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Chemical Geology 199 (2003) 243–276
Spatial and temporal isotopic domains of contrasting igneous suites
in Western and Northern Sulawesi, Indonesia
Marlina Elburga,*, Theo van Leeuwenb, John Fodena, Muhardjob
aDepartment of Geology and Geophysics, University of Adelaide, Adelaide SA 5005, AustraliabPT Rio Tinto, Jakarta, Indonesia
Received 30 July 2002; accepted 21 February 2003
Abstract
Palaeocene to Pliocene magmatism in NW Sulawesi shows a progression from an Older Series with calc-alkaline/tholeiitic
signatures (51–17 Ma) to a Younger Series of mafic-intermediate high-K magmas (f 14–5 Ma) and felsic K-rich calc-alkaline
(CAK) magmas (9–2 Ma). The isotopic and geochemical compositions of the Older Series samples indicate that the more
westerly samples have been generated in a continental arc setting and the more easterly samples in an oceanic arc; this
distinction defines the boundary between the Western and Northern Sulawesi tectonic terranes. The Younger Series high-K
magmas have unusual isotopic compositions, with variable but low 143Nd/144Nd, high 87Sr/86Sr values, and high 208Pb/204Pb for
their 206Pb/204Pb ratios compared to subduction-related magmas. The diversity of the isotopic compositions points towards a
source with a long and heterogeneous geochemical evolution, most likely located within the Australian subcontinental
lithospheric mantle. The Younger Series felsic CAK magmatism has a more homogeneous isotopic and geochemical signature
and reflects melting of continental crust of Australian origin.
This geochemical progression in time is very similar to that seen in central Sulawesi [Chem. Geol. 156 (1999a) 67], and is
best explained by normal subduction of an oceanic plate followed by melting of an underthrust sliver of Australian continent.
The size of this microcontinent can be estimated from the areal extent of low-Nd-isotope magmas in Western Sulawesi, ranging
from approximately 4jS to 1jN. Underthrusting must have happened prior to 14 Ma, indicating that this event cannot be
equated to the collision between Sulawesi and the Sula platform, which occurred at 5 Ma.
While subduction beneath western Sulawesi ceased prior to the onset of potassic magmatism in this region, it continued
beneath northern Sulawesi producing predominantly calc-alkaline suites.
D 2003 Elsevier Science B.V. All rights reserved.
Keywords: Sr-Nd-Pb isotopes; Indonesia; Sulawesi; Subduction; Continent collision; Trace elements
1. Introduction
The Indonesian archipelago lies in a tectonically
complicated area, where three major plates, Philip-
0009-2541/03/$ - see front matter D 2003 Elsevier Science B.V. All right
doi:10.1016/S0009-2541(03)00084-6
* Corresponding author. Now at: Max-Planck Institute for
Chemistry, P.O. Box 3060, 55020 Mainz, Germany.
E-mail address: elburg@mpch-mainz.mpg.de (M. Elburg).
pine, Australian and Eurasian, interact. Tectonic
reconstructions indicate that the area has seen rapid
changes in plate geometry over the past 50 Ma (Hall,
1996, 2002), but precise definition of tectonic events
is still lacking.
Sedimentological, stratigraphic and structural data
are commonly used to unravel tectonic histories, but
the potential of igneous rocks to provide additional
s reserved.
Fig. 1. (a) Location of Sulawesi. (b) Location map of samples analysed and discussed. Samples of Pompangeo Schists fall outside the map area.
(c) Geological map of NW Sulawesi. (d) Map of Sulawesi, showing relief (1000- and 2000-m contours) and the main faults and thrusts. Solid
triangles indicate active volcanoes of the Sangihe Arc.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276244
Fig. 1 (continued ).
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 245
information is sometimes underutilised. Thus, although
it has been known for some time that the geochemistry
of igneous rocks is a reflection of their broad tectonic
situation (Pearce and Norry, 1979; Pearce et al., 1984;
Pearce and Peate, 1995), the potentially powerful
ability of geochemical variation in magmatic rocks to
track tectonic changes in time and space is often
neglected. The resolution of this tool is further
enhanced when, in addition to major and trace element
signatures, the radiogenic isotope compositions of
igneous rocks are also determined. Sr, Nd and Pb
isotopic signatures reflect the age and geological his-
tory of the mantle and crustal domains involved in
tectonic events (White and Patchett, 1984; Nelson et
al., 1986; McDonough and McCulloch, 1987).
In this contribution we will present new field,
geochemical and isotopic data for igneous rocks from
northwest Sulawesi in the now extinct part of the
Indonesian arc (Fig. 1a–d), which span an age range
of 51 to 2 Ma. The main focus will be on the Sr, Nd
and Pb isotopic characteristics of the various igneous
suites, which range from normal tholeiitic and calc-
alkaline arc volcanism to high-K magmatism. The
geochemistry of the different groups of igneous rocks
of Eocene to Pleistocene age will be compared, and
the implications for the tectonic regime in the area
discussed. These new data will be integrated with
existing data sets on central, south and north Sulawesi
(Kavalieris et al., 1992; Priadi et al., 1993, 1994;
Bergman et al., 1996; Polve et al., 1997, 2001; Elburg
M. Elburg et al. / Chemical Geology 199 (2003) 243–276246
and Foden, 1998, 1999a,b; Elburg et al., 2002b) to
achieve a better picture of Sulawesi’s geochemical
evolution in space and time.
2. Tectonic setting
Northwest Sulawesi occupies the central part of a
Cainozoic magmatic belt that encompasses the south
arm of Sulawesi, central Sulawesi, the neck and the
north arm (Fig. 1d), and is known as the West(ern)
Sulawesi (Plutono-Volcanic) Arc or Western Sulawesi
(Magmatic) Province. It straddles two disparate ter-
ranes referred to by Taylor and Van Leeuwen (1980)
as Western Sulawesi and Northern Sulawesi, which
represent continental margin and oceanic arc setting,
respectively. The boundary between these two ter-
ranes remains ill-defined.
The northern Sulawesi terrane consists of a Neo-
gene volcanic arc with associated sedimentary deposits
(North Sulawesi Arc) built on a highly deformed
Palaeogene basement composed dominantly of basal-
tic rocks, which is probably underlain by oceanic crust
(Kavalieris et al., 1992; Pearson and Caira, 1999). The
Neogene volcanic and intrusive rocks are dominantly
of calc-alkaline affinity (Polve et al., 1997; Elburg and
Foden, 1998). Radiometric age dating of these rocks
(Surmont et al., 1994; Polve et al., 1997; Elburg and
Foden, 1998; Pearson and Caira, 1999) suggests that
they were formed between 22 and 0.9 Ma. Active
volcanism presently takes place only at the eastern tip
of the north arm.
Western Sulawesi started to develop in the Late
Mesozoic at the southeast margin of Sundaland. Its
basement consists of several metamorphic complexes.
Those exposed in the southern half of the terrane,
including the Bantimala Complex (Wakita et al.,
1996), together with the Pompangeo Schist Complex,
which crops out in eastern Sulawesi (Parkinson,
1998), form part of an arcuate zone of dismembered
accretionary complexes that extends through south-
east Kalimantan into west Java. They were metamor-
phosed in a northerly dipping subduction system
during the mid-Cretaceous (Parkinson et al., 1998).
The metamorphic complexes are in thrust or deposi-
tional contact with weakly metamorphosed deep
marine clastics of Late Cretaceous age, which are
interpreted as fore-arc basin deposits related to a
northerly directed subduction system (Van Leeuwen,
1981; Hasan, 1991; Sukamto and Simanjuntak, 1983).
During the Early Tertiary, plate readjustments in SE
Asia caused widespread extension. Western Sulawesi
rifted away from Sundaland, resulting in the formation
of the Makassar Straits; this event was probably
connected to the formation of the Celebes Sea (Hall,
1996). Syn-rift siliciclastics deposited in graben
basins were succeeded by platform carbonates and
other neritic to deeper marine deposits during the Late
Eocene to Middle Miocene (Coffield et al., 1993;
Wilson and Bosence, 1996; Calvert, 2000). Calc-
alkaline arc volcanism commenced as early as the
Palaeocene (Van Leeuwen, 1981; Polve et al., 1997)
and continued into the Late Eocene in the south arm
and until mid-Oligocene times further to the north.
Following a possible cessation of magmatic activity,
the next recorded arc volcanism event took place
around 19–15 Ma (Elburg and Foden, 1999a; Priadi
et al., 1997; Yuwono, 1987; this study).
The Neogene geology of Western Sulawesi is
characterised by the widespread occurrence of potassic
to ultrapotassic volcanic and volcaniclastic deposits
and co-magmatic intrusives, which in the central and
northern parts are found together with high-K calc-
alkaline granitic intrusives and subordinate felsic vol-
canics (Leterrier et al., 1990; Priadi et al., 1993, 1994;
Bergman et al., 1996; Polve et al., 1997, 2001; Elburg
and Foden, 1999a,b; Elburg et al., 2002b). Neogene
potassic magmatism, which began to develop f 14
Ma ago, is thought to be related to a series of collision
events between the Western Sulawesi arc that com-
menced in the Late Oligocene–Early Miocene, involv-
ing oceanic and microcontinental fragments derived
from the Pacific Plate and the northern margin of
Australian Plate (Hamilton, 1979; Lee and Lawver,
1995; Bergman et al., 1996; Charlton, 1996; Hall,
1996, 2002). Which fragments were colliding and
the timing and location of these collisions are still
not well understood, although good evidence exists
that the last collision between Western Sulawesi and
the Sula platform occurred around 5 Ma (Hall and
Wilson, 2000; Hall, 2002).
In Western Sulawesi the effects of the collision
events become evident only towards the end of the
Miocene (Hall, 2002). These include west-verging
thrusting and folding (Bergman et al., 1996), the
development of a NNW-trending strike-slip fault sys-
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 247
tem, including the Palu-Koro Fault that has exhumed
parts of the lower crust (Helmers et al., 1990; Polve et
al., 2001), and rapid elevation of mountains to about
2.5 km with deposition of molasse deposits along their
flanks. During the Pliocene the north arm underwent a
20j to 25j clockwise rotation (Sasajima et al., 1980;
Surmont et al., 1994), causing subduction of the south-
ern part of the Celebes Sea beneath the north arm. The
only volcanic activity related to this event is Una-Una
volcano in the Gulf of Gorontalo (Vroon et al., 2000).
Some plate tectonic models assume that Northern
Sulawesi was originally located further to the east (e.g.
Daly et al., 1991). However, palaeomagnetic measure-
ments suggest that it remained more or less close to its
present day position throughout its history (Surmont et
al., 1994). This in turn suggests that during the
Cainozoic, Western and Northern Sulawesi formed a
continuous magmatic arc (Rangin et al., 1999), cross-
ing from continental to oceanic crust. Subduction
beneath this arc was in a northerly to westerly direc-
tion, with western Sulawesi initially orientated NE and
rotating counterclockwise about 40j, together with
Borneo, between 25 and 10 Ma (Hall, 2002).
3. Local geology
The study area from which samples were collected
falls approximately between 2jS and 1jN. Its geology(Fig. 1c) consists of a basement of two metamorphic
complexes (Malino and Palu Complexes) and a
sequence of Upper Cretaceous metasediments, which
are overlain by Palaeogene volcanic-sedimentary for-
mations (Papayato Volcanics and Tinombo Formation).
The Neogene to Quaternary stratigraphy includes sedi-
mentary sequences deposited in marine basins, syn-
orogenic deposits of Plio-Pleistocene age (Celebes
Molasse), and intrusive and volcanic rocks of high-K
calc-alkaline to shoshonitic affinity in the continental
margin segment, and of normal calc-alkaline affinity
(including the Bolano Andesite) in the oceanic arc
segment.
In this paper the Palaeogene and Neogene igneous
units that were sampled are referred to as the Older
Series and Younger Series, respectively. The Miocene
series of calc-alkaline rocks (Bolano Andesite), which
does not fit well into either group, will be referred to as
the CA suite. Appendices A and B give more infor-
mation on the lithologies, mineral content, age con-
straints, alteration and deformation of the units
studied.
3.1. Metamorphic complexes
The Malino Complex (Kavalieris et al., 1992; Fig.
1c) is located in the western part of the north arm. It
consists predominantly of muscoviteF biotite schists
and gneisses, with intercalations of quartzite, graphite
schist, marl and amphibolite. Greenschists form a
discontinuous selvage around the complex; they were
derived from the overlying Tinombo Formation in the
west and the Papayato Volcanics in the east (Van
Leeuwen et al., in preparation). The contact between
the complex and Palaeogene formations is likely to be
tectonic rather than depositional.
The Palu Complex (Van Leeuwen et al., in prepa-
ration) represents a medium-P metamorphic belt, rang-
ing from chlorite up to staurolite zone, which is
exposed in the southeastern part of the study area. Its
lithologies are dominated by biotite gneisses and
schists, with subordinate amphibolites, granulites,
migmatites, peridotites, calc-silicate rocks and meta-
granitoids. The medium-P metamorphic rocks have
been overprinted by low-P metamorphism that is
thought to be related to young magmatic activity
(Egeler, 1946). High-pressure metamorphic rocks
occur as blocks and lenses along the Palu-Koro fault
and include garnet peridotite, garnet-clinopyroxene
granulite and felsic granulite (Egeler, 1946; Parkinson
et al., 1998). The maximum pressure that these rocks
were exposed to varies from 6 to 38 kbar (Helmers et
al.,1990; Parkinson et al., 1998; Kadarusman and
Parkinson, 2000; Polve et al., 2001). Several samples
have been analysed by Polve et al. (2001) for their
geochemical and isotopic composition.
The two metamorphic complexes are the subject of
continuing research (Van Leeuwen et al., in prepara-
tion), but preliminary U-Pb zircon dating and Sr-Nd-
Pb isotope analysis indicate that their igneous and
sedimentary protoliths were old continental crust,
probably of Australian derivation. Reconnaissance
U/Pb, Ar/Ar and K/Ar dating indicates that the Malino
rocks were metamorphosed in the mid-Miocene (23–
11 Ma); predominantly Early Pliocene ages were
obtained for the Palu Complex, but Oligocene and
Mesozoic dates have also been reported (Siahaan et
M. Elburg et al. / Chemical Geology 199 (2003) 243–276248
al., 1994; Priadi et al., 1996, 1999; Kadarusman and
Parkinson, written comm., 2000).
3.2. Older series
The Papayato Volcanics (PV) (Kavalieris et al.,
1992) forms the basement of Northern Sulawesi. The
formation consists of a thick pile of basaltic lava flows
and breccias with rare intercalations of deep marine
sedimentary rocks, which are cut by dykes and stocks
of gabbroic to dioritic composition. Less voluminous
felsic rocks occur in bimodal association with the
mafic volcanics as dykes, lava flows and volcaniclas-
tic deposits. The PV extends beyond the eastern
boundary of the study area, having a total strike length
of about 275 km. Limited palaeontological and radio-
metric age dating (T. van Leeuwen, unpublished data;
Polve et al., 1997) suggests that they have a Middle
Eocene to Earliest Miocene age.
Within the study area the PV has been subdivided
into three units based on their geochemical character-
istics; ‘‘PV mafic’’ and ‘‘PV felsic’’, which are both of
tholeiitic affinity, and ‘‘PVKCA’’, which includes
both mafic and felsic rocks displaying medium to
high-K calc-alkaline features. Limestone intercala-
tions in PV mafic and PVKCA rocks dated at Mid-
dle–Late Eocene and Earliest Miocene, respectively,
could possibly indicate a change from tholeiitic to
calc-alkaline magmatism with time.
The Tinombo Formation (Brouwer, 1934) is a thick
sequence of weakly metamorphosed pelitic sediments
with interbedded greywacke, arkose, limestone, marl
and volcanic rocks, showing in places flysch-like
features. It is widely exposed in the neck, where it
overlies the Palu Complex (in the southern part) and in
the Toli-Toli area. It is also found in a fault block to
the west of the Palu-Koro Fault and in the Donggala
Peninsula. Brouwer (1934) and Sukamto (1973)
assigned a Late Cretaceous to Eocene age to the
formation, but recent palaeontological dating (T. van
Leeuwen, unpublished data) suggests a similar age
range as that of the PV, i.e. Middle Eocene to Earliest
Miocene.
The volcanic rocks associated with the Tinombo
Formation range in composition from basalt to rhyolite.
They occur as intercalations in the Tinombo Formation,
as dykes cutting this formation and the underlying Palu
Complex, and locally as volcanic piles with only minor
sedimentary rocks. Based on their geographic location
and geochemical characteristics, they have been sub-
divided into the following units: Tinombo Volcanics
(TV; exposed in the neck), Tinombo Volcanics D
(TVD; Donggala Peninsula) and Toli-Toli Volcanics
A and B (TTVA and TTVB; Toli-Toli area).
Co-magmatic intrusive stocks, ranging in composi-
tion from diorite to granodiorite, intrude the Tinombo
Formation and Palu Complex, and are referred to as
Tinombo Intrusives (TI). Limited available radiometric
age dates for TI, TV and TVD samples range between
about 51.5 and 30 Ma (Sukamto, 1973; Polve et al.,
1997; T. Van Leeuwen and C. Allen, unpublished data;
this study, Table 1). Limestones found as lenses within
or close to TV rocks contain Middle and Late Eocene
benthonic foraminifera assemblages (Brouwer, 1934;
T. van Leeuwen, unpublished data).
The Renangkali Granite (RG), a two mica granite,
is found as stocks and late dykes intruded in the Palu
Complex east of Tompe. Two dyke samples yielded K/
Ar ages of around 34 Ma (Table 1). Slightly older40Ar/39Ar ages (37–42 Ma) were obtained from three
samples collected from the main intrusive stock (T. van
Leeuwen and P. Vasconcelos, unpublished data).
Both the RG and TI rocks show evidence of
moderate to strong deformation. This in contrast to
the Tondopado Microdiorite (TM) that occurs as a
series of dykes in the neck to the east of Tompe and in
the Donggala Peninsula. A dyke sample from the
latter area yielded a whole rock K/Ar age of 17.7
Ma (Polve et al., 1997). Diorite rocks found to the
south of Palu, which have been dated at about 15.5
Ma (Siahaan et al., 1994), may belong to the same
magmatic event.
The Papayato Volcanics and Tinombo Formation
have both undergone low-grade greenschist facies
metamorphism. The latter shows strong isoclinal fold-
ing and thrusting in the northern neck and Toli-Toli
area (Brouwer, 1934; Ratman, 1976). The relationship
between these two units has not been clearly estab-
lished. Ratman (1976) thinks they possibly interfinger;
most authors (e.g. Polve et al., 1997) regard the PV to
be a volcanic member of the Tinombo Formation.
3.3. CA suite
Following Polve et al. (1997), we refer to the calc-
alkaline (CA) rocks that make up the bulk of the
Table 1
K/Ar dates of selected samples
Suite Sample Material 40Ar (� 10� 10 mol/g) 40Ar/40Artot %K Age (Ma)
TI NWS53 Hbl 4.076 0.39 0.527 44.1F1.0a
4.143 0.48 44.8F 0.9
TI NWS25 Hbl 0.2575 0.622 0.3913 37.5F 0.3a
0.3920
RG NWS11 Mu 5.2009 0.731 8.887 33.4F 0.2b
RG NWS14 Mu 39.654 0.84 6.737 33.7F 0.7a
41.317 0.83 35.1F 0.7
BA NWS40 WR 0.2102 0.32 1.045 11.6F 0.2b
0.30
HK NWS401 Bt 1.5728 0.201 6.503 14.1F 0.4c
1.6058 0.196 6.434
HK NWS414 Bt 1.4390 0.237 7.054 11.6F 0.3c
1.4063 0.233 7.044
HK NWS422 Kfsp 0.4698 0.141 5.985 4.6F 0.2c
0.4920 0.116 6.098
HK NWS424 Bt 0.5188 0.137 5.987 4.9F 0.2c
0.5025 0.136 6.076
HK NWS319 Bt 0.5804 0.54 4.32 7.7F 0.2a
HK MLP4 Bt 0.5267 0.59 4.53 6.7F 0.1a
HK MKE1 Bt 0.9598 0.43 6.20 8.9F 0.2a
O NWS35 WR 0.4121 0.12 3.541 6.7F 0.2a
DSS (L) NWS17 Mu 0.4860 0.476 8.151 3.4F 0.1b
8.134
HK=Younger Series High-K; BA=Bolano Andesite; O =Ongka Volcanics; D =Dondo; RG=Renangkali Granite; TI = Tinombo Intrusives;
Bt = biotite; Kfsp =K-feldspar; WR=whole rock; Mu =muscovite.a Analysed by Institute of Geological and Nuclear Sciences.b Analysed by AMDEL.c Analysed by Geochron Laboratories.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 249
Neogene North Sulawesi Arc as the ‘‘CA Suite’’. In
the study area, their occurrence is restricted to the
eastern part where they are found as andesitic and
dacitic stocks, dykes and epiclastics associated with
Early–Middle Miocene marine deposits. The unit was
sampled only at one locality, south of the Malino
Complex, where a group of small orthopyroxene–
hornblende andesite stocks, given the name here of
Bolano Andesite (BA), intrude the Papayato Vol-
canics. The BA yielded a K/Ar age of 11.6 Ma (Table
1), which falls roughly in the middle of the age range
of the North Sulawesi Arc (see above).
3.4. Younger series
Magmatic activity during the Late Miocene to
Pleistocene produced two igneous suites in the con-
tinental margin part of the study area, which we
denote as the Younger Series igneous rocks, consist-
ing of an intermediate to felsic high-K suite and a
high-K to shoshonitic/ultrapotassic suite.
3.4.1. HK suite
The high-K to shoshonitic/ultrapotassic suite con-
sists of intrusives and extrusives with mafic to felsic
compositions of which outcrops and float have been
found in a number of scattered locations in NW
Sulawesi. These have not been previously described.
However, Polve et al. (1997) report a single location
of shoshonitic rocks to the east of the study area dated
at 11 Ma. Similar rocks are widespread in central
Sulawesi and the south arm where they have been
classified as shoshonitic, alkaline potassic or ultra-
potassic (SH, AK, UK; Polve et al., 1997), or simply
as high-potassium (HK; Priadi et al., 1994). We will
use the latter term to refer to this series.
The HK suite rocks have been observed as dykes
and stocks cutting the Palu Complex, Upper Creta-
Table 2
Whole rock analyses of representative samples
NWS74,
PVKCA
NWS252,
PVKCA
NWS41B,
PV mafic
NWS540,
PV felsic
NWS68A,
TTVA
NWS66B,
TTVB
NWS322,
TVD
NWS325,
TVD
SiO2 45.2 75.4 51.3 73.58 50.4 52.5 58.0 48.5
Al2O3 20.9 12.5 16.0 11.74 16.3 18.4 17.0 18.2
Fe2O3 8.90 2.34 11.40 4.55 7.68 8.08 5.80 9.12
MnO 0.16 0.05 0.35 0.14 0.16 0.15 0.15 0.17
MgO 5.77 0.47 7.40 0.63 7.75 4.49 4.51 6.01
CaO 9.82 0.27 7.70 3.03 8.75 5.56 7.48 11.24
Na2O 2.54 3.99 2.40 3.95 4.09 5.06 3.24 2.62
K2O 1.32 3.07 0.29 0.55 0.04 1.36 0.29 0.16
TiO2 0.65 0.12 0.84 0.54 0.95 1.33 0.49 0.72
P2O5 0.10 0.03 0.07 0.13 0.13 0.62 0.16 0.09
LOI 4.25 1.19 2.39 1.58 2.84 3.65 2.89 2.60
Total 99.56 97.72 100.14 100.42 99.06 100.70 100.04 99.42
Sc 38 13 47 37 35 31 15 38
V na 11 na 26 198 235 120 313
Cr 26 170 52 77 330 118 148 109
Co 37 3 35 2 23 22 15 31
Ni 16 14 13 nd 92 49 40 27
Cu 95 nd 44 nd 135 33 45 103
Zn 67 47 19 60 61 82 43 54
Ga 16 15 16 13 14 15 18 18
Rb 19 23 2 6 2 22 3 5
Sr 531 51 109 149 120 448 530 378
Y 12 85 16 38 20 16 15 17
Zr 26 156 32 93 26 125 64 41
Nb 1.4 1.1 1.1 nd 1.2 16.5 0.7 0.1
Cs 0.05 0.24 0.08 nd 0.48 1.20 1.02 0.70
Ba 130 198 21 53 28 207 62 70
La 3.36 12.38 1.85 4.7 4.26 9.83 5.27 2.20
Ce 7.77 17.64 4.98 13 11.95 16.80 13.66 6.40
Pr 0.95 3.87 0.72 2.29 1.87 2.17 1.67 0.90
Nd 5.14 22.15 4.22 12 9.36 9.32 9.16 5.90
Sm 1.60 7.60 1.61 3.9 2.74 2.23 2.17 1.90
Eu 0.62 1.05 0.63 1.35 0.90 0.93 0.77 0.64
Gd 1.90 9.93 2.27 5.0 3.03 2.51 2.24 2.40
Tb 0.32 1.91 0.41 0.9 0.54 0.48 0.37 0.40
Dy 2.14 13.63 2.87 6.3 3.29 2.98 2.37 2.90
Ho 0.44 2.95 0.62 1.4 0.74 0.61 0.48 0.60
Er 1.40 9.51 1.93 4.1 1.83 1.82 1.59 1.90
Tm 0.21 1.44 0.28 0.66 0.26 0.29 0.22 0.29
Yb 1.27 9.67 1.83 4.1 1.71 1.88 1.68 1.90
Lu 0.20 1.53 0.30 0.67 0.28 0.28 0.30 0.32
Hf 0.79 5.55 0.99 2.8 1.11 2.90 2.19 1.30
Ta 0.08 0.05 0.04 nd 0.11 1.30 0.07 0.03
Pb nd nd 5 nd 13 6 nd nd
Th 0.83 1.72 0.57 0.5 0.28 1.10 0.45 0.76
U 0.18 0.46 0.08 nd 0.15 0.35 0.18 0.10
M. Elburg et al. / Chemical Geology 199 (2003) 243–276250
Table 2 (continued)
NWS45,
TV
TNB3,
TV
TNB19,
TI
NWS25,
TI
NWS53,
TI
NWS9,
TM
NWS557,
RG
NWS40,
BA
SiO2 49.9 54.8 48.3 58.60 54.70 51.0 65.0 62.0
Al2O3 16.1 17.7 17.0 17.50 17.90 19.3 17.72 16.6
Fe2O3 8.24 8.43 5.97 7.00 7.90 8.30 3.12 4.30
MnO 0.17 0.90 0.11 0.14 0.14 0.10 0.06 0.10
MgO 8.35 4.68 8.85 3.40 4.00 4.40 1.6 2.24
CaO 6.95 1.67 11.79 7.00 8.20 10.50 4.33 4.75
Na2O 4.55 6.94 2.59 3.05 3.10 3.25 4.48 3.96
K2O 0.43 0.35 0.67 1.16 0.91 0.38 1.18 1.29
TiO2 0.77 0.82 0.53 0.80 0.97 0.97 0.33 0.32
P2O5 0.17 0.24 0.12 0.14 0.20 0.14 0.1 0.20
LOI 4.77 3.82 4.21 1.00 1.66 1.30 0.65 4.65
Total 100.40 100.33 100.90 99.79 99.68 99.64 98.57 100.35
Sc na na 33 na na 29 7 12
V na na 140 na na na 50 99
Cr 40 596 459 57 57 57 313 21
Co 36 26 32 17 17 27 7 10
Ni 56 61 128 13 13 15 19 nd
Cu 27 132 21 5 18 90 nd 12
Zn 51 123 37 80 85 26 40 nd
Ga na 16 15 na na 18 17 17
Rb 7 6 20 35 27 13 36 19
Sr 629 365 446 293 315 317 501 380
Y 19 17 13 35 23 20 10 7
Zr 66 73 52 125 137 72 113 44
Nb 3.0 4.6 3.2 6 7 3.5 2.0 nd
Cs 0.50 0.32 0.64 1.49 0.62 1.20 4.10 0.53
Ba 121 123 88 273 158 80 104 218
La 7.72 6.05 6.37 19 15.3 6.18 7.50 4.25
Ce 15.30 11.82 14.13 35.9 30.5 14.91 16.0 9.20
Pr na 1.51 1.56 4.59 na 1.82 1.96 1.08
Nd 10.80 7.94 7.85 20.5 18 9.22 8.10 4.90
Sm 2.88 2.26 2.10 5 3.93 2.74 1.80 1.20
Eu 1.02 0.72 0.73 2 1.15 0.97 0.74 0.50
Gd na 2.45 2.13 5.78 na 3.03 1.80 1.23
Tb 0.54 0.44 0.36 1.04 0.62 0.53 0.30 0.21
Dy na 2.89 2.43 5.99 na 3.45 1.70 1.27
Ho 0.78 0.62 0.50 1.34 0.76 0.71 0.40 0.27
Er na 1.83 1.43 3.44 na 2.21 1.00 0.78
Tm 0.38 0.29 0.20 0.61 0.23 0.32 0.15 0.11
Yb 2.15 1.87 1.43 3.49 2.64 2.12 1.10 0.79
Lu 0.25 0.27 0.24 0.31 nd 0.34 0.17 0.13
Hf 1.60 2.07 1.34 3.4 3.71 2.01 2.90 1.51
Ta 0.30 0.31 0.20 0.56 0.54 0.20 0.3 nd
Pb 24 8 nd 17 14 na nd nd
Th 1.45 1.13 1.23 6.45 3.95 2.14 3.5 1.17
U 0.36 0.79 0.28 0.62 0.46 0.29 1.7 0.41
(continued on next page)
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 251
Table 2 (continued)
NWS737,
HK
NWS217,
HK
NWS376,
HK
MKE1,
HK
NWS316,
HK
NWS411,
HK
NWS511,
HK
SiO2 55.7 57.1 49.9 50.9 51.6 56.9 50.0
Al2O3 18.1 17.1 9.6 11.4 12.5 14.1 16.0
Fe2O3 6.39 6.34 7.35 9.08 7.96 5.82 9.24
MnO 0.10 0.10 0.19 0.15 0.14 0.07 0.26
MgO 2.91 3.96 11.25 11.68 7.86 2.35 4.31
CaO 5.64 5.58 6.63 7.99 7.20 4.23 8.62
Na2O 3.64 2.64 0.93 1.72 1.70 1.95 2.54
K2O 4.59 3.62 5.87 4.72 5.83 7.57 4.36
TiO2 0.72 0.82 1.02 0.84 1.00 0.81 0.87
P2O5 0.52 0.21 1.03 0.59 1.12 0.56 0.57
LOI 1.85 1.17 5.03 0.50 1.69 4.46 1.82
Total 99.76 98.78 98.71 99.53 99.42 98.89 98.63
Sc 17 18 19 28 25 15 26
V 208 125 131 177 177 125 285
Cr 100 101 636 772 360 112 85
Co 13 21 40 58 32 13 29
Ni 223 33 433 399 118 17 44
Cu 76 24 90 79 10 35 155
Zn 53 59 99 70 44 74 297
Ga 15 20 16 19 19 21 19
Rb 88 154 313 308 201 353 121
Sr 1310 343 904 725 1192 597 1380
Y 8 25 21 26 33 23 23
Zr 106 198 350 157 264 291 152
Nb 7.3 14.2 17.0 11.2 15.5 17.0 12.0
Cs 1.00 9.00 10.70 17.10 3.40 3.30 2.60
Ba 2270 806 3913 1891 5075 1700 3740
La 10.80 40.20 50.60 47.10 101.60 47.00 55.00
Ce 17.50 75.20 112.20 94.00 194.20 94.00 99.00
Pr 2.12 6.99 11.65 9.73 18.62 10.70 11.50
Nd 8.60 31.10 50.20 48.20 85.40 41.00 42.00
Sm 1.86 5.70 9.40 8.70 14.30 7.90 7.00
Eu 0.76 1.29 3.83 1.91 2.13 1.65 1.80
Gd 1.75 4.90 9.20 7.00 10.50 6.20 6.60
Tb 0.28 0.70 0.90 0.90 1.30 0.80 0.80
Dy 1.57 4.40 4.10 4.80 6.50 4.20 3.90
Ho 0.32 0.80 0.70 0.90 1.10 0.80 0.80
Er 0.91 2.60 2.40 2.50 3.10 2.10 2.10
Tm 0.13 0.37 0.21 0.33 0.39 0.32 0.29
Yb 0.91 2.30 1.40 2.10 2.50 2.00 1.80
Lu 0.14 0.37 0.25 0.32 0.40 0.28 0.25
Hf 2.80 5.80 9.40 4.50 7.00 7.70 4.20
Ta 0.50 1.44 1.15 0.66 0.70 1.00 0.60
Pb 11 33 130 11 6 36 65
Th 4.21 20.64 31.00 24.00 34.52 33.00 26.00
U 0.79 5.18 6.40 6.33 5.68 5.60 3.90
M. Elburg et al. / Chemical Geology 199 (2003) 243–276252
(continued on next page)
Table 2 (continued)
NWS639,
HK
NWS910,
HK
NWS401,
HK
NWS414,
HK
NWS319,
HK
MLP4,
HK
SiO2 48.7 59.2 55.90 52.60 52.38 57.61
Al2O3 11.7 16.8 14.64 16.89 14.01 14.86
Fe2O3 10.55 6.67 5.89 8.80 9.12 6.61
MnO 0.17 0.12 0.12 0.14 0.15 0.12
MgO 10.17 2.98 3.23 3.89 6.86 6.66
CaO 10.85 5.50 5.28 5.08 9.24 6.37
Na2O 1.54 3.61 2.93 3.07 1.80 2.34
K2O 3.77 6.28 5.88 6.32 3.62 2.94
TiO2 1.09 0.74 0.60 0.86 0.80 0.63
P2O5 1.04 0.49 0.49 0.81 0.53 0.24
LOI 0.58 0.78 4.31 2.17 0.36 1.49
Total 100.17 100.15 99.27 100.64 99.00 99.87
Sc 39 17 18 20 37 18
V 239 132 124 178 233 131
Cr 431 112 135 56 235 409
Co 40 16 15 20 33 28
Ni 140 26 34 nd 23 125
Cu 71 30 41 61 55 44
Zn 71 62 61 83 29 42
Ga 15 18 18 20 17 19
Rb 192 224 323 325 204 119
Sr 933 1270 593 840 529 674
Y 26 28 23 28 19 19
Zr 132 268 264 270 97 132
Nb 10.0 15.0 17 17 5.2 10.57
Cs 12.30 18.80 13 5.7 4.7 8.07
Ba 2780 2180 981 1710 857 1165
La 49.20 51.80 51 50 20.2 40.93
Ce 100.00 98.60 93 97 42.4 74.46
Pr 12.60 12.20 10.5 11.5 4.42 6.67
Nd 52.00 47.00 39 47 22.4 27.72
Sm 10.40 9.10 7 9.2 4.6 5.27
Eu 2.42 2.74 1.5 1.96 1.18 1.23
Gd 8.20 7.80 5.9 7.1 4 4.22
Tb 1.10 1.00 0.8 1 0.6 0.59
Dy 5.60 5.00 3.9 5 3.5 3.42
Ho 1.00 0.90 0.7 0.9 0.7 0.66
Er 2.50 2.50 2.2 2.5 2.1 1.89
Tm 0.35 0.36 0.34 0.42 0.29 0.29
Yb 2.10 2.10 2 2.4 1.9 1.87
Lu 0.30 0.33 0.3 0.33 0.3 0.29
Hf 3.90 6.00 7.7 6.8 2.8 4.06
Ta 0.70 1.00 1.8 1.1 0.36 0.86
Pb 27 66 45 33 nd 33
Th 25.10 26.70 49 39 8.16 17.98
U 6.10 9.30 12 8.7 1.96 4.478
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 253
Table 2 (continued)
NWS35,
Ongka V
NWS238A,
Ongka V
NWS300,
DSS
M21,
DSS
NWS17,
DSS (L)
NWS357,
DSS (L)
NWS645,
Gimpu V
SiO2 66.90 69.1 65.7 70.4 75.60 70.4 68.85
Al2O3 16.00 13.3 15.3 14.2 14.20 14.8 15.28
Fe2O3 2.98 3.05 4.05 2.14 0.78 1.32 2.76
MnO 0.09 0.04 0.07 0.03 0.10 0.03 0.05
MgO 1.85 1.74 2.30 0.76 0.15 0.54 1.09
CaO 2.67 2.82 3.78 1.97 0.75 1.19 2.42
Na2O 3.75 2.86 2.99 3.93 2.85 4.82 4.25
K2O 4.83 4.23 4.17 4.08 4.80 5.35 4.34
TiO2 0.53 0.55 0.52 0.29 0.07 0.13 0.36
P2O5 0.26 0.26 0.19 0.12 0.09 0.10 0.21
LOI 0.70 1.14 0.38 0.97 0.68 0.49 0.62
Total 100.56 99.08 99.57 98.93 100.09 99.15 100.22
Sc 10 9 10 5 3 3 5
V 85 71 71 32 na 28 34
Cr 100 181 167 114 126 204 151
Co 17 8 10 5 2 3 3
Ni 26 26 16 60 6 32 nd
Cu 17 7 na 82 4 88 nd
Zn 49 33 40 nd 9 nd nd
Ga – 11 18 17 21 15 18
Rb 200 163 187 133 314 171 127
Sr 622 467 306 558 81 1039 904
Y 24 26 24 14 17 11 20
Zr 217 178 160 152 37 124 203
Nb na 15.2 13.4 9.0 21 19.0 14.0
Cs 6.07 4.60 9.20 1.60 20.7 7.50 3.1
Ba 1590 1377 677 1196 113 2028 1920
La 45.40 52.40 47.80 29.90 9.15 19.30 66.70
Ce 82.00 95.30 88.00 61.60 17.7 48.80 118.00
Pr na 9.07 7.95 5.53 na 4.93 12.6
Nd 36.70 39.60 34.10 21.40 8.42 20.20 41.90
Sm 6.48 6.70 5.90 3.90 2.19 4.00 6.60
Eu 1.37 1.17 1.11 1.43 0.27 1.93 1.44
Gd na 5.30 4.90 4.40 na 3.70 4.9
Tb 0.91 0.80 0.70 0.50 0.37 0.40 0.70
Dy na 4.40 4.10 2.40 na 1.90 3.7
Ho 0.61 0.90 0.80 0.50 0.38 0.30 0.70
Er na 2.70 2.50 1.50 na 1.10 2.00
Tm 0.48 0.40 0.38 0.20 0.23 0.12 0.32
Yb 2.53 2.60 2.40 1.40 1.25 0.80 2.10
Lu nd 0.42 0.39 0.22 nd 0.13 0.33
Hf 0.89 5.50 5.00 4.50 1.6 5.00 5.80
Ta 1.98 1.52 1.36 0.75 4.7 1.73 1.3
Pb 7.00 13 7 30 8 183 29
Th 21.50 28.40 30.61 19.50 11.3 51.00 33.80
U 4.45 8.52 6.82 6.10 3.83 10.90 7.80
Abbreviations as in text. Oxides in weight percent; elements in ppm. na = not analysed; nd = not detected. All iron as Fe2O3.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276254
ceous metasediments, Tinombo Formation and RG.
In three localities extrusiveF intrusive complexes
were observed, consisting of various pyroclastics,
epiclastics and lavas. Intrusive lithologies of the
high-K suite include lamprophyre, nepheline gabbro,
quartz-syenite, melanosyenite and monzodiorite. Ex-
trusive rocks are mainly basanite, trachyte and latite.
K/Ar age dating of seven intrusive and extrusive
Table 3
Rb-Sr and Sm-Nd isotopic compositions (by TIMS) and elemental concentrations (by ICP-MS)
Sample Age 87Sr/86Sr 87Sr/86Sri Rb
(ppm)
Sr
(ppm)
143Nd/144Nd
Nd
(ppm)
Sm
(ppm)
147Sm/144Nd
Papayato KCA
NWS74 40 0.704453 0.704394 19.1 531 0.512874 5.36 1.57 0.1766
CSW III 40 0.704037 0.703807 43 305 0.512977 9.53 2.63 0.1670
NWS534 40 0.704058 0.703997 7.0 190 0.512952 8.78 2.71 0.1867
Papayato mafic
NWS41D 40 0.705508 0.705407 1.2 18.8 0.512984 1.97 0.65 0.1983
NWS249 40 0.705255 0.704941 27.6 144 0.513006 3.54 1.29 0.2202
NWS532 40 0.703906 0.703883 3.0 218 0.512933 9.38 2.60 0.2103
Toli-Toli Volcanics A
MB 2 40 0.706749 0.705884 20 38 0.512734 4.21 1.03 0.1475
NWS68A 40 0.706929 0.706905 1.7 120 0.512968 10.28 3.05 0.1794
Toli-Toli Volcanics B
NWS66B 40 0.704797 0.704716 22 448 0.512923 13.30 3.27 0.1487
Tinombo Volcanics D
NWS325 40 0.703559 0.703539 4.6 378 0.512990 5.36 1.86 0.2096
Tinombo Volcanics
NWS45 40 0.707404 0.707386 6.7 629 0.512766 9.99 2.73 0.1654
Tinombo Intrusives
TNB 19 40 0.703725 0.703651 20 446 0.512797 8.62 2.17 0.1520
NWS323 31 0.706210 0.706152 94 163 0.512602 14.97 3.51 0.1416
NWS53 40 0.704567 0.704457 27 315 0.512658 15.93 3.72 0.1414
Renangkali Granite
NWS557 40 0.703953 0.703926 36 501 0.512736 7.15 1.74 0.1472
Tondopado Microdiorite
NWS9 17.7 0.704482 0.704452 13 317 0.512864 9.50 2.63 0.1671
Bolano Andesite
NWS40 11.4 0.706114 0.706091 18.6 380 0.512919 4.55 1.08 0.1440
Gimpu Volcanics
NWS645 2 0.711138 0.711127 127 904 0.512181 41.90 6.60
NWS652 2 0.715907 0.715882 177 575 0.512108 32.90 5.50
Ongka Volcanics
NWS238A 6.7 0.712953 0.712857 163 467 0.512176 39.60 6.70
NWS238B 6.7 0.712045 0.711914 211 445 0.512220 36.30 6.40
NWS238B leacht 0.512203
Dondo Supersuite Volcanics
NWS300 3.4 0.716716 0.716631 187 306 0.512070 34.10 5.90
NWS301 3.4 0.719323 0.719274 204 578 0.512098 44.20 6.70
NWS69 3.4 0.710839 0.710804 152 606 0.512177 24.90 4.30
M21 3.4 0.710160 0.710127 133 558 0.512268 21.40 3.90
(continued on next page)
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 255
Table 3 (continued)
Sample Age 87Sr/86Sr 87Sr/86Sri Rb
(ppm)
Sr
(ppm)
143Nd/144Nd
Nd
(ppm)
Sm
(ppm)
147Sm/144Nd
Dondo Supersuite Leucocratic
NWS357 3.4 0.712056 0.712033 171 1039 0.512188 20.20 4.00
High-K Suite
MLP 4 6.7 0.711459 0.711410 120 674 0.512215 27.70 5.30
NWS66 6.7 0.707509 0.707488 96 1250 0.512584 27.40 4.10
NWS66 leacht 0.707484 0.512594
NWS66 unl 0.707537 0.512581
NWS68B 6.7 0.711463 0.711424 148 1065 0.512132 38.40 7.30
NWS737 6.7 0.707463 0.707444 88 1310 0.512630 8.60 1.86
NWS217 9? 0.719141 0.719012 154 343 0.512159 31.10 5.70
NWS319 7.7 0.708749 0.708627 204 529 0.512365 22.40 4.60
NWS375 7.2 0.714047 0.713928 271 674 0.512092 38.80 7.10
NWS376 7.2 0.713820 0.713718 313 904 0.512124 50.20 9.40
NWS376 leacht 0.713715 0.512144
NWS385 7.2 0.714332 0.714268 286 1317 0.512079 49.80 9.90
NWS644 0.715269 0.715146 315 757 0.512017 51.30 9.20
NWS335 7? 0.713635 0.713599 132 1054 0.512097 47.50 8.30
NWS335 leacht 0.714030 0.512085
MKE 1 10 0.714420 0.714245 308 725 0.512133 48.20 8.70
NWS316 10 0.714071 0.714002 201 1192 0.512183 85.40 14.30
NWS411 7 0.716898 0.716728 353 597 0.511846 41.00 7.90
NWS411 leacht 0.714975 0.511878
NWS412 7 0.716196 0.716081 257 642 0.511935 49.00 9.30
NWS412 leacht 0.714966 0.511917
NWS414 7 0.714317 0.714206 325 840 0.512035 47.00 9.20
NWS511 7 0.713820 0.713795 121 1380 0.512058 42.00 7.00
NWS639 9 0.715316 0.715240 192 933 0.512085 52.00 10.40
NWS682 9 0.713340 0.713283 216 1390 0.512247 48.30 9.30
NWS910 9 0.713322 0.713256 224 1270 0.512264 47.00 9.10
Palu Complex
NWS203 0.736314 78 110 0.511790 30.99 5.72 0.1116
NWS584 0.709422 113 453 0.512248 33.46 5.97 0.1078
NWS602 0.717917 233 269 0.512097 23.60 4.59 0.1174
NWS604 0.712562 26 1100 0.512176 72.95 12.83 0.1063
NWS610 0.708420 63 612 0.512305 33.99 6.15 0.1093
NWS373 0.739167 46 34 0.511815 11.76 5.21 0.2679
NWS757 0.710111 3 214 0.512127 35.76 7.31 0.1235
NWS903 0.706775 na na 0.512393 21.39 4.16 0.1177
NWS612 0.703479 na na 0.513154 9.73 3.17 0.1972
NWS612 rep 0.703466
NWS580 0.704627 na na 0.512985 8.35 2.82 0.2042
NWS596 0.709494 na na 0.512277 37.46 6.06 0.0978
Malino Complex
IKA19 0.705054 5 142 0.512969 4.50 1.60
NWS941 0.704394 nd 181 0.512960 9.72 2.79 0.1732
NWS942 0.730166 47 173 0.511696 18.77 3.29 0.1060
NWS38 0.743278 na na 0.511685 39.24 6.62 0.1020
NWS63 0.781940 na na 0.511619 25.70 4.75 0.1117
NWS526 0.705204 na na 0.513009 13.04 4.43 0.2052
NWS523 0.704367 na na 0.513015 12.73 3.05 0.1449
M. Elburg et al. / Chemical Geology 199 (2003) 243–276256
Table 3 (continued)
Sample Age 87Sr/86Sr 87Sr/86Sri Rb
(ppm)
Sr
(ppm)
143Nd/144Nd
Nd
(ppm)
Sm
(ppm)
147Sm/144Nd
Tinombo Fmt, Toli-Toli
NWS510 0.711449 na na 0.512352 0.1163
Tinombo fmt, Donggala
NWS568 0.710495 na na 0.512353 20.61 4.09 0.1199
Tinombo fmt, Palu
NWS590 0.707873 na na 0.512680 0.1478
Pompangeo Schists
NWS920 0.708479 44.0 162 0.512413 6.17 1.24 0.1217
NWS920 rep 0.708480
NWS921 0.705111 6.7 138 0.512918 1.15 0.43 0.2278147Sm/144Nd ratio given for samples for which this was determined by isotope dilution measurements. See Appendix A for the constraints on the
ages. unl = unleached; leacht = leachate; rep = repeat.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 257
samples yielded ages ranging between 14 and 5 Ma
(Table 1).
3.4.2. CAK suite
The youngest suite consists of the Dondo Super
Suite (DSS) of intrusive rocks and co-magmatic vol-
canic rocks (Kavalieris et al., 1992; Polve et al., 1997,
2001; this study). These have been classified as being
high-K calc-alkaline (CAK) by previous workers, and
will be referred to as the CAK suite. They are found
along a N-NE-trending belt, 300-km long (which
extends into central Sulawesi), as stocks and batholiths
up to 2 km in diameter, commonly showing contact
metamorphic aureoles. Intrusive lithologies include
porphyritic and equigranular monzogranite and quartz
monzonite, and late leucocratic syenogranite dykes.
The DSS has ages ranging predominantly between 9
and 1.6 Ma (OCTA, 1971; Van Leeuwen et al., 1994;
Polve et al., 1997; Bellier et al., 1998; Widiasmoro et
al., 1997; this study, Table 1).
Volcanic equivalents are the Ongka Volcanics (Van
Leeuwen et al., 1994) and the Gimpu Volcanics
(Polve et al., 1997). The former is exposed near the
village of Ongka, where they cover f 200 km2, and
to the SW of Tinombo in outcrops of restricted size.
The Gimpu Volcanics is found along the Palu-Koro
Fault Zone in the vicinity of Gimpu and to the north of
Lake Lindu. Both units consist of pyroclastics includ-
ing ignimbrites, and subordinate lavas of predomi-
nantly rhyodacitic composition. K/Ar dating yielded
ages of 6–7 Ma for the Ongka Volcanics (Polve et al.,
1997; this study, Table 1), and 2–4 Ma for the Gimpu
Volcanics (Polve et al., 1997).
4. Analytical techniques
A selection of 184 (70 from the Older Series, 45
CAK and 69 HK) samples was analysed by Actlabs
(Canada) for major oxides and a wide range of trace
elements by fusion-ICP and fusion-ICP-MS methods,
respectively, using methods described by Elburg et al.
(2002b), with accuracy for major elements around 1%
(Table 2). Analysed samples were selected to obtain a
representative coverage of the geographical areas and
rock types involved.
Samples were selected for isotope analyses on the
basis of their freshness (low loss on ignition), low
silica content (when possible) and their being repre-
sentative of their suite. Sr, Nd and Pb isotope ratios
were analysed at the Department of Geology and
Geophysics at the University of Adelaide on a Fin-
nigan MAT 262 Thermal Ionisation Mass Spectrom-
eter in static mode. All ground samples were leached in
3 N HCl for 30 min at approximately 100 jC. Thesupernatant was pipetted off, the sample washed in
deionised water and the water pipetted off. The residue
was then analysed for its isotopic composition. In
selected cases, the leachate was analysed too (Tables
3 and 4). Nd and Pb isotopic compositions of leachate
Table 4
U-Th-Pb isotopic compositions (by TIMS) and elemental concentrations (by ICP-MS)
Sample 206Pb/204Pb corr 207Pb/204Pb corr 208Pb/204Pb corr U (ppm) Pb (ppm) Th (ppm)
Papayato KCA
NWS74 17.246 15.520 37.255 0.18 nd 0.83
CSW III 18.207 15.523 38.109 0.41 nd 1.11
NWS534 18.185 15.577 38.179 0.20 nd 0.60
Papayato Mafic
NWS41D 18.591 15.613 38.748 0.05 nd 0.26
NWS249 18.313 15.543 38.224 0.29 nd 0.34
NWS532 18.241 15.578 38.295 0.10 nd 0.80
Toli-Toli Volcanics A
MB 2 18.700 15.632 38.890 0.37 19 0.10
NWS68A 18.651 15.632 38.934 0.15 13.4 0.28
Toli-Toli Volcanics B
NWS66B 18.470 15.589 38.502 0.35 6 1.10
Tinombo Volcanics D
NWS325 18.216 15.535 38.151 0.10 nd 0.76
Tinombo Volcanics
NWS45 18.469 15.589 38.517 0.36 24 1.45
Tinombo Intrusives
TNB 19 18.440 15.606 38.589 0.28 nd 1.23
NWS323 18.668 15.633 38.802 1.60 nd 7.04
NWS53 18.617 15.638 38.795 0.46 14.00 3.95
Renangkali granite
NWS557 18.463 15.594 38.492 1.70 nd 3.50
Tondopado Microdiorite
NWS9 18.582 15.622 38.723 0.29 nd 2.14
Bolano Andesite
NWS40 18.414 15.576 38.606 0.41 nd 1.17
Gimpu Volcanics
NWS645 18.750 15.609 39.001 7.80 29.00 33.80
NWS652 18.771 15.682 39.038 7.60 10.00 31.60
Ongka Volcanics
NWS238A 18.845 15.631 39.029 8.52 13.00 28.40
NWS238B 18.822 15.649 39.051 6.50 8.00 24.62
Dondo Supersuite Volcanics
NWS300 18.822 15.666 39.169 6.82 7.00 30.61
NWS301 19.145 15.743 39.436 10.17 8.00 36.03
NWS69 18.546 15.607 38.889 2.10 7.00 14.20
M21 18.761 15.654 39.035 6.10 30.00 19.50
Dondo Supersuite Leucocratic
NWS357 18.745 15.668 39.022 10.9 183 51
M. Elburg et al. / Chemical Geology 199 (2003) 243–276258
Table 4 (continued)
Sample 206Pb/204Pb corr 207Pb/204Pb corr 208Pb/204Pb corr U (ppm) Pb (ppm) Th (ppm)
High-K Suite
MLP 4 18.718 15.626 39.013 4.5 33 18.0
NWS66 17.894 15.541 38.828 0.6 34 12.1
NWS66 unl 17.907 15.576 38.931
NWS68B 18.456 15.605 38.943 2.1 36.6 11.9
NWS737 17.911 15.547 38.859 0.8 11 4.2
NWS217 19.009 15.670 39.266 5.2 33 20.6
NWS319 18.328 15.588 39.009 2.0 nd 8.2
NWS375 18.633 15.638 38.879 7.1 15 33.4
NWS376 18.651 15.636 38.861 6.4 130 31
NWS376 leacht 18.666 15.653 38.922
NWS385 18.651 15.654 38.890 4.4 99 21.7
NWS644 18.657 15.670 38.984 7.3 20 30.9
NWS335 18.621 15.640 38.842 3.1 12 17.8
NWS335 leacht 18.614 15.637 38.782
MKE 1 18.557 15.629 38.948 6.3 11 24
NWS316 18.917 15.668 39.012 5.7 6 34.5
NWS411 18.012 15.589 38.944 5.6 36 33.0
NWS411 leacht 18.043 15.607 38.960
NWS412 18.172 15.588 39.009 8.9 34 45
NWS412 leacht 18.149 15.600 39.007
NWS414 18.342 15.610 39.119 8.7 33 39
NWS511 17.329 15.501 38.718 3.9 65 26
NWS639 18.520 15.678 39.123 6.1 27 25.1
NWS682 19.074 15.713 39.230 14.4 44 48.2
NWS910 19.049 15.685 39.142 9.3 66 26.7
Palu Complex
NWS203 18.868 15.662 38.938 2.9 nd 15.2
NWS584 18.787 15.654 39.063 1.4 5 13.0
NWS602 18.830 15.650 38.858 13 45 36.2
NWS604 18.707 15.645 38.912 4.2 13 29.8
NWS610 18.671 15.624 38.775 2.1 nd 6.6
NWS373 17.508 15.543 37.308 0.3 nd 1.5
NWS757 18.761 15.633 38.778 0.23 15.58 0.39
NWS903 18.968 15.682 39.086 na na na
NWS612 17.825 15.545 37.600 na na na
NWS612 rep 17.712 15.548 37.577
NWS580 17.863 15.482 37.766 na na na
NWS596 18.737 15.626 38.973 na na na
Malino Complex
IKA19 18.253 15.554 38.296 0.10 nd 0.20
NWS941 18.394 15.592 38.444 0.26 nd 1.01
NWS942 18.182 15.610 38.845 2.07 20.84 9.85
NWS38 18.388 15.621 38.730 na na na
NWS63 19.044 15.756 39.059 na na na
NWS526 18.076 15.507 38.068 0.18 nd 0.81
NWS523 17.991 15.497 38.075 na na na
Tinombo fmt, Toli-Toli
NWS510 18.732 15.654 38.930 na na na
(continued on next page)
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 259
Table 4 (continued)
Sample 206Pb/204Pb corr 207Pb/204Pb corr 208Pb/204Pb corr U (ppm) Pb (ppm) Th (ppm)
Tinombo fmt, Donggala
NWS568 18.775 15.653 38.947 na na na
Tinombo fmt, Palu
NWS590 18.633 15.648 38.813 na na na
Pompangeo Schists
NWS920 18.668 15.638 38.774 0.96 12.94 2.03
NWS921 18.601 15.643 38.700 nd nd 0.26
na = not analysed; nd = not detected. Pb isotopic ratios have been corrected for fractionation during mass spectrometry.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276260
and leached sample are generally within error. Sr
isotopic compositions of the leachate can be both
higher and lower than that of the leached sample,
reflecting influences of alteration and selective leach-
ing. Separation procedures have been described by
Elburg and Foden (1998).
The long-term average for the in-house Nd stand-
ard (J&M specpure Nd2O3) is 0.511603F 9 (1r of
total population, n = 105). The LaJolla standard gave
0.511828F 11 (n = 9) and BCR-1 was 0.512593F 16
(n= 12). Typical blanks are in the order of 100–200
pg for Nd. The average for the NBS987 Sr standard is
0.710258F 18 (n = 56). Typical Sr blanks are better
than 1.5 ng, which is negligible compared to a typical
sample size of 10–100 Ag of Sr. All Pb isotopic
analyses were performed at approximately the same
temperature of 1150 jC, and a mass fractionation
factor of 0.08% per amu was used, based on replicate
analyses of the NBS981 Pb standard. Typical Pb
blanks are in the order of 500 pg.
K/Ar dating of some samples (Table 1) was per-
formed at AMDEL analytical laboratories, on a modi-
fied MS-10 mass spectrometer, following the techni-
ques described byWebb et al. (1986); at the Institute of
Geological and Nuclear Sciences Ltd, Rafter Labora-
tories, following the techniques described by Elburg et
al. (2002b); and at Geochron Laboratories, of which
the procedure is as follows. Potassium was analysed in
duplicate on a Beckman Model DU flame spectrom-
eter. For the argon analyses a measured amount of the
sample is fused in molybdenum crucible using an Rf
induction furnace. During the fusion very pure 38Ar
tracer gas is admitted to the system. The mixed
sample-tracer Ar is analysed in an AEI model MS-10
mass spectrometer. The reported uncertainties on the
measured K/Ar ages are based on the expected pre-
cisions on the K and Ar analyses, and a 1% error
allowing for uncertainties in the calibration.
5. Major and trace element geochemistry
The analyses for the Older Series of samples span a
wide range in SiO2 (40–76%) and MgO (0.3–32%)
concentrations (Figs. 2 and 3). These samples fall
within the low- to medium-K fields in a K2O versus
SiO2 diagram (Fig. 2), except some of the PVKCA
samples, which fall within the high-K field.
The Miocene HK suite of the Younger Series has
MgO contents between 0.7% and 17.8%, and SiO2
contents range between 45% and 65%. These samples
mainly fall within the shoshonitic field, with fewer
analyses in the high-K field.
The Younger Series CAK suite (Dondo Super
Suite, DSS Leucocratic, Gimpu and Ongka Volcanics)
is more felsic than the other two groups, with SiO2
contents between 62% and 76%, and MgO contents
not exceeding 2.8%. They plot on the boundary
between the high-K and shoshonitic fields. Only a
few samples of either the Younger or the Older Series
have TiO2 values greater than 1.3% (Fig. 3); these low
values of TiO2 are characteristic for arc-type lavas
(Pearce, 1982).
MORB-normalised trace element diagrams for
selected samples from the different groups are shown
in Fig. 4A–D. Most of the TV, TI and TVD samples
show distinct Nb-Ta anomalies and LREE-enriched
patterns (Fig. 4A). They also display geochemical
characteristics that are typical of continental arc rocks,
such as relatively high Zr/Y (>3; Fig. 5) and La/Yb
(3.5–6) ratios and elevated K, Sr, Rb, Zr and Th
contents. This is consistent with their setting (meta-
Fig. 2. K2O versus SiO2 diagram for the samples analysed. Divisions following Gill (1981). Note that the samples from the Eocene–Miocene
Older Series have significantly lower K2O content than those for the Miocene–Pliocene Younger Series.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 261
morphic basement of largely continental derivation).
The RG and TM have arc-type patterns too. The TV
and TVD rocks have been previously classified by
Polve et al. (1997) as back-arc basin (BAB) basalts
(based on only three samples) because of their reduced
Nb-Ta anomalies, significant depletion in Hf, Zr or Y
and flat to slightly depleted LREE patterns. However,
Fig. 3. TiO2 versus MgO for the Older and
our more extensive data do not support this interpre-
tation.
The various PV samples mostly show very pro-
nounced negative Nb-Ta anomalies (Fig. 4A) and
strongly resemble oceanic island arc basalts, as is
indicated by, for instance, their low Zr/Y ( < 3; Fig. 5)
and La/Yb ( < 2) ratios.
Younger Series. Symbols as in Fig. 2.
Fig. 4. (A–D) N-MORB normalised trace element diagrams for selected samples from the different groups. Both the CAK and HK samples
from the Younger Series show strong enrichments in incompatible elements, relatively high Nb/Zr ratios, and the negative Nb-Ta and Ti
anomalies typical for arc-type rocks. The Older Series samples have lower levels of incompatible elements and lower Nb/Zr ratios. Normalising
values and order from Sun and McDonough (1989).
M. Elburg et al. / Chemical Geology 199 (2003) 243–276262
Fig. 5. Zr/Y versus Zr diagram (after Pearce, 1982) for the Older
Series, showing the mainly oceanic arc character of the Papayato
Volcanics, and the mainly continental arc character of the TV, TVD,
TTV and TM samples. Symbols as in Fig. 2.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 263
The two groups of TTV, A and B, have very distinct
trace element patterns, unlike typical arc basalts,
neither showing well-developed negative Nb-Ta or Ti
anomalies (Fig. 4B). However, they do have strong
positive Pb anomalies, one of the other signatures of
subduction-related basalts. The TTVB samples show
distinct continental arc features whereas the TTVA
samples display more mixed signatures.
The trace element patterns for representative sam-
ples from the different groups of Miocene HK rocks
show very strong enrichments in the most incompat-
ible elements (on the left hand side of the diagram,
Fig. 4C), and most show the overall pattern of arc-
type rocks. MORB-normalised values of Nb are
generally higher than for Zr, a sign of either a
continental arc or a collisional signature (Pearce
and Peate, 1995; Elburg and Foden, 1999b). The
patterns for the three groups of Miocene–Pliocene
CAK samples are nearly identical (Fig. 4D), with the
leucocratic DSS intrusives showing a slightly more
fractionated pattern with strong depletions in P
(apatite fractionation) and Ti (Fe-Ti-oxide fractio-
nation). Our analyses for the CAK samples closely
resemble the samples analysed by Polve et al.
(2001).
The normalised trace element patterns of the HK
and CAK suites are surprisingly similar considering
the difference in fractionation stage. They are distin-
guished from the Older Series by their much greater
enrichment in incompatible elements, both the fluid-
mobile ones such as Rb and Ba, and the fluid-immo-
bile ones such as Nb and Ta.
6. Radiogenic isotopes
Isotope and elemental data for Rb-Sr, Sm-Nd and U-
Th-Pb are given in Tables 3 and 4. No age correction
has been applied for 143Nd/144Nd (close to being within
error of the analysis) or Pb isotopes (owing to Pb levels
below the detection limit for many of the samples from
the older series), but all Sr isotopic ratios have been
recalculated to their measured or assumed age (see
Appendix A for the age constraints).
In terms of Sr and Nd isotopes, there is a clear
distinction between samples of the Older and those of
the Younger Series, with the former having lower87Sr/86Sr and higher 143Nd/144Nd than the latter (Fig.
6). The Older Series encompasses the field for the
Celebes Sea basement (Serri et al., 1991) and that for
samples from the Sangihe Arc in NW Sulawesi
(Elburg and Foden, 1998). The range of Sr-Nd isotopic
compositions of the Younger Series broadly overlaps
with that of Miocene–Pliocene (18–1 Ma) igneous
samples from central Sulawesi (Bergman et al., 1996;
Elburg and Foden, 1999a). Within the Younger Series,
the CAK samples have a slightly more restricted range
in isotopic compositions, particularly in 143Nd/144Nd.
Interestingly, central Sulawesi also experienced mafic,
high-K magmatism in the Middle Miocene which gave
way to more felsic CAK magmatism in Late Mio-
cene–Pliocene times (Priadi et al., 1994; Polve et al.,
2001). The link between this CAK magmatism and the
present-day dacitic products of the volcano Una-Una
(or Colo) in the Gorontalo Basin, which was suggested
by Priadi et al. (1993), is not borne out by their Sr-Nd
isotopic data. Una-Una has very constant isotopic
characteristics at 87Sr/86Sr 0.7061 and 143Nd/144Nd =
0.5126 (Vroon et al., 2000), while all the analysed
samples from the CAK series have 143Nd/144Nd <
0.5123 and 87Sr/86Sr>0.709. Our analyses for the
CAK series overlap with those from Polve et al.
(2001). The isotopic values for the NW Sulawesi
Younger Series extend to more ‘continental’ compo-
sitions (higher 87Sr/86Sr, lower 143Nd/144Nd) than
those of analysed low-grade sedimentary rocks from
K
Fig. 6. 87Sr/86Sr versus 143Nd/144Nd of the igneous samples from NW Sulawesi (top) and the same groups of samples compared to other
igneous, sedimentary and metamorphic samples from the area (bottom). Data from: Serri et al. (1991): Celebes Sea; Elburg and Foden (1998):
NE Sulawesi; Elburg and Foden (1999b) and Elburg et al. (2002a,b): south Sulawesi and north Australian sediment; Bergman et al. (1996) and
Elburg and Foden (1999a,b): central Sulawesi; Housh and McMahon (2000): Upper Miocene–Pliocene intrusives from Irian Jaya; Vroon et al.
(1996): south Sulawesi sediment; Vroon et al. (2000): Una-Una volcano; Polve et al. (2001): CAK and basement (peridotites and granulites).
Note that the low-grade sedimentary rocks from Sulawesi (south Sulawesi sediment, Tinombo Formation Phyllite and Pompangeo Schists) have
relatively unradiogenic Sr and Pb, and radiogenic Nd isotopic ratios.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276264
the Tinombo Formation or the Pompangeo Schists
(Table 3, Fig. 6), or from other sedimentary rocks in
central and south Sulawesi (Vroon et al., 1996; Elburg
and Foden, 1999a). Some of the samples trend towards
the field for north Australian sediments (Elburg et al.,
2002a), in which several metamorphic samples from
the Malino and Palu complexes fall as do the lower
crustal samples analysed by Polve et al. (2001). The
slightly steeper samples trend towards low 143Nd/
144Nd at intermediately high 87Sr/86Sr (towards
NWS411) that two of the Miocene high-K samples
follow a trend somewhat similar to the seen in
Miocene intrusive rocks from Irian Jaya (Housh and
McMahon, 2000).
The Older Series samples overlap with the Younger
Series on the unradiogenic end of their trends in a207Pb/204Pb versus 206Pb/204Pb diagram, but do not
reach significantly more radiogenic values than the NE
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 265
Sulawesi Sangihe arc. The samples from the Younger
Series show a wide span (Fig. 7), broadly ranging from
Indian Ocean Mid-Ocean Ridge Basalt (I-MORB)
towards the field for north Australian sediments. This
is a wider range than seen in samples from equivalent
age in central Sulawesi. Within the Younger Series, the
Fig. 7. 207Pb/204Pb versus 206Pb/204Pb for the same samples as in Fig. 6. F
from Nelson et al. (1986).
CAK samples fall on the more radiogenic end of the
trend.
There is a pronounced distinction between the
Younger and the Older Series in the 208Pb/204Pb
(Fig. 8) versus 206Pb/204Pb diagram, with the Older
Series running from the I-MORB field towards the
ield for Western Australia and New South Wales ultrapotassic rocks
Fig. 8. 208Pb/204Pb versus 206Pb/204Pb for the same samples as in Fig. 6. Note the relatively high 208Pb/204Pb ratios for the HK samples.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276266
low-grade sediments from NW and south Sulawesi,
encompassing the range for the NE Sulawesi samples,
and overlapping on the lower side of the field for
igneous rocks from south Sulawesi. The high-K
samples from the younger series are characterised by
high 208Pb/204Pb ratios for their 206Pb/204Pb ratios,
indicating a source component with long-term enrich-
ment of Th over U. The trend towards low 206Pb/204Pb
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 267
values does not point towards any easily identifiable
end member, but the high 206Pb/204Pb side of the trend
overlaps with that of the CAK samples and points
towards the field of north Australian sediments. The
overlap between the CAK series and Australian sedi-
ments was also noted by Polve et al. (2001) for the
samples they analysed from central and northwest
Sulawesi.
7. Discussion
7.1. Source of the older series
The isotopic compositions of the Older Series are
generally similar to those of subduction-related vol-
canics. Most of the PV Group isotopic values resem-
ble those for oceanic arc rocks, such as the products
of the Sangihe Arc. Only one PVKCA sample falls
squarely in the field for MORB in terms of its Pb
isotopic composition. Most of the TV, TI and TTVA
samples have lower 143Nd/144Nd and higher 87Sr/86Sr
ratios than the PV samples. Although it is possible
that alteration has affected the Rb-Sr system, leading
to unreliable initial 87Sr/86Sr ratios, this generally
does not change the 143Nd/144Nd ratios. The lower
Nd isotopic ratios are more similar to rocks from
continental arcs, or magmas that have suffered con-
tamination with sedimentary materials, either within
the subduction zone, or in high-level magma cham-
bers. This is also reflected in their relatively high Zr/
Y (Fig. 5) and Nb/Zr ratios, and by 87Sr/86Sr ratios in
excess of 0.707870 shown by the associated Tinombo
sediments (Table 3), indicating a continental prove-
nance. The mixed oceanic–continental arc signature
of the TTV samples may represent subduction under-
neath an area of thin continental crust, or varying
degrees of sediment subduction underneath an oce-
anic arc.
The presence of the Older Series of igneous rocks,
with its subduction signature, in NW Sulawesi
extends the areal extent of subduction-related magma-
tism in Western Sulawesi. According to Polve et al.
(1997), subduction-related magmatism in this region
was largely restricted to the Palaeocene Alla/Bua
Volcanics in south Sulawesi. Our data show that the
TV, TI, TVD and TTV in NW Sulawesi are also
subduction-related. Moreover, Eocene–Lower Oligo-
cene subduction-related magmatism has also been
recognised in the south arm of Sulawesi (Langi Vol-
canics; Van Leeuwen, 1981; Elburg et al., 2002b) and
several locations in central Sulawesi (T. van Leeuwen,
unpublished data). It agrees with several plate recon-
structions (Lee and Lawver, 1995; Hall, 1996; Rangin
et al., 1999) that both Western and Northern Sulawesi
were part of a volcanic arc over a west dipping subduc-
tion zone.
The fact that the PV has isotopic and geochemical
signatures more similar to those of oceanic arc rocks,
while the samples from the more westerly TV and TI
show a more continental arc signature, is interpreted
as reflecting a break in the character of the basement
underlying the deposits. This supports Taylor and
Van Leeuwen’s (1980) division of the West Sulawesi
Magmatic Province into two terranes, the boundary
of which we interpret to lie between the TV/TI and
PV, with the TTV being located in the boundary area.
An apparent gap in subduction-related magmatism
in the continental (western) part of the study area
exists between the Late Oligocene and Early Miocene,
with the youngest ages of the TV/TI around 30 Ma,
while the next phase of arc-type volcanism (Tondo-
pado Microdiorite) occurring at 18 Ma. It is not clear
yet whether this gap in magmatic activity is real or
reflects the poor geological record for this period of
time. However, it is interesting to note that a similar
gap in magmatism may exist in the central and south-
ern parts of Western Sulawesi as is suggested by
available stratigraphic and radiometric age dating
evidence (Polve et al., 1997). This apparent absence
of arc-related magmatism in Western Sulawesi could
reflect plate reorganisations, as suggested by the
tectonic reconstructions of Hall (2002). Arc-type
magmatism of the Papayato Volcanics continued
probably without any major breaks until the Early
Miocene (approximately 22 Ma). At Labuanaki, about
220 km east of the study area, it was preceded by/
coincided with the production of Eocene BAB basalts
that show similar geochemical characteristics to Cel-
ebes Sea basalts (Priadi et al., 1997).
7.2. Source of the younger series high-K samples
The high-K samples of the Younger Series show an
exceptional range in isotopic signatures. A significant
number of analyses display isotopic characteristics
M. Elburg et al. / Chemical Geology 199 (2003) 243–276268
that appear to have been influenced by upper crustal
rocks or sediments, with 87Sr/86Sr z 0.713, 143Nd/144Nd V 0.5121, 206Pb/204Pb>18.6, 207Pb/204Pb>
15.64, 208Pb/204Pb around 39 (Figs. 6–8). Represen-
tatives of this group are samples NWS376 and
NWS217. Several other end members can be found
within the high-K set. One representative is sample
NWS411, which is extending towards rather low143Nd/144Nd for its 87Sr/86Sr content; this sample
has low 206Pb/204Pb (18), but 208Pb/204Pb relatively
high at 38.9. Samples NWS66 and 737 have the least
‘continental’ Sr and Nd (0.708, 0.5126) isotopic
signature, but their Pb isotopes are only slightly less
radiogenic than those of NWS411. Finally, sample
NWS511 has Sr and Nd isotopic ratios similar to
NWS376, but combines this with the lowest Pb
isotopic signature of all high-K samples.
The isotopic signature of the HK suite does not
overlap with arc suites, nor with values for magmas
derived from the asthenospheric mantle such as mid-
ocean ridge basalt (MORB) or ocean island basalt
(OIB). Not even the high-K volcanoes from the Sunda
Arc (Muriah or Ringgit-Beser; Edwards et al., 1991,
1994) or high-K syn- and post-collisional samples
from the south arm of Sulawesi (Elburg and Foden,
1999b; Elburg et al., 2002b) have 143Nd/144Nd ratios
that even approach the low values seen in the HK
samples from NW Sulawesi.
The isotopic signature of a significant group of
these samples points towards that of clastic sediment
derived from Proterozoic upper crust, such as that from
north Australia (Elburg et al., 2002a). Interestingly,
this signature is more ‘continental’ than that of low-
grade sedimentary rocks from Sulawesi, such as phyl-
lites from the Palaeogene Tinombo Formation, or the
Mesozoic Pompangeo Schists. Some metasediments
from the Pre-Tertiary Palu and Malino Metamorphic
Complexes, as well as the lower crustal samples
analysed by Polve et al. (2001), have appropriate Sr
and Nd isotopic compositions that have been involved
in the petrogenesis of these samples, but none of them
have suitably high 208Pb/204Pb to explain the most
radiogenic high-K samples in Pb isotopic space. All
the high-K samples that trend towards low 206Pb/204Pb
ratios have significantly higher 208Pb/204Pb ratios than
subduction-related rocks from south or NE Sulawesi,
and also somewhat higher 207Pb/204Pb ratios. This
feature is shared by some Miocene high-K samples
from the Sassak area in central Sulawesi (Elburg and
Foden, 1999a), although the latter samples do not
reach the same relative enrichment in 208Pb/204Pb,
nor similarly low 206Pb/204Pb ratios. Although upper
Miocene to Pliocene high-K rocks from Irian Jaya also
show relatively high 208Pb/204Pb values for their206Pb/204Pb, the enrichment is not as extreme as seen
in NW Sulawesi.
A commonly invoked reservoir with high 207Pb/204Pb and 208Pb/204Pb for its relatively unradiogenic206Pb/204Pb ratios is the subcontinental lithospheric
mantle, as sampled by kimberlites and lamproites.
Data from such ultrapotassic rocks in Western
Australia and New South Wales (McCulloch et
al., 1983; Nelson et al., 1986) do indeed show
enrichment in 207Pb/204Pb and 208Pb/204Pb ratios for
their 206Pb/204Pb ratios compared to subduction-
related rocks, although neither group is an exact
fit for our HK data set. Nevertheless, we think that
the great diversity of isotopic compositions can
only be explained by melting of material with a
long and diverse geological history, with variable
enrichments and depletions in certain elements at
certain times. The high magnesium and low silica
content for many of the samples and the lack of
correlation between isotopic composition and indi-
ces of fractionation indicate that the magmas must
have been derived from the mantle, and that their
isotopic composition is unlikely to reflect contam-
ination in an upper crustal magma chamber. We
therefore propose that the HK samples in NW
Sulawesi reflect small degree melts from the Aus-
tralian lithospheric mantle, similar to the HK sam-
ples from central Sulawesi (Bergman et al., 1996;
Elburg and Foden, 1999a). This interpretation dif-
fers from that by Polve et al. (1997, 2001) and
Macpherson and Hall (1999), who propose that the
HK magmatism in central Sulawesi reflects melting
of Sundaland lithosphere, metasomatised by pre-
vious subduction.
7.3. Source of the younger series CAK samples
The CAK samples distinguish themselves from the
HK samples by their higher SiO2 contents, and their
more homogeneous isotopic and trace element com-
position. They overlap in isotopic composition with
the HK samples that have the more ‘continental’
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 269
isotopic composition, with high 87Sr/86Sr, low 143Nd/144Nd and high Pb isotope ratios, plotting close to the
field for north Australian sediments (Figs. 6–8), as
also noticed by Polve et al. (2001). There are four
ways in which these samples could have obtained
this continental geochemical signature: (1) Fractiona-
tion of mafic, mantle derived magmas that obtained
their isotopic signature by subduction of sedimentary
material into the mantle. This idea is contradicted by
the absence of any mafic and intermediate CAK
magmas and the fact that none of the CAK samples
show the unusual isotopic signature observed in the
mantle-derived HK samples (low 206Pb/204Pb ratios
combined with relatively high 208Pb/204Pb ratios) or
MgO contents in equilibrium with mantle rocks; (2)
Assimilation of crustal materials by mantle-derived
magmas. If this theory were correct, we would expect
to see a correlation between the samples MgO or
SiO2 content (as a measure of fractionation) and their
isotopic signature, which is not the case; (3) Mixing
of crustal and mantle-derived melts. The absence of
mafic samples or a correlation between isotopes and
indices of fractionation argues against this option; (4)
Melting of continental crust. This is our preferred
model and that of previous authors (Priadi et al.
1993; Bergman et al., 1996; Polve et al., 1997,
2001; Elburg and Foden, 1999a). Supporting evi-
dence includes the fact that we see only felsic
materials and no parental magmas that are in equili-
brium with the mantle, the predominantly peralumi-
nous character of the CAK rocks, and the presence of
cordierite and garnet in some samples, minerals that
are typical for crustally derived granites (White and
Chappell, 1988).
The crust that melted to form the granites cannot
be represented by the upper, Sundaland plate, since
the analyses of sedimentary rocks (Tinombo For-
mation Phyllite, Pompangeo Schist) indicate that
this plate does not show suitably high Sr and Pb
isotopic signatures, or low enough Nd isotopic
signatures. The CAK series magma must have
originated by melting of the Australian upper crust
that has been thrust underneath the younger Sunda-
land plate. High-pressure rocks exposed along the
Palu-Koro fault (Helmers et al.,1990; Parkinson et
al., 1998; Kadarusman and Parkinson, 2000) are
likely to represent this underthrust piece of Austral-
ian material, since their isotopic composition (Polve
et al., 2001) is broadly similar to that of the CAK
samples.
7.4. Isotopic signature in space and time
Fig. 9 shows the Nd isotopic composition through
time for different areas in Sulawesi. Fig. 10 shows a
map view of this information, with samples classified
as being either ‘‘Pre-Miocene’’ (i.e. the Older Series
of NW Sulawesi, ‘‘pre-collisional’’ samples of south
Sulawesi), ‘‘Miocene’’ (the HK samples of NW and
central Sulawesi, the Bolano Andesite, syn-collisional
samples from south Sulawesi, 12–14 Ma samples
from NE Sulawesi) or ‘‘Miocene-Recent’’ (CAK
samples from NW and central Sulawesi; post-colli-
sional (Gunung Lompobatang) samples from south
Sulawesi, 4 Ma and recent samples from NE Sula-
wesi and the recent products from Una-Una Volcano).
Data sources are given in the figure caption. The
threefold grouping in Fig. 10 neglects the fact that the
different groups overlap in time, as can be gleaned
from Fig. 9, and in this way the figures are comple-
mentary. The size of the points in Fig. 10 represents
the Nd isotopic compositions, and this shows very
well that for central and NW Sulawesi, Nd isotopic
values decrease markedly in the Miocene, whereas
this is not the case for south or NE Sulawesi. This
clearly points towards a different source for Miocene
HK magmatism in south Sulawesi and that in central/
NW Sulawesi (Macpherson and Hall, 1999), with
south Sulawesi magmatism representing melting of
metasomatised Sundaland mantle (Yuwono et al.,
1988) with input of sediments derived from an
Australian microcontinent (Elburg et al., 2002b),
while the source in central/NW Sulawesi is under-
thrust Australian lithospheric mantle.
Normal subduction-related magmatism overlapped
in time with high-K magmatism, as seen from the age
range of North Sulawesi arc magmatism (22–0.9 Ma),
including the date of the calc-alkaline Bolano Ande-
site (11 Ma). The Bolano Andesite occurs to the east
of the area in which we have evidence for Miocene
HK magmatism with low-Nd isotopic signatures, and
Miocene–Pliocene CAK magmatism. We propose
that its spatial position defines the eastern boundary
of the underthrust Australian sliver. This would then
coincide with the boundary between Northern and
Western Sulawesi, defined by the Papayato Volcanics
Fig. 10. Map view of Nd isotopic compositions for the same samples as in Fig. 9. The size of the circle corresponds to the value of the143Nd/144Nd ratio, with small circles denoting low values, and the colour of the circle indicating its age group. The shaded area indicates the
position of the underthrust piece of Australian continent, inferred from the spatial distribution of low-143Nd/144Nd samples.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 271
and igneous suites of the Tinombo Formation. There-
fore, the spatial extent of the piece of underthrust
Australian lithosphere and crust extends from approx-
imately 4jS to 1jN.
7.5. Timing of underthrusting and cause of melting
There are two possible scenarios for the timing of
underthrusting of the Australian sliver and the cause
of its melting.
(1) Underthrusting occurred shortly before the
onset of HK magmatism, which started around 14
Fig. 9. Nd isotopic composition versus time for different areas within Sula
the diagram indicate the range of Nd isotopic ratios of the Celebes Sea bas
NW Sulawesi show similar evolutionary trends, with the low-Nd isotopic
central Sulawesi, if a single analysis by Bergman et al., 1996 is taken into
samples. This strongly contrast with the trends seen in SW and NE Sulaw
Ma, apart from an isolated lamprophyre date at 17 Ma
from central Sulawesi (Bergman et al., 1996). Under-
thrusting of a piece of Australian continent would have
doubled the lithospheric thickness. Adjustment of the
isograds after underthrusting caused heating and melt-
ing, first of the Australian lithospheric mantle (HK
magmatism), and later of the overlying crust (CAK
magmatism). Melting may also have been promoted by
break-off of the leading oceanic portion of the sub-
ducted slab and subsequent influx of hot astheno-
spheric material (Sacks and Secor, 1990; Polve et al.,
2001). The area of central and NW Sulawesi where we
wesi. Data sources as in Fig. 6. Rectangles on the right hand side of
ement and several metamorphic and sedimentary suites. Central and
signature in HK rocks coming in around 11–14 Ma (or 17 Ma for
account). Both areas also have a Miocene–Pliocene series of CAK
esi, where Nd isotopic values do not decrease in the same manner.
M. Elburg et al. / Chemical Geology 199 (2003) 243–276272
find Miocene high-K magmatism with very low Nd
isotopic ratios, and Miocene–Pliocene felsic CAK
magmatism, roughly coincides with an area of high
topographic relief, with mountain ranges up to 3000-m
high (Fig. 1d). Rapid uplift of the area is also indicated
by the exposure of very young granites (3–6 Ma;
Polve et al., 1997; Bellier et al., 1998; Elburg and
Foden, 1999a; this study) and metamorphism ages
(Van Leeuwen et al., in preparation). This could be a
reflection of the underthrusting event.
There is only limited data from disciplines other
than geochemistry to support this underthrusting
event in the Late Oligocene–Early Miocene. As
Calvert (2000) and Hall and Wilson (2000) have
pointed out, the sedimentary record of the southern
part of NW Sulawesi and central Sulawesi shows
evidence for a tectonic event only around the Mio-
Pliocene boundary. However, some radiometric age
dating, structural and stratigraphic evidence from the
Palu Complex, the north arm, and Luwuk area in
the east arm could point towards Late Oligocene–
Early Miocene collision events in NW Sulawesi.
Kadarusman et al. (in preparation) obtained a Sm-
Nd date of 27 Ma for garnet from a peridotite
sample collected south of Palu, which they interpret
to represent the age of peridotite emplacement in the
Palu Complex as the result of a collision event
between Western Sulawesi and a microcontinent.
In the north arm, Neogene formations overlie with
a regional unconformity the more strongly deformed
Middle Eocene–Earliest Miocene Tinombo Forma-
tion and Papayato Volcanics (Brouwer, 1934; Rat-
man, 1976; Kavalieris et al., 1992); the Malino
Complex yielded metamorphic (uplift) ages ranging
between 23 and 14 Ma; and its contact with the
overlying formations is probably tectonic. In the
Luwuk area, Mesozoic sediments have been folded
and overthrust by an ophiolitic nappe, which is
overlain by less deformed Middle-Miocene molasse
(Villeneuve et al., 2000). Underthrusting of a con-
tinental fragment during the Late Oligocene–Early
Miocene may explain the apparent gap in magma-
tism in Western Sulawesi during this period.
(2) The Australian continental sliver was under-
thrust long before the onset of HK magmatism. In this
case, it could represent the Cretaceous collisional
event documented in some of the high-pressure com-
plexes around Western Sulawesi (Parkinson et al.,
1998; Wakita, 2000). This would agree with the
interpretation of Hall (2002) that Miocene-age mag-
matism in Western Sulawesi was a response to exten-
sion, resulting in melting of the subcontinental
lithospheric mantle. In the case of the low-Nd area
of Western Sulawesi, this lithospheric mantle and
overlying crust would have been tectonically
emplaced underneath the Sundaland plate during the
Cretaceous. If this scenario is correct, the area of high
relief in Western Sulawesi is likely to be a response to
Pliocene thrusting (Hall, 2002) and the fact that it
overlaps with that of the low-Nd isotopic signature
must be purely coincidental. The change from sub-
duction-related magmatism to HK magmatism would
only reflect a change in tectonic regime from con-
vergent to extensional.
Whatever the cause of melting in the Miocene and
the timing of underthrusting of the continental sliver,
the extent of the low-Nd signature in Western Sulawesi
represents the size of the underthrust Australian con-
tinental fragment. Its northeastern limit appears to
coincide with the limit of the Eocene continental arc
of Western Sulawesi.
8. Conclusions
New geochemical and isotopic data for samples
from NW Sulawesi indicate that the area was part of
an arc system between f 51 and f 18 Ma, with
eruption and intrusion of subduction-related magmas
of continental affinity in the western part of the area
and of oceanic affinity in the east. This defines the
boundary between Western and Northern Sulawesi.
High-K magmatism in Western Sulawesi started
around 14 Ma, and its isotopic signature can only
be explained by a source with a long and varied
geochemical history, probably located within the
Australian subcontinental lithospheric mantle. The
end of the high-K event overlapped in time with
the start of felsic CAK magmatism around 9 Ma,
which continued until approximately 2 Ma. This
magmatism reflects melting of continental crust of
Australian affinity, most likely the material overlying
the lithospheric mantle that melted to produce high-K
magmatism. This sequence of magmatic events, from
normal subduction-related volcanism through HK and
CAK magmatism, is also seen in central Sulawesi,
M. Elburg et al. / Chemical Geology 199 (2003) 243–276 273
but not in the south arm or in Northern Sulawesi. It is
best explained by melting of an underthrust piece of
Australian continent. The areal extent of this continen-
tal sliver can be estimated from the area containing the
aforementioned HK and CAK magmatism, located
between 4jS and 1jN. The underthrusting event must
have taken place prior to the first occurrence of high-K
magmatism at 14 Ma, so it is not related to the collision
with the Sula platform around 5 Ma (Hall, 2002). It is
as yet unclear whether the underthrusting event took
place shortly before HK magmatism, or represents a
much earlier event.
Appendix A. Characteristics of the Older Series igneou
Unit Description Ages P
Tinombo Volcanics (D) basalt-rhyolite 34–533 pl
Tinombo Intrusives gabbro, diorite, qz-diorite,
granodiorite
37.5–44.51 pl
Papayato Volcanics diabase, spillite, pillow lava;
basalt, dacite– rhyolite
22–502,3 ba
pl
Toli-Toli Volcanics basalt–dacite Miocene5 pl
Renangkali Granite mu-bt granite, granodiorite 41.94 pl
Tondopado
Microdiorite
andesite–diorite
diorite porphyry
17.73 pl
Bolano Andesite andesite 11.47 pl
Appendix B. Characteristics of the Younger Series igne
Unit Description Ages Ph
Gimpu Volcanics pyroclastics, rhyodacitic lava 2–4 Ma2 pl,
Ongka Volcanics pyroclastics, rhyodacitic lava 6–7 Ma3 pl,
Dondo Supersuite
(DSS)
(qz diorite), monzonite,
monzogranite, syenogranite
1.6–73,6 pl,
(FHK Series lamprophyre–monzodiorite,
basanite– latite
14.1–4.63,7 ol,
ksp
Acknowledgements
ME was a recipient of an ARC APD Fellowship
when the analytical work was carried out, and was
supported by an EU Marie Curie Fellowship during
writing of the manuscript. David Bruce is acknowl-
edged for his help in the isotope lab. Al Hofmann is
thanked for supporting ME’s appointment in Germany
and Tuti Mariani for her secretarial support to TvL.
The manuscript benefited from comments by C.
Macpherson and R. Hall, and official reviews by M.
Polve, R. Maury and T. Housh. [RR]
s units
henocrysts Alteration Deformation
, cpx, opx greenschist facies strong folding
, hbl, qz ser, chl, ep, act, cb moderate– strong
salt: pl, cpx, (ol) felsic:
, hbl, px, bt
chl, ep, ab, cb, qz,
ill/ser, (ksp, qz), ze
strong folding
, cpx, hbl, bt moderate
, qz, ksp, bt, mu weak–moderate ser,
chl, ep, cb
weak–strong
, am (qz, ksp, bt) < 10%, chl, ep, py,
ser, cb, sph
minor
(microfracturing)
, hbl, opx, qz, op none none
Pl = plagioclase, hbl = hornblende, am = amphibole,
qz = quartz, cpx = clinopyroxene, px = pyroxene, opx =
orthopyroxene, bt = biotite, ksp =K-feldspar, op = opa-
ques, sph = sphene, ser = sericite, chl = chlorite, ep =
epidote, ab = albite, act = actinolite, cb = carbonate,
ill = illite, ser = sericite, ze = zeolite, py =pyrite,
crd =cordierite, gt = garnet. (1) Unpublished K/Ar
ages (Rio Tinto); (2) K/Ar age, Priadi et al.
(1993); (3) K/Ar age, Polve et al. (1997); (4)
unpublished 40Ar/39Ar date on muscovite (van
Leeuwen and Vasconcelos, 2001 unpublished data);
(5) paleontological data from penecontemporaneous
Buol Beds; (6) K/Ar age, Van Leeuwen et al.
(1994); (7) this study.
ous units
enocrysts Alteration Deformation
qz, bt, hbl, FK-sp very weak none
qz, bt, hbl, FK-sp very weak none
qz, bt, K-sp, F hbl
crd, gt: xenocryst?)
generally weak foliation only near
Palu-Koro Fault
cpx, bt,F hblFF pl
weak–moderate
lamprophyre: weak–
strong: act, chl, cb
M. Elburg et al. / Chemical Geology 199 (2003) 243–276274
Abbreviations as in Appendix A.
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