A. KADARUSMAN AND C. D. PARKINSON-- Petrology and P–T evolution of garnet peridotites from Central...

8/3/2019 A. KADARUSMAN AND C. D. PARKINSON-- Petrology and PT evolution of garnet peridotites from Central Sulawesi

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J. metamorphic Geol., 2000, 18, 193209

Petrology and PTevolution of garnet peridotites from centralSulawesi, Indonesia

A . K A DA R US M AN * A N D C . D . PA R KI N SO N

Department of Earth and Planetary Science, Tokyo Institute of Technology, O-okayama 2-12-1, Meguro, Tokyo 152-8551, Japan(E-mail: [email protected])

A B S T R A C T Alpine-type orogenic garnet-bearing peridotites, associated with quartzo-feldspathic gneisses of a 140115 Ma high-pressure/ultra-high-pressure metamorphic (HP-UHPM) terrane, occur in two regions ofthe Indonesian island of Sulawesi. Both exposures are located within NWSE-trending strikeslip faultzones. Garnet lherzolite occurs as 28 kbar, peak Tofc. 760 C) meta-morphic basement terrane, which was recrystallized and uplifted in a N-dipping continental collisionzone at the southern Sundaland margin in the mid-Cretaceous. The low-T, low-P and metasomatizedspinel lherzolite precursor to the garnet lherzolite probably represents mantle wedge rocks that weredragged down parallel to the slabwedge interface in a subduction/collision zone by induced corner flow.Ductile tectonic incorporation into the underthrust continental crust from various depths along theinterface probably occurred during the exhumation stage, and the garnet peridotites were subsequentlyuplifted within the HP-UHPM nappe, suffering a similar decompression history to that experienced bythe regional schists and gneisses. Final exhumation from upper crustal levels was clearly facilitated byentrainment in Neogene granitic plutons, and/or Oligocene trans-tension in deep-seated strikeslipfault zones.

Key words: continental collision; garnet peridotite; geothermobarometry; petrology; Sulawesi.

region of Norway ( Brueckner & Medaris, 1998), whereIN T R OD U CT IONthey commonly occur as tectonic intercalations withinrecrystallized supra-crustal sequences. These orogenicGarnet-bearing peridotites are widespread but volu-

metrically minor constituents of A-type (collisional) ultramafic rocks provide important information on thenature of the interaction between mantle and crustalorogenic belts such as the Bohemian massif and the

Lepontine Alps (Medaris & Carswell, 1990), and ultra- materials during collisional orogenesis; for this reasonthe petrology, geochemistry and geochronology ofhigh-pressure metamorphic (UHPM) terranes such as

the Dabie-Sulu terranes of eastern China (Zhang et al., garnet peridotites in the aforementioned localities havebeen the subject of intensive recent study. Of particular1994; Liou & Zhang, 1998) and the Western Gneiss

193 Blackwell Science Inc., 0263-4929/00/$15.00Journal of Metamorphic Geology, Volume 18, Number 2, 2000


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194 A . K A D A R U S M A N & C . D . P A R K I N S O N

significance are mineralogical and textural indicators garnet peridotites. Our interpretation of the tectonicsetting of generation and uplift differs significantlyof wadsleyite, clinoenstatite and majorite precursors in

some orogenic peridotites, suggesting that they may from that proposed by Helmers et al. (1990).Abbreviations for mineral assemblages and molarhave been derived from mid-mantle depths. On the

basis of thermobarometric and geochemical variations components follow Kretz (1983) .of garnet peridotites in different orogens, it is widelyaccepted that they may represent either (1) the mantle

G E O L O G I C A L S E T T I N G A N D F I E L Dunderpinning of subducted oceanic or continental

R ELAT ION SH IP Scrust, or (2 ) mantle wedge peridotites transferred to

the subducting slab during subductioncollision, or (3) The island of Sulawesi has a central position withinthe complex Indonesian tectonic collage, such that itsproducts of subduction zone metamorphism of peri-dotites previously emplaced in the crust (e.g. Zhang geological framework is diverse, complicated and still

incompletely characterized. The constituent lithotec-et al., 1994; Brueckner & Medaris, 1998).On the Indonesian island of Sulawesi (formerly tonic units include Cenozoic magmatic arcs, Palaeozoic

microcontinental fragments of Australian provenance,Celebes), Alpine-type MgCr garnet peridotites occuras tectonic intercalations and blocks associated with late Cretaceous to Oligocene ophiolite massifs and two

types of high-P/Tmetamorphic terranes. A serpentinitedunite, spinel peridotite, eclogite, garnet granulite andquartzo-feldspathic gneisses in two regions of a (locally) blueschist melange of ophiolitic fragments of Oligocene

age crops out in eastern Sulawesi (Parkinson, 1996),coesite-bearing high-pressure/ultra-high-pressure meta-morphic (HP-UHPM) terrane of mid-Cretaceous age and an extensive, coherent terrane of c. 140115 Ma

quartzo-feldspathic schist, gneiss, blueschist and eclo-(Parkinson et al., 1998) (Fig. 1). Both exposures arelocated within profound NWSE-trending strikeslip gite ( Parkinson, 1998; Parkinson et al., 1998) consti-

tutes the geological basement throughout central andfault zones: garnet lherzolite occurs as 28 kbar indicated by coesite inclusionsin zircon in jadeite quartzites of the Bantimalafault in the Bongka river valley (Fig. 2b). Despite their

geographical separation (about 200 km) and differing Complex of South Sulawesi; Parkinson et al., 1998;Parkinson & Katayama, 1999); some rocks clearlygeological settings, the garnet peridotites have signifi-

cant petrological and thermobarometric similarities. suffered burial to depths in excess of 90 km.Small quantities of garnet peridotite associated withAs with most pre-Tertiary basement rocks in the

Indonesian region, the Sulawesi garnet peridotites have greenschist, amphibolite and granulite facies gradequartzo-feldspathic gneiss and eclogite of the midbeen subject to only limited reconnaissance study.

Egeler (1947) reported some petrographic characteristics Cretaceous HP-UHPM terrane crop out in twolocalities in western and eastern central Sulawesi. Inof these rocks and associated schist and gneiss samples

collected by H. A. Brouwer and his co-workers in 1929 the former, within the Palu-Koro fault zone, garnetperidotite occurs as


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P E T R O L O G Y O F S U L A W E S I G A R N E T P E R I D O T I T E S 195

Fig. 1. Highly simplified map ofthe major lithotectonic units inSulawesi (modified afterParkinson, 1998), showing thelocations of garnet peridotite inthe Palu-Koro fault valley of west

central Sulawesi, and the Bongkariver of the East Arm. The locationof coesite-bearing jadeitequartzitein the Bantimala Complex is alsoindicated.

ophiolite, and to be a constituent within the mid- garnet, orthopyroxene, olivine and clinopyroxene.Garnet (which may constitute up to 10 vol% of theCretaceous, high-P/T Pompangeo schist complex,

which constitutes the underthrust quartzo-feldspathic rock) attains a diameter of 28 mm in Palu-Korosamples and up to 15 mm in BR ones. Olivinecontinental basement to the ophiolite massif.

Despite their geographical separation and differing constitutes 4060 vol%, and orthopyroxene andclinopyroxene, about 1025 and 510 vol%, respect-geological settings, the garnet peridotites from both

localities have very similar mineral assemblages, over- ively. Spinel, amphibole and phlogopite are minorconstituents, and generally constitute


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Fig. 2. Geological maps and localities of garnet peridotite samples in (a) the Palu-Koro region and (b) the Bongka river, modifiedafter Sukamto (1975) and Parkinson (1998), respectively.

described from olivine in Alpe Arami (Lepontine Alps) (P-K) and 14 mm ( BR). Inner and outer zones canbe easily discerned in BR samples, but less so in P-Kand Sulu (eastern China) peridotites (Dobrzhinetskaya

et al., 1996; Hacker et al., 1997). In most samples, samples. The inner zones of kelyphites are composedof orthopyroxene, clinopyroxene and spinel (Fig. 4f ),garnet cores display exsolution of very fine, acicular

rutile. Orthopyroxene invariably displays exsolution whereas the outer zones consist of orthopyroxeneand/or amphibole and minor zoisite. In some sampleslamellae of clinopyroxene and spinel, and clinopyrox-

ene contains lamellae of orthopyroxene, spinel and from P-K (9445K & 9517G) and BR (P-135 & P-134),garnet is completely replaced by kelyphitic Opx+amphibole.

Most garnet contains numerous inclusions compris- Cpx+Spl.Serpentinization is moderate (515%) in theing clinopyroxene, orthopyroxene, olivine, spinel,

ilmenite, Ni-sulphides and the hydrous phases majority of P-K samples and strong (1525%) in thosefrom BR, but is generally restricted to fractures inpargasitic amphibole, phlogopite and Mg-chlorite

(Figs 3 & 4b,c,d). Inclusions are generally 12 mm olivine, where serpentine minerals (antigorite) areassociated with magnetite, chlorite, pentlandite andacross. Those inclusions which are not contiguous

with later-stage fractures and kelyphitization, com- minor tremolite, pectolite, Mg-rich ilmenite, talc orcalcite.positionally different from matrix phases where

present and do not display recrystallization orpseudomorph textures, are interpreted to represent

M E TA M O R P H I C E V O L U T I O Npre-garnet-growth phases. Amphibole, phlogopite andspinel also occur along the grain boundaries of garnet Six evolutionary stages of recrystallization can be

recognized in most garnet lherzolites from bothand pyroxene (Fig. 4e).Garnet porphyroblasts are strongly kelyphitized localities, based on microtextural analyses and mineral-

ogical investigation. Mineral parageneses are shown in(Fig. 3), and kelyphitic zones attain widths of 12 mm


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in response to increasing pressure, and from thebreakdown of pargasitic amphibole to form garnetand clinopyroxene according to reaction (2).

Opx1+Cpx

1+Spl

1=Grt

1+Ol

2(1)

Prg-Amp1=2 Cpx

2+Grt

1+H

2O (2)

Stage III, defined by a spinelgarnet lherzolite assem-blage, Ol

3+Opx

3+Cpx

3Spl

2Grt

2 Hbl

2Phl

2,

is generally fine-grained due to granulation defor-

mation, and includes hydrous phases. Stage III is notalways present in BR peridotites. Pargasitic amphibolereplaces stage II clinopyroxene, and occasionally isdeveloped along garnet rims. The presence of thehydrous phases indicates metasomatism and hydrationduring uplift, and they were probably generated byreactions (3) for hydration and reaction (4) of Arai &Takahashi (1989) for metasomatism.

Cpx2+Grt

1+H

2O=Prg-Amp

2(3)

K-rich fluid+Ol2+Opx

2=2 Phl

2(4)

The granulite facies assemblage of stage IV is manifestas kelyphitic development of fibrous Opx

4+

Cpx4+(green) Spl

3in inner coronas around coarse-

grained garnet porphyroblasts. The development ofthe inner kelyphitic assemblages may have resultedfrom the decompression reaction:

Grt2+Ol

2=Opx

4+Cpx

4+Spl

3(5)

The amphibolite facies assemblage of stage V is presentas kelyphitic development of Opx

5+Spl

4Prg-Amp

3 Ep in outer coronas around garnet. This stage is

1.0 mm

Grt

Ol

Opx

Cpx

serpentine

nickel-sulphides inner kelyphite

outer kelyphite

OpxCpx

Phl

Amp

Ol

Cpxcomposite inclusion

only poorly developed in many P-K samples, andFig. 3. Partially schematic sketch of typical garnet overgrowthsome BR samples. Clinopyroxene probably reactedtextures in sample P-136 (Bongka river). The garnet contains

composite inclusions of olivine, clinopyroxene, orthopyroxene, with Opx+Spl to form pargasitic amphibole by thepargasitic amphibole and phlogopite (see also Fig. 4b) and hydration reaction:inner/outer kelyphitic coronas. Geothermobarometric data

were obtained from pyroxene and olivine which are in contact Cpx4+Opx

4+Spl

3+H

2O=Prg-Amp

3+Ol

3(6)

with garnet with very thin or no kelyphitic corona.

The final (greenschist facies) retrogressive stage VI ischaracterized by recrystallization of Serp+Chl

Fig. 5 and the idealized equilibrium mineral assem-MagCalTlcTr in fractures. Stage VI is more

blages of the recognized stages are listed in Table 1.pervasively developed in BR peridotites than those

However, in individual samples from both localities,from P-K. This stage can be represented by reaction

all mineralogical stages are not always present.(7) of Sill (1982), whereby excess Na

2O may have been

Stage I, the precursor spinel lherzolite assemblage,removed by a fluid phase.

is characterized by Ol1+Cpx

1+Opx

1(brown) Spl

14 Hbl

2+9 Opx

3+8 Ol

3+24 H

2O (7) Prg-Amp

1RtPhl

1, as inclusions within garnet.

In some BR samples, Mn-rich (c. 2530 wt% MnO) =4 Tr+6 Chl+2 Na2

Oilmenite, Ni-sulphides (heazlewoodite, with >70 wt%NiO, and pentlandite) and the hydrous phases of

D EFOR MAT ION FAB R ICSpargasitic amphibole and Mg-chlorite also occur asinclusions in garnet, and from textural evidence, Olivine, garnet, clinopyroxene and orthopyroxene in

some peridotites from both localities have sufferedprobably also constitute stable phases of the stage Iassemblage. ductile granulation and warping and kinking of grains

resulting in undulose extinction and strong curvatureStage II, the main garnet lherzolite assemblage,consists of coarse-grained Ol

2+Opx

2+Cpx

2+Grt

1. of cleavage traces and exsolution lamellae (particularly

apparent in orthopyroxene); granulation is moreWe interpret the stage I to stage II transformation tohave progressed by reaction of spinel with orthopyrox- intense in the P-K peridotites, kinking in BR peri-

dotites. From textural evidence (e.g. overprinting ofene and clinopyroxene to form garnet and olivine (1)


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Fig. 4. Photomicrographs and back-scattered electron image showing mineral assemblages and textures of garnet lherzolite fromboth localities in Sulawesi. (a) Blackbrown rods of exsolved ilmenite within core of large olivine grain (sample P-136); width offield 120 mm, plane polars. (b) Inclusion aggregates of Ol+Cpx+Opx+pargasitic-Amp+Phl in garnet core (sample P-136); widthof field 2.5 mm, plane polars. (c) Back-scattered electron image of spinel inclusion (Spl) in garnet core (sample EA-11); scale bar is10 mm. (d) Euhedral phlogopite (Phl) inclusion within garnet porphyroblast (sample C-12); width of field 0.7 mm, plane polars. (e)Phlogopite (Phl), orthopyroxene (Opx), olivine (Ol) and amphibole (Prg) as constituents of stage III (sample 9477B); width of field1.0 mm, plane polars. (f ) Back-scattered electron image of part of inner (Opx+Cpx+Spl) and outer (orthopyroxene) kelyphite rims(sample P-136); scale bar is 10 mm.


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Fig. 5. Mineral paragenesis of thedifferent metamorphic stages inSulawesi garnet peridotite.

I II III IV V VIStage

Mineral

OlivineEnstatiteDiopside

Garnet

PhlogopiteSpinel

Pargasite

Edenite

Tremolite

Zoisite

Chlorite

Rutile

Antigorite

MagnetitePentlandite

Table 1. Metamorphic evolution of Sulawesi garnet peridotites.

Stage Mineral parageneses Textural evidence Interpretation

I Ol1+Opx

1+Cpx

1Spl

1Phl

1Hbl

1Rt Inclusions Spl lherzolite protolith

II Ol2+Opx

2+Cpx

2+Grt

1Coarse-grained Grt lherzolite

III Ol3+Opx3+Cpx3Grt2Spl2Hbl2Phl2 Neoblastic, fine-grained High-Teclogite faciesIV Opx

4+Cpx

4+Spl

3Inner radial kelyphite Granulite

facies

V Opx5Spl

4Hbl

3Zo

1Outer radial kelyphite Amphibolite facies

VI Srp+ChlMagCalTrTlcNi-sulphides Serpentinization Greenschist facies

deformation fabrics by kelyphite coronas), this ductileGarnet

event closely post-dates stage II and pre-dates stageIII recrystallization. Later cataclastic fracturing A representative compositional profile of stage II garnet is shown in

Fig. 7(a) for sample EA-11. Profiles are relatively flat, particularlyaccompanies stage VI recrystallization. Post-stage VIfor core/mantle regions, rims display a slight decrease in MgO anddeformation is restricted to P-K peridotites and isincrease in FeO+MnO contents. The narrow outermost rim,

defined by a weak fabric associated with further however, shows a much stronger compositional variation, with aserpentinization. This event may be related to shallow- sharp decrease in MgO. The compositional zoning profile is similar

to that of garnet in Alpe Arami garnet peridotite described bylevel left-lateral shear in the Palu-Koro fault zone.Brenker & Brey (1997), who interpreted garnet cores to reflectfrozen equilibrium of the peak stage, and rims to reflect the firstretrograde stage. The narrow outermost rims are interpreted to beM I N E R A L C O M P O S I T I O N Srelated to late reaction with kelyphite minerals.

Stage II garnet core compositions are typically in the range:Sixteen representative garnet peridotite samples from both localitieswere selected for analyses of mineral compositions. Analyses were prp

7074, alm

1318, grs

1113, sps

0.30.7, while rim compositions are

prp6772

, alm1523

, grs1014

, sps0.31.3

. Cr2O

3contents are low andperformed using a JEOL 8800 EPMA (electronprobe microanalyser)

with accelerating voltage of 15 kV, beam current of 12 nA, and a differences between samples probably reflect differing bulk composi-tions, with ranges ofc. 0.591.70 wt% for cores and c. 0.701.77 wt%beam spot of


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Table 2. Representative mineral analyses of Sulawesi garnet periodites.

9532a(PK)

Sample

Mineral Ol Ol Ol Opx Opx Opx Opx Cpx Cpx Cpx Grt Grt Grt Amp

Point no. 32-r 26-c 57-c 20-c 21-r 34-c 55-c 22-c 23-r 28-c 1-r 9-c 33-c 44-c

Stage I II III II II III IV II II III II II III V

SiO2

41.47 41.45 41.23 57.66 57.77 57.73 58.43 55.94 55.34 55.91 41.83 42.68 42.60 44.49

TiO2

0.02 0.00 0.04 0.03 0.03 0.06 0.16 0.19 0.31 0.22 0.22 0.34 0.09 0.36

Al2O

20.01 0.02 0.00 1.50 1.30 1.36 1.15 3.25 3.20 2.87 22.85 22.73 22.62 17.81

Cr2O

20.04 0.04 0.00 0.16 0.14 0.16 0.21 1.19 1.23 0.62 1.51 1.69 0.88 0.58

FeO* 9.72 9.33 10.45 6.57 6.62 6.26 7.03 2.42 2.40 2.47 8.75 8.15 8.72 3.50

MnO 0.15 0.09 0.19 0.16 0.09 0.16 0.04 0.07 0.04 0.33 0.20 0.22 0.11

NiO 0.41 0.29 0.42 0.00 0.12 0.05 0.08 0.00 0.07 0.08 0.02 0.03 0.01 0.10MgO 49.36 49.97 48.37 34.34 35.18 33.20 32.34 15.91 15.93 16.18 20.48 20.37 20.54 17.65

CaO 0.00 0.00 0.01 0.29 0.25 0.28 0.28 19.74 19.64 20.62 4.27 4.80 4.54 10.64

Na2O 0.00 0.00 0.04 0.00 0.00 0.02 0.02 1.83 1.86 1.57 0.03 0.03 0.00 3.48

K2O 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.01 0.00 0.02 0.03 0.00 0.01 0.01

Total 101.17 101.20 100.74 100.75 101.56 99.21 99.85 100.50 100.03 100.60 100.31 101.02 110.20 98.73

Si 1.00 1.00 1.00 1.97 1.96 2.00 2.01 2.00 1.99 2.00 2.97 3.00 3.02 6.17

Ti 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.02 0.00 0.04

Al 0.00 0.00 0.00 0.06 0.05 0.06 0.05 0.14 0.14 0.12 1.91 1.88 1.89 2.91

Cr 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.03 0.03 0.02 0.08 0.09 0.05 0.06

Fe2+ 0.20 0.19 0.21 0.19 0.19 0.18 0.20 0.07 0.07 0.07 0.52 0.48 0.52 0.41

Mn 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.01 0.01 0.01

Ni 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01

Mg 1.78 1.80 1.76 1.75 1.78 1.71 1.66 0.85 0.85 0.86 2.17 2.14 2.17 3.65

Ca 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.76 0.76 0.79 0.32 0.36 0.34 1.58

Na 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.13 0.13 0.11 0.00 0.00 0.00 0.94

K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Total 2.99 2.99 2.99 3.99 4.01 3.97 3.95 3.98 3.98 3.98 8.02 7.99 8.01 15.77

XMg

0.90 0.91 0.89 0.90 0.90 0.90 0.89 0.92 0.92 0.92 0.81 0.82 0.81 0.90

EA-11 (BR)

Sample

Mineral Ol Cpx Cpx Opx Opx Opx Grt Grt Amp Amp Amp Amp Spl Spl

Point no. 54-r 52-c 55-r 46-c 64-r 65-c 20-r 28-c 85-c 10-r4-r 96-c 87-c 77-c

Stage II II II I II II II II I III V VI I III

SiO2

40.50 53.58 53.98 56.96 56.25 55.92 42.48 42.77 43.46 45.47 45.52 57.95 0.08 0.03

TiO2

0.00 0.15 0.09 0.06 0.00 0.06 0.29 0.33 0.56 0.53 0.24 0.09 0.10 0.73

Al2O

30.00 2.00 1.82 1.74 2.39 2.77 22.51 22.49 15.70 12.51 14.70 0.27 46.42 26.09

Cr2O

30.00 0.62 0.72 0.19 0.40 0.38 0.69 0.76 1.35 0.78 0.57 0.07 21.84 27.60

FeO* 10.36 3.42 2.20 7.36 7.08 7.15 8.55 7.82 2.89 4.24 5.17 1.29 12.70 36.63

MnO 0.09 0.11 0.05 0.13 0.14 0.16 0.24 0.18 0.06 0.07 0.14 0.01 0.14 0.45

NiO 0.41 0.03 0.05 0.04 0.01 0.10 0.01 0.00 0.17 0.07 0.07 0.03 0.14 0.27

MgO 49.23 17.34 17.28 33.80 33.36 33.49 20.00 20.71 18.59 18.52 16.97 24.46 18.44 7.07

CaO 0.07 22.34 24.16 0.22 0.23 0.21 4.50 4.66 10.77 12.52 11.14 12.87 0.17 0.01

Na2O 0.04 0.31 0.37 0.04 0.04 0.02 0.06 0.00 2.05 2.95 2.57 0.23 0.05 0.07

K2

0.00 0.01 0.01 0.00 0.01 0.00 0.01 0.00 0.45 0.02 0.01 0.05 0.02 0.02

Total 100.70 99.90 100.81 100.54 99.91 100.26 99.33 99.73 96.03 97.68 97.10 97.32 100.07 98.96

Si 0.99 1.95 1.95 1.96 1.95 1.93 3.02 3.02 6.19 6.44 6.45 7.92 0.02 0.01

Ti 0.00 0.00 0.01 0.00 0.00 0.00 0.02 0.02 0.06 0.06 0.03 0.01 0.02 0.14

Al 0.00 0.09 0.08 0.07 0.10 0.11 1.89 1.88 2.64 2.09 2.45 0.04 11.93 8.09

Cr 0.00 0.02 0.02 0.01 0.01 0.01 0.04 0.04 0.15 0.09 0.06 0.01 3.77 5.74

Fe2+ 0.21 0.10 0.07 0.21 0.21 0.21 0.51 0.46 0.34 0.50 0.61 0.15 2.32 8.06

Ni 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.01 0.01 0.00 0.02 0.06

Mg 1.79 0.94 0.93 1.73 1.72 1.72 2.13 2.19 3.95 3.91 3.58 4.99 6.00 2.77

Ca 0.00 0.87 0.93 0.01 0.01 0.01 0.34 0.35 1.64 1.90 1.69 1.89 0.04 0.00

Na 0.00 0.02 0.03 0.00 0.00 0.00 0.01 0.00 0.57 0.81 0.71 0.06 0.02 0.04

K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.08 0.00 0.00 0.01 0.00 0.01

Total 3.00 4.00 4.01 4.00 4.00 4.00 7.98 7.98 15.66 15.81 15.61 15.08 24.15 25.02

XMg

0.89 0.90 0.93 0.89 0.89 8.89 0.81 0.83 0.92 0.89 0.85 0.97 0.72 0.26

P-136 (BR) C-12(BR) 9477b(PK)

Sample

Mineral Ol Opx Opx Opx Opx Cpx Cpx Cpx Grt Grt Spl Spl Spl Amp Amp Amp Phl Phl

Point no. 28-c 4-c 5-r 12-c 30-r 430c 44-r 34-c 1-r 22-c 20-c 11-c 36-c 53-c 2-c 10-r 27-r 44-c

Stage II II II IV V II II IV II II III V IV I III V I III

SiO2

40.67 56.99 58.05 50.85 58.56 53.86 53.70 54.90 42.51 42.27 0.03 0.16 0.15 45.28 45.64 45.19 41.84 38.83

TiO2

0.00 0.09 0.08 0.05 0.07 0.21 0.16 0.24 0.23 0.21 0.01 0.03 0.01 0.87 00.79 0.68 1.90 2.40

Al2O

30.00 2.06 1.22 6.76 1.14 1.45 1.28 3.08 22.42 22.41 46.36 60.41 64.83 15.95 13.31 15.04 17.20 17.55

Cr2O

30.43 0.32 0.22 0.28 0.01 0.52 0.30 0.19 1.35 1.48 19.91 7.13 3.88 0.86 1.29 1.19 0.50 0.77

FeO* 10.28 6.49 6.46 8.47 7.22 2.02 2.17 2.31 7.97 7.59 16.84 13.52 11.93 2.34 3.81 4.06 1.82 3.36

MnO 0.19 0.15 0.15 0.28 0.19 0.12 0.01 0.13 0.31 0.33 0.18 0.22 0.16 0.02 0.09 0.17 0.03 0.00

NiO 0.00 0.08 0.12 0.02 0.06 0.09 0.00 0.06 0.05 0.00 0.14 0.78 0.13 0.06 0.11 0.09 0.28 0.18

MgO 48.63 33.17 34.29 31.93 32.94 16.91 16.46 15.66 20.18 19.96 14.71 18.04 19.64 18.95 17.61 16.63 23.38 22.99

CaO 0.00 0.38 0.23 0.22 0.13 23.45 23.50 24.03 5.00 5.00 0.00 0.05 0.00 11.78 12.15 12.37 0.04 0.02

Na2O 0.00 0.00 0.00 0.00 0.00 0.26 0.28 0.07 0.03 0.00 0.01 0.01 0.01 2.97 1.85 1.05 0.58 0.74

K2O 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.02 0.00 0.01 0.03 0.09 0.06 8.44 8.68

Total 100.20 99.72 1 00.83 98.86 1 00.32 98.88 97.86 1 00.69 1 00.04 99.25 98.22 1 00.35 1 00.74 99.09 96.73 97.51 95.98 95.51


9/17


Table 2. (Continued)

P-136 (BR) C-12(BR) 9477b(PK)

Sample

Mineral Ol Opx Opx Opx Opx Cpx Cpx Cpx Grt Grt Spl Spl Spl Amp Amp Amp Phl Phl

Point no. 28-c 4-c 5-r 12-c 30-r 430c 44-r 34-c 1-r 22-c 20-c 11-c 36-c 53-c 2-c 10-r 27-r 44-c

Stage II II II IV V II II IV II II III V IV I III V I III

Si 1.00 1.97 1.98 1.80 2.01 1.97 1.99 1.97 3.02 3.02 0.01 0.03 0.03 6.24 6.48 6.37 5.74 5.45

Ti 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.01 0.01 0.01 0.00 0.00 0.00 0.09 0.08 0.07 0.20 0.25

Al 0.00 0.08 0.05 0.28 0.05 0.06 0.06 0.13 1.88 1.89 12.33 14.79 15.38 2.59 2.23 2.50 2.78 2.90

Cr 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.08 0.08 3.55 1.17 0.62 0.09 0.14 0.13 0.05 0.08

Fe2+ 0.21 0.19 0.18 0.25 0.21 0.06 0.07 0.07 0.47 0.45 3.18 2.35 2.01 0.27 0.45 0.48 0.21 0.39

Mn 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.02 0.02 0.03 0.04 0.03 0.00 0.01 0.02 0.00 0.00

Ni 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.03 0.03 0.02 0.01 0.01 0.01 0.03 0.02Mg 1.78 1.71 1.75 1.69 1.69 0.92 0.91 0.84 2.14 2.13 4.95 5.59 5.89 3.89 3.73 3.50 4.78 4.81

Ca 0.00 0.01 0.01 0.01 0.00 0.92 0.93 0.92 0.38 0.38 0.00 0.01 0.00 1.74 1.85 1.87 0.01 0.00

Na 0.00 0.00 0.00 0.00 0.00 0.02 0.02 0.01 0.00 0.00 0.01 0.00 0.00 0.79 0.51 0.56 0.16 0.20

K 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.02 0.01 1.48 1.55

Total 3.00 3.98 3.99 4.05 3.96 3.99 3.99 3.96 7.99 7.98 24.09 24.02 23.99 15.72 15.51 15.52 15.43 15.66

MMg

0.89 0.90 0.90 0.87 0.89 0.94 0.93 0.92 0.82 0.82 0.61 0.70 0.75 9.94 0.89 0.88 0.96 0.92

Note: FeO*=Fe total as Fe2+, XMg=Mg/(Mg+Fe*), cm core composition; r, rim composition

Mg/(Mg+Fe*) ratios are c. 0.72, 0.580.75, 0.640.89 and 0.650.74for stages I, III, IV and V, respectively (Fig. 9). The spinel fromkelyphites is more aluminous than those of other stages. The higherCr

2O

3contents of stage III spinel may be related to the decreased

Cr2O

3content of stage III neoblastic garnet, relative to stage II

garnet.

Amphibole

Amphibole is present in stages I, III, V and VI, and varies slightlyin composition. Stage I amphibole inclusions are pargasitic, withrelatively low K

2O (c. 0.51 wt%), Na

2O (2.042.97 wt%), TiO

2(c. 0.87%) and Cr

2O

3(c. 1.35 wt%); Mg/(Mg+Fe2+) values are

0.910.94. Stage III comprises pargasitic and edenitic amphibole,the latter mostly occurs as exsolution lamellae in clinopyroxene.Stage III amphibole contains relatively high K

2O (0.051.47 wt%),

Na2

O (1.85 3.0 8 wt %), TiO2

(0.871.47%) and Cr2O

3(0.781.39 wt%) compared with stage I amphibole; but

9493929190898887

40

30

20

10

Fo (mol%) in Ol

No.ofAnalyses

Ol1

Ol2

Ol3

Mg/(Mg+Fe2+) values (0.860.91) are significantly lower thanFig. 6. Frequency diagram of fosterite (Fo) composition ofstage I (Fig. 10). The amphibole of stage V is also pargasitic inolivine from stage I to stage III.composition, and Mg/(Mg+Fe2+) values are c. 0.850.90, but theCr

2O

3(0.572.50 wt%) and Na

2O (2.353.48 wt%) contents are

c. 3.157.64 wt% and in Opx5

c. 1.132.94 wt% (Fig. 8). Opx2

andhigher than in stage III amphibole. Stage VI amphibole has tremoliteOpx

3in sample 9477b (P-K) have anomalously high alumina

compositions (Table 2).contents ranging from 3.684.79 and 3.383.90 wt%, respectively.Stage V is very poorly developed in P-K peridotites. Orthopyroxenein stage II is relatively homogeneous in terms of Mg /(Mg+Fe), but Phlogopitelarger grains which are contact with garnet generally show a slightdecrease in Al

2O

3and MgO from core to rim. Phlogopite occurs as inclusions within garnet (stage I ) and as a

primary matrix phase (stage III) in some garnet peridotites. The formermode of occurrence is characterized by euhedral grains up to 0.5 mmin size; in the latter phlogopite is present along boundaries of garnetClinopyroxeneand other stage II minerals, but is clear that this phlogopite is not a

Clinopyroxene also varies in composition from stage I to IV. It product of kelyphitic retrogression. Mg/(Mg+Fe*) for phlogopiteis generally Cr-bearing diopside (e.g. Cr

2O

3contents are inclusions is 0.930.96, significantly higher than those from the matrix

c. 0.291.12 wt%), and Na2O, Cr

2O

3and Al

2O

3contents decrease, (0.900.93 mol%) (Fig. 11). Furthermore, phlogopite inclusions have

whereas the CaO content increases from stage II to IV. Stage II higher MgO, Cr2O

3and SiO

2contents than those in the matrix (e.g.

clinopyroxene has Mg/(Mg+Fe*) of around 0.910.96, whereas Cr2O

3contents are c. 0.770.96 and c. 0.470.81 wt%, for inclusion

those of stage III and IV are slightly lower (0.900.93 and 0.880.92, and matrix phlogopite, respectively). The Al/(Al+Si) of inclusion

respectively). Stage II clinopyroxene is relatively compositionally phlogopite is higher than that of matrix phlogopite. The decreasinghomogenous, except for a slight decrease in Al

2O

3and Na

2O Al/(Al+Si) ratio in phlogopite can be attributed to decreasing pressure

contents, from core to rim. at constant temperature (Arai, 1984).

SpinelPT D ET ER MIN AT ION S

Stage I spinel, which occurs as tiny inclusions in garnet (up toSulawesi garnet peridotites contain a variety of mineral

30 mm) has Cr2

O3

c. 21.822.5 wt%, whereas kelyphite spinels (stagesassemblages that can constrain PT conditions forIV & V) have lower Cr

2O

3contents (c. 2.58.7 wt%). Stage III

spinel diplays a wide range of Cr2

O3

contents of 9.227.6 wt%. each stage of metamorphic recrystallization. However,


10/17


Fig. 7. (a) Zoning profile of garnet showing relatively flat plateaux in the core, with minor variation at the grain rim. (b)Composition of garnet plotted on ternary diagram of AlmPrpGrs+Sps, showing decreasing pyrope content from stage II tostage III.

such PTestimation for garnet peridotites is a complex & Wood, 1979) as well as orthopyroxeneclinopyroxenesolvus geothermometers ( Brey & Kohler, 1990) . Forproblem because disequilibrium assemblages reflecting

different stages may exist in an individual samples recalculation, all Fe was assumed to be ferrous; becausein general, the Fe3+ content of ultramafic minerals is(Medaris & Carswell, 1990). PT estimates were

accomplished by combining data from a variety of considered to be negligible (e.g. Krogh & Carswell,geothermometers and geobarometers for each stage.These include the garnetorthopyroxene barometers(Al in orthopyroxene) of Harley (1984b), Nickel &Green (1985) and Brey & Kohler (1990), and thethermometers utilizing FeMg exchange betweengarnetclinopyroxene (Powell, 1985), garnetorthopy-

roxene (Harley, 1984a) and garnetolivine (ONeill

50

40

30

20

10

0 1 2 3 4 5 6 7 8

Al2O3 (wt %) in Opx

No.ofanalyses Stage I

Stage II

Stage IV

Stage III

Stage V

0.8

0.6

0.4

0.2

01.0 0.8 0.6 0.4 0.2

Mg/(Mg+Fe*)

Cr/(Cr+Al)

Stage I

Stage III

Stage IV

Stage V

Fig. 9. Cr/(Cr+Al) versus Mg/(Mg+Fe*) of spinel in SulawesiFig. 8. Frequency diagram of Al2

O3

(wt%) content of Opxfrom stage I to stage VI. Generally, Al

2O

3contents in garnet peridotites. Spinel in kelyphites generally have higher

MgO+Al2

O3

and lower Cr2O

3contents than those occurringindividual samples increase from stage I to stage IV, and

decrease in stage VI. as inclusions and in the fine-grained matrix.


11/17


stage II serpentinization of the stage I protolith, butthis is difficult to demonstrate.

Due to uncertainties about the effect of unidentifiedFe3+/Fe2+ ratios on different geothermobarometriccalibrations, PTdetermination of the peak stage IIrequired integration of a number of methods to obtainbest fit results. For example, at lower temperatureequilibration (1200 C) using the calibrations of Harley (1984a)and ONeill & Wood ( 1979), which may indicate aproblem with FeMg exchange reaction equilibriarelated to unidentified variations in Fe3+/Fe2+ ratios

between paired minerals (e.g. Krogh & Carswell, 1996).Using Fe3+ data from wet chemical analyses of AlpeArami peridotite samples, Brenker & Brey (1997)favoured a combination of the garnetolivine FeMgexchange thermometer (ONeill & Wood, 1979) andthe Al in orthopyroxene geobarometer (Brey & Kohler,1990) for the best estimation of PT conditions. Dueto the lack of Fe3+ data, we favour estimation of PTconditions based on a graphically derived best-fitmethod following Krogh & Carswell (1996) andutilizing all seven geothermometers and geobarometersfor individual samples (Fig. 12, Table 3). These resultsindicate that the PTconditions for stage IIc (i.e. from

1.000.90 0.92 0.94 0.96 0.98

(Phl) 6.0

5.5

(Ea) 5.0

S ipe

rF

orm

ula

(O =2

2)

Mg/(Mg+Fe*)

Stage I (BR)

Stage III (BR/P-K)

Fig. 11. Relationship between Mg/(Mg+Fe*) and Si per core compositions) for the Palu-Koro samples areformula unit (O=22) of phlogopite in Sulawesi garnet 3638 kbar at 10701110 C and 1921 kbar at 1070peridotites. Phlogopite of stage III contains more of the

1090 C, and for the Bongka River samples areeastonite (Ea) component than the phlogopite end-member.4048 kbar at 12051290 C and 2637 kbar at 10251210 C.

The PT conditions of stage IIr (i.e. derived from1996; Zhang et al., 1994). For our samples, chargebalance stoichiometric recalculations maximizing Fe3+ rim compositions of the stage II assemblage) may have

limited quantitative significance due to difficulty inby the method of Schumacher (1991) consistentlyyielded near to zero or negative contents. selecting rim compositions which adequately reflect

the presumed equilibrium four-phase assemblage givenRepresentative PT estimations are summarized inTable 3, and the evaluation of PT conditions for the complexity of compositional zonation etc. However,

we follow Brenker & Brey (1997) and assume that thestages II and III for individual representative samplesis shown in Fig. 12. rim compositions give at least an indication of earliest

retrograde PT conditions. They generally recordThe PTconditions of the hydrated precursor spinel

lherzolite stage I cannot be defined with any great decompression of around 412 kbar accompanied bycooling of 50240 C from the IIc peak stage.precision, but temperature was probably about 750

780 C (Al & Cr in orthopyroxene, Witt-Eickschen & Generalized PT values based on the graphicallyderived best-fit method (Fig. 12, Table 3) for the Palu-Seck, 1991) at 1520 kbar. Abundant Ni sulphide

inclusions in garnet of BR peridotites, and the presence Koro samples are 3032 kbar at 960980 C and1921 kbar at 10151045 C, and for the Bongka Riverof hydrated phases (phlogopite, Mg-chlorite and

pargasitic amphibole) may indicate that the spinel samples are 2434 kbar at 9401075 C and 1924 kbarat 870955 C.peridotite protolith suffered metasomatism and/or

lower PT recrystallization, possibly related to pre- Co-existence of garnet and spinel in the stage III


12/17


Table 3. PTestimates for representative garnet peridotites samples from Palu-Koro (P-K) and Bongka river (BR).

T(C) at P=30 kbar P (kbar) at T=1000 C

Ol-?Grt Grt-Cpx Grt-Opx Opx-Cpx Al2O

3in Opx Best fit result***

Sample Stage OW79 P85 H84a BK90 NG85 H84b BK90 T(C) P(kbar)

9477B (P-K) II-c 107216 111918 109316 111652 181 181 171 108010 201

II-r 115025 105310 109950 109236 212 202 192 103015 221

9532A (P-K) II-c 99121 97823 10608 106622 330 300 310 109020 371

II-r 88816 96220 9854 105832 342 302 322 98020 322

III* 85322 802 805 720 26 25 26 75025 232

P-136 (BR) II-c 122843 96622 111516 838 334 293 324 124025 462II-r 11853 96221 102585 773 320 281 310 102550 322

IV** 662 862 15

EA-11 (BR) II-c 12415 1003 119423 1000 295 274 285 127020 411

II-r 93052 95818 105860 853 275 255 265 100060 273

III* 7972 685 151 161 162 73050 162

C-6 ( BR) II-c 97347 102121 10989 1029 262 233 243 106035 282

II-r 8973 95833 94070 976 272 222 252 94015 231

IV** 647 647 15

C-12 ( BR) II-c 1249 1135 1117 1010 230 211 220 117040 343

II-r 102940 96466 89487 932 251 231 241 99050 292

C-22 ( BR) II-c 114535 997 109123 899 261 231 241 111040 302

II-r 94139 868 89725 865 251 211 231 90030 201

P-135 ( BR) III* 844

IV** 781

OW79: ONeill & Wood ( 1979); P85: Powell ( 1985); H84a: Harley (1984a); H84b: Harley (1984b); BK90: Brey & Kohler (1990); NG85: Nickel & Green (1985). * Calculated using

P=20 kbar and T=800 C; ** Calculated using P=15 kbar. *** See explanation in the text on PTestimation section and Fig. 12.

assemblage indicates pressures of around 1820 kbar evolutionary PT history. The PT t paths for theperidotites can be deduced by interpolating between(Webb & Wood, 1986); temperatures were estimated

to be in the range 614844 C (clinopyroxene PT conditions determined for each stage. DetailedPT paths for the stage IIc to IIr evolution of sixorthopyroxene geothermometer; Brey & Kohler, 1990).

PT estimations for the stage III assemblage (i.e. representative samples are presented in Fig. 12 toillustrate the variation amongst samples (outcrops),Ol

3+Opx

3+Cpx

3+Grt

2, Fig. 12, Table 3 ), are

222 kbar at 75025 C for P-K samples and and synoptic PT t paths, integrating all availablePTdata, are presented in Fig. 13. PTdeterminations162 kbar at 73040 C BR samples (Fig. 12). Stage

IV kelyphitic orthopyroxene and clinopyroxene yielded of the peak stage IIc (garnet cores) display considerablevariation for samples derived from different outcrops,temperatures in the range 647862 C at 15 kbar

applying the two-pyroxene geothermometers of Brey with clustering at 2638 kbar and 10251210 C (P-K& BR), 1921 kbar and 10701090 C (P-K), and& Kohler (1990).

Orthopyroxene, pargasitic amphibole and spinel are 4048 kbar and 12051290 C (P-K). These PTdataare higher than those reported by Helmers et al. (1990)the main constituents of stage V and represent an

upper amphibolite facies assemblage. Approximate for P-K samples and by Parkinson et al. (1998) forBR samples.temperature estimates based on the Ca content in

orthopyroxene (Brey & Kohler, 1990) yielded a Stage IIr (garnet rims) generally records decom-pression of around 412 kbar accompanied by coolingtemperature of c. 580635 C at c. 1012 kbar. The

stage VI assemblage indicates PT conditions within of 50240 C from the IIc peak stage, although somesamples display some degree of cooling and burialthe greenschist facies, probably 350400 C and

47 kbar. from stages IIc to IIr (e.g. sample 9477B). Thegranuliteamphibolitegreenschist decompressionsequence reflects uplift to upper crustal levels, and is

PT T P AT H Sidentical to the sequence recorded in some garnetgranulite, quartzo-feldspathic gneiss and eclogiteThe overgrowth textures and PT determinations

described above indicate that central Sulawesi garnet (Fig. 13), with which the garnet peridotites are locallyintercalated.peridotites experienced a complex and prolonged

Fig. 12. Thermobarometric calculations and inferred PTevolution of six representative garnet peridotite samples. Solid, dashed andfine lines represent calculated reaction equilibria for stage IIc, IIr and III, respectively. Shaded areas are the favoured estimated PTfields for each stage, and the white circles are the median values of the PTestimation. GrtOpx barometersH84(Al ): Harley(1984b); NG85: Nickel & Green (1985); BK90(Al): Brey & Kohler (1990). FeMg exchange thermometersP85: Powell (1985);H84: Harley (1984a); OW79: ONeill & Wood (1979), BK90 (Al): Brey & Kohler (1990). For further explanation see text and Table 3.


13/17


III?

IIr

IIc

IIr

IIc

IV ?

H84(Al)

NG85

BK90(Al)

BK90

OW79P85

H84

H84(Al)

NG85

BK90(Al)

BK90OW79

P85H84

H84(Al)

NG85

BK90(Al)

BK90

OW79

P85H84

H84(Al)

NG85

BK90(Al)

BK90

OW79P85

H84

IIc

IIr

III?

30

35

40

25

20

15

10700600 800 900 1000 1100 1200 1300

Temperature ( C)o

Pre

ssure

(kbar)

H84(Al)

NG85

BK90(Al)

BK90

OW79

P85

H84

H84(Al)

NG85

BK90(Al)

BK90OW79

P85H84

H84(Al)

NG85BK90(Al)

BK90

OW79

P85

H84

H84(A

l)

NG85

BK90

(Al)

BK90

OW79

P85

H84

H84(Al)

NG85

BK90(Al)

BK90

OW79

P85

H84

H84(Al)

NG85

BK90(Al)

BK90OW79

P85

H84

H84(Al)

NG85

BK90(Al)BK90 OW79

P85

H84

H84(Al)

NG85

BK90(Al)

BK90

OW79

P85

H84

H84(Al)

NG85

BK90

(Al)

BK90

OW79

P85

H84

C-22(BR) C-6(BR)

IIc

IIr

III?

P-136(BR)EA-11(BR)IIc

III?

IV

V?

BK90

H84(Al)BK90(Al)NG85

H84

IIc

IIr

III

IV?

IV

9532A(PK) 9477B(PK)

III

30

35

40

25

20

15

10

Pre

ssure

(kbar)

700600 800 900 1000 1100 1200 1300Temperature ( C)o

700600 800 900 1000 1100 1200 1300Temperature ( C)o

700600 800 900 1000 1100 1200 1300Temperature ( C)o

30

35

40

25

20

15

10

Pressure

(kba

r)

30

35

40

25

20

15

10

Pressure

(kba

r)

30

35

40

25

20

15

10

Pressure

(kbar)

30

35

40

25

20

15

10

Pressure

(kbar)

700600 800 900 1000 1100 1200 1300Temperature ( C)o

700600 800 900 1000 1100 1200 1300Temperature ( C)o

IIr

45

50


14/17


Fig. 13. Synoptic, generalizedPT t path for the Sulawesigarnet peridotite. Although PTestimates for most stages for most

samples are more or lessconsistent, those for the peakstage IIa show considerablevariation. Additional PTdata forassociated granulite and eclogiteof the HP-UHPM unit elsewherein Sulawesi are derived from thefollowing: garnet granuliteHelmers et al. (1990) andKadarusman (unpublished data,1995); coesite-bearingJd-quartziteParkinson et al.(1998); PrpKyTlc rockKadarusman and Parkinson(unpublished data, 1997). Thepetrogenetic grid is based on thatof Maruyama et al. (1996),diamondgraphite equilibriumfrom Bundy (1980), coesitequartzequilibrium from Bohlen &Boettcher (1982) and the garnetspinel lherzolite transition fromWebb & Wood (1986). Stabilitylimits of pargasitic amphibole, andchlorite and serpentine inultramafic rocks are from Niida &Green (1999) and Ulmer &

200 400 600 800 1000 1200

Temperature (C)

40

30

20

10

ressu

re(kbar)

50

25

75

100

125

150

Dep

th(km

)

0

Prp-Ky-Tlc rock

coesite-bearing

Jd quartzite

(Bantimala)

(Palu-Koro)

Grtlh

erzolit

e

Spllh

erzolit

e

Dry

perid

otites

olidus

Grt-S

pllhe

rzolite

garnet granulite(Palu-Koro)

IIc

IIc

IIcIIr

IIr

IIc

coesite

quartz

diam

ond

graphite

BS

EC

EA

AM

PA

PPGSZEO

PrA

GR

serpe

ntin

estability

limit

HGR

Cpx+Opx

+Sp

An+F

o

IV

V

III

IIr

chl

orit

estability

limit

VI

amphibolestability

limit

?I

IIr

IIr

50

Trommsdorff (1999), respectively.

in the garnet granulite may have been obliterated byA S S O C I A T E D G R A N U L I T E A N D E C L O G I T E higher temperature recrystallization and retrogression.In the Palu-Koro fault valley, garnet peridotite isassociated with three types of granulite: (1 ) mafic

O R I G I N A N D U P L I F T W I T H I N T H E S U L A W E S Iclinopyroxenegarnet granulite, (2) felsic plagioclase

C O L L I S I O N Z O N Eclinopyroxene granulite, and (3) felsic feldsparquartzgarnet granulite. The petrology of these rocks has From the available field evidence and regional geologi-

cal considerations, we interpret the Sulawesi garnetpreviously been described by Helmers et al. (1990),who estimated peak PT conditions to be c. 12 kbar peridotites to be tectonic intercalations within the

extensive HP to UHPM (locally coesite-bearing)and c. 750 C. In addition to the granulites, there isdunite (with abundant phlogopite veins), spinel peri- A-type metamorphic belt, which extends through

Sulawesi to south-east Kalimantan and central Javadotite and eclogite. The garnet (with >50% pyropecomponent)+kyanite+talc equilibrium assemblage in (Parkinson et al., 1998). Their occurrence is thus

comparable to the volumetrically minor but widespreadthe eclogite may indicate peak pressures in excess of

28 kbar (cf. Liou & Zhang, 1995), and this is supported distribution of garnet peridotites in other UHPMterranes, such as the Sulu Terrane of China, theby the widespread occurrence of radial fractures

around quartz inclusions in garnet, suggestive of the Bohemian massif, the Western Gneiss Region ofNorway and the Kokchetav massif of Kazakhstan. Informer presence of coesite. Ultra-high pressures of

metamorphism of country rock granulite and eclogite Sulawesi, at least some continental protoliths weresubducted to depths in excess of 100 km, recrystallizedare also consistent with the discovery of coesite-

bearing UHPM rocks ( jadeite-bearing quartzites) else- and uplifted in a EW-trending Alpine-type orogeniczone at the southern Sundaland margin in the mid-where in Sulawesi (Parkinson et al., 1998). We believe

that evidence of an earlier stage of UHP metamorphism Cretaceous (c. 140115 Ma), due to the collision of an


15/17


400

800

1200

mechanicallithosphere

thermal lithosphere

serpentine +talc + brucite

1200

800

400

I

IIc

IIc

IIcIIr

IIr

IIr

amphibole +phlogopite

100 km

0

50

150

200

100 400

depth(km)

Fig. 14. Schematic two-dimensional tectonic cartoon of subduction zone showing possible original tectonic setting of Sulawesigarnet peridotite. Thermal structure is from the numerical modelling of Peacock (1996) for steady-state subduction with subductingplate velocity=10 mm/year, t (shear heating component)=5%; downward arrows material transfer, by negative buoyancy of wedgeassemblages to subducting slab. Spinel peridotite at relatively shallow levels (60 70 km) in the mantle wedge is subject to hydrationand metasomatism by K-rich fluids migrating from the dehydrating continental slab (white upward arrows) yielding the stage Iassemblage. As subduction progresses, the spinel peridotite is dragged down parallel to the slabwedge interface into the garnetlherzolite stability field (stage IIc), by induced convective corner flow (black arrow). The garnet peridotite is transferred from thewedge to the slab due to the negative buoyancy effect at the interface (cf. Brueckner, 1998), and is incorporated into the coesite-grade recrystallized sialic material of the slab (stage IIrIII). Transfer probably occurred at various depths along the interface atdepths from 75 to 150 km, and may have been related to termination of underflow and slab break-offdue to entrance ofcontinental material into the subduction zone. Subsequent to transfer, the garnet peridotite suffers the same metamorphic upliftas the regional schists and gneisses (stage IVVI).

Australian-derived continental fragment with the of around 150 km (Fig. 14). Although there is consider-able variation in the PT estimates amongst differentEurasian continent. Although there are as yet no

radiometric age constraints for the garnet peridotites, outcrops for the peak garnet lherzolite recrystallization(stage II), most are comparable to PT conditionsfrom the circumstantial evidence at least, it is reason-

able to interpret the metamorphic evolution of the within the mantle wedge adjacent to the slabwedgeinterface of a steady-state subduction zone, calculatedgarnet peridotites within this overall tectonic framework.

As stated before, orogenic garnet peridotites may by two-dimensional numerical modelling (e.g. Peacock,1996). Tectonic incorporation into the underthrustoriginate in the mantle underpinning of subducted

oceanic or continental crust, in the mantle wedge prior continental crust from various depths along theinterface probably occurred during the exhumationto transferral to the subducting slab during subduc-

tioncollision, or be products of subduction zone stage of the continental package, by negative buoyancy-driven ductile flow (cf. Brueckner, 1998). The garnetmetamorphism of peridotites previously emplaced in

the crust by asthenospheric upwelling (perhaps related peridotites were subsequently uplifted within theHP-UHPM nappe, suffering a similar granuliteto slab break-off). The high temperatures recorded by

the peak stage II (up to 1200 C) suggest that an amphibolitegreenschist decompression sequence asthat experienced by the regional schists and gneisses.origin within the subducting slab is extremely unlikely;

the low-temperature and low-pressure early stage I, Final exhumation from upper crustal levels wasfacilitated by entrainment in Neogene granitic plutons,although poorly characterized, appears difficult to

reconcile with an asthenospheric upwelling (and/or and/or Oligocene transtension in deep-seated strikeslip fault zones.subsequent subduction) origin. Therefore, we believe

an early history within the overlying mantle wedge ofthe subduction/collision zone to be the most reasonable

C O N C L U S I O N Sexplanation for parts of the estimated PTtrajectory.

The low-temperature, low-pressure and metasomat- Orogenic, Alpine-type garnet peridotites occur in thecentral region of Sulawesi. The main conclusions fromized (phlogopite- and amphibole-bearing) spinel lher-

zolite precursor to the garnet lherzolite probably field and petrological work on these rocks areas follows:represents mantle assemblages that were initially at

relatively high levels (5075 km depths) in the wedge. 1 The garnet peridotites experienced a long, complexhistory with six evolutionary stages of recrystallization.These rocks were dragged down parallel to the slab

wedge interface in the subduction/collision zone by PT determinations of the peak metamorphic con-ditions (stage IIc) display considerable variation forviscous coupling with the subducting slab, and experi-

enced heating to temperatures up to 1100 C at depths samples derived from different outcrops, with clustering


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ment of garnet-bearing peridotites into continent collisionat 2632 kbar and 10251210 C ( P-K & BR),orogens. Geology, 26, 631634.1921 kbar and 10701090 C (P-K), and 4048 kbar

Brueckner, H. K. & Medaris, L. G., 1998. A tale of two orogens:and 12051290 C (BR). the contrasting PT t history and geochemical evolution of2 The garnet peridotites are interpreted to be compo- mantle in high- and ultrahigh-pressure metamorphic terranes of

the Norwegian Caledonides and the Czech Variscides. Schweizernents of an extensive HP-UHPM basement terrane,Mineralogische und Petrolographische Mitteilungen, 78, 293307.which was recrystallized and uplifted in a north-

Bundy, F. R., 1980. The PTphase reaction diagrams for elementaldipping continental collision zone in the mid- carbon. Journal of Geophysical Research, 85, 69306936.Cretaceous. The spinel lherzolite precursors probably Deer, W. A., Howie, R. A. & Zussman, J., 1992. An Introduction to

the Rock-Forming Minerals, 2nd edn. Longman, London.represent mantle wedge assemblages that were draggedDobrzhinetskaya, L., Green, H. W. & Wang, S., 1996. Alpe Arami:

down parallel to the slabwedge interface in a a peridotite massif from depths of more than 300 kilometers.subduction/collision zone by corner flow, and the Science, 271, 18411845.garnet peridotites were subsequently uplifted within Egeler, C. G., 1947. Contributions to the petrology of the

metamorphic rocks of Western Celebes. In: Geologicalthe HP-UHPM nappe, suffering a similar decom-Explorations in the Island of Celebes Under the L eadership of H.pression sequence as that experienced by the countryA. Brouwer, pp. 175346. North Holland, Amsterdam.

rock schists and gneisses. Hacker, B. R., Sharp, T., Zhang, R., Liou, J. G. & Hervig, R. L.,1997. Determining the origin of the ultrahigh-pressure lherzol-ites. Science, 278, 702704.ACK N OW LED G EMEN T S

Harley, S. L., 1984a. An experimental study of the partitioning ofFe and Mg between garnet and orthopyroxene. Contributions toSamples from the Bongka river were collected byMineralogy and Petrology, 86, 359373.C.D.P. during field seasons in 1988 and 1997, funded

Harley, S. L., 1984b. The solubility of alumina in orthopyroxeneby the University of London Consortium for coexisting with garnet in FeOAl

2O

3SiO

2and CaOFeO

MgOAl2O

3SiO

2. Journal of Petrology, 25, 665696.Geological Research in SE Asia and the Science and

Helmers, H., Maaskant, P. & Hartel, T. H. D., 1990. GarnetTechnology Agency of Japan, respectively. Samplesperidotite and associated high-grade rocks from Sulawesi,

from the Palu-Koro region were collected by A.K. Indonesia. L ithos, 25, 171188.during an integrated research programme funded Kretz, R., 1983. Symbols for rock-forming minerals. AmericanMineralogist, 68, 277279.by the Indonesian Government (RUT-Palu-Koro

Krogh, E. J. & Carswell, D. A., 1996. HP and UHP eclogites and19941995). A.K. thanks all members of RUT-Palu-garnet peridotites in the Scandinavian Caledonides. In: Ultra-

Koro for sharing field investigations in the Palu-Koro High Pressure Metamorphism (eds Coleman, R. G. & Wang, X.),region and providing rock samples. We are grateful to pp. 244 297. Cambridge University Press, Cambridge.

Leake, B. E. et al., 1997. Nomenclature of amphiboles: Report ofJ. G. Liou for inviting us to contribute this paper tothe Subcommittee an Amphiboles of the Internationalthe special issue on Garnet Peridotites and UltradeepMineralogical Association, Commission on New Minerals and

Minerals, and for improving the manuscript. We thank Mineral Names. American Mineralogist., 82, 10191037.T. Carswell, S. Maruyama, J. Sopaheluwakan and R. Liou, J. G. & Zhang, R. Y., 1995. Significance of ultrahigh-P talc-

bearing eclogitic assemblages. Mineralogical Magazine, 59,Hall for valuable advice during the protracted gestation93102.period of this research. We particularly thank journal

Liou, J. G. & Zhang, R. Y., 1998. Petrogenesis of an ultrahigh-referees G. Medaris and S. Banno for many helpful pressure garnet-bearing ultramafic body from Maowu, Dabiecomments and suggestions on an earlier version of the Mountains, east-central China. Island Arc, 7, 115134.

Maruyama, S., Liou, J. G. & Terabayashi, M., 1996. Blueschistsmanuscript. A postgraduate scholarship to A.K. fromand eclogites of the world and their exhumation. Internationalthe Japanese Government (Ministry of Education,Geological Review, 38, 485594.

Monbusho) is acknowledged. Medaris, L. G. & Wang, H. F., 1986. A thermaltectonic modelfor the high-pressure rocks in the Basal Gneiss ComplexNorway. L ithos, 19, 299315.R E F E R E N C E S

Medaris, L. G. & Carswell, D. A., 1990. Petrogenesis of MgCrgarnet peridotite in European metamorphic belts. In: EclogiteArai, S., 1984. Pressuretemperature dependent compositionalFacies Rocks (ed. Carswell, D. A.), pp. 260290, Chapman &variation of phlogopitic micas in upper mantle peridotites.Hall, New York.Contributions to Mineralogy and Petrology, 87, 260264.

Nickel, K. G. & Green, D. H., 1985. Empirical geothermobarome-Arai, S. & Takahashi, N., 1989. Formation and compositionaltry for garnet peridotites and implications for the nature of thevariation of phlogopites in the Horoman peridotite complex,lithosphere, kimberlites and diamonds. Earth and PlanetaryHokkaido, northern Japan: implications for origin and fraction-Sciences L etters, 73, 240253.ation of metasomatic fluids in the upper mantle. Contributions

Niida, K. & Green, D. H., 1999. Stability and chemical compositionto Mineralogy and Petrology, 101, 165175.of pargasitic amphiboles in MORB pyrolite under upper mantleBohlen, S. R. & Boettcher, A. L., 1982. The quartzcoesiteconditions. Contributions to Mineralogy and Petrology, 135,

transformation: a pressure determination and the effects of other1840.components. Journal of Geophysical Research, 87, 70737078.

ONeill, H.StC. & Wood, B. J., 1979. An experimental study ofBrenker, F. E. & Brey, G. P., 1997. Reconstruction of the FeMg partitioning between garnet and olivine and its appli-

exhumation path of the Alpe Arami garnet-peridotite body from cation as a geothermometer. Contributions to Mineralogy anddepths exceeding 160 km. Journal of Metamorphic Geology, Petrology, 70, 5970.15, 581592. Parkinson, C. D., 1996. The origin and significance of metamorphic

Brey, G. P. & Kohler, T., 1990. Geothermobarometry in four- tectonics blocks in melanges: evidence from Sulawesi, Indonesia.phase lherzolite II. New thermobarometers, and practical T erra Nova, 8, 34123323.assessment of existing thermobarometers. Journal of Petrology, Parkinson, C. D., 1998. Emplacement of the East Sulawesi31, 13531378. ophiolite: evidence from subophiolite metamorphic rocks.

Journal of Asian Earth Sciences, 16, 1328.Brueckner, H. K., 1998. Sinking intrusion model for the emplace-


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Parkinson, C. D. & Katayama, I., 1999. Present day ultrahigh- Sulawesi. In: Proceedings of the Sixth International Congress onpressure conditions of coesite inclusions in garnet and zircon: Pacific Neogene Stratigraphy and IGCP 355, Puspitek-Serpong,Evidence from laser Raman microspectroscopy. Geology, 27, West Java, L IPI-Bandung, Indonesia, 29 July, pp. 7783.979982. Sukamto, R., 1975. Geological Map of the Ujung Pandang Sheet,

Parkinson, C. D., Miyazaki, K., Wakita, K., Barber, A. J. & scale 151000000. Geological Research and DevelopmentCarswell, D. A., 1998. An overview and tectonic synthesis of the Centre, Bandung, Indonesia.very high pressure and associated rocks of Sulawesi, Java and Ulmer, P. & Trommsdorff, V., 1999. Phase relations of hydrousKalimantan, Indonesia. Island Arc, 7, 184200. mantle subducting to 300 km. In: Field Observations and High

Peacock, S., 1996. Thermal and petrologic structure of subduction Pressure Experimentation: A T ribute to Francis R. Boyd(eds Fei,zones. In: Subduction: T op to Bottom (eds Bebout, G. E. Scholl, Y., Bertka, C. M. & Mysen, B. O.). Geochemical Society SpecialD. W. Kirby, S. H. & Platt, J. P.). American Geophysical Union, Publication, 6, in press.Geophysical Monographs, 96, 119133. Webb, S. A. C. & Wood, B. J., 1986. Spinel-pyroxene-garnet

Powell, R., 1985. Regression diagnostic and robust regression in relationships and their dependence on Cr/Al ratio. Contributionsgeothermometer/ geobarometer calibration: the garnetclinopy- to Mineralogy and Petrology, 92, 471480.roxene geothermobarometer revisited. Journal of Metamorphic Witt-Eickschen, G. & Seck, H. A., 1991. Solubility of Ca and Al inGeology, 3, 231243. orthopyroxene from spinel peridotite: an improved version of

Schumacher, J. C., 1991. Empirical ferric iron correction: necessity, an empirical geothermometer. Contributions to Mineralogy andassumptions, and effect on selected geothermobarometers. Petrology, 106, 431493.Mineralogical Magazine, 55, 318. Zhang, R. Y., Liou, J. G. & Cong, B., 1994. Petrogenesis of garnet-

Sills, J. D., 1982. The retrogression of ultramafic granulites from bearing ultramafic rocks and their associated eclogites in thethe Scourian of NW Scotland. Mineralogical Magazine, 46, Su-Lu ultrahigh-P metamorphic terrane. Journal of Metamorphic5561. Geology, 12, 169186.

Sopaheluwakan, J., Kadarusman, A., Priadi, B. & Utoyo, H., 1995.The nature of basement rocks in the Palu region, Central Received 8 February 1999; revision accepted 11 July 1999.

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