300Solidus temperature (Ts, °C) 800Equilibration temperature (Teq, °C) 900Isobaric specific heat of magma (Cp,m, J/kg per K) 1200Isobaric specific heat of Assimilant (Cp,a, J/kg per K) 900Crystallization enthalpy (Δhcry, J/kg) 396,000Fusion enthalpy (Δhcry, J/kg) 354,000

Compositional parametersMagma initial Sr content (Csr,m°, ppm) 985.8Magma initial Nd content (CNd,m°, ppm) 191.2Magma Sr isotope ratio (ɛsr,m) 0.720952Magma Nd isotope ratio (ɛNd,m) 0.511982Magma bulk distribution coefficient for Sr (Dsr,m) 0.8Magma bulk distribution coefficient for Nd (DNd,m) 1.45Assimilant initial Sr content (Csr,a°, ppm) 551.32Assimilant initial Nd content (CNd,a°, ppm) 15.57Assimilant Sr isotope ratio (ɛsr,a) 0.704056Assimilant Nd isotope ratio (ɛ Nd,a) 0.512849Assimilant bulk distribution coefficient for Sr (Dsr,a) 0.1Assimilant bulk distribution coefficient for Nd (DNd,a) 0.2

The thermal parameters are taken from Bohrson and Spera (2007). The compositionalparameters of primitive magmas are from Guo et al. (2013). The assimilants are theGangdese batholith with average compositions reported by Dong et al. (2008).

23L. Zhang et al. / Gondwana Research 41 (2017) 9–28

upper crust of the Lhasa terrane. Thus, the component of the Linzizongmagmas can be used as that of the middle-upper crust beneath theLhasa terrane; and (4) the whole-rock Sr–Nd–Pb isotopic compositionsexhibit linear trends between enriched mantle-derived maficultrapotassic magmas and relatively depleted crustal contaminants(e.g., the Gangdese batholith and/or Linzizong volcanic rocks) in theLhasa terrane.

Compositions of the crustal assimilant in the Lhasa terrane are listedin Table 4. As indicated by the calculated results, the liquidus tempera-ture, solidus temperature and initial temperature of the crustalassimilant (i.e., the Gangdese batholith and/or the Linzizong volcanicrocks) are 1000 °C, 800 °C and 230–300 °C, respectively. In addition,the liquidus temperature, initial temperature of the primitive magmaand the equilibration temperature between magma and the countryrocks are 1200 °C, 1200 °C and 900 °C, respectively. In consideration ofthe ultrapotassic magmatic rocks have not been discovered in Yangyingvolcanic field, we select somemafic ultrapotassic rocks with the highestMgO, Cr and Ni content in the western Lhasa terrane as the primitivemagmas for the EC–AFC model simulation (Table 4). As shown inFig. 9, the YPVR can be explained by an EC–AFC model with a best-fitprimitive K-rich magma with Sr = 985.8 ppm, Nd = 191.2 ppm,(87Sr/86Sr)i = 0.720952, and (143Nd/144Nd)i = 0.511982.

Before the country rocks were heated up to solidus temperature(800 °C), Sr content of the mantle-derived ultrapotassic magmas firstlyincreased whereas (87Sr/86Sr)i remained constant as indicated by a flattrajectory in Fig. 9a, suggesting that fractional crystallization(e.g., clinopyroxene and phlogopite) dominated this stage before addi-tion of melts from country rocks into the mantle-derived ultrapotassicmagmas. When the temperatures reached solidus of the country rocks(800 °C), Sr content continued to increase while (87Sr/86Sr)i decreaseddramatically due to involvement of partialmelts derived from the coun-try rocks with relatively less radiogenic (87Sr/86Sr)i ratios. By the end ofthe magma evolution, Sr content of the contaminated primitiveultrapotassic magma decreased in response to the fractional crystalliza-tion of Sr-rich plagioclase (Fig. 9a). Therefore, YPVR can be well ex-plained by fractional crystallization and contamination (by partial

melts from the Gangdese batholith and/or the Linzizong volcanic rockswith depleted Sr–Nd isotopic compositions) of mantle-derivedultrapotassic magmas, which gains support from petrographic evidence(Fig. 2). For example, YPVR shows that plagioclase appears to have expe-rienced stages of growth assimilation and overgrowth (Fig. 2), implyingthat the Yangyingmagmas underwent complicated EC–AFCprocesses. Inaddition, the AFC calculation proposed by DePaolo (1981) was also per-formed, and the results (Fig. 9b) show that the YPVR have undergone avery high rate of assimilation (r =Ṁa/Ṁc = 0.6;Ṁa, the mass of assim-ilation;Ṁc, the mass of fractional crystallization) which is nearly consis-tent with the results displayed by the EC–AFC (Ma⁎/Mc = 0.675; Ma⁎, theamount of assimilant partial melt; Mc, the mass of cumulate).

The thermal and compositional parameters are generally used toexplain the site at which EC–AFC processes occurred (Guo et al.,2006). Chan et al. (2009) proposed a geothermal gradient (16 °C/km)for crust of the Lhasa terrane based on the xenolith temperatureestimations. Therefore, the depth atwhich the EC–AFC process occurredfor the YPVR ranges from 14.40 to 18.75 km, similar to depth of thecrustal magma chamber provided by the clinopyroxene-liquid thermo-barometers (Fig. 13). Based on the depth of crustalmagma chamber andcrustal thicknesses in the Lhasa terrane (Zhang and Klemperer, 2005;Searle et al., 2011), we suggest that the assimilation and fractional crys-tallization process took place in the middle crust of the Lhasa terrane(11.60–18.75 km).

6.5. Petrogenetic model of the Yangying potassic volcanic rocks

Based on the abovediscussions, we present a two-stage petrogeneticmodel for the Yangying potassic volcanic rocks (Fig. 13). The first stageof themodel involves formation of themafic ultrapotassic magmas. Thesubducted Indian continent crustal materials and mantle wedge weremechanically mixed in subduction channel forming the Indian mé-langes at the slab-mantle interface as a consequence of the northwardsubduction of Indian continental lithosphere followed the Asia–Indiacollision during 55–25 Ma (Guo et al., 2013, 2014a, 2015). Then, theenriched Indian mélanges rose buoyantly from the surface of theIndian subducting slab and underplated beneath the base of theTibetan lithosphere (Marschall and Schumacher, 2012; Guo et al.,2014a, 2015). India–Asia continent convergence rate decreased duringthe period of 25–8 Ma (Lee and Lawver, 1995; Chung et al., 2005; Guoet al., 2013), leading to rollback of the subducted Indian slab(Fig. 13a), and more importantly, decompression partial melting ofthe Indian mélanges and the generation of the post-collisionalultrapotassic mafic magmas (Fig. 13b). Moreover, age of E–Wextensionof the Yadong-Gulu rift in South Tibet has been constrained to be ~12–8Ma (Harrison et al., 1995; Edwards and Russell, 1998;Wu et al., 1998),which is in accordancewith the ages of the slab rollback (25–8Ma), im-plying that lithospheric extensional tectonics beneath the Lhasa terranemight be closely related to slab rollback process. These can also explainthe spatial correlation between the post-collisional potassic–ultrapotassic magmatism and the NS trending rifts in South Tibet (Guoet al., 2013, 2015).

The second stage of the model involves the AFC processes ofthe mantle-derived ultrapotassic magmas in middle crust (11.60–18.75 km) beneath the Lhasa terrane (Fig. 13c). During this stage,mantle-derived ultrapotassic mafic magmas were contaminated bythe Gangdese batholith and/or Linzizong volcanic rocks with depletedSr–Nd isotopic compositions (Fig. 9), accompanied by fractional crystal-lization processes, giving rise to formation of the Yangying potassicmagmas (Fig. 13c). The linear trends between mantle-derivedultrapotassic magmas and the Gangdese batholiths and/or Linzizongvolcanics in the Sr–Nd–Pb isotope diagrams are consistent with thisAFC inference (Fig. 5). Geophysical studies (e.g., Zhou and Murphy,2005; Li et al., 2008; Zhao et al., 2010; W. Zhao et al., 2011; J. Zhaoet al., 2014; Q. Xu et al., 2015; Zhang et al., 2015) have indicated thecontinuous presence of a northward dipping subducted slab of Indian

Fig. 13. Petrogeneticmodel for post-collisional potassicmagmatism in the Yangying volcanic field of the Lhasa terrane, South Tibet. The diagram shows anNS cross section and ismodifiedafter studies of Guo et al. (2007, 2013, 2014a);Marschall and Schumacher (2012) and Cashman and Sparks (2013). Abbreviations are as follows: BNS, Bangong-Nujiang suture; ITS, Indus-Tsangpo suture; MBT, the Main Boundary thrust; MCT, the Main Central thrust; STD, South Tibetan detachment; SCLM, subcontinental lithospheric mantle; P, potassic magmatism; UP,ultrapotassic magmatism. Outcrops of ultrapotassic volcanic rocks in Yangying volcanic field have not been discovered, as shown by the question mark.

24 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

continental lithosphere beneath the Lhasa terrane, and a low-velocityanomaly zone with depth of ~15 km beneath the Yadong-Gulu rift isclearly imaged which has been interpreted as partial melts in middlecrust (e.g., Nelson et al., 1996; Brown et al., 1996; Wei et al., 2001).We suggest that the residual magma beneath the Yadong-Gulu rift canprovide continuous heat for extensive hydrothermal activities atpresent (e.g. hot springs, soil microseepage; Guo et al., 2014b; L.H.Zhang et al., 2014) in Yangying and Yangbajing, which are releasingconsiderable amounts of volatiles (e.g., CO2; Guo et al., 2014b; L.H.Zhang et al., 2014). Moreover, hydrothermal gases released from theYadong-Gulu rift are characterized by “mantle signature” (3He/4He =0.1–0.14 RA; Yokoyama et al., 1999; Hoke et al., 2000; L.H. Zhang et al.,2014), suggesting that the excess 3He might have close affinities withresidual mantle-derived magmas in middle crust beneath the Yadong-Gulu rift in the Lhasa terrane.

7. Conclusions

Based on the whole-rock major and trace elements and Sr–Nd–Pbisotopic compositions of the Yangying volcanic rocks, and comprehen-sive mineralogical and petrological data, combined with in situ zirconU–Pb dating and Hf–O isotopic compositions, we conclude that:

(1) SIMS zircon U–Pb dating analyses yield ages of 10.61 ± 0.10 Maand 10.70 ± 0.18 Ma (weighted mean ages); their ƐHf(t) valuesrange from −4.79 to −0.17, combined with O isotope (5.51–7.22‰), imply an addition of crustal material in their source.

(2) Based on the EC–AFC model and the clinopyroxene-liquidthermobarometers, the assimilation and fractional crystallizationprocesses of the mantle-derived ultrapotassic magmas mighthave taken place in middle crust with the depth ranging from11.60 km to 18.75 km beneath the Lhasa terrane.

(3) A two-stage model for the petrogenesis of the YPVR wasproposed, which involves (a) formation of the ultrapotassicmafic magmas due to partial melting of the Indian mélangesbeneath base of the Tibetan lithosphere during rollback of thesubducted Indian lithosphere, and (b) occurrence of the YPVR

as a result of AFC processes of the mantle-derived primitiveultrapotassic magmas in middle crust of the Lhasa terrane.

Acknowledgments

This studywas supported by the Strategic Priority Research Program(B) of Chinese Academy of Sciences (Grant No. XDB03010600). We aregrateful to Drs. Xianhua Li, QianMao, Qiuli Li and Xiaoxiao Ling for theirassistance in laboratory. Drs.WenfengGuo and Yanan Yang are thankedfor helpful discussion.

Appendix A. Supplementary data

Supplementary data to this article can be found online at http://dx.doi.org/10.1016/j.gr.2015.11.007.

References

Ahmad, T., Harris, N., Bickle, M., Chapman, H., Bunbury, J., Prince, C., 2000. Isotopicconstraints on the structural relationships between the Lesser Himalayan Seriesand the High Himalayan Crystalline Series, Garhwal Himalaya. Geological Society ofAmerica Bulletin 112, 467–477.

Aitchison, J.C., Xia, X., Baxter, A.T., Ali, J.R., 2011. Detrital zircon U–Pb ages alongthe Yarlung–Tsangpo suture zone, Tibet: implications for oblique convergence andcollision between India and Asia. Gondwana Research 20, 691–709.

Allègre, C.J., Ben Othman, D., 1980. Nd–Sr isotopic relationship in granitoid rocks and con-tinental crust development: a chemical approach to orogenesis. Nature 286, 335–342.

Arnaud, N., Vidal, P., Tapponnier, P., Matte, P., Deng, W., 1992. The high K2O volcanism ofnorthwestern Tibet: geochemistry and tectonic implications. Earth and PlanetaryScience Letters 111, 351–367.

Ave Lallemant, H., Mercier, J., Carter, N., Ross, J., 1980. Rheology of the upper mantle: in-ferences from peridotite xenoliths. Tectonophysics 70, 85–113.

Balintoni, I., Balica, C., Ducea, M.N., Stremţan, C., 2011. Peri-Amazonian, Avalonian-typeand Ganderian-type terranes in the South Carpathians, Romania: the Danubiandomain basement. Gondwana Research 19, 945–957.

Barnes, C.G., Prestvik, T., Sundvoll, B., Surratt, D., 2005. Pervasive assimilation of carbonateand silicate rocks in the Hortavær igneous complex, north-central Norway. Lithos 80,179–199.

Bohrson, W.A., Spera, F.J., 2007. Energy-constrained recharge, assimilation, and fractionalcrystallization (EC–RAχFC): a visual basic computer code for calculating traceelement and isotope variations of open-system magmatic systems. Geochemistry,Geophysics, Geosystems 8, Q11003. http://dx.doi.org/10.1029/2007GC001781.

25L. Zhang et al. / Gondwana Research 41 (2017) 9–28

Bouvier, A., Vervoort, J.D., Patchett, P.J., 2008. The Lu–Hf and Sm–Nd isotopic compositionof CHUR: constraints from unequilibrated chondrites and implications for the bulkcomposition of terrestrial planets. Earth and Planetary Science Letters 273, 48–57.

Brown, L., Zhao, W., Nelson, K., Hauck, M., Alsdorf, D., Ross, A., Cogan, M., Clark, M., Liu, X.,Che, J., 1996. Bright spots, structure, andmagmatism in southern Tibet from INDEPTHseismic reflection profiling. Science 274, 1688–1690.

Bulle, F., Bröcker,M., Gärtner, C., Keasling, A., 2010. Geochemistry and geochronology of HPmélanges from Tinos and Andros, cycladic blueschist belt, Greece. Lithos 117, 61–81.

Cashman, K.V., Sparks, R.S.J., 2013. How volcanoes work: a 25 year perspective. GeologicalSociety of America Bulletin 125, 664–690.

Chan, G.H.N., Waters, D.J., Searle, M.P., Aitchison, J., Horstwood, M., Crowley, Q., Lo, C.H.,Chan, J.S.L., 2009. Probing the basement of southern Tibet: evidence from crustal xe-noliths entrained in a Miocene ultrapotassic dyke. Journal of the Geological Society166, 45–52.

Chen, J., Huang, B., Sun, L., 2010. New constraints to the onset of the India–Asia collision:paleomagnetic reconnaissance on the Linzizong Group in the Lhasa Block, China.Tectonophysics 489, 189–209.

Chen, J.L., Xu, J.F., Wang, B.D., Kang, Z.Q., Jie, L., 2010. Origin of Cenozoic alkaline potassicvolcanic rocks at KonglongXiang, Lhasa terrane, Tibetan Plateau: products of partialmelting of a mafic lower-crustal source? Chemical Geology 273, 286–299.

Chen, J.L., Xu, J.F., Zhao, W.X., Dong, Y.H., Wang, B.D., Kang, Z.Q., 2011. Geochemical vari-ations in Miocene adakitic rocks from the western and eastern Lhasa terrane: impli-cations for lower crustal flow beneath the Southern Tibetan Plateau. Lithos 125,928–939.

Chen, J.L., Zhao, W.X., Xu, J.F., Wang, B.D., Kang, Z.Q., 2012. Geochemistry of Miocene tra-chytes in Bugasi, Lhasa block, Tibetan Plateau: mixing products betweenmantle- andcrust-derived melts? Gondwana Research 21, 112–122.

Cheng, S., Kusky, T., 2007. Komatiites from west Shandong, North China craton: implica-tions for plume tectonics. Gondwana Research 12, 77–83.

Chiu, H.Y., Chung, S.L., Wu, F.Y., Liu, D., Liang, Y.H., Lin, I.J., Iizuka, Y., Xie, L.W., Wang, Y.,Chu, M.F., 2009. Zircon U–Pb and Hf isotopic constraints from easternTranshimalayan batholiths on the precollisional magmatic and tectonic evolution insouthern Tibet. Tectonophysics 477, 3–19.

Chung, S., Chu, M., Zhang, Y., Xie, Y., Lo, C., Lee, T., Lan, C., Li, X., Zhang, Q., Wang, Y., 2005.Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism. Earth-Science Reviews 68, 173–196.

Chung, S.L., Chu, M.F., Ji, J., O'Reilly, S.Y., Pearson, N.J., Liu, D., Lee, T.Y., Lo, C.H., 2009. Thenature and timing of crustal thickening in Southern Tibet: geochemical and zirconHf isotopic constraints from post-collisional adakites. Tectonophysics 477, 36–48.

Chung, S.L., Liu, D., Ji, J., Chu, M.F., Lee, H.Y., Wen, D.J., Lo, C.H., Lee, T.Y., Qian, Q., Zhang, Q.,2003. Adakites from continental collision zones: melting of thickened lower crust be-neath southern Tibet. Geology 31, 1021–1024.

Class, C., Miller, D.M., Goldstein, S.L., Langmuir, C.H., 2000. Distinguishing melt and fluidsubduction components in Umnak Volcanics, Aleutian Arc. Geochemistry, Geophys-ics, Geosystems 1, 1004. http://dx.doi.org/10.1029/1999GC000010.

Corfu, F., Hanchar, J.M., Hoskin, P.W., Kinny, P., 2003. Atlas of zircon textures. Reviews inMineralogy and Geochemistry 53, 469–500.

Dahren, B., Troll, V.R., Andersson, U.B., Chadwick, J.P., Gardner, M.F., Jaxybulatov, K.,Koulakov, I., 2012. Magma plumbing beneath Anak Krakatau volcano, Indonesia: ev-idence for multiple magma storage regions. Contributions to Mineralogy and Petrol-ogy 163, 631–651.

Dan, W., Li, X.H., Guo, J., Liu, Y., Wang, X.C., 2012. Paleoproterozoic evolution of the east-ern Alxa Block, westernmost North China: evidence from in situ zircon U–Pb datingand Hf–O isotopes. Gondwana Research 21, 838–864.

Dan, W., Li, X.H., Wang, Q., Wang, X.C., Wyman, D.A., Liu, Y., 2016. Phanerozoic amalgam-ation of the Alxa Block and North China Craton: evidence from Paleozoic granitoids,U–Pb geochronology and Sr–Nd–Pb–Hf–O isotope geochemistry. Gondwana Re-search 32, 105–121.

Davidson, J., Turner, S., Plank, T., 2013. Dy/Dy*: variations arising frommantle sources andpetrogenetic processes. Journal of Petrology 54, 525–537.

Deng, W., 1998. Cenozoic Intraplate Volcanic Rocks in the Northern Qinghai–Xizang (Ti-betan) Plateau. Geological Publishing House, Beijing (180 pp. (in Chinese with En-glish abstract)).

Deniel, C., Vidal, P., Fernandez, A., Le Fort, P., Peucat, J.J., 1987. Isotopic study of theManaslu granite (Himalaya, Nepal): inferences on the age and source of Himalayanleucogranites. Contributions to Mineralogy and Petrology 96, 78–92.

DePaolo, D.J., 1981. Trace element and isotopic effects of combined wallrock assimilationand fractional crystallization. Earth and Planetary Science Letters 53, 189–202.

Ding, L., Kapp, P., Wan, X., 2005. Paleocene-Eocene record of ophiolite obduction and ini-tial India–Asia collision, south central Tibet. Tectonics 24. http://dx.doi.org/10.1029/2004TC001729.

Ding, L., Kapp, P., Zhong, D., Deng, W., 2003. Cenozoic volcanism in Tibet: evidence for atransition from oceanic to continental subduction. Journal of Petrology 44, 1833–1865.

Ding, L., Yue, Y., Cai, F., Xu, X., Zhang, Q., Lai, Q., 2006. 40Ar/39Ar geochronology, geochem-ical and Sr–Nd–O isotopic characteristics of the high-Mg ultrapotassic rocks in Lhasablock of Tibet: implications in the onset time and depth of NS-striking rift system.Acta Geologica Sinica 80, 1252–1261 (in Chinese with English abstract).

Dobosi, G., Fodor, R., 1992.Magma fractionation, replenishment, andmixing as inferred fromgreen-core clinopyroxenes in Pliocene basanite, southern Slovakia. Lithos 28, 133–150.

Dong, G.C., 2002. Linzizong Volcanic Rocks in Linzhou Volcanic Basin, South Tibet: Impli-cation for India–Eurasia Collision Process PhD Thesis China University of Geosciences(134 pp. (in Chinese with English abstract)).

Dong, G.C., Mo, X.X., Zhao, Z.D., Guo, T.Y., Wang, L.L., Chen, T., 2005. Geochronologicconstraints on the magmatic underplating of the gangdese belt in the India–Eurasiacollision: evidence of SHRIMP II zircon U–Pb dating. Acta Geologica Sinica-EnglishEdition 79, 787–794.

Dong, G.C., Mo, X.X., Zhao, Z.D., Zhu, D.C., Song, Y.T., Wang, L., 2008. Gabbros from south-ern Gangdese: implication for mass exchange between mantle and crust. ActaPetrologica Sinica 24, 203–210 (in Chinese with English abstract).

Douce, A.E.P., 1999. What do experiments tell us about the relative contributions of crustand mantle to the origin of granitic magmas? Geological Society, London, SpecialPublications 168, 55–75.

Edwards, B.R., Russell, J.K., 1998. Time scales of magmatic processes: new insights fromdynamic models for magmatic assimilation. Geology 26, 1103–1106.

Eyal, M., Be'eri-Shlevin, Y., Eyal, Y., Whitehouse, M.J., Litvinovsky, B., 2014. Three succes-sive Proterozoic island arcs in the Northern Arabian-Nubian Shield: evidence fromSIMS U–Pb dating of zircon. Gondwana Research 25, 338–357.

Farahat, E., Shaaban,M., Aal, A.A., 2007. Mafic xenoliths from Egyptian Tertiary basalts andtheir petrogenetic implications. Gondwana Research 11, 516–528.

Foland, K., Landoll, J., Henderson, C., Chen, J., 1993. Formation of cogenetic quartz andnepheline syenites. Geochimica et Cosmochimica Acta 57, 697–704.

France-Lanord, C., Derry, L., Michard, A., 1993. Evolution of the Himalaya since Miocenetime isotopic and sedimentological evidence from the Bengal Fan. The Geological So-ciety 74, 603–621.

Gao, Y., Hou, Z., Kamber, B.S., Wei, R., Meng, X., Zhao, R., 2007a. Adakite-like porphyriesfrom the southern Tibetan continental collision zones: evidence for slabmelt metaso-matism. Contributions to Mineralogy and Petrology 153, 105–120.

Gao, Y., Hou, Z., Kamber, B.S., Wei, R., Meng, X., Zhao, R., 2007b. Lamproitic rocks from acontinental collision zone: evidence for recycling of subducted Tethyan oceanic sed-iments in the mantle beneath southern Tibet. Journal of Petrology 48, 729–752.

Gao, Y., Wei, R., Ma, P., Hou, Z., Yang, Z., 2009. Post-collisional ultrapotassic volcanism inthe Tangra Yumco-Xuruco graben, south Tibet: constraints from geochemistry andSr–Nd–Pb isotope. Lithos 110, 129–139.

Gao, Y., Yang, Z., Santosh, M., Hou, Z., Wei, R., Tian, S., 2010. Adakitic rocks from slab melt-modified mantle sources in the continental collision zone of southern Tibet. Lithos119, 651–663.

Gnos, E., Immenhauser, A., Peters, T., 1997. Late Cretaceous/early Tertiary convergence be-tween the Indian and Arabian plates recorded in ophiolites and related sediments.Tectonophysics 271, 1–19.

Griffin, W.L., Pearson, N.J., Belousova, E., Jackson, S.E., van Achterbergh, E., O'Reilly, S.Y.,Shee, S.R., 2000. The Hf isotope composition of cratonic mantle: LAM–MC–ICPMSanalysis of zircon megacrysts in kimberlites. Geochimica et Cosmochimica Acta 64,133–147.

Griffin, W.L., Wang, X., Jackson, S.E., Pearson, N.J., O'Reilly, S.Y., Xu, X., Zhou, X., 2002. Zir-con chemistry and magma mixing, SE China: in situ analysis of Hf isotopes, Tongluand Pingtan igneous complexes. Lithos 61, 237–269.

Guan, Q., Zhu, D.C., Zhao, Z.D., Dong, G.C., Zhang, L.L., Li, X.W., Liu, M., Mo, X.X., Liu, Y.S.,Yuan, H.L., 2012. Crustal thickening prior to 38 Ma in southern Tibet: evidencefrom lower crust-derived adakitic magmatism in the Gangdese Batholith. GondwanaResearch 21, 88–99.

Guo, Z., Wilson, M., Liu, J., Mao, Q., 2006. Post-collisional, potassic and ultrapotassicmagmatism of the northern Tibetan Plateau: constraints on characteristics of themantle source, geodynamic setting and uplift mechanisms. Journal of Petrology 47,1177–1220.

Guo, Z., Wilson, M., 2012. The Himalayan leucogranites: constraints on the nature of theircrustal source region and geodynamic setting. Gondwana Research 22, 360–376.

Guo, Z., Hertogen, J., Liu, J., Pasteels, P., Boven, A., Punzalan, L., He, H., Luo, X., Zhang,W., 2005.Potassic magmatism in western Sichuan and Yunnan provinces, SE Tibet, China: petro-logical and geochemical constraints on petrogenesis. Journal of Petrology 46, 33–78.

Guo, Z., Wilson,M., Liu, J., 2007. Post-collisional adakites in south Tibet: products of partialmelting of subduction-modified lower crust. Lithos 96, 205–224.

Guo, Z., Wilson, M., Zhang, L., Zhang, M., Cheng, Z., Liu, J., 2014a. The role of subductionchannel mélanges and convergent subduction systems in the petrogenesis of post-collisional K-rich mafic magmatism in NW Tibet. Lithos 198, 184–201.

Guo, Z., Zhang, M., Cheng, Z., Zhang, L., Liu, J., 2014b. Fluxes and genesis of greenhousegases emissions from typical volcanic fields in China. Acta Petrologica Sinica 30,3467–3480 (in Chinese with English abstract).

Guo, Z., Wilson, M., Zhang, M., Cheng, Z., Zhang, L., 2013. Post-collisional, K-richmafic magmatism in south Tibet: constraints on Indian slab-to-wedge transportprocesses and plateau uplift. Contributions to Mineralogy and Petrology 165,1311–1340.

Guo, Z., Wilson, M., Zhang, M., Cheng, Z., Zhang, L., 2015. Post-collisional ultrapotassicmafic magmatism in South Tibet: products of partial melting of pyroxenite in themantle wedge induced by roll-back and delamination of the subducted Indian conti-nental lithosphere slab. Journal of Petrology 56, 1365–1406.

Guynn, J.H., Kapp, P., Pullen, A., 2006. Tibetan basement rocks near Amdo reveal “missing”Mesozoic tectonism along the Bangong suture, central Tibet. Geology 34, 505–508.

Haase, K.M., Hartmann, M., Wallrabe-Adams, H.J., 1996. The geochemistry of ashes fromVesterisbanken Seamount, Greenland Basin: implications for the evolution of an alka-line volcano. Journal of Volcanology and Geothermal Research 70, 1–19.

Handley, H.K., Macpherson, C.G., Davidson, J.P., 2010. Geochemical and Sr–O isotopic con-straints on magmatic differentiation at Gede Volcanic Complex, West Java, Indonesia.Contributions to Mineralogy and Petrology 159, 885–908.

Harris, N., Caddick, M., Kosler, J., Goswami, S., Vance, D., Tindle, A., 2004. The pressure-temperature-time path of migmatites from the Sikkim Himalaya. Journal of Meta-morphic Geology 22, 249–264.

Harrison, M.T., Grove, M., Mckeegan, K.D., Coath, C.D., Lovera, O.M., Fort, P.L., 1999. Originand episodic emplacement of the Manaslu intrusive complex, central Himalaya. Jour-nal of Petrology 40, 3–19.

Harrison, T.M., Copeland, P., Kidd, W., Lovera, O.M., 1995. Activation of theNyainqentanghla shear zone: implications for uplift of the southern Tibetan Plateau.Tectonics 14, 658–676.

26 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

Hart, S.R., 1984. A large-scale isotope anomaly in the Southern Hemisphere mantle. Na-ture 309, 753–757.

Hawkesworth, C., Turner, S., McDermott, F., Peate, D., Van Calsteren, P., 1997. U–Th iso-topes in arc magmas: implications for element transfer from the subducted crust. Sci-ence 276, 551–555.

Hébert, R., Guilmette, C., Dostal, J., Bezard, R., Lesage, G., Bédard, É., Wang, C., 2014. Mio-cene post-collisional shoshonites and their crustal xenoliths, Yarlung Zangbo SutureZone southern Tibet: geodynamic implications. Gondwana Research 25, 1263–1271.

Hofmann, A.W., 1997. Mantle geochemistry: the message from oceanic volcanism. Nature385, 219–229.

Hoke, L., Lamb, S., Hilton, D.R., Poreda, R.J., 2000. Southern limit of mantle-derived geo-thermal helium emissions in Tibet: implications for lithospheric structure. Earthand Planetary Science Letters 180, 297–308.

Hoskin, P.W.O., Schaltegger, U., 2003. The composition of zircon and igneous and meta-morphic petrogenesis. Reviews in Mineralogy and Geochemistry 53, 27–62.

Hou, Z., Zhao, Z., Gao, Y., Yang, Z., Jiang, W., 2006. Tearing and dischronal subduction ofthe Indian continental slab: evidence from Cenozoic Gangdese volcano-magmaticrocks in south Tibet. Acta Petrologica Sinica 22, 761–774 (in Chinese with Englishabstract).

Hou, Z., Zheng, Y., Yang, Z., Rui, Z., Zhao, Z., Jiang, S., Qu, X., Sun, Q., 2013. Contribution ofmantle components within juvenile lower-crust to collisional zone porphyry Cu sys-tems in Tibet. Mineralium Deposita 48, 173–192.

Hou, Z.Q., Gao, Y.F., Qu, X.M., Rui, Z.Y., Mo, X.X., 2004. Origin of adakitic intrusives gener-ated duringmid-Miocene east–west extension in southern Tibet. Earth and PlanetaryScience Letters 220, 139–155.

Hu, D., Wu, Z., Jiang, W., Shi, Y., Ye, P., Liu, Q., 2005. SHRIMP zircon U–Pb age and Nd iso-topic study on the Nyainqêntanglha Group in Tibet. Science in China Series D: EarthSciences 48, 1377–1386.

Hu, X., Sinclair, H.D., Wang, J., Jiang, H., Wu, F., 2012. Late Cretaceous-Palaeogene strati-graphic and basin evolution in the Zhepure Mountain of southern Tibet: implicationsfor the timing of India–Asia initial collision. Basin Research 24, 520–543.

Hu, X., Wang, J., BouDagher-Fadel, M., Garzanti, E., An, W., 2015. New insights into thetiming of the India–Asia collision from the Paleogene Quxia and Jialazi formationsof the Xigaze forearc basin, South Tibet. Gondwana Research http://dx.doi.org/10.1016/j.gr.2015.02.007.

Hu, Y., Liu, J., Ling,M., Ding,W., Liu, Y., Zartman, R.E., Ma, X., Liu, D., Zhang, C., Sun, S., 2015.The formation of Qulong adakites and their relationship with porphyry copper de-posit: geochemical constraints. Lithos 220, 60–80.

Huang, F., Chen, J., Xu, J., Wang, B., Li, J., 2015. Os–Nd–Sr isotopes inMiocene ultrapotassicrocks of southern Tibet: partial melting of a pyroxenite-bearing lithospheric mantle?Geochimica et Cosmochimica Acta 163, 279–298.

Husson, L., Conrad, C.P., Faccenna, C., 2012. Plate motions, Andean orogeny, and volcanismabove the South Atlantic convection cell. Earth and Planetary Science Letters317–318, 126–135.

Inger, S., Harris, N., 1993. Geochemical constraints on leucogranite magmatism in theLangtang Valley, Nepal Himalaya. Journal of Petrology 34, 345–368.

Ji, W.Q., Wu, F.Y., Chung, S.L., Liu, C.Z., 2014. The Gangdese magmatic constraints on a lat-est Cretaceous lithospheric delamination of the Lhasa terrane, southern Tibet. Lithos210–211, 168–180.

Ji, W.Q., Wu, F.Y., Liu, C.Z., Chung, S.L., 2009a. Geochronology and petrogenesis of graniticrocks in Gangdese batholith, southern Tibet. Science in China Series D: Earth Sciences52, 1240–1261.

Ji, W.Q., Wu, F.Y., Chung, S.L., Li, J.X., Liu, C.Z., 2009b. Zircon U–Pb geochronology and Hfisotopic constraints on petrogenesis of the Gangdese batholith, southern Tibet.Chemical Geology 262, 229–245.

Ji, W.Q., Wu, F.Y., Liu, C.Z., Chung, S.L., 2012. Early Eocene crustal thickening in southernTibet: new age and geochemical constraints from the Gangdese batholith. Journalof Asian Earth Sciences 53, 82–95.

Jiang, W., Mo, X., Zhao, C., Guo, T., Zhang, S., 1999. Geochemistry of granitoid and its maficmicrogranular enclave in Gangdise belt, Qinghai-Xizang Plateau. Acta PetrologicaSinica 15, 89–97 (in Chinese with English abstract).

Jiang, Y., 2003. Mesozoic and Cenozoic tectonomagmatic evolution and mineralization inthe Cuoqin area, Mid-Gangdise, Tibet PhD thesis Chengdu University of Technology,Beijing (205 pp. (in Chinese with English abstract)).

Jiang, Y.S., Zhou, Y.Y.,Wang,M.G., Xie, Y.X., Li, J.B., Feng, B., 2003. Characteristics and geolog-ical significance of Quaternary volcanic rocks in the central segment of the Gangdisearea. Geological Bulletin of China 1, 16–19 (in Chinese with English abstract).

Jiang, Z.Q., Wang, Q., Wyman, D.A., Li, Z.X., Yang, J.H., Shi, X.B., Ma, L., Tang, G.J., Gou, G.N.,Jia, X.H., Guo, H.F., 2014. Transition from oceanic to continental lithosphere subduc-tion in southern Tibet: evidence from the Late Cretaceous-Early Oligocene(~91–30 Ma) intrusive rocks in the Chanang-Zedong area, southern Gangdese. Lithos196–197, 213–231.

Johnson, M.C., Plank, T., 1999. Dehydration and melting experiments constrain the fate ofsubducted sediments. Geochemistry, Geophysics, Geosystems 1, 1007. http://dx.doi.org/10.1029/1999GC000014.

Kapp, P., DeCelles, P.G., Gehrels, G.E., Heizler, M., Ding, L., 2007. Geological records of theLhasa-Qiangtang and Indo-Asian collisions in the Nima area of central Tibet. Geolog-ical Society of America Bulletin 119, 917–933.

Kapp, P., Murphy, M.A., Yin, A., Harrison, T.M., Ding, L., Guo, J., 2003. Mesozoic and Ceno-zoic tectonic evolution of the Shiquanhe area of western Tibet. Tectonics 22 (1029),2003. http://dx.doi.org/10.1029/2001TC001332.

King, J., Harris, N., Argles, T., Parrish, R., Charlier, B., Sherlock, S., Zhang, H.F., 2007. Firstfield evidence of southward ductile flow of Asian crust beneath southern Tibet. Geol-ogy 35, 727–730.

Le Bas, M., Le Maitre, R., Streckeisen, A., Zanettin, B., 1986. A chemical classification of vol-canic rocks based on the total alkali-silica diagram. Journal of Petrology 27, 745–750.

Le Maitre, R.W., Bateman, P., Dudek, A., Keller, J., Lameyre, J., Le Bas, M., Sabine, P., Schmid,R., Sorensen, H., Streckeisen, A., 1989. A Classification of Igneous Rocks andGlossary ofTerms: Recommendations of the International Union of Geological Sciences Subcom-mission on the Systematics of Igneous Rocks. Blackwell Scienctific, Oxford (236 pp.).

Lee, H., Chung, S., Wang, Y., Zhu, D., Yang, J., Song, B., Liu, D., Wu, F., 2007. Age, petrogen-esis and geological significance of the Linzizong volcanic successions in the Linzhoubasin, southern Tibet: evidence from zircon U–Pb dates and Hf isotopes. ActaPetrologica Sinica 23, 493–500 (in Chinese with English abstract).

Lee, H.Y., Chung, S.L., Ji, J., Qian, Q., Gallet, S., Lo, C.H., Lee, T.Y., Zhang, Q., 2012. Geochem-ical and Sr–Nd isotopic constraints on the genesis of the Cenozoic Linzizong volcanicsuccessions, southern Tibet. Journal of Asian Earth Sciences 53, 96–114.

Lee, H.Y., Chung, S.L., Lo, C.H., Ji, J., Lee, T.Y., Qian, Q., Zhang, Q., 2009. Eocene Neotethyanslab breakoff in southern Tibet inferred from the Linzizong volcanic record.Tectonophysics 477, 20–35.

Lee, T.Y., Lawver, L.A., 1995. Cenozoic plate reconstruction of Southeast Asia.Tectonophysics 251, 85–138.

Li, C., Van der Hilst, R.D., Meltzer, A.S., Engdahl, E.R., 2008. Subduction of the Indian lith-osphere beneath the Tibetan Plateau and Burma. Earth and Planetary Science Letters274, 157–168.

Li, J.X., Qin, K.Z., Li, G.M., Xiao, B., Chen, L., Zhao, J.X., 2011. Post-collisional ore-bearingadakitic porphyries from Gangdese porphyry copper belt, southern Tibet: meltingof thickened juvenile arc lower crust. Lithos 126, 265–277.

Li, J.Z., Sun, S.P., Zhang, Y.Y., Luo, H.Y., 1994. A study on formation characteristics and ap-praisal of the Yangying village geothermal field, Dangxiong, Tibet. Geoscience 8,50–57 (in Chinese with English abstract).

Li, J.Z., Zhang, Y.Y., Luo, H.Y., 1992. A research on petrological characters and genesis of theCenozoic volcanic rocks in the Yangying village geothermal field, Dangxiong, Tibet.Geoscience 6, 96–109 (in Chinese with English abstract).

Li, Q.L., Li, X.H., Wu, F.Y., Yin, Q.Z., Ye, H.M., Liu, Y., Tang, G.Q., Zhang, C.L., 2012. In–situSIMS U–Pb dating of phanerozoic apatite with low U and high common Pb. Gondwa-na Research 21, 745–756.

Li, X.H., 1997. Geochemistry of the Longsheng Ophiolite from the southern margin ofYangtze Craton, SE China. Geochemical Journal 31, 323–337.

Li, X.H., Li, W.X., Li, Q.L., Wang, X.C., Liu, Y., Yang, Y.H., 2010. Petrogenesis and tectonicsignificance of the ~850 Ma Gangbian alkaline complex in South China: evidencefrom in situ zircon U–Pb dating, Hf–O isotopes and whole-rock geochemistry. Lithos114, 1–15.

Li, X.H., Liu, Y., Li, Q.L., Guo, C.H., Chamberlain, K.R., 2009. Precise determination of Phan-erozoic zircon Pb/Pb age by multicollector SIMS without external standardization.Geochemistry, Geophysics, Geosystems 10, Q04010. http://dx.doi.org/10.1029/2009GC002400.

Liao, S.P., Chen, Z.H., Luo, X.C., Zhou, A.J., 2002. Discovery of leucite phonolite in the TangraYumco area, Tibet and its geological significance. Geological Bulletin of China 11,735–738 (in Chinese with English abstract).

Liao, Z., Zhao, P., 1999. Yunnan-Tibet Geothermal Belt-Geothermal Resources and CaseHistories. Science Press, Beijing, pp. 1–153 (in Chinese with English abstract).

Liu, C.Z., Wu, F.Y., Chung, S.L., Li, Q.L., Sun,W.D., Ji, W.Q., 2014. A ‘hidden’ 18O-enriched res-ervoir in the sub-arc mantle. Scientific Reports 4, 4232. http://dx.doi.org/10.1038/srep04232.

Liu, C.Z., Wu, F.Y., Chung, S.L., Zhao, Z.D., 2011. Fragments of hot andmetasomatizedman-tle lithosphere in Middle Miocene ultrapotassic lavas, southern Tibet. Geology 39,923–926.

Liu, D., Zhao, Z.D., Zhu, D.C., Niu, Y., Liu, S.A., Wang, Q., Liu, Y.S., Hu, Z.C., 2013. Zircon re-cords form Miocene ultrapotassic rocks from southern Lhasa sub-terrane, TibetanPlateau. Acta Petrologica Sinica 29, 3703–3715 (in Chinese with English abstract).

Liu, D., Zhao, Z.D., Zhu, D.C., Wang, Q., Sui, Q.L., Liu, Y.S., Hu, Z.C., Mo, X.X., 2011. The pet-rogenesis of post-collisional potassic–ultrapotassic rocks in Xungba basin, westernLhasa terrane: constraints from zircon U–Pb geochronology and geochemistry. ActaPetrologica Sinica 27, 2045–2059 (in Chinese with English abstract).

Liu, D., Zhao, Z., Zhu, D.C., Niu, Y., Widom, E., Teng, F.Z., DePaolo, D.J., Ke, S., Xu, J.F., Wang,Q., 2015. Identifying mantle carbonatite metasomatism through Os–Sr–Mg isotopesin Tibetan ultrapotassic rocks. Earth and Planetary Science Letters 430, 458–469.

Liu, D., Zhao, Z., Zhu, D.C., Niu, Y., DePaolo, D.J., Harrison, T.M., Mo, X., Dong, G., Zhou, S.,Sun, C., Zhang, Z., Liu, J., 2014. Post-collisional potassic and ultrapotassic rocks insouthern Tibet: mantle and crustal origins in response to India–Asia collision andconvergence. Geochimica et Cosmochimica Acta 143, 207–231.

Liu, J., 1999. Volcanoes in China. Science Press, Beijing 219 pp (in Chinese).Ma, L., Wang, B.D., Jiang, Z.Q., Wang, Q., Li, Z.X., Wyman, D.A., Zhao, S.R., Yang, J.H., Gou,

G.N., Guo, H.F., 2014. Petrogenesis of the Early Eocene adakitic rocks in the Napuriarea, southern Lhasa: partial melting of thickened lower crust during slab break-offand implications for crustal thickening in southern Tibet. Lithos 196–197, 321–338.

Mahéo, G., Guillot, S., Blichert-Toft, J., Rolland, Y., Pêcher, A., 2002. A slab breakoff modelfor the Neogene thermal evolution of South Karakorum and South Tibet. Earth andPlanetary Science Letters 195, 45–58.

Marschall, H.R., Schumacher, J.C., 2012. Arc magmas sourced frommélange diapirs in sub-duction zones. Nature Geoscience 5, 862–867.

Masotta, M., Mollo, S., Freda, C., Gaeta, M., Moore, G., 2013. Clinopyroxene-liquid ther-mometers and barometers specific to alkaline differentiated magmas. Contributionsto Mineralogy and Petrology 166, 1545–1561.

McCarthy, T.C., PatiÑO Douce, A.E., 1998. Empirical calibration of the silica-Ca-tschermak's-anorthite (SCAn) geobarometer. Journal of Metamorphic Geology 16,675–686.

Melekhova, E., Annen, C., Blundy, J., 2013. Compositional gaps in igneous rock suites con-trolled by magma system heat and water content. Nature Geoscience 6, 385–390.

Miller, C., Schuster, R., Klötzli, U., Frank, W., Purtscheller, F., 1999. Post-collisional potassicand ultrapotassic magmatism in SW Tibet: geochemical and Sr–Nd–Pb–O isotopic

27L. Zhang et al. / Gondwana Research 41 (2017) 9–28

constraints for mantle source characteristics and petrogenesis. Journal of Petrology40, 1399–1424.

Mo, X., Zhao, Z., Deng, J., Flower, M., Yu, X., Luo, Z., Li, Y., Zhou, S., Dong, G., Zhu, D., 2006a.Petrology and geochemistry of post-collisional volcanic rocks from the Tibetan pla-teau: implications for lithosphere heterogeneity and collision-induced asthenospher-ic mantle flow. Geological Society of America Special Papers 409, 507–530.

Mo, X., Zhao, Z., Depaolo, D.J., Zhou, S., Dong, G., 2006b. Three types of collisional and post-collisional magmatism in the Lhasa block, Tibet and implications for India intra-continental subduction and mineralization: evidence from Sr–Nd isotopes. ActaPetrologica Sinica 22, 795–803 (in Chinese with English abstract).

Mo, X., Dong, G., Zhao, Z., Guo, T., Wang, L., Chen, T., 2005. Timing of magmamixing in theGangdisê Magmatic Belt during the India–Asia collision: zircon SHRIMP U–Pb dating.Acta Geologica Sinica-English Edition 79, 66–76.

Mo, X., Hou, Z., Niu, Y., Dong, G., Qu, X., Zhao, Z., Yang, Z., 2007. Mantle contributions tocrustal thickening during continental collision: evidence from Cenozoic igneousrocks in southern Tibet. Lithos 96, 225–242.

Mo, X., Zhao, Z., Deng, J., Dong, G., Zhou, S., Guo, T., Zhang, S., Wang, L., 2003. Response ofvolcanism to the India–Asia collision. Earth Science Frontiers 10, 135–148 (in Chinesewith English abstract).

Morimoto, N., 1988. Nomenclature of pyroxenes. Mineralogy and Petrology 39, 55–76.Najman, Y., Appel, E., Boudagher-Fadel, M., Bown, P., Carter, A., Garzanti, E., Godin, L., Han,

J., Liebke, U., Oliver, G., 2010. Timing of India–Asia collision: geological, biostrati-graphic, and palaeomagnetic constraints. Journal of Geophysical Research (SolidEarth) 115, 12416.

Nelson, K., 1992. Are crustal thickness variations in old mountain belts like the Appala-chians a consequence of lithospheric delamination? Geology 20, 498–502.

Nelson, K.D., Zhao, W., Brown, L., Kuo, J., Che, J., Liu, X., Klemperer, S., Makovsky, Y.,Meissner, R., Mechie, J., 1996. Partially molten middle crust beneath southern Tibet:synthesis of project INDEPTH results. Science 274, 1684–1688.

Nomade, S., Renne, P.R., Mo, X., Zhao, Z., Zhou, S., 2004. Miocene volcanism in the Lhasablock, Tibet: spatial trends and geodynamic implications. Earth and Planetary ScienceLetters 221, 227–243.

Nowell, G., Kempton, P., Noble, S., Fitton, J., Saunders, A., Mahoney, J., Taylor, R., 1998. Highprecision Hf isotope measurements of MORB and OIB by thermal ionisation mass spec-trometry: insights into the depleted mantle. Chemical Geology 149, 211–233.

Parrish, R.R., Hodges, V., 1996. Isotopic constraints on the age and provenance of the Less-er and Greater Himalayan sequences, Nepalese Himalaya. Geological Society ofAmerica Bulletin 108, 904–911.

Patriat, P., Achache, J., 1984. India–Eurasia collision chronology has implications for crust-al shortening and driving mechanism of plates. Nature 311, 615–621.

Plank, T., Langmuir, C.H., 1998. The chemical composition of subducting sediment and itsconsequences for the crust and mantle. Chemical Geology 145, 325–394.

Putirka, K., Condit, C.D., 2003. Cross section of a magma conduit system at the margin ofthe Colorado Plateau. Geology 31, 701–704.

Putirka, K., Johnson, M., Kinzler, R., Longhi, J., Walker, D., 1996. Thermobarometry of maficigneous rocks based on clinopyroxene-liquid equilibria, 0–30 kbar. Contributions toMineralogy and Petrology 123, 92–108.

Putirka, K.D., 2008. Thermometers and barometers for volcanic systems. Reviews in Min-eralogy and Geochemistry 69, 61–120.

Putirka, K.D., Mikaelian, H., Ryerson, F., Shaw, H., 2003. New clinopyroxene-liquidthermobarometers for mafic, evolved, and volatile-bearing lava compositions, withapplications to lavas from Tibet and the Snake River Plain, Idaho. American Mineral-ogist 88, 1542–1554.

Replumaz, A., Capitanio, F.A., Guillot, S., Negredo, A.M., Villaseñor, A., 2014. The couplingof Indian subduction and Asian continental tectonics. Gondwana Research 26,608–626.

Replumaz, A., Guillot, S., Villaseñor, A., Negredo, A.M., 2013. Amount of Asian lithosphericmantle subducted during the India/Asia collision. Gondwana Research 24, 936–945.

Replumaz, A., Negredo, A.M., Villasenor, A., Guillot, S., 2010. Indian continental subductionand slab break-off during Tertiary collision. Terra Nova 22, 290–296.

Richards, A., Argles, T., Harris, N., Parrish, R., Ahmad, T., Darbyshire, F., Draganits, E., 2005.Himalayan architecture constrained by isotopic tracers from clastic sediments. Earthand Planetary Science Letters 236, 773–796.

Rickwood, P.C., 1989. Boundary lines within petrologic diagrams which use oxides ofmajor and minor elements. Lithos 22, 247–263.

Robinson, D.M., DeCelles, P.G., Patchett, P.J., Garzione, C.N., 2001. The kinematic evolutionof the Nepalese Himalaya interpreted from Nd isotopes. Earth and Planetary ScienceLetters 192, 507–521.

Royden, L.H., Burchfiel, B.C., van der Hilst, R.D., 2008. The geological evolution of the Tibet-an Plateau. Science 321, 1054–1058.

Rudnick, R.L., Gao, S., 2003. Composition of the continental crust. In: Holland, H.D.,Turekian, K.K. (Eds.), Treatise on Geochemistry. Elsevier, Amsterdam (1–63 pp.).

Salters, V.J., Stracke, A., 2004. Composition of the depleted mantle. Geochemistry, Geo-physics, Geosystems 5, Q05B07. http://dx.doi.org/10.1029/2003GC000597.

Searle, M.P., Elliott, J.R., Phillips, R.J., Chung, S.L., 2011. Crustal-lithospheric structure andcontinental extrusion of Tibet. Journal of the Geological Society 168, 633–672.

Seyler, M., Bonatti, E., 1994. Na, AlIV and AlVI in clinopyroxenes of subcontinental and sub-oceanic ridge peridotites: a clue to different melting processes in the mantle? Earthand Planetary Science Letters 122, 281–289.

Shaw, C., Klügel, A., 2002. The pressure and temperature conditions and timing of glassformation in mantle-derived xenoliths from Barley, West Eifel, Germany: the casefor amphibole breakdown, lava infiltration and mineral–melt reaction. Mineralogyand Petrology 74, 163–187.

Shellnutt, J.G., Lee, T.Y., Brookfield, M.E., Chung, S.L., 2014. Correlation betweenmagmatism of the Ladakh Batholith and plate convergence rates during the India–Eurasia collision. Gondwana Research 26, 1051–1059.

Sheppard, S., Taylor, W.R., 1992. Barium-and LREE-rich, olivine-mica-lamprophyres withaffinities to lamproites, Mt. Bundey, Northern Territory, Australia. Lithos 28, 303–325.

Smith, J.V., 1974. Feldspar minerals. Crystal Structure and Physical Properties 1. Springer-Verlag, Berlin (318 pp.).

Söderlund, U., Patchett, P.J., Vervoort, J.D., Isachsen, C.E., 2004. The 176Lu decay constantdetermined by Lu–Hf and U–Pb isotope systematics of Precambrian mafic intrusions.Earth and Planetary Science Letters 219, 311–324.

Spera, F.J., Bohrson, W.A., 2001. Energy-constrained open-system magmatic processes I:general model and energy-constrained assimilation and fractional crystallization(EC–AFC) formulation. Journal of Petrology 42, 999–1018.

Spera, F.J., Bohrson, W.A., 2004. Open-system magma chamber evolution: an energy-constrained geochemical model incorporating the effects of concurrent eruption, re-charge, variable assimilation and fractional crystallization (EC–E′RAχFC). Journal ofPetrology 45, 2459–2480.

Su, B.X., Qin, K.Z., Sakyi, P.A., Li, X.H., Yang, Y.H., Sun, H., Tang, D.M., Liu, P.P., Xiao, Q.H.,Malaviarachchi, S.P.K., 2011. U–Pb ages and Hf–O isotopes of zircons from Late Paleo-zoic mafic-ultramafic units in the southern central Asian orogenic belt: tectonic im-plications and evidence for an early-Permian mantle plume. Gondwana Research20, 516–531.

Sun, C.G., Zhao, Z., Mo, X., Zhu, D.C., Dong, G.C., Zhou, S., Dong, X., Xie, G.G., 2007.Geochernistry and origin of the Miocene sailipu ultrapotassic rocks in westernLhasa block, Tibetan plateau. Acta Petrologica Sinica 23, 2715–2726 (in Chinesewith English abstract).

Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts:implications for mantle composition and processes. Geological Society, London, Spe-cial Publications 42, 313–345.

Tam, P.Y., Zhao, G., Liu, F., Zhou, X., Sun, M., Li, S., 2011. Timing of metamorphism in thePaleoproterozoic Jiao–Liao–Ji Belt: new SHRIMP U–Pb zircon dating of granulites,gneisses and marbles of the Jiaobei massif in the North China Craton. Gondwana Re-search 19, 150–162.

Tapponnier, P., Xu, Z., Roger, F., Meyer, B., Arnaud, N., Wittlinger, G., Yang, J., 2001. Obliquestepwise rise and growth of the Tibet Plateau. Science 294, 1671–1677.

Tian, S., Hu, W., Hou, Z., Mo, X., Yang, Z., Zhao, Y., Hou, K., Zhu, D., Su, A., Zhang, Z., 2012.Enriched mantle source and petrogenesis of Miocene Sailipu ultrapotassic rocks inwestern Lhasa block, Tibetan Plateau: lithium isotopic constraints. Mineral Deposits31, 791–812 (in Chinese with English abstract).

Turner, S., Hawkesworth, C., Liu, J.Q., Rogers, N., Kelley, S., Van Calsteren, P., 1993. Timingof Tibetan uplift constrained by analysis of volcanic rocks. Nature 364, 50–54.

Turner, S., Hawkesworth, C., 1997. Constraints on flux rates andmantle dynamics beneathisland arcs from Tonga-Kermadec lava geochemistry. Nature 389, 568–573.

Turner, S., Arnaud, N., Liu, J., Rogers, N., Hawkesworth, C., Harris, N., Kelleyv, S., Calsteren,P.V., Deng, W., 1996. Post-collision, shoshonitic volcanism on the Tibetan Plateau: im-plications for convective thinning of the lithosphere and the source of ocean islandbasalts. Journal of Petrology 37, 45–71.

Valley, J.W., 2003. Oxygen isotopes in zircon. Reviews in Mineralogy and Geochemistry53, 343–385.

Vidal, P., Bernard-Griffiths, J., Cocherie, A., Le Fort, P., Peucat, J., Sheppard, S., 1984. Geo-chemical comparison between Himalayan and Hercynian leucogranites. Physics ofthe Earth and Planetary Interiors 35, 179–190.

Vidal, P., Cocherie, A., Le Fort, P., 1982. Geochemical investigations of the origin of theManaslu leucogranite (Himalaya, Nepal). Geochimica et Cosmochimica Acta 46,2279–2292.

Wang, B., Chen, J., Xu, J., Wang, L., 2014. Geochemical and Sr–Nd–Pb–Os isotopic compo-sitions of Miocene ultrapotassic rocks in southern Tibet: petrogenesis and implica-tions for the regional tectonic history. Lithos 208–209, 237–250.

Wang, B., Xu, J., Zhang, X., Chen, J., Kang, Z., Dong, Y., 2008. Petrogenesis of Miocene vol-canic rocks in the Sailipu area, western Tibetan Plateau: geochemical and Sr–Nd iso-topic constraints. Acta Petrologica Sinica 24, 265–278 (in Chinese with Englishabstract).

Wang, Y., Zhao, C., Zhang, F., Liu, J., Wang, J., Peng, R., Liu, B., 2015. SIMS zircon U–Pb andmolybdenite Re–Os geochronology, Hf isotope, and whole-rock geochemistry of theWunugetushan porphyry Cu–Mo deposit and granitoids in NE China and their geo-logical significance. Gondwana Research 28, 1228–1245.

Wei, W., Unsworth, M., Jones, A., Booker, J., Tan, H., Nelson, D., Chen, L., Li, S., Solon, K.,Bedrosian, P., 2001. Detection of widespread fluids in the Tibetan crust bymagnetotelluric studies. Science 292, 716–718.

Wen, D.R., Liu, D., Chung, S.L., Chu, M.F., Ji, J., Zhang, Q., Song, B., Lee, T.Y., Yeh, M.W., Lo,C.H., 2008. Zircon SHRIMP U–Pb ages of the Gangdese Batholith and implicationsfor Neotethyan subduction in southern Tibet. Chemical Geology 252, 191–201.

Whittington, A., Foster, G., Harris, N., Vance, D., Ayres, M., 1999. Lithostratigraphic corre-lations in the western Himalaya—an isotopic approach. Geology 27, 585–588.

Wiedenbeck, M., Hanchar, J.M., Peck, W.H., Sylvester, P., Valley, J., Whitehouse, M., Kronz,A., Morishita, Y., Nasdala, L., Fiebig, J., 2004. Further characterisation of the 91500 zir-con crystal. Geostandards and Geoanalytical Research 28, 9–39.

Williams, H.M., Turner, S.P., Pearce, J.A., Kelley, S.P., Harris, N.B.W., 2004. Nature of thesource regions for post-collisional, potassic magmatism in southern and northernTibet from geochemical variations and inverse trace element modeling. Journal of Pe-trology 45, 555–607.

Williams, H., Turner, S., Kelley, S., Harris, N., 2001. Age and composition of dikes in south-ern Tibet: new constraints on the timing of east–west extension and its relationshipto post-collisional volcanism. Geology 29, 339–342.

Wilson, M., 1989. Igneous Petrogenesis: A Global Tectonic Approach. Unwin Hyman,London, pp. 1–466.

Woodhead, J., Hergt, J., Davidson, J., Eggins, S., 2001. Hafnium isotope evidence for ‘con-servative’ element mobility during subduction zone processes. Earth and PlanetaryScience Letters 192, 331–346.

28 L. Zhang et al. / Gondwana Research 41 (2017) 9–28

Workman, R.K., Hart, S.R., 2005. Major and trace element composition of the depletedMORB mantle (DMM). Earth and Planetary Science Letters 231, 53–72.

Wu, C., Nelson, K., Wortman, G., Samson, S.D., Yue, Y., Li, J., Kidd, W., Edwards, M., 1998.Yadong cross structure and South Tibetan Detachment in the east central Himalaya(89–90°E). Tectonics 17, 28–45.

Wu, F., Li, X., Zheng, Y., Gao, S., 2007. Lu–Hf isotopic systematics and their applications inpetrology. Acta Petrologica Sinica 23, 185–220 (in Chinese with English abstract).

Wu, F.Y., Ji, W.Q., Wang, J.G., Liu, C.Z., Chung, S.L., Clift, P.D., 2014. Zircon U–Pb and Hf iso-topic constraints on the onset time of India–Asia collision. American Journal of Sci-ence 314, 548–579.

Wu, S., Zheng, Y.Y., Sun, X., Liu, S.A., Geng, R.R., You, Z.M., Ouyang, H.T., Lei, D., Zhao, Z.Y.,2014. Origin of the Miocene porphyries and their mafic microgranular enclaves fromDabu porphyry Cu–Mo deposit, southern Tibet: implications for magma mixing/min-gling and mineralization. International Geology Review 56, 571–595.

Xia, L., Li, X., Ma, Z., Xu, X., Xia, Z., 2011. Cenozoic volcanism and tectonic evolution of theTibetan plateau. Gondwana Research 19, 850–866.

Xu, H., Zhang, J., Yu, T., Rivers, M., Wang, Y., Zhao, S., 2015. Crystallographic evidence forsimultaneous growth in graphic granite. Gondwana Research 27, 1550–1559.

Xu, Q., Zhao, J., Yuan, X., Liu, H., Pei, S., 2015. Mapping crustal structure beneath southernTibet: Seismic evidence for continental crustal underthrusting. Gondwana Research27, 1487–1493.

Xu, W.C., Zhang, H.F., Guo, L., Yuan, H.L., 2010. Miocene high Sr/Y magmatism, southTibet: product of partial melting of subducted Indian continental crust and its tecton-ic implication. Lithos 114, 293–306.

Yi, Z., Huang, B., Chen, J., Chen, L., Wang, H., 2011. Paleomagnetism of early Paleogenema-rine sediments in southern Tibet, China: implications to onset of the India–Asia colli-sion and size of Greater India. Earth and Planetary Science Letters 309, 153–165.

Yin, A., Harrison, T.M., 2000. Geologic evolution of the Himalayan-Tibetan orogen. AnnualReview of Earth and Planetary Sciences 28, 211–280.

Yokoyama, T., Nakai, S., Wakita, H., 1999. Helium and carbon isotopic compositions of hotspring gases in the Tibetan Plateau. Journal of Volcanology and Geothermal Research88, 99–107.

Yu, X., 1994. Titanphlogopites from Cenozoic alkaline volcanic rock in western Qinling,Gansu province. Acta Petrologica et Mineralogica 13, 319–327 (in Chinese with En-glish abstract).

Zartman, R.E., Haines, S.M., 1988. The plumbotectonic model for Pb isotopic systematicsamong major terrestrial reservoirs—a case for bi-directional transport. Geochimicaet Cosmochimica Acta 52, 1327–1339.

Zeng, Y.C., Chen, J.L., Xu, J.F., Lei, M., Xiong, Q.W., 2017. Origin of Miocene Cu-bearing por-phyries in the Zhunuo region of the southern Lhasa subterrane: constraints from geo-chronology and geochemistry. Gondwana Research 41, 51–64.

Zhang, H., Zhao, D., Zhao, J., Liu, H., 2015. Tomographic imaging of the underthrustingIndian slab and mantle upwelling beneath central Tibet. Gondwana Research 28,121–132.

Zhang, L.Y., Ducea, M.N., Ding, L., Pullen, A., Kapp, P., Hoffman, D., 2014. Southern TibetanOligocene-Miocene adakites: a record of Indian slab tearing. Lithos 210–211,209–223.

Zhang, L.H., Guo, Z.F., Zhang, M.L., Cheng, Z.H., 2014. Study on soil micro-seepage gas fluxin the high temperature geothermal area: an example from the Yangbajing geother-mal field, South Tibet. Acta Petrologica Sinica 30, 3612–3626 (in Chinese with Englishabstract).

Zhang, S.Q., 1996. Mesozoic and Cenozoic Volcanism in Central Gangdese: Implicationsfor Lithospheric Evolution of the Tibetan Plateau Ph. D. thesis in Beijing China Univer-sity of Geosciences (in Chinese with English abstract).

Zhang, Z., Klemperer, S.L., 2005. West–east variation in crustal thickness in northernLhasa block, central Tibet, from deep seismic sounding data. Journal of GeophysicalResearch: Solid Earth 110, B09403. http://dx.doi.org/10.1029/2004JB003139.

Zhao, J., Yuan, X., Liu, H., Kumar, P., Pei, S., Kind, R., Zhang, Z., Teng, J., Ding, L., Gao, X.,2010. The boundary between the Indian and Asian tectonic plates below Tibet. Pro-ceedings of the National Academy of Sciences 107, 11229–11233.

Zhao, J., Zhao, D., Zhang, H., Liu, H., Huang, Y., Cheng, H., Wang, W., 2014. P-wave tomog-raphy and dynamics of the crust and uppermantle beneathwestern Tibet. GondwanaResearch 25, 1690–1699.

Zhao,W., Kumar, P., Mechie, J., Kind, R., Meissner, R., Wu, Z., Shi, D., Su, H., Xue, G., Karplus,M., 2011. Tibetan plate overriding the Asian plate in central and northern Tibet. Na-ture Geoscience 4, 870–873.

Zhao,W., Nelson, K., Che, J., Quo, J., Lu, D., Wu, C., Liu, X., 1993. Deep seismic reflection ev-idence for continental underthrusting beneath southern Tibet. Nature 366, 557–559.

Zhao, X., Xue, C., Symons, D.T.A., Zhang, Z., Wang, H., 2014. Microgranular enclaves inisland-arc andesites: a possible link between known epithermal Au and potentialporphyry Cu–Au deposits in the Tulasu ore cluster, western Tianshan, Xinjiang,China. Journal of Asian Earth Sciences 85, 210–223.

Zhao, Z., Mo, X., Dilek, Y., Niu, Y., DePaolo, D.J., Robinson, P., Zhu, D., Sun, C., Dong, G., Zhou,S., 2009. Geochemical and Sr–Nd–Pb–O isotopic compositions of the post-collisionalultrapotassic magmatism in SW Tibet: petrogenesis and implications for Indiaintra-continental subduction beneath southern Tibet. Lithos 113, 190–212.

Zhao, Z., Mo, X., Nomade, S., Renne, P.R., Zhou, S., Dong, G., Wang, L., Zhu, D., Liao, Z., 2006.Post-collisional ultrapotassic rocks in the Lhasa block, the Tibetan plateau: specialand temporal distribution and its implications. Acta Petrologica Sinica 22, 787–794(in Chinese with English abstract).

Zhao, Z.D., Zhu, D.C., Dong, G.C., Mo, X.X., Depaolo, D., Jia, L.L., Hu, Z.C., Yuan, H.L., 2011.The similar to 54 Ma gabbro-granite intrusive in southern Dangxung area, Tibet: pet-rogenesis and implications. Acta Petrologica Sinica 27, 3513–3524 (in Chinese withEnglish abstract).

Zhou, H.W., Murphy, M.A., 2005. Tomographic evidence for wholesale underthrusting ofIndia beneath the entire Tibetan plateau. Journal of Asian Earth Sciences 25, 445–457.

Zhou, S., Mo, X., Zhao, Z., Qiu, R., Niu, Y., Guo, T., Zhang, S., 2010. 40Ar/39Ar geochronologyof post-collisional volcanism in the middle Gangdese Belt, southern Tibet. Journal ofAsian Earth Sciences 37, 246–258.

Zhu, D.C., Mo, X.X., Niu, Y., Zhao, Z.D., Wang, L.Q., Pan, G.T., Wu, F.Y., 2009. Zircon U–Pbdating and in–situ Hf isotopic analysis of Permian peraluminous granite in theLhasa terrane, southern Tibet: implications for Permian collisional orogeny and pa-leogeography. Tectonophysics 469, 48–60.

Zhu, D.C., Pan, G.T., Chung, S.L., Liao, Z.L., Wang, L.Q., Li, G.M., 2008. SHRIMP zircon age andgeochemical constraints on the origin of Lower Jurassic volcanic rocks from the Yebaformation, southern Gangdese, South Tibet. International Geology Review 50,442–471.

Zhu, D.C., Zhao, Z.D., Niu, Y., Dilek, Y., Hou, Z.Q., Mo, X.X., 2013. The origin and pre-Cenozoic evolution of the Tibetan plateau. Gondwana Research 23, 1429–1454.

Zhu, D.C., Zhao, Z.D., Niu, Y., Mo, X.X., Chung, S.L., Hou, Z.Q., Wang, L.Q.,Wu, F.Y., 2011. TheLhasa terrane: record of a microcontinent and its histories of drift and growth. Earthand Planetary Science Letters 301, 241–255.

Zindler, A., Hart, S., 1986. Chemical geodynamics. Annual Review of Earth and PlanetarySciences 14, 493–571.

Zou, H., Zindler, A., Xu, X., Qi, Q., 2000. Major, trace element, and Nd, Sr and Pb isotopestudies of Cenozoic basalts in SE China: mantle sources, regional variations, and tec-tonic significance. Chemical Geology 171, 33–47.