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: m.cottam@es.rhul.ac.uk)

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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