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Journal of the Geological Society, London, Vol. 167, 2010, pp. 49–60. doi: 10.1144/0016-76492009-028.
49
Pulsed emplacement of the Mount Kinabalu granite, northern Borneo
M. COTTAM 1*, R. HALL 1, C. SPERBER1 & R. ARMSTRONG 2
1SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, UK2PRISE, Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia
*Corresponding author (e-mail: [email protected])
Abstract: High-precision U–Pb ion microprobe analyses provide new constraints on the emplacement and
origin of the Kinabalu granite in Sabah, northern Borneo. The granite is a sheeted laccolith-like body
comprising dyke-fed granitic units that young downwards, each emplaced beneath the previous sheet.
Analyses of concentric growth zones in zircons indicate crystallization between 7.85 � 0.08 and 7.22 �0.07 Ma, and show that the entire pluton was emplaced and crystallized within less than 800 ka. Several
pulses of magmatism are recognized, each lasting for a maximum of 250 ka, and possibly as briefly as 30 ka.
The oldest ages coincide with the highest elevations whereas the youngest ages are found at lower elevations
around the edge of the body. Based on these new age data and field observations we identify the biotite
granodiorite, hornblende granite and porphyritic facies as the Upper, Middle and Lower Units respectively.
Inherited zircon ages indicate different protoliths for the Upper and Middle Units. The Upper Unit is derived
from attenuated continental crust of the South China margin subducted beneath Sabah. The Middle Unit is
sourced from melting of the crystalline basement in Sabah with little or no contribution from South China
crust.
Supplementary material: Full U–Pb ion microprobe analytical data, and modal and major element
composition data are available at http://www.geolsoc.org.uk/SUP18385.
Granite magmatism plays a fundamental role in the growth
and differentiation of the continental crust but there is still
significant controversy about the generation and intrusion of
granitic magmas in the crust. In particular, the physical
processes of magma ascent and emplacement have been the
subjects of considerable recent debate (e.g. McCaffrey &
Petford 1997; Petford & Clemens 2000; Petford et al. 2000).
Early ideas of granite diapirism (e.g. Mrazec 1915; Nicolesco
1929) are being substantially revised by studies employing
present-day geophysical and geochronological techniques (e.g.
Evans et al. 1993; Michel et al. 2008). A growing body of
evidence suggests that many plutons are emplaced at shallow
levels as tabular laccoliths (e.g. Vigneresse 1990; Evans et al.
1993; McCaffrey & Petford 1997) that grow incrementally in
a number of discrete magmatic pulses over a range of time
scales (e.g. Coleman et al. 2004; Matzel et al. 2006; Michel
et al. 2008). Single pulses are interpreted to be injected either
as dyke-fed horizontal sheets (e.g. Evans et al. 1993; Michel
et al. 2008) or as subvertical dykes (e.g. Glazner et al. 2004)
that subsequently inflate.
The Kinabalu pluton provides an opportunity to test models
of granite emplacement. It is exposed over an area of c.
120 km2 and forms the peak of Mt Kinabalu (c. 4100 m),
situated at the northern end of the Crocker Ranges in the
Malaysian state of Sabah (Fig. 1). This collisional mountain
range results from the Eocene to Early Miocene subduction
of the proto-South China Sea beneath northern Borneo (Hall
& Wilson 2000; Hutchison et al. 2000). The Mt Kinabalu
granite is the only pluton to intrude the deformed rocks of
the Crocker Ranges. Most of the granite body is extremely
well exposed on the relatively flat western and eastern summit
plateaux of Mt Kinabalu (both c. 4000 m), well above the
regional tree line at c. 2500 m. Rainforest cover and steep
topography restrict geological observations below 3000 m. The
northeastern area of the pluton remains extremely inaccessible
because of thick rainforest cover, lack of roads and trails, and
difficulty of the terrain (Connaughton 1996).
Controversy still surrounds the origin and emplacement of
the Kinabalu Pluton. Amphibole geobarometry suggests intru-
sion at depths of between 3 and 10 km (Vogt & Flower
1989). Previous workers have proposed various models related
to southward subduction of the proto-South China Sea beneath
Borneo (Vogt & Flower 1989), melting during Miocene
isostatic rebound after subduction (Swauger et al. 2000), or
crustal anatexis during post-subduction relaxation (Hutchison
et al. 2000; Chiang 2002). Evaluating such models depends
in part on the exact age of the body. Jacobson (1970) first
estimated the age of the Kinabalu granite to be c. 9 Ma,
based on K–Ar dating of biotite and hornblende. Subsequent
K–Ar dating produced a wider spread of ages, ranging from
13.7 to 1.3 Ma (e.g. Rangin et al. 1990; Bellon & Rangin
1991; Hutchison et al. 2000; Swauger et al. 2000). Swauger
et al. (2000) suggested that the granite was formed by a
tectonic event at 15 Ma that also led to the formation of the
important offshore unconformity known as the Deep Regional
Unconformity (e.g. Hutchison 1996; Sandal 1996). Similar U–
Pb ages (13–15 Ma) from the Capoas granite along-strike in
Palawan (Encarnacion & Mukasa 1997) may indicate that
melting was more widespread and linked to a regional
tectonic event.
This study presents the results of secondary ionization mass
spectrometry (SIMS) U–Pb analyses on zircons from nine
samples of the Kinabalu granite. Based on these new data we
suggest that the entire Kinabalu pluton was emplaced in less than
800 ka as a series of dyke-fed subhorizontal granite sheets
between 8 and 7 Ma, intruded in several pulses.
Geological background
Country rocks
The Kinabalu granite is intruded into Mesozoic igneous and
metamorphic rocks and their Cenozoic sedimentary cover (Fig.
2). Basement rocks in the Kinabalu area include variably
serpentinized peridotites and small exposures of rocks described
as crystalline basement (Reinhard & Wenk 1951). The ultrabasic
rocks form part of a Middle Jurassic to Early Cretaceous
ophiolite (Hutchison 2005) emplaced in the Late Cretaceous or
Early Palaeogene (Newton-Smith 1967; Omang & Barber 1996).
Crystalline basement rocks are Triassic to Cretaceous in age
(Reinhard & Wenk 1951; Dhonau & Hutchison 1966; Koopmans
1967; Kirk 1968; Leong 1974), and most resemble deformed
Fig. 1. (a) Location map showing the
position of Borneo within SE Asia.
(b) Simplified outline map of Borneo
showing the position of Mt Kinabalu, at the
northern end of the Crocker Ranges, which
form part of the Central Borneo Mountains
(dark grey, elevation .1000 m; white,
elevation .1500 m). Black dotted lines
represent international boundaries between
Malaysian Borneo (Sabah and Sarawak),
Indonesian Borneo (Kalimantan) and
Brunei (B).
Fig. 2. Simplified geological map of the Mt
Kinabalu region, modified from Jacobson
(1970). Line X–Y shows line of cross-
section reproduced in Figure 5.
M. COTTAM ET AL .50
ophiolitic rocks intruded by arc plutonic rocks, suggesting an
origin in a Mesozoic intra-oceanic arc (Hall & Wilson 2000).
Imai & Ozawa (1991) described unusual peridotites that are
exposed close to Mt Kinabalu and suggested that they represent
subcontinental mantle.
Throughout Sabah basement rocks are observed in faulted
contact with steeply dipping sedimentary cover sequences,
predominantly deep-water turbidites and related deposits as-
signed to the Eocene to Lower Miocene Trusmadi and Crocker
Formations (Collenette 1965). All of these rocks were folded and
faulted during the Early Miocene Sabah orogeny (Hutchison
1996) when the extended passive continental margin of South
China collided with north Borneo (Hall & Wilson 2000;
Hutchison et al. 2000) and subduction terminated. Much of the
area then became emergent but most of present-day Sabah
subsided again below sea level in the Late Early Miocene (Hall
et al. 2008). Neogene sedimentary rocks rest unconformably on
folded Eocene to Early Miocene rocks across Sabah. Fluviatile
and marginal marine sediments were deposited across large areas
of south Sabah (Balaguru et al. 2003; Balaguru & Nichols 2004)
during the Middle and Late Miocene. Offshore of northern Sabah
shelf sequences pass northwards into deep marine sediments
(Ingram et al. 2004; Franke et al. 2008), and the shelf edge
moved progressively north from the Middle Miocene (e.g.
Hazebroek & Tan 1993; Sandal 1996). Onland in northern Sabah
marine clastic sediments are interpreted to have been deposited,
but have now been removed by erosion after the region became
emergent once more in the Late Miocene or Early Pliocene (Hall
2002; Balaguru et al. 2003; Tongkul & Chang 2003; Morley &
Back 2008). No younger sedimentary rocks are known from the
Kinabalu area except Pleistocene glacial tills of the Pinosuk
Gravels (Collenette 1958).
The Kinabalu granite
The Kinabalu pluton has a roughly elliptical shape with a long
axis oriented approximately NE–SW. The major axis is about
16 km and the minor axis about 10 km (Fig. 2). The igneous
rocks of the Kinabalu pluton have been described at different
times as quartz monzonite, adamellite, granodiorite and granite
reflecting changes in classification and nomenclature, and differ-
ent observations (Reinhard & Wenk 1951; Kirk 1968; Jacobson
1970; Kasama et al. 1970; Vogt & Flower 1989). We recognize
three distinct granitic lithologies: a biotite granodiorite, a
hornblende granite and a porphyritic hornblende granite. Based
on new age data and field observations we term these the Upper,
Middle and Lower Units respectively.
Reinhard & Wenk (1951) gave the first detailed petrological
account with a small number of chemical and modal analyses
and reported that the rocks belonged to ‘the family of quartz-
monzonites’. Kirk (1968) preferred the term adamellite from
Nockolds’ (1954) classification scheme. Jacobson (1970) com-
pleted the most extensive study of Mt Kinabalu and considered
the dominant lithology to be hornblende adamellite using the
classification of Bateman et al. (1963) based on visual estimates
of modes. Vogt & Flower (1989) carried out a mineralogical and
chemical study using Jacobson’s samples. They described Kina-
balu as a batholith that ‘comprises variably phyric hornblende
quartz monzonite and biotite quartz monzodiorite’ without
specifying their classification scheme, and presented modes for
26 samples. Kasama et al. (1970) presented modes for 15
samples described as granites, granodiorites and porphyritic
adamellites.
In this study point counting was carried out on 36 granitoid
samples and six aplites, and 22 of the samples were stained for
potassium feldspar (Sperber 2009). Five porphyritic rocks con-
tain phenocrysts of K-feldspar that are very large compared with
the thin-section size. For two of these samples the modal
proportion of K-feldspar was corrected based on an estimate
from the hand specimen. According to our study, the Upper Unit
samples are biotite granodiorites or biotite tonalites, whereas the
Middle and Lower Unit samples are almost all granites with a
few samples plotting as quartz monzonites or quartz syenite (Fig.
3c) using the classification scheme of Le Maitre (1989). Our
modal plots are similar to those of Reinhard & Wenk (1951),
Kirk (1968) and Kasama et al. (1970) (Fig. 3b) whereas the Vogt
Fig. 3. QAP diagram (Le Maitre 1989) of the Kinabalu granite. (a) According to the data of Vogt & Flower (1989); (b) as proposed by Reinhard & Wenk
(1951), Kirk (1968) and Kasama et al. (1970); (c) according to this study.
PULSED EMPLACEMENT OF THE MT KINABALU GRANITE 51
& Flower (1989) modes appear to be more plagioclase-rich (Fig.
3a), and although several would now be classified (Le Maitre
1989) as granites or granodiorites many plot as quartz monzo-
nites, quartz monzodiorites or quartz diorites.
To investigate the differences we compared rock compositions
reported by Reinhard & Wenk (1951), Kirk (1968) and Vogt &
Flower (1989) with bulk-rock compositions calculated from their
modes using mineral composition data from Vogt & Flower
(1989). We repeated this exercise for our own samples using our
own rock and mineral analyses. Vogt & Flower (1989) reported 18
samples for which there are modes and major element composi-
tions and we have 11 samples. The comparisons are shown for
SiO2 and K2O in Figure 4. The Vogt & Flower (1989) observed
and calculated compositions show a great deal of scatter (e.g. Fig.
4a and c), in contrast to our compositions, which show very good
agreement for all major elements (e.g. Fig. 4b and d). The
observed and calculated compositions for the small number of
samples from Reinhard & Wenk (1951) and Kirk (1968) are also
very similar; Kasama et al. (1970) provided no chemical analyses.
Vogt & Flower (1989) did not report their methods but we suspect
that they did not stain the sections, may have misidentified K-
feldspars and quartz, and may not have corrected their modes for
the very large size of the phenocrysts in the porphyritic granites.
The major lithologies are granites not monzonites according to
current classification schemes (Le Maitre 1989).
The Upper Unit is referred to here as a biotite granodiorite,
although it varies from biotite–hornblende tonalite to granodior-
ite. It is exposed in a small area (about 2 km2) coinciding with
the highest elevations of the western plateau. It contains
abundant biotite, which appears texturally to be in equilibrium
with less common hornblende, although in some samples
hornblende is replaced by biotite. The Middle Unit forms most
of the exposed body and is a hornblende granite. Hornblende
occurs as small phenocrysts texturally in equilibrium with minor
biotite and potassium feldspar, plagioclase feldspar and quartz.
The colour varies from darker to lighter grey, which corresponds
to the abundance of hornblende. The Lower Unit is a porphyritic
hornblende granite that is megacrystic in places. It is chemically
similar to the Middle Unit but contains large potassium feldspar
phenocrysts (2–3 cm in length) and megacryst-rich zones. The
Lower Unit is exposed in a band running along the southern and
western edges of the pluton, varying in width from 0.5 to 1.7 km
(Fig. 2).
Each of the three units is intruded by dykes and the number of
dykes varies from place to place. Field observations indicate
there are two broad types: abundant aplites and a range of
microgranites including porphyritic and pyroxene-bearing vari-
eties (Jacobson 1970).
Based on observations of steeply dipping contacts (Jacobson
1970) and apparent geochemical zonation (Vogt & Flower 1989),
previous workers have interpreted the granite as a composition-
ally zoned, steep-sided pluton consistent with diapiric models
(e.g. Mrazec 1915; Nicolesco 1929). The relationships of the
various granites are unusual. The Lower Unit has previously been
interpreted as a ‘shell’ or marginal facies surrounding the
pluton’s ‘main body’ of hornblende granite (e.g. Jacobson 1970;
Vogt & Flower 1989) despite the fact that it contains the largest
crystals. We regard the ‘main body’ as the Middle Unit. Intrusive
and/or chilled contacts are observable on steep cliff sections
within the Middle Unit, identified by contrasts between light and
dark hornblende granites. The nature of the contact of the biotite
granodiorite (our Upper Unit) with the hornblende granites
(Middle Unit) is not clear. Jacobson (1970) reported a narrow (c.
1 m) gradational contact between the Upper and Middle Units on
the western summit plateau without interpreting any relative age
relationship between them. Vogt & Flower (1989) made no new
field observations but interpreted the observations of Jacobson of
a narrow gradational contact and flow structures to suggest that
the magmas were only partially crystallized during intrusion.
Based on a geochemical model they concluded that the biotite
granodiorite was the youngest part of the body. However, we
crossed the boundary in several places and saw no clear margin.
The Middle and Lower Unit hornblende granites are magnesian,
predominantly calc-alkalic and metaluminous (e.g. Frost et al.
2001). Upper Unit biotite granodiorite samples are peraluminous.
All resemble most closely the Cordilleran granitoids of Frost et al.
(2001). The Upper Unit rocks have been termed volcanic arc
granites (Pearce et al. 1984), island arc and continental arc
granitoids (Maniar & Piccoli 1989), or amphibole-bearing calc-
alkalic granites (Barbarin 1999). Samples plot as volcanic arc
granites on the Y, Nb and Rb plots of Pearce et al. (1984); the
evolved samples (aplites and some porphyritic samples) plot in
the syncollisional granite field. Several workers have suggested
that trace element classifications reflect the melt protolith rather
than the tectonic setting in which melting occurred (Arculus
1987; Twist & Harmer 1987; Roberts & Clemens 1993; Frost et
al. 2001). Least-squares modelling confirms the suggestion (Vogt
& Flower 1989) that the upper biotite granodiorite cannot be
derived from the hornblende granite by closed-system fractional
crystallization alone. The other granites can be related by
fractional crystallization involving K-feldspar, plagioclase, quartz,
hornblende, magnetite and biotite.
Fig. 4. Comparison of observed and calculated values for SiO2 and K2O for Kinabalu granites using data reported by Vogt & Flower (1989) and this
study. The major element compositions for the rocks were calculated from the modes and mineral analyses.
M. COTTAM ET AL .52
Analytical methods
Zircon separates from nine samples were analysed by sensitive
high-resolution ion microprobe (SHRIMP) on the SHRIMP II (at
the Australian National University: one sample from the Upper
Unit, five from the Middle Unit, and three from the Lower Unit;
Table 1). Three of the five Middle Unit samples were collected
from the western summit plateau (two hornblende granites and an
aplite dyke), and two from the eastern plateau. The three Lower
Unit samples include two megacrystic samples and an associated
pyroxene microgranite dyke. Samples were crushed and graded
using disposable nylon cloth sieves in a brass holder. Zircon
separates were prepared from the resulting 100–250 �m fraction
using standard heavy liquid and Frantz isodynamic separation
techniques. High-purity zircon separates were then hand picked
and the grains were mounted in epoxy resin, alongside the Temora
zircon standard (Black et al. 2003) and the SL13 standard
(Claoue-Long et al. 1995) of the Research School of Earth
Sciences, The Australian National University. The grains were
then sectioned and polished until exposed through their midsec-
tions and Au coated. The internal zonation and structure of single
grains were mapped using cathodoluminescence and reflected
light images, allowing spot analyses to be targeted on grain areas
free of cracks and inclusions.
U–Pb analyses were performed following the analytical
procedures outlined by Williams (1998). Data reduction and all
age calculations were achieved using the SQUID 1.03 and
Isoplot/Ex 2.29 programs of Ludwig (2001a,b). Uranium and
thorium concentrations were calibrated against the SL-13 stan-
dard. Young ages are assumed to be concordant, and were
determined solely using the 238U/206Pb ratio; common Pb was
estimated using the 206Pb/207Pb ratio. This method has been
shown to be very reliable for analyses that have low inherent
common Pb and lie close to the concordia (e.g. Muir et al.
1994), as is the case here. Rare Precambrian crystals and cores
were corrected for common Pb using the 204Pb/206Pb ratio, and
the age was based on the 206Pb/207Pb ratio. Uncertainties in
isotopic ratios and ages (including data tables and error bars for
plotted data) are reported at the 1� level. Final, weighted mean
ages are reported as 95% confidence limits.
Magmatic ages
Analyses of concentric growth zones from all nine samples
reveal tightly clustered Late Miocene ages. These ages are
interpreted to represent the magmatic age of the zircons and thus
the crystallization age of the Kinabalu pluton. The results of
these analyses are plotted as isotopic compositions, uncorrected
for common Pb, in the form of Tera–Wasserburg concordia
diagrams (Tera & Wasserburg 1972) in Figs 5 and 6. Mean
sample ages (Table 1) were calculated using the SQUID 1.03 and
Isoplot/Ex 2.29 programs of Ludwig (2001a,b). Data points
plotting off a regression line from common lead are not included
in mean age calculations.
Upper Unit: biotite granodiorite
Thirty-one spot analyses were made on 24 grains from a biotite
granodiorite sample CS-021. Twenty-five analyses form a coher-
ent group interpreted as reflecting the magmatic age. Six
analyses yield ages that are clearly inherited, being more than
twice the mean magmatic age. Twenty-four of the magmatic ages
plot close to concordia, elongated along the mixing line to
common Pb. This group defines a mean magmatic age of 7.85 �0.08 Ma (Fig. 5a). A single analysis with an abnormal uranium
content plots off the common lead mixing line and is not
included in magmatic age calculations.
Middle Unit: hornblende granite, Western plateau
The two hornblende granite samples from the western plateau
(CS-018 and CS-020) and an aplite dyke (CS-059) were
collected close to the mapped contact with the Upper Unit.
Thirty-one spot analyses on 23 grains from CS-018 yield 20
coherent magmatic ages. Excluding an outlier that plots off the
common Pb mixing line (Fig. 5b), and one analysis rejected on
the basis of an anomalously high uranium content, 18 data points
define a mean magmatic age of 7.64 � 0.11 Ma. There are 11
inherited ages. Nineteen analyses from CS-020, sampling 17
crystals, yield 17 coherent magmatic ages. Two analyses yield
inherited ages. Discarding a single analysis with abnormally high
uranium, the remaining 16 magmatic analyses are tightly clus-
tered (Fig. 5c), defining a mean age of 7.69 � 0.07 Ma. Twenty-
six grains were analysed from the aplite dyke (CS-059). Two
analyses were discarded because they have abnormal uranium
contents. The 24 remaining analyses yield a mean magmatic age
of 7.58 � 0.07 Ma (Fig. 5d). No inherited ages were observed for
sample CS-059.
Table 1. Sample locations, descriptions and mean magmatic ages
Samplenumber
Longitude(decimaldegrees)
Latitude(decimaldegrees)
Elevation(m)
Lithology Spotanalyses*
Magmaticanalyses†
Age(Ma)‡
Error �(Ma)§
Upper UnitCS-021 E 116.551 N 6.078 3827 Biotite granodiorite 31 25 7.85 0.08Middle UnitCS-020 E 116.562 N 6.068 3847 Hornblende granite 19 16 7.69 0.07CS-018 E 116.567 N 6.065 4096 Hornblende granite 31 19 7.64 0.11CS-059 E 116.560 N 6.071 3980 Aplite dyke 26 26 7.58 0.07CS-070 E 116.583 N 6.097 3527 Hornblende granite 18 18 7.44 0.09CS-072 E 116.579 N 6.074 4007 Hornblende granite 27 22 7.46 0.08Lower UnitCS-027 E 116.565 N 6.056 3096 Porphyritic hb granite 21 21 7.32 0.09CS-054 E 116.598 N 6.056 2125 Porphyritic hb granite 32 17 7.22 0.07CS-007 E 116.563 N 6.048 2888 Microgranite dyke 18 13 7.38 0.08
* Total number of spot analyses made on sample.† Number of analyses giving magmatic ages.‡ Mean age of all accepted magmatic analyses.§ Errors are 1�.Longitude and latitude data are based on global positioning system (GPS) measurements. Altitude data are based on position within a detailed digital elevation model (DEM).
PULSED EMPLACEMENT OF THE MT KINABALU GRANITE 53
Middle Unit: hornblende granite, Eastern plateau
Two hornblende granite samples (CS-070 and CS-072) were
collected from the mountain’s eastern plateau. Eighteen spot
analyses from different grains yield exclusively magmatic ages
for sample CS-070. The data form a coherent group (Fig. 5e)
close to concordia, with a single analysis that plots further along
the mixing line with common lead. These analyses have a mean
age of 7.44 � 0.09 Ma. Twenty-seven spot analyses on 22 zircons
from sample CS-072 give 23 magmatic ages. Twenty-one
analyses define a continuous array towards common Pb (Fig. 5f)
that yields a mean age of 7.46 � 0.08 Ma. Two data points with
anomalously high uranium contents are not included in age
calculations. Four analyses yield inherited ages.
Lower Unit: porphyritic hornblende granite
Three samples from the Lower Unit were dated. Two are
porphyritic hornblende granites (CS-027 and CS-054) and the
third is a microgranite dyke (CS-007) intruding country rock
close to the south margin of the pluton. Twenty-one spot analyses
on 20 crystals from sample CS-027 all yield coherent magmatic
age data (Fig. 6a) giving a mean age of 7.32 � 0.09 Ma. No
inherited ages were observed. Twenty-three spot analyses on a
total of 20 zircons from the second sample, CS-054, give 17
magmatic ages and yield a mean age of 7.22 � 0.07 Ma (Fig.
6b). There are six inherited ages. Eighteen spot analyses were
made on 11 grains from a microgranite dyke (CS-007). Two
analyses yield inherited ages. Sixteen analyses form a coherent
group of magmatic ages. Two analyses plot off the mixing line to
common Pb; a third has anomalously high uranium content.
These analyses are not included in calculations of mean mag-
matic age. The remaining 13 data points give a mean age of 7.38
� 0.08 Ma (Fig. 6c).
Crustal inheritance patterns: ages of zircon cores
All three lithological units contain inherited zircon that forms a
small but significant age population (Table 2). Thirty-one of the
214 spot analyses give ages that are unquestionably inherited,
being greater than twice the magmatic age. All represent
analyses of crystal cores. The small number is a true reflection
of the proportion of older cores. Overall, there is a strong peak
Fig. 5. Tera–Wasserburg concordia
diagrams (Tera & Wasserburg 1972)
showing zircon SHRIMP U–Pb analyses for
samples from the Upper Unit (a) and
Middle Unit (b–f). Data-point error ellipses
are 68.3 confidence. Grey ellipses reflect
data points plotting off the mixing line to
common Pb, which are not included in
mean magmatic age calculations. Analyses
with anomalously high uranium contents
(not included in mean magmatic age
calculations) are not shown. Uncertainties
are 1�; weighted mean ages are reported as
95% confidence limits.
M. COTTAM ET AL .54
of Mesozoic ages, accounting for 67% of all inherited ages,
dominated by 16 Early Cretaceous ages.
Upper Unit: biotite granodiorite
The Upper Unit biotite granodiorite (CS-021) contains the oldest
inherited ages found in any of the Kinabalu samples (Table 2)
and they are very different from those for the Middle and Lower
Units. This sample contains two zircons with Palaeoproterozoic
ages (1658 � 18 and 1896 � 20 Ma). There is one Permian
(289 � 4 Ma), one Early Triassic (242 � 3 Ma) and one Early
Jurassic age (179 � 3 Ma). There are no Early Cretaceous ages.
A single sector-zoned grain has an Eocene (49 � 1 Ma) core
with a younger magmatic rim.
Middle Unit: hornblende granite, Western plateau
The two hornblende granites from the western plateau (CS-018
and CS-020) and the aplite dyke (CS-059) contain 15 inherited
ages (Table 2). There are two Jurassic (186 � 2 Ma, 173 � 2 Ma)
ages, eight Early Cretaceous (138 � 2 to 102 � 1 Ma) one Late
Cretaceous (68 � 1 Ma), and two Cenozoic ages (41 � 1 and
25 � 1 Ma). There are no ages older than Jurassic.
Middle Unit: hornblende granite, Eastern plateau
Only one of the two hornblende granite samples from the
mountain’s eastern plateau yielded inherited cores (CS-072); CS-
070 was not examined for inherited grains because of limitations
on the machine time available. There are four ages from CS-072:
three are Early Cretaceous (142 � 1 to 114 � 1 Ma) and one is
Eocene (43 � 1 Ma) (Table 2). Again, there are no ages older
than Jurassic.
Lower Unit: porphyritic hornblende granite
Because of time constraints, only one sample from the Lower
Unit was searched for inherited cores. The porphyritic hornble-
nde granite (CS-054) contains six inherited ages (Table 2). There
is a single Neoproterozoic (970 � 11 Ma) age, one Ordovician
(469 � 7 Ma), one Jurassic (182 � 2 Ma), and three Early Cre-
taceous ages (130 � 2 to 105 � 1 Ma).
Discussion
The U–Pb age data from zircons reported here record the
emplacement of the Kinabalu pluton and provide information on
the crust beneath Kinabalu that was the source of the melt.
Age of the Kinabalu granite
It has always been difficult to interpret the previous K–Ar ages
obtained from the Kinabalu granite, which range between 13.7
and 1.3 Ma (e.g. Jacobson 1970; Rangin et al. 1990; Bellon &
Rangin 1991; Hutchison et al. 2000; Swauger et al. 2000). The
new ages presented here provide a precise age for the Kinabalu
pluton. They show that the entire body was intruded in a narrow
time interval between c. 7.85 and c. 7.22 Ma, and that there were
several separate pulses of magmatism.
The Upper Unit is not the youngest part of the pluton as
suggested by Vogt & Flower (1989) but is in fact the oldest
lithology with a mean magmatic age of 7.85 � 0.08 Ma. This is
the first recorded magmatic episode (Pulse 1).
Zircons from the Middle Unit range in age from 7.69 � 0.07
Fig. 6. Tera–Wasserburg concordia diagrams (Tera & Wasserburg 1972)
showing zircon SHRIMP U–Pb analyses for samples from the Lower
Unit. Data-point error ellipses are 68.3 confidence. Grey ellipses reflect
data points plotting off the mixing line to common Pb, which are not
included in mean magmatic age calculations. Analyses with anomalously
high uranium contents (not included in mean magmatic age calculations)
are not shown. Uncertainties are 1�; weighted mean ages are reported as
95% confidence limits.
PULSED EMPLACEMENT OF THE MT KINABALU GRANITE 55
to 7.44 � 0.09 Ma. The two hornblende granite samples from the
western plateau have crystallization ages of 7.69 � 0.07 and
7.64 � 0.11 Ma. An aplite dyke that intruded these granites
yields an age of 7.58 � 0.07 Ma. These ages are interpreted to
record one complete intrusive pulse terminating with a fractio-
nated aplitic end product (Pulse 2). Less than 3 km away, the two
hornblende granite samples from the eastern plateau yield young-
er ages of 7.46 � 0.08 to 7.44 � 0.09 Ma. These ages may
represent a second intrusive pulse within the Middle Unit (Pulse
3). However, given the uncertainties associated with these mean
ages (1–1.5%) it is not possible to distinguish these two pulses
based solely on age data. Recent studies have shown that zircon
growth in silicic magmas may predate eruption by several 100
ka, biasing U–Pb mean ages towards older ages (Simon et al.
2008). For the young ages reported here, even relatively short
zircon residence times of c. 200 ka would significantly increase
errors associated with U–Pb mean ages and further preclude
distinction between pulses.
Field observations suggest that further dating, with an in-
creased spatial resolution and precision, would probably identify
additional intrusive pulses within the Middle Unit. Observations
of a chilled contact between light and dark hornblende granite
within the Middle Unit (e.g. Jacobson 1970; this study) support
multiple intrusive pulses. Complex cross-cutting dyke sets may
reflect the fractionated end products of several intrusive pulses.
The porphyritic Lower Unit yields ages of 7.32 � 0.09 and
7.22 � 0.07 Ma. The microgranite dyke intruding country rock
gives an age of 7.38 � 0.08 Ma, within error of the two Lower
Unit ages. These three ages represent a further magmatic episode
(Pulse 4). The younger ages of the Lower Unit rule out the
suggestion that it was emplaced first, as a shell into which the
Middle and Upper Units were intruded (Jacobson 1970). Field
observations of porphyritic granite intruded locally as dykes
within the Middle Unit (Jacobson 1970) are entirely consistent
with its younger age.
Duration and rates of emplacement
These data show that the Kinabalu granite was incrementally
assembled by several discrete episodes of magmatism. The entire
pluton was emplaced and crystallized within a period of less than
800 ka. The ages from the Middle Unit provide some constraint
on the duration of an individual magma pulse. The oldest
hornblende granite on the western plateau has an age of
7.69 � 0.07 Ma and the fractionated aplite intruding it has an
age of 7.58 � 0.07 Ma. Considering the associated errors, these
ages constrain the duration of this pulse to less than 250 ka, and
it could possibly have been as brief as 30 ka.
Such time scales necessitate rapid magma ascent and emplace-
ment via fracture propagation and dyking (e.g. Clemens &
Table 2. Ion microprobe U–Pb zircon analyses of inherited zircons
Sample spot U (ppm) Th (ppm) 204/206 % error 207Pb/206Pb % error 206Pb/238U % error Age(Ma)*
Error �(Ma)†
Upper UnitCS021-1.2 282 146 0.000199 39.5 0.050394 1.8 0.093743 1.7 242 3CS021-2.2 257 254 0.000052 43.2 0.124594 0.4 0.857335 2.0 1896 20CS021-13.1 102 42 – – 0.045264 6.2 0.026295 1.7 180 3CS021-17.2 1579 316 0.000076 99.0 0.049668 1.6 0.018429 4.1 49 1CS021-19.1 61 25 0.001091 41.6 0.061051 3.3 0.099810 2.1 289 4CS021-23.1 184 110 – – 0.112315 1.1 0.741135 1.3 1658 18Middle Unit (western plateau)CS018-2.1 189 142 0.047755 3.5 0.034497 1.1 102 1CS018-3.1 533 184 0.000217 49.5 0.053919 2.4 0.023424 1.8 68 1CS018-4.1 153 141 0.000634 40.8 0.052761 3.5 0.037452 2.6 103 1CS018-6.2 156 117 0.000593 37.8 0.054089 2.9 0.053495 1.5 138 2CS018-7.2 93 89 – – 0.054909 4.5 0.036341 3.1 105 2CS018-12.1 97 57 0.005684 47.6 0.080352 7.4 0.009213 2.9 25 1CS018-18.1 267 325 0.000489 44.7 0.052408 4.1 0.015204 2.4 41 1CS018-23.1 991 385 0.000023 99.0 0.050193 1.0 0.041208 6.9 123 2CS018-10.2 198 130 0.000191 79.9 0.052104 2.4 0.042833 2.7 121 1CS018-16.2 619 382 0.000039 99.0 0.049340 1.1 0.063382 1.6 173 2CS018-20.2 441 338 0.000256 38.3 0.051025 1.3 0.056993 3.7 187 2CS020-6.1 327 234 – – 0.048954 2.6 0.041453 1.8 113 1CS020-7.2 1189 558 �0.000062 60.9 0.049565 1.2 0.053706 1.8 140 1Middle Unit (eastern plateau)CS072-14.2 238 136 0.000196 56.6 0.052501 2.1 0.045437 2.6 142 1CS072-16.2 170 135 0.000480 40.8 0.052439 2.6 0.040786 1.9 114 1CS072-19.2 435 349 0.000158 72.5 0.050567 1.9 0.030833 3.0 121 1CS072-22.1 418 231 0.000587 53.3 0.053572 2.7 0.016557 5.3 43 1Lower UnitCS054-3.1 260 111 0.000072 54.1 0.056256 1.1 0.176941 1.5 469 7CS054-4.1 83 37 0.001785 33.3 0.087591 3.3 0.042086 3.3 108 2CS054-5.1 69 178 �0.000057 60.9 0.070595 1.3 0.376629 2.2 970 11CS054-7.1 89 69 0.000793 35.4 0.052836 4.3 0.067108 1.2 182 2CS054-8.1 233 115 0.000540 40.6 0.046909 2.9 0.037406 3.1 105 1CS054-16.1 133 159 �0.000403 67.9 0.047509 3.5 0.047564 2.3 130 2Aplite dykeCS007-6.2 70 61 0.000210 99.0 0.048417 5.6 0.044557 3.0 115 2CS007-10.2 94 84 0.000599 78.6 0.047903 4.6 0.048319 1.9 122 2
* Based on 207Pb-corrected 206Pb/238U age.† Errors are 1�.
M. COTTAM ET AL .56
Mawer 1992; Petford 1996) rather than slower diapiric ascent
(Miller & Paterson 1999). Field observations of sharp magmatic
contacts suggest minimal interaction between the products of
each pulse, implying that each was fully crystallized prior to
subsequent pulses.
Morphology and internal structure
The new data presented here are inconsistent with earlier
interpretations (Fig. 7) of the Kinabalu granite as a composition-
ally zoned, steep-sided diapir-like pluton (e.g. Jacobson 1970;
Vogt & Flower 1989). The oldest ages of the Upper Unit coincide
with the highest elevations of the western plateau, and the
youngest ages of the Lower Unit are found at the edges of the
body at lower elevations. The age and field relationships can be
explained if the Kinabalu pluton is a subhorizontally layered
body comprising multiple granite sheets (Fig. 7). This is
consistent with recent models of plutons (e.g. Evans et al. 1993;
McCaffrey & Petford 1997; Petford & Clemens 2000), which
have been shown to grow incrementally as a number of dyke-fed
horizontal sheets (e.g. Petford et al. 2000) that become younger
downwards (Michel et al. 2008).
Recent geophysical studies have shown that many small
granite plutons are emplaced at shallow levels as tabular
laccoliths (e.g. Vigneresse 1990; Evans et al. 1993; McCaffrey &
Petford 1997; Ameglio & Vigneresse 1999; Vigneresse et al.
1999; Petford & Clemens 2000; Petford et al. 2000). Their
dimensions may follow a power-law relationship (McCaffrey &
Petford 1997). With a major axis of c. 16 km and a minor axis of
c. 10 km the power-law relationship predicts a maximum thick-
ness for the Kinabalu granite of 1.82 km. Based on the observed
height difference between the Kinabalu summit and the bottom
of Low’s Gully, the deep chasm that cuts through the pluton, the
Kinabalu granite is at least 2 km thick. However, neither the roof
nor the base of the Kinabalu body is seen. Low’s Gully remains
dangerous and almost unvisited (Connaughton 1996) and it is not
known if the bottom of the granite is exposed in it. Tilting and
post-intrusive extensional faulting (Fig. 7) may have increased
the apparent vertical thickness of the pluton. If the roof of the
granite were just above the present summit of the mountain, and
the body is assumed to extend no deeper than the lowest
observed outcrop on the flanks, the granite would have a
thickness broadly consistent with the power-law prediction.
Melt protoliths
The inherited zircons in the Middle Unit are predominantly Early
Cretaceous and have no ages greater than Jurassic. In contrast,
the Upper Unit contains the oldest zircon ages, which are
Proterozoic, and there are no Cretaceous zircon cores. The
different crustal inheritance patterns suggest a number of differ-
ent sources.
The Proterozoic zircons within the Upper Unit necessitate an
extremely old protolith. The thinned South China continental
crust subducted beneath northern Borneo during the Early
Miocene collision (Hall & Wilson 2000; Hutchison et al. 2000)
is a potential source. Little is known of the basement age of this
crust. It must have formed part of the South China margin before
Oligocene to Miocene opening of the South China Sea, and
consequently is part of the Cathaysian South China block. A
Proterozoic basement is probable (Sewell et al. 2000; Li et al.
2001). Gravity data indicate that the Kinabalu pluton was
intruded directly above the position of maximum crustal thick-
ness in northern Borneo, reflecting the subduction of South
China continental crust and collisional thickening (Hutchison et
al. 2000; Milsom & Holt 2001). Therefore we suggest that the
Upper Unit represents the melting of the thinned South China
continental crust deep beneath Kinabalu.
There are two possible sources for the Mesozoic zircons that
dominate inheritance within the Middle Unit (Table 2). The
subducted South China continental crust beneath Sabah is a
potential source. A belt of granitic rocks of Jurassic and Early
Fig. 7. Simplified cross-sections of the Mt
Kinabalu region drawn along the line X–Y
shown in Figure 2. (a) Redrawn from
Jacobson (1970) based on original plutonic
interpretations. (b) New interpretation of
the Kinabalu granite as a sheeted laccolith-
like body.
PULSED EMPLACEMENT OF THE MT KINABALU GRANITE 57
Cretaceous age is known to have extended through SE China
(Jiang et al. 2006; Zhou et al. 2006) and potentially continued
SW towards the region involved in the collision. However, the
absence of the Proterozoic ages similar to those of the Upper
Unit suggests that the Middle Unit was generated without the
involvement of South China continental crust. An alternative
source is basement rocks known from other parts of Sabah. Early
Cretaceous ages have been reported from ophiolitic and probable
arc plutonic rocks exposed in other parts of Sabah (Hall &
Wilson 2000; Hutchison 2005). This hypothesis is supported by
geochemical studies (Chiang 2002), which suggest generation of
the Kinabalu hornblende granites from deep fluid-absent melting
of arc crust (Chiang 2002).
Inherited Mesozoic core ages suggest that the Lower Unit has
a similar source to the Middle Unit. The Neoproterozoic and
Palaeozoic ages hint at the involvement of older crustal material,
possibly as a result of mixing with previously intruded material
or mixing of melts at depth. There are too few data to speculate
further.
The different crystallization ages and sources for the Upper
and Middle Units are consistent with the observation that these
two units cannot be linked by closed-system fractional crystal-
lization (Vogt & Flower 1989). The Upper Unit represents an
older and distinct intrusive pulse (Pulse I) derived by melting of
a different source. In contrast, the Middle and Lower Units can
be linked by fractionation.
Finally, the Cenozoic ages in the Upper and Middle Units
suggest melting of arc rocks formed during Eocene to Early
Miocene subduction of the proto-South China Sea.
Emplacement model
The new data provide compelling evidence to reinterpret the
Kinabalu granite as a sheeted laccolith (Fig. 7), comprising
multiple dyke-fed sheets. The Upper Unit was emplaced first,
sourced by melting of the deep continental crust thrust beneath
Sabah following orogenic thickening. Intrusion of the Upper Unit
may have heated the middle crust, leading to further melting.
The intra-oceanic arc crystalline basement at this level provided
the source for the hornblende granites of the Middle and Lower
Units, which were intruded sequentially beneath the Upper Unit.
The porphyritic nature of the Lower Unit is attributed here to
textural coarsening of feldspar crystals (e.g. Vernon 1986;
Higgins 1999); large crystals coarsening at the expense of
dissolved smaller crystals. This phenomenon suggests that the
Lower Unit was intruded before the Middle Unit had fully
cooled, with the remaining heat from the latter buffering the
magma’s temperature at the K-feldspar liquidus for a substantial
time (Higgins 1999). Migration of interstitial melt during this
period, enhancing coarsening along fluid flow channels, may
explain field observations of megacryst-rich zones within the
Lower Unit exposed near Mesilau (Fig. 1). Conversely, the
absence of megacrysts within the Middle Unit suggests that the
Upper Unit was fully cooled before subsequent emplacement.
Sills and laccoliths emplaced at shallow depths have been
widely reported to preferentially intrude along shale horizons
(e.g. Corry 1988). The ductile response of such layers limits the
ability of the feeder dykes to propagate upwards via vertical
fracturing, forcing the magma to intrude sideways (Thomson &
Schofield 2008). Such effects may be enhanced by the volatiliza-
tion of pore fluids upon contact with the magma, dramatically
increasing pore fluid pressures (Bjorlykke 1993), reducing the
effective strength of the rock and thus aiding horizontal intrusion
(Thomson & Schofield 2008).
Regional mapping demonstrates that the Kinabalu granite is in
contact with serpentinized ultrabasic basement rocks along its
western margin (Jacobson 1970). We suggest that the relatively
weak serpentinized rocks may have acted in a similar fashion to
shales, with ductile deformation restricting upward propagation
of feeder dykes and forcing lateral emplacement. Dehydration of
serpentinites and the associated increase in pore fluid pressures
could aid this process. Contact metamorphism at the Kinabalu
contact has been observed in both ultrabasic and Crocker
Formation rocks. This may imply that the level at which the
granite was emplaced was influenced by the thrust contact
between the serpentinite and the Crocker Formation.
Summary
The U–Pb age data reported here provide important constraints
on the emplacement and origin of the Kinabalu granite. Several
separate pulses of intrusion can be recognized between
7.85 � 0.08 and 7.22 � 0.07 Ma. Magmatic pulses lasted no
longer than 250 ka but could possibly be as short as 30 ka. The
oldest ages coincide with the highest elevations; the youngest
ages are found at lower elevations around the edge of the body.
Based on these age data and field observations the units
previously regarded as the central biotite granodiorite, main
hornblende granite and marginal porphyritic facies are renamed
the Upper, Middle and Lower Units respectively.
Our data suggest that the Kinabalu pluton is a sheeted
laccolith (Fig. 7) incrementally assembled over a period of less
than 800 ka. These data add to a growing body of evidence that
small granitic plutons are incrementally assembled over relatively
short time scales by the intrusion of multiple granitic sheets that
young downwards (e.g. McCaffrey & Petford 1997; Petford &
Clemens 2000; Michel et al. 2008).
The Upper Unit biotite granodiorite is the oldest part of the
pluton and requires a source that includes old zircons, which is
most likely to be subducted attenuated continental crust of the
South China margin. Inherited zircon ages from the Middle and
Lower Units imply melting of the crystalline basement exposed
today in part of Sabah with little or no contribution from South
China crust. Cenozoic inherited zircon ages probably indicate
some contribution of arc material formed during subduction of
the Proto-South China Sea.
The Late Miocene age of the Kinabalu pluton indicates that it
is not a subduction product (compare Vogt & Flower 1989), as
subduction terminated in the Early Miocene (Hall & Wilson
2000; Hutchison et al. 2000; Hall 2002). The granite melting
occurred more than 10 Ma after the Early Miocene collision.
The industrial member companies of the SE Asia Research Group
Consortium provided financial support for our work. The authors thank
J. Nias (Sabah Parks), F. Tongkul (Universiti Malaysia Sabah) and the
staff of Sabah Parks for facilitating our work in the Kinabalu National
Park. M. Fanning, B. Armstrong, S. Mehrtens and G. Lister are thanked
for assistance with SIMS U–Pb work at ANU. M. Thirlwall and A. Beard
assisted with geochemical analyses. C. Hutchison has provided helpful
discussion over many years.
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Received 23 February 2009; revised typescript accepted 27 August 2009.
Scientific editing by Martin Whitehouse.
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