an overview and tectonic synthesis of the pre-tertiary very-high-pressure metamorphic and associated...

Thematic Article

An overview and tectonic synthesis of the pre-Tertiary very-high-pressuremetamorphic and associated rocks of Java, Sulawesi and Kalimantan,

Indonesia

C. D. PARKINSONARKINSON,1 K. MIYAZAKIIYAZAKI,2 K. WAKITAAKITA,2 A. J. BARBERARBER3

ANDAND D. A. CARSWELLARSWELL4

1Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro, Tokyo152, Japan, E-mail: <[email protected]>, 2Geological Survey of Japan, 1-1-3 Higashi, Tsukuba, Ibaraki 305,

Japan, 3Geology Department, Royal Holloway, University of London, Egham, Surrey TW20 0EX, UK and4Department of Earth Sciences, University of Sheeld, Sheeld S3 7HF, UK

Abstract High-pressure metamorphic rocks are widely distributed in Cretaceous ac-cretionary complexes throughout Java, Sulawesi (formerly Celebes) and southeastKalimantan (Indonesian Borneo). Many of these rocks occur as imbricate slices of car-bonate, quartzose and pelitic schists of shallow marine or continental margin parentage,interthrust with subordinate basic schists and serpentinite. They are predominantly oflow-to-intermediate metamorphic grade (300 < T < 550 °C; 4 < P < 12 kbar) and yieldmica K±Ar radiometric ages of 110±120 Ma. Metamorphic rocks that exhibit evidence ofexhumation from much greater depths (> 60 km), however, are sporadically exposed,usually as tectonic blocks, throughout the Cretaceous accretionary complexes. Theyinclude eclogite, garnet±glaucophane rock (P � 18±24 kbar, T � 580±620 °C), andjadeite±garnet±quartz (?coesite) rock (?P > 27 kbar, T � 720±760 °C) in Bantimala,southwest Sulawesi; eclogite and garnet granulite in west central Sulawesi; eclogite andjadeite-glaucophane-quartz rock (P � 22 kbar, T � 530 °C) in Luk Ulo, Central Java;and Mg±chloritoid-bearing whiteschists (P � ?18 kbar) in the Meratus Mountains,southeast Kalimantan. Garnet lherzolites from depths of > 60 km are also associatedwith schists in east central Sulawesi (P � 22±28 kbar, T � 1000±1100 °C), west cen-tral Sulawesi (P � 16±20 kbar, T � 1050±1100 °C); and garnet pyroxenite(P � 20 kbar, T � 850 °C) occurs as blocks with pyrope±kyanite amphibolite, eclogiteand blueschist, within Miocene conglomerate in Sabah, northeast Borneo. Many of themetamorphic rocks were probably recrystallized in a north-dipping subduction zone atthe margin of the Sundaland craton in the Early Cretaceous. Exhumation may havebeen facilitated by the collision of a Gondwanan continental fragment with the Sunda-land margin at ca 120±115 Ma.

Key words: blueschist, eclogite, garnet±lherzolite, Indonesia, Java, Kalimantan, Sul-awesi, tectonic synthesis, VHP metamorphism.

INTRODUCTION

Over the past 10 years, collaborative geologicalresearch on the pre-Tertiary accretionary com-plexes distributed along the southeast margin ofSundaland has been conducted independently andjointly by the University of London, the Geologi-

cal Survey of Japan, Indonesian Institute of Sci-ence (LIPI) and the Geological Research andDevelopment Centre (GRDC), Bandung (Indone-sia). This work has included detailed ®eld inves-tigations, structural analysis, lithostratigraphicand biostratigraphic studies as well as geochro-nological, petrological and geochemical analyses.

The widely dispersed rocks of the pre-Tertiarybasement in the Indonesian region comprise

The Island Arc (1998) 7, 184±200

Accepted for publication July 1997.

variably metamorphosed accretionary complex-es, imbricated terranes, meÂ lange, turbidite andbroken formations, and ophiolite. These rockshave suffered considerable dismemberment,tectonic and structural modi®cation, and thermaloverprinting due to tectonic and metamorphicactivity throughout the Tertiary, related to theconvergence of the Indo-Australian, Eurasianand western Paci®c microplates.

MESOZOIC ACCRETIONARY COMPLEXES OFSULAWESI, JAVA AND SOUTHEAST KALIMANTAN

Accretionary and metamorphic complexes con-stitute the pre-Tertiary basement throughoutmuch of central Indonesia. They are sporadicallyexposed in an arc extending from southwest andcentral Java, through the Meratus and Bobarisranges of southeast Kalimantan and the nearbyisland of Laut, northwards into the ManghalihatPeninsula and adjacent areas of northeast Kali-mantan. To the east, across the Makassar Strait,

basement metamorphic rocks crop out in theSouth Arm of Sulawesi, throughout central Sul-awesi and the Southeast Arm and the island ofKabaena (Fig. 1). Most of these complexes arepoorly exposed and incompletely characterized.Previously, the constituent rocks have been (er-roneously) considered to represent typicalsubduction-generated `meÂ lange' complexes gen-erated by simple under¯ow of Tethys oceanic li-thosphere beneath the Sundaland continentalmargin throughout Late Mesozoic times (Su-kamto 1975; Hamilton 1979; Hehuwat 1986).

The accretionary complexes contain a varietyof petrologically and structurally diverse meta-morphic material, ranging from high-grade tec-tonic blocks in meÂlange terranes, throughimbricate thrust packets to extensive, relativelycoherent tracts of crystalline schist. Low-gradeschists from most of these complexes yieldedphengite K±Ar ages in the range 110±130 Ma(Hamilton 1979; Parkinson 1991; Wakita et al.1996; Wakita et al. 1998; Parkinson 1998a;Fig. 2). In addition to the relatively close syn-

Natuna

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K–Ar ages of metamorphics

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KALIMANTAN SULAWESI

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Barru

Fig. 6

Fig. 9

TIMOR

Fig. 1 Distribution of Mesozoic accretionary complexes in the central Indonesian region. All contain blueschist or higher pressure meta-morphic rocks. Open circles are locations of metamorphic material for which K±Ar data (from a wide range of sources, see Fig. 2) is available.Closed circles are locations of offshore boreholes (with K±Ar data for metamorphics) from Hamilton (1979).

VHPM rocks of Java, Sulawesi and Kalimantan 185

chrony in metamorphic ages, gross lithological,structural and petrological similarities suggestthat many of the complexes may belong to asingle, arcuate southwest±northeast-trendingorogenic belt of Cretaceous age, and extending�1500 km. Fragmentary evidence that someparts of such a belt may have been exhumed from

depths in excess of 60 km are provided by rocksfrom a number of widely dispersed locations(Fig. 3).

In the present paper we present an overview ofthe setting and petrology of very high-pressure(P > 18 kbar) metamorphic (VHPM) and associ-ated rocks from some of these complexes based

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Pompangeo schists(Central Sulawesi)

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Latimodjong Complex(Central Sulawesi)

140 90

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Barru Complex(SW Sulawesi)

Fig. 2 Histogram of K±Ar radiometric data forgreenschists, blueschists and eclogites from thecentral Indonesian region, compiled from variouspublished and unpublished sources. 1, Parkinson inHasan (1990); 2, Obradovich in Hamilton (1979); 3,Parkinson (1991); 4, Parkinson (1996); 5, Wakita etal. (1996); 6, Brown & Earle (1983); 7, Wakita et al.(1994); 8, Sikumbang (1986); 9, Hamilton (1979);10, Bergman et al. (1996); 11, Sikumbang andHeryanto (1994); 12, Wakita et al. (1997).

Fig. 3 Locations (denoted by stars) of recognized and suspected very-high-pressure metamorphic (VHPM) rocks and garnetiferous ultrama®csin the central Indonesian region. Lettered stars refer to locations of rocks for which P±T data are presented in Figs 5 and 10.

186 C. D. Parkinson et al.

on our own studies and a review of the rathersparse literature on other complexes, and offer apreliminary interpretation of their tectonic set-ting(s) of metamorphism, uplift and dispersal.

Field and petrological studies of these rocks arehampered by extreme ®eld conditions associatedwith problems of vegetation, access, physio-graphy and climate in the Indonesian region. Inmany forested areas, exposure is poor to non-ex-istent, and often, where rocks do crop out or aremade accessible by road-cuts and excavations,severe tropical weathering quickly obliteratesprimary minerals to depths of several metres.River and stream ¯oat generally offers good, freshmaterial for petrologic analysis, but, consequently,meaningful interpretation is limited because ofuncertainty over exact provenance.

Very high-pressure metamorphic rocks appearto represent a very small volumetric proportion(probably < 1%) of the total exposed metamor-phic rocks in central Indonesian accretionary

complexes. Most VHPM rocks occur as small(< 5 m) tectonic blocks, associated with exten-sive tracts or imbricate slices of lower grade(epidote amphibolite grade or lower) schist.

THE POMPANGEO SCHIST COMPLEXAND OTHER METAMORPHIC COMPLEXESOF CENTRAL SULAWESI

The Pompangeo Schist Complex crops out over� 5000 km2 in central Sulawesi, and is predomi-nantly composed of interbanded phyllitic marble,calcareous phyllite, graphitic schist, quartziteand metaconglomerate; rocks predominantly ofshallow marine, continental margin origin(Fig. 4). K±Ar dating of phengite from threeschist samples yielded ages of ca 111 Ma (Par-kinson 1991; Parkinson 1998a). The complex isoverthrust in the east by a metamorphosedophiolitic meÂlange of Oligocene age (Parkinson

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3Fig. 4 Highly simpli®ed lithotectonic units ofSulawesi. (1) is the location of garnet lherzo-lite, eclogite and garnet granulite in the Palu±Koro fault valley; (2) that of garnet lherzoliteand garnet granulite in the Bongka River regionof eastern central Sulawesi; and (3) very-high-pressure metamorphic (VHPM) tectonic blocksin the Bantimala region of the South Arm ofSulawesi.


1996; 1998b). Along the eastern exposed ex-tremity of the Pompangeo Schist Complex, low-grade schists are in fault contact with unmeta-morphosed Jurassic sandstones (Sukamto &Westermann 1992; Parkinson 1998a). Locally(e.g. southeast of Lake Poso), the schists areunconformably overlain by pelagic sedimentswith an Albian±Cenomanian biostratigraphy.Synmetamorphic progressive deformation of thePompangeo Schist Complex has resulted in re-peated isoclinal folding and a strong transposi-tion foliation striking north-northwest±south-southeast and dipping west, subparallel to thecompositional banding of the complex. On a re-gional scale the Pompangeo Schist Complex islithostratigraphically coherent, and an east±westmetamorphic ®eld gradient is apparent from theappearance (and disappearance) of stilpnome-lane, ferrocarpholite, crossite, lawsonite, ferro-chloritoid, almandine, oligoclase and biotite(Willems 1937; de Roever 1947; Parkinson 1991,1998a). Peak P±T conditions range from �200±300 °C at 4±6 kbar for Ab + Qtz + Cal + Chl+ Ms + Stp + Gr schists in the east (in thePompangeo Mtns) to � 450 °C at 10±12 kbar forGln + Grt + Lws + Czo metabasic intercalationsin the west (in the Tokorondo Mountains). Thelatter rocks appear to be petrologically andstructurally identical to graphitic schists withmetabasic intercalations which crop out in theRumbia and Mendoke Mountains of the south-west extremity of the Southeast Arm (de Roever1950; Helmers et al. 1989), which may, therefore,represent the southern continuation of this partof the belt (Parkinson 1991, 1998a).

In western central Sulawesi, 40 km west ofLake Poso, Pompangeo schists overthrustgranodiorite of the western Sulawesi magmaticprovince. This north±south-trending structuraldiscontinuity, the `median line', has been inter-preted by a number of workers as a clear demar-cation, analogous to the Median Tectonic Line ofJapan, separating the magmatic arc of westernSulawesi from the blueschists of eastern centralSulawesi and the Southeast Arm (van Bemmelen1949; Miyashiro 1973; Audley-Charles 1974; Su-kamto 1975; Hamilton 1979). However, there is noclear evidence that the median line is a profoundtectonic suture, and high-pressure (HP) schistscorrelative with the Pompangeo Schist Complexcrop out west of the median line, within the mag-matic province of western Sulawesi, where theyconstitute part of the Latimodjong Complex(Simandjuntak et al. 1991a; 1991b). In the Lati-

modjong Mountains these rocks include glaucop-hane±lawsonite schist, crossite±epidote meta-basite and, possibly, eclogite (Gisolf 1917;Parkinson & Barber unpubl. data, 1993). Schistsfrom the Latimodjong Mountains yielded musco-vite K±Ar ages of 114, 123 and 128 Ma (Bergmanet al. 1996), similar to those for the Pompangeoschists of central Sulawesi.

GARNET PERIDOTITE AND ASSOCIATED ROCKSIN CENTRAL SULAWESI

Loose blocks of garnet peridotite and garnet±clinopyroxene granulite are associated withrocks of the East Sulawesi Ophiolite andPompangeo Schist Complex in the Bongka riverof northeast central Sulawesi (see Fig. 5 forapproximate locality). Garnet in the garnetperidotite has a composition typical of that ofsubcontinental lithospheric mantle (Xpyr �0.68±0.70, Xalm � 0.17±0.18, Xgros � 0.12±0.13, Xsps � 0.00±0.01), and rather low Cr2O3

contents of � 1.2±1.5 wt%. Garnet grains aresurrounded by ®ne-grained kelyphite reactioncoronas of orthopyroxene + green spinel, whichare partially overgrown by wider coronas ofclinoamphibole and chlorite. Orthopyroxene andCpx display coarse exsolution textures sugges-tive of a long, slow cooling history. Geothermo-barometric data indicate that initial `peak' P±Tconditions were � 22 kbar (sample EA01) and28 kbar (sample EA04A) at 1030±1100 °C, andthat re-equilibration and uplift may have occurredalong a relatively cool geotherm to calculated P±Tconditions of 10 kbar at 580 °C (EA01) and15 kbar at 765 °C (EA04A) for the outer, mostretrogressed coronas (Fig. 5). However, theseuplift paths, which are deduced from mineralthermobarometry, may be spurious as a conse-quence of the unfavourable kinetics of the nettransfer reaction controlling the Al content of Opx(principal monitor of pressure) compared to thosefor the Fe2+±Mg2+exchange reactions whichclosely monitor the cooling history. Hence, theactual uplift paths may, in fact, have involvedsigni®cant, unmonitored near-isothermal decom-pression prior to cooling.

Similar garnet peridotites and high-grademetamorphic rocks of uncertain age also crop outas basement into which Neogene granodioritehas intruded, 200 km to the west, in northwestcentral Sulawesi. These rocks occur in scarps andas loose blocks along both ¯anks of the activePalu±Koro fault valley, 20±30 km southeast of


Palu, and occasionally as xenoliths within theadjacent Palu granite. Major element geochemi-cal characteristics of the Palu garnet peridotitesuggest that it may be of oceanic af®liation, andgeothermobarometric data (peak P±T conditions:1050±1100 °C and 16±20 kbar) indicate relativelyrapid re-equilibration from depths of 60 km(Helmers et al. 1990). Calculated peak P±T con-ditions for the associated Cpx±Grt granulite are700±750 °C and 12±17 kbar (Helmers et al. 1990;A. Kadarusman pers. comm., 1996).

BANTIMALA COMPLEX OF SOUTHWEST SULAWESI

The 10 km-wide Bantimala Complex is located� 40 km northeast of Ujung Pandang in the South

Arm of Sulawesi (Fig. 4). It is the best describedof the pre-Tertiary accretionary complexes ofSulawesi, and consists of an assemblage ofnortheast-dipping imbricate slices comprising HPschist, schist breccia (unconformably overlain byLate Cretaceous radiolarian chert), shallow ma-rine clastic rocks of Jurassic age (ParembaSandstone) and peridotite, separated by thinzones of black shale-matrix tectonic meÂlange(Wakita et al. 1996; Miyazaki et al. 1996; Fig. 6).Many of the non-metamorphic sequences havepreviously been described by Wakita et al. (1994a;1996). The imbricated metamorphic rocks consistof three main types of glaucophane schist: very®ne-grained lawsonite-bearing glaucophaneschist, hematite-bearing glaucophane schist andgarnet±glaucophane schist, interlayered with

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S U L A W E S I

Fig. 5 Comparative P±T data for garnetiferous ultrama®c rocks from two locations in Sulawesi (a, b) and from the Dent Peninsula of Sabah (c).Locations of rocks are depicted in Fig. 3. Calculated P±T paths for two garnet lherzolite samples (EA01 and EA04) from the Bongka region ofeastern central Sulawesi from D. A. Carswell (unpubl. data, 1996). Palu±Koro garnet peridotite data from Helmers et al. (1990). Sabah garnetpyroxenite data from Morgan (1974).


garnet±glaucophane±ferrochloritoid schist, al-bite-actinolite-chlorite schist and chlorite-micaschist. These rocks are petrologically similar tothe Pompangeo schists and yielded contempora-neous phengite K-Ar ages in the range 111±114 Ma (Hamilton 1979; Hasan 1990; Wakita et al.1996; C. Parkinson unpubl. data, 1996). They arealso locally overlain by cherts with a Late Albian±Early Turonian biostratigraphy (Wakita et al.1994a).

VERY HIGH PRESSURE TECTONIC BLOCKSIN THE BANTIMALA COMPLEX

Along the courses of the Pangkajene, Bontorio,Koraja, Paremba and Pattetejang Rivers, withinthe schist portions of the complex, a variety of1±3 m-wide high-grade tectonic blocks occur,associated with sheared serpentinite. The mostcommon lithologies are eclogite (Omp + Grt +Ep + phengite + Rt � Qtz � Hbl � Gln) and gar-net±glaucophane rock. The petrology of theserocks has been described by Miyazaki et al.(1996). The eclogite comprises < 1 cm garnet

porphyroblasts in a matrix essentially composedof ®ne-grained omphacite with minor epidote,phengite, quartz, rutile and glaucophane. Retro-gression is highly variable, but domains in somerocks are composed of Lws + Chl, with lawsonitecontaining inclusions of all the primary phases.Omphacite is typically rimmed by chloromelanite(Xjd � 0.21±0.28), glaucophane by crossite, andrutile by titanite. Thus, the retrograde assem-blage is chloromelanite + crossite + Lws + Chl+ Ttn. Miyazaki et al. (1996) estimated maximumand minimum peak P±T conditions of 24±27 kbarat 580±650 °C (samples Mg-47a, Mg-51; Gln +Czo + Qtz � Omp + Lws reaction equilibriumand Grt-Cpx geothermometry) and 16±17 kbar at580±620 °C (samples Mg-49A, Mg2-18a; Ep +Ttn � Grt + Rt + Qtz reaction equilibrium andGrt±Cpx geothermometry), respectively. Theretrograde P±T trajectory for the eclogite liesat �15 kbar and 450 °C (sample P-04; calculatedstability of lawsonite + chloromelanite, presenceof rutile rimmed by titanite as inclusions withinlawsonite) and 5 kbar at 350 °C (sample Mg-51;Act + Qtz + Hem + Ab + Chl stability) for thegarnet±glaucophane rock. These retrogradeP±T conditions suggest that the high-gradetectonic blocks were refrigerated during exhu-mation. Furthermore, the retrograde P±T con-ditions are comparable with the peak P±Tconditions of the regional, low-grade blueschistsin Bantimala, as well as the Latimodjong andPompangeo schists, and may, therefore, haveshared a common P±T history during exhuma-tion.

The K±Ar ages of phengite for these rocks aregenerally older than for the low-grade schistcountry rocks; they are as follows: 132 � 7 Ma,113 � 6 Ma and 124 � 6 Ma (garnet±glaucophanerock; Wakita et al. 1996) and 137 � 3 Ma (eclo-gite; C. Parkinson unpubl. data, 1996).

Other, much less abundant and smaller (gen-erally < 1 m) tectonic blocks include a glauco-phane±fuchsite rock with abundant primarychromite, in which the fuchsite constitutes� 10 vol%, and contains 3±4 mol% Cr2O3 (Pang-kajene River), coarse-grained garnet amphiboliteand a barroisite±epidote±garnet±quartz rock(Pattetetjang and Koraja Rivers), and a jadeite±garnet±quartz rock (Koraja River).

The Jd±Grt±Qtz rock, found only as two small(0.5 m) boulders in the Koraja River is medium-grained (with jadeite and garnet grains generallynot exceeding 1 mm) and has a granoblastictexture. The prograde assemblage comprises:

Bantimala

Paleogenediorite stocks

Propylitizedvolcanics

Mangilu

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Ultrabasic rocks

Mélange, clastic rocks, chert

Lawsonite-bearing glaucophaneand chlorite–mica schists

Hematite-bearing glaucophane schists,albite–actinolite schists and chlorite schists

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S U L A W E S I

Tectonic blocks(associated with serpentinite)

Eclogite

Garnet–glaucophane rockJadeite–garnet–quartz rock

Barroisite–garnet–epidote–quartz rock

Glaucophane–fuchsite rock

Fig. 6 Simpli®ed geologic map of the Bantimala Complex ofsouthwest Sulawesi (after Miyazaki et al. 1996), showing the loca-tions of very-high-pressure metamorphic (VHPM) tectonic blocks.


Jd + Qtz + Grt + Rt. Jadeite (Xjd � 0.71±0.82,Xac � 0.02±0.10 and Xdi � 0.10±0.19; Fig. 7)accounts for 35±45 vol% of the rock, quartz 35±45 vol% and garnet (Xpyr � 0.32±0.39, Xalm �0.48±0.53, Xgros � 0.10±0.13, Xsps � 0.01±0.02;Fig. 8) � 10±20%. Petrographic evidence sug-gests that this is an equilibrium assemblage.Retrogression is variable, but is restricted tothin, ®ne-grained symplectites at grain bound-aries. These comprise jadeite-poor clinopyroxene(Xjd � 0.15±0.24; Fig. 7) and sodic plagioclase(Xan � 0.05±0.10) symplectites at jadeite-quartz and, occasionally, jadeite±jadeite grainboundaries.

Many jadeite grains contain bleb-like, fre-quently elongated polycrystalline quartz inclu-sions, which are 20±100 lm in size. All displayconspicuous concentric and radial crack texturescomparable to those described by, among others,Smyth (1977) for mantle-derived kyanite eclogitefrom South Africa, Smith (1984) for Norwegianeclogite, Wang et al. (1989) for eclogite fromDabie Mountains, Central China, Yang & Smith(1989) for eclogite from Su-Lu, east China, andSchmaÈdicke (1991) for eclogite from Erzgebirge,Germany. In all of these cases the tensionalcracking is thought to result from the volumeincrease associated with the coesite to quartztransformation and the subsequent contrast incompressibility and thermal expansion of thequartz inclusion and the host grain (van derMolen & van Roermund 1986). The crackingpatterns alone, although suggestive of the formerpresence of coesite, are not diagnostic, and it hasbeen demonstrated that radial tensional crackscan originate from the dilation of a-quartz with-out a phase transformation (Wendt et al. 1993).Therefore, in the absence of actual relics, otherevidence of coesite pre-existence can only beprovided by the preservation of characteristicquartz inclusion textures which are geneticallylinked to the breakdown of coesite (Chopin &Sobolev 1995). In common with the quartz in-clusions in the Erzgebirge and Dabie eclogites,most jadeite-hosted quartz inclusions in theBantimala rock display poorly recrystallized, of-ten feathery polycrystalline mosaic cores andcoarser rims with a palisade appearance, char-acteristic of the coesite±quartz transformation.

The Grt±Cpx gethermometer of Powell (1985)yielded temperatures of 710±760 °C (sampleBN15a). For these temperatures the jadeitegeobarometer of Holland (1980; 1983) yields aminimum pressure of � 20 kbar. Assuming thepre-existence of coesite, the coesite stability ®eld(Bohlen & Boettcher 1982), indicates that peakmetamorphic pressures must have been 27 kbaror higher during the prograde stage. This iscomparable to the maximum peak P±T conditions(27 kbar at 650 °C) of the Bantimala eclogitecalculated by Miyazaki et al. (1996). However, wehave not, so far, detected coesite or its pseudo-morph in the Bantimala eclogite. The recrystal-lization of the Jd±Grt±Qtz rock must haveoccurred on a low geothermal gradient of � 7±7.5 °C/km or lower, which is also similar to thatestimated for the Bantimala eclogite (Miyazakiet al. 1996).

Fig. 7 Representative compositions of sodic pyroxene in very-high-pressure metamorphic (VHPM) tectonic blocks from the Ban-timala Complex, Sulawesi, and the Luk Ulo Complex, central Java,compiled from Miyazaki et al. (1996), Miyazaki et al. (1998) andParkinson (unpubl. data, 1996). (s), jadeite±garnet±quartz rock(Bantimala, Sulawesi); (h), eclogite (Bantimala, Sulawesi); ( ),garnet±glaucophane rock (Bantimala, Sulawesi); (e) jadeite±glau-cophane-quartz rock (Luk Ulo, Java). Retrograde cpx: (sá ), jadeite±garnet-quartz rock; (há ), eclogite.

Fig. 8 Representative compositions of garnet in very-high-pres-sure metamorphic (VHPM) tectonic blocks from the BantimalaComplex, Sulawesi, and the Luk Ulo Complex, central Java, com-piled from Miyazaki et al. (1996), Miyazaki et al. (1998) and Par-kinson (unpubl. data, 1996). (s), jadeite±garnet±quartz (?coesite)rock (Bantimala, Sulawesi); (h), eclogite (Bantimala, Sulawesi);( ), garnet±glacophane rock (Bantimala, Sulawesi); (e), jadeite±glaucophane±quartz rock (Luk Ulo, Java).


BARRU COMPLEX OF SW SULAWESI

The Barru Complex is situated � 30 km north ofthe Bantimala area (Fig. 1). Lithologies are simi-lar to those in the Bantimala Complex, and includeserpentinized peridotite, clastic sedimentaryrocks and variably garnetiferous quartz-micaschists. A phengite K±Ar age of 106 Ma was re-ported for a quartz±mica schist (Wakita et al.1994a). The complex is not well characterized andcrops out over a much more restricted area thanthe Bantimala Complex. Syafri et al. (1995) re-ported lawsonite eclogite (Grt + Omp + Gln+ Ep + phengite + Rt + Lws + Qtz) with tworetrograde blueschist overprints. They estimatedthe peak P±T conditions of the eclogite stage to be� 21 kbar and 520 °C, and the successive blue-schist retrograde stages to be � 13 kbar and500 °C, and 8 kbar and 360 °C.

LUK ULO COMPLEX, CENTRAL JAVA

Pre-Tertiary rocks of the Luk Ulo AccretionaryComplex crop out over a small area (15 ´ 5 km)in the Karangsambung area of Central Java(Fig. 3). Like the Bantimala Complex, they con-sist of east-northeast±west-southwest-trendingtectonic slabs and black shale-matrix tectonicmeÂlange (Asikin 1974). The slabs consist of dis-membered ophiolite of uncertain age (Suparka1988), pillow basalt unconformably overlain bycoherent packages of Cretaceous sedimentaryrocks (alternating beds of chert and limestoneoverlain by a sequence of chert, shale and grey-wacke; Ketner et al. 1976; Wakita et al. 1994b),and metasedimentary and metama®c schists.

The ®ne-grained sedimentary schists containQtz + Ms + Ab + Chl + Ttn + Gr � Grt � Ep, invarying proportions; some coarse-grained schistsalso contain hornblende and/or biotite. Metabasicintercalations, generally no more that 0.5 mwide, are recrystallized to epidote amphibolitegrade and typically contain Hbl + Ep + Grt+ Ab + Bt + Ms. The K±Ar dating of muscovitefrom quartz±mica schists yielded ages of 117 Ma(Ketner et al. 1976), 115 Ma and 110 Ma (Mi-yazaki et al. 1998).

Small (generally 0.5±2.0 m across), coarse-grained tectonic blocks associated with shearedserpentinite, which crops out in thin zones be-tween the low-grade schists and sedimentaryrocks, occur in and along the valley slopes of theMuntjar River, 8 km northeast of Karansambung

campus. Lithologies include garnet amphibolite(Hbl + Grt + Pl + Zo + Qtz), eclogite (Grt +Omp + barroisite + Ep + Pg + Rt), lawsoniteeclogite (Grt + Omp + Gln + phengite + Rt +Lws), glaucophane rock (Gln + Omp + Ep +phengite + Grt) in which some glaucophaneprisms attain remarkable lengths of 3±4 cm, anda jadeite-glaucophane-quartz rock (Jd + Qtz +Gln + Grt + phengite + Rt).

The latter rock is composed of three distinctdomains: (i) 2±5 mm dusty jadeite patches, withjadeite (Xjd � 0.89±0.95; Fig. 7) rims replacedby albite, and containing inclusions of quartz (upto 20%), glaucophane (XFFe2+ � 0.44±0.49,YFFe3+ � 0.68±0.87) and minor garnet; (ii) ®ne-grained, glaucophane-rich domains with � 1 mmalbite spots; and (iii) equigranular quartz-richdomains with minor glaucophane, phengite, ru-tile, albite and titanite. Small euhedral garnets(Xalm � 0.48 [cores] ) 0.73 [rims]) are dis-persed between domains. Modal% of mineralsare: jadeite, 16%; quartz, 19%; glaucophane, 43%;garnet, 3%; phengite, 2%; and others (rutile,titanite, opaques) < 2% (Miyazaki et al. 1998).

The peak P±T conditions of the Jd±Gln±Qtzrock, calculated using Pg + Gln � Jd + Grt+ Qtz + H2O and Cld + Gln � Grt + Jd + Qtz+ H2O reaction equilibria and garnet±phengitegeothermometry (Krogh & Raheim 1978) are 20±24 kbar and 490±570 °C (Miyazaki et al. 1998).These calculated P±T conditions indicate peakmetamorphism on a remarkably low geothermalgradient of � 7 °C/km at a burial depth of� 80 km.

The K±Ar dating of Luk Ulo tectonic blocksyielded two ages of 124 � 2 Ma (samplesJAV103, whole rock and JAV104, phengite) forthe Jd±Gln±Qtz rock and 119 � 2 Ma (sampleJAV105D, whole rock) for the eclogite (C. Par-kinson unpubl. data, 1996). These ages arebroadly contemporaneous with those for theBantimala eclogite.

OTHER ACCRETIONARY COMPLEXES IN JAVA

Highly sheared and disrupted ophiolitic andother rocks similar to those in Luk Ulo also cropout in a small area of the Jiwo Hills, about 10 kmeast of Yogyakarta in central Java. They includeamphibolite, greenschist, phyllite, quartzite,limestone, radiolarian chert, gabbro andserpentinized peridotite (Hamilton 1979). Theserocks are poorly exposed and incompletely


characterized. Neither blueschist nor eclogitehave been reported.

The pre-Tertiary Ciletuh Complex (Fig. 3),which crops out along the coast of the southwestextremity of Java, is a northeast±southwest-trending assemblage of rocks comprising inter-thrust slices of serpentinized ultrama®cs withpartially amphibolitized gabbro dykes, pillowbasalt, volcanic breccia, hyaloclastite and grey-wacke. Metamorphic rocks occur as rare, looseblocks in streams cutting through serpentinite inthe Citisuk area. They include glaucophane-bearing quartzite, epidote amphibolite andcrossite±epidote metama®c rock (C. Parkinsonunpubl. data, 1992). Eclogite has not been re-ported from this complex.

MERATUS COMPLEX, SOUTHEAST KALIMANTAN

A northeast±southwest-trending pre-Tertiaryassemblage of chaotically intercalated rocks cropout over large areas of the Meratus and BobarisMountains of southeast Kalimantan and neigh-bouring Laut Island (Fig. 3). Various aspects ofthe geology of this region have been described bySupriatna et al. (1983), Sikumbang (1986), Sup-riatna (1989), Heryanto and Sanyoto (1994),Heryanto et al. (1994) and Wakita et al. (1998).Dominant lithologies include serpentinizedperidotite and pyroxenite with gabbro andplagiogranite intrusions (Bobaris and Meratusophiolites), shale-matrix meÂlange with clasts oflimestone, chert and basalt (Laut Island only),pelagic sediments with a Middle Jurassic±lateEarly Cretaceous radiolarian biostratigraphy(Wakita et al. 1998), clastic and carbonate sedi-ments, and a variety of low-grade schists(Pelaihari and Hauren schists). The assemblageis unconformably overlain by Late Cretaceousturbidites and volcaniclastics (Manunggul andAlino Groups, respectively).

The faulted southeast margin of the Bobarisophiolite is locally overlain by Late Cretaceousturbidites (Manunggul Fm) and sedimentaryconglomerates containing serpentinite, pyroxe-nite, gabbro and greenstone (Fig. 9). These tur-bidites and conglomerates, which include the`Pamali breccia', are diamondiferous. The pri-mary source of the southeast Kalimantan dia-monds has been debated for many decades, and isstill unclear (Bergman et al. 1987). However,since clasts in the conglomerate are almost ex-clusively ophiolitic (Burgath & Mohr 1991), and

there are no known occurrences of kimberlite orlamproite in southeast Kalimantan, a Bobarisophiolite provenance appears likely (Bergmanet al. 1987). Small amounts of garnet pyroxenite(a possible source of diamonds in orogenic zones)have been described from the Bobaris ophiolite(Burgath & Mohr 1991), but not in signi®cantamounts, and usually as stream ¯oat. However,the presence of larger amounts of in situ garnetpyroxenite within the Bobaris and Meratusophiolites cannot be discounted since large areasof these bodies have not been studied in detail.

Sikumbang (1986) subdivided the metamorphicrocks of the Meratus region into the widelydistributed greenschist-to-epidote amphibolite-grade Hauren Schists (including quartz±musco-vite schist, micaceous metaquartzite, barroisite±epidote schist and metagabbro) and the lower-grade, gold-bearing Pelaihari Phyllites, whichare poorly exposed and restricted to the Pelaih-ari area. The K±Ar dating of various Haurenschists yielded ages in the range 108±119 Ma(Sikumbang 1986; Sikumbang & Heryanto 1994;Wakita et al. 1997).

Along the northwest margin of the HaurenSchist terrane in the Martapeura region, nearthe fault contact with the Bobaris ophiolite,

Martapoera

Tjempaka

Mt Melati

Mt Batuditabang

ManunggulBobaris ophiolite

Meratus ophiolite

10 km

Upper CretaceousManunggul Fm (turbidites)

Ophiolite (Cretaceous)

Upper CretaceousAlino Fm (volcaniclastics)

Early Cretaceous Hauren Schists

Quaternary alluviumTertiary sediments

Eocene diorite porphyry

Jurassic Paniungan Beds

Diamond-bearing conglomerate localities

Mg-chloritoid bearing whiteschists

Meratus Accretionary Complex

Fig. 9 Simpli®ed geologic sketch map of the Meratus region ofsoutheast Kalimantan (for location refer to Fig. 1) after Sikumbang(1986), Bergman et al. (1987), Supriatna (1989), Heryanto andSanyoto (1994), Heryanto et al. (1994) and Wakita et al. (1997).


glaucophane, kyanite and/or chloritoid-bearingquartz schists crop out. They may constitute adiscrete tectonic block separate from the HaurenSchist suite; the paucity of exposure makes ®eldrelations unclear. The sialic nature of these rockssuggests that, unlike the other Hauren schists,they are of continental parentage.

The most common assemblages are Gln+ Qtz � Ep, Ky + Qtz + phengite + Rt, Ky + Pg+ phengite + Hem � Mg-Chl, Ky + Qtz + Mg-

Cld + Tlc(?), and Cld + phengite + Qtz. Kyaniterims are partially retrogressed to pyrophyllite.Mineral compositions for most rocks have yet tobe fully characterized, but preliminary analysesindicate that in the Cld + Qtz + phengite schistthe chloritoid contains 44±49 mol% Mg end-member. In some rocks, colorless Mg-chloritoidcontains � 200 lm inclusions of corrodedKy + Mg-Chl, which may be indicative of themetastable prograde reaction Chl + Ky + H2O� Cld + Qtz (Chopin & Schreyer 1983). Al-though peak P±T conditions have yet to be esti-mated, the presence of Mg-rich chloritoidsuggests these rocks may have been recrystal-lized at pressures of � 18 kbar or higher(Fig. 10).

OTHER HIGH-PRESSURE METAMORPHIC ROCKSIN THE CENTRAL INDONESIAN REGION

The HP metamorphic and related rocks havebeen reported from one other locality in thecentral Indonesian region: as blocks and boulderswithin Miocene `boulder beds' in the Dent Pen-insula of eastern Sabah (Fig. 3). Lithologies ofthe exotic blocks include Gln±Tlc schist, eclogite,Grt±Ky schist, corundum±pyrope amphiboliteand garnet pyroxenite (Haile & Wong 1965;Morgan 1974; Hamilton 1979). The latter rockconsists of Ca±tschermakite-rich augite andcoarse garnet with a rather wide compositionalrange (Xpyr � 0.28±0.56, Xalm � 0.19±0.41,Xgros � 0.18±0.30, Xsps � 0.01). Garnet haskelyphitic mantles of ®ne-grained amphibole, butMorgan (1974) reports there is no petrographicevidence of breakdown or exsolution of the pri-mary clinopyroxene. Estimated P±T conditionsare 850 °C � 150 °C and 19 kbar � 4 kbar (Mor-gan 1974). The provenance and age(s) of the Sa-bah metamorphic rocks are not known.

COMPARISON AND CORRELATION OFMETAMORPHIC ROCKS IN CENTRAL INDONESIANACCRETIONARY COMPLEXES

A combination of uncertainty concerning theexact provenance, nature of occurrence as smalltectonic blocks, and insuf®ciently reliable radio-metric age data for many of the VHPM rocks incentral Indonesia hampers reconstruction oftheir tectonic histories. However, certain con-straints may be provided by the low-grade

200 300 400 500 600 700 800 900

Temperature (˚C)

HGR

GR

AM

EA

GSPP

PA

BS

5

10

15

20

25

30

35

40

Diamon

d

Gra

phite

Coesite

Quartz

Lw EC

Dry EC

Jd + Qtz

LAb

PrA

Pre

ssur

e (k

bar)

ZEO

max.

4 4

6

2

1

5

3

Am EC

EpEC

min.

retrograde overprint ofeclogite (B);

amphibole stability inhematite-bearing basic schist

?

?

4 4

retrograde overprint of Jd-Grt-Qtz rock(C); barroisite stability, Jd in Cpx

Prograde metamorphismof regional schists

?

C

A

B

Jd + Q

tz

HAb

Br

Cr

uplift path of S

ulawesi garnet lh

erzolite

s

min.

?

?

7

D

E

Er

max.

Fig. 10 Compilation of available P±T data for very-high-pressuremetamorphic (VHPM) rocks from Sulawesi, Java and Kalimantan. A,jadeite±glaucophane±quartz rock from Luk Ulo, Java (Miyazaki et al.1998); B/Br, peak/retrograde P±T conditions of eclogite from Ban-timala, Sulawesi (Miyazaki et al. 1996); C/Cr, peak/retrograde P±Tconditions of jadeite±quartz±garnet rock from Bantimala, Sulawesi(Parkinson, unpubl. data); D, tentative peak P±T conditions of Mg-chloritoid-bearing whiteschist from the Meratus region of southeastKalimantan (Miyazaki & Parkinson, unpubl. data); E/Er, peak/retro-grade P±T conditions of lawsonite eclogite from Barru, Sulawesi(Syafri et al. 1995). Locations are depicted in Fig. 3. Generalizeduplift paths for VHPM rocks and Sulawesi garnet lherzolites areinferred. Petrogenetic grid from Maruyama et al. (1996), P/T sta-bilities of diamond-graphite (Bundy 1980), coesite±quartz (Bohlen& Boettcher 1982), jadeite + quartz � high albite (Holland 1980),jadeite + quartz � low albite (Newton & Smith 1967) are shown.For sources of reaction equilibria refer to text. 1, paragonite +Gln � Jd + Grt + Qtz + water; 2, Cld + Gln � Jd + Grt + Qtz +water; 3, Grt±phengite geothermometry (Krogh & Raheim 1978); 4,Grt±Cpx geothermometry (Powell 1985); 5, Omp + Lws �Gln + Czo + Qtz + water; 6, Czo + Ttn � Gros + Rt + Qtz + wa-ter; 7, Ky + Chl + water � Mg-Cld + Qtz.


metamorphic and other rocks with which theyare associated.

Relatively close synchrony (generally no morethan � 5 Ma deviation from 115 Ma) in theavailable phengite K±Ar ages of low-gradeschists in the Pompangeo, Latimodjong, Ban-timala, Meratus and Luk Ulo Complexes indi-cates that these rocks were all recrystallized atthe same time, in the Aptian/Barremian. Fur-thermore, their present disposition, in an arcuatezone at the southeast margin of the Sundalandcraton suggests that they were metamorphosedin the same north/northwest-dipping subductionsystem, related to under¯ow of Meso-Tethysoceanic lithosphere beneath the Sundaland mar-gin. The present-day locus of this palaeo-sub-duction zone has been interpreted to trend in anortheast±north direction and extend from westJava, through the Java Sea to the western ¯ankof the Meratus Mountains. This line representsthe southeast limit of Cretaceous continentalbasement (in west Kalimantan, west Java andSumatra) and the northwest limit of Cretaceous`meÂlange' (Hamilton 1979).

Gross geological patterns in the present-daydistribution of the Mesozoic accretionary com-plexes and included metamorphic rocks can yieldinsights into the generation and uplift of the re-crystallized terranes. There is a clear east towest progression, through Sulawesi into south-east Kalimantan, in the predominating protoli-thologies (continental ® oceanic ® oceanic/continental), metamorphic grade (low grade ®medium grade plus VHP tectonic blocks) andstructural styles (relatively coherent tracts ®imbricated terrane ® meÂlange terrane ® im-bricated terrane). Salient features of this pro-gression are summarized below in the followingsection.

In central Sulawesi and the Southeast Arm,greenschist and low-grade blueschist arepredominantly of continental supracrustal par-entage (including orthogneiss, marble, metacon-glomerate, quartzite and metapelite), and areinterthrust with unmetamorphosed clastic rockswith a Jurassic biostratigraphy (Sukamto &Westermann 1992). The schists are relativelycoherent and increase in metamorphic gradefrom east to west in central Sulawesi. Rocks ofthe poorly known Latimodjong Complex appearto be petrologically similar but also include mi-nor ophiolitic fragments (serpentinite, meta-gabbro and metabasite). Further west, in theSouth Arm, interthrust constituents of the

Bantimala Complex are predominantly ophiolitic(although slices of Jurassic continental marginsediments do occur); regional schists are of epi-dote amphibolite grade, and structurally dis-rupted zones contain VHP inclusions. To thewest, across the Makassar Straits, ophioliticmeÂlange containing chert with radiolarian as-semblages ranging from the early Middle Jur-assic to early Late Cretaceous (Wakita et al.1998) crops out on Laut Island. The MeratusComplex is dominated by the Meratus andBobaris ophiolite massifs, which are interthrustwith epidote amphibolite and amphibolite facies-grade schists; associated VHP whiteschists havea continental anity.

The mode of occurrence and petrology ofregional schists and VHPM rocks in the LukUlo Complex of central Java are similar tothose in the Bantimala Complex. There are,however, differences in gross geological char-acteristics of the two complexes. Within theLuk Ulo Complex no metamorphosed or un-metamorphosed rocks of clear continental par-entage have been recognized, and the complexcontains discrete structural packages composedof off-scraped successions of oceanic crust andsedimentary cover (basalt ® alternating ra-diolarian chert and limestone ® radiolarianchert ® alternating shale and sandstone), withbiostratigraphic ages ranging from earliestEarly Cretaceous to latest Late Cretaceous(Wakita et al. 1994b).

Low-grade schists in central and south Sula-wesi are unconformably overlain by chert with aCenomanian radiolarian biostratigraphy, delim-iting the timing of their exhumation. Mesozoicaccretionary complexes in west Sulawesi, south-east Kalimantan and central Java are all uncon-formably overlain by Late Cretaceous to Eoceneturbidite sequences. These include the Karang-sambung Fm of central Java (overlying the LukUlo Complex), the Tinombo, Marada and Lati-modjong Fms of west central Sulawesi, theBalangbaru Fm of south Sulawesi (overlying theBantimala Complex), and the Manunggul Gp ofsoutheast Kalimantan (overlying the MeratusComplex). The latter two sequences, at least,have been interpreted to be forearc basin de-posits (Sikumbang 1986; Hasan 1990). The Man-unggul Gp is inter®ngered with volcaniclastics ofthe Alino Gp, which has been interpreted torepresent the product of a Late Cretaceous `Al-ino Arc' in southeast Kalimantan (Sikumbang1986).


TECTONIC SYNTHESIS

The paleogeographic status of southeast Sunda-land (including south Borneo and southwestSulawesi) in the Tertiary is controversial, sincepaleomagnetic data offer contradictory inter-pretations: one that the region has undergonelarge-scale counterclockwise rotation (Fulleret al. 1991), the other with no rotation (Lee &Lawver 1994). Regional geological consider-ations (Hall 1996), however, support the viewthat the continental edi®ce of southeast Sunda-land has undergone a counterclockwise rotationof up to 45±50° since the Late Oligocene. Ac-cepting this premise and synthesizing the avail-able data from the accretionary complexes ofcentral Indonesia, we present the followingspeculative synopsis of the tectonic evolution ofthose complexes and their metamorphic consti-

tuents (see Fig. 11 for late Cretaceous paleotec-tonic reconstruction).

JURASSIC±EARLY CRETACEOUS: ANDEAN-TYPESUBDUCTION OF MESO-TETHYS

North-directed subduction of Meso-Tethys oce-anic lithosphere beneath the Sundaland marginduring the Late Jurassic±Early Cretaceous re-sulted in the development of the Early Creta-ceous continental arc (Pieters & Supriatna 1990)in the Schwaner Mountains of south centralKalimantan. Variably disrupted packages of mid-ocean ridge basalt (MORB) basalt and overlyingpelagic and clastic sediment offscraped at thetrench are presently distributed in Luk Ulo,Laut Island, and possibly in the Ciletuh area ofsouthwest Java (Fig. 1).

Paternoster

Lolotoi-Mutis ??

??

'Ceno' Tethys Ocean

?

Laut

'Meso' Tethys Ocean (consumed)

?

Late Palaeozoic – Early MesozoicSundaland basement

Mesozoic magmatic arcs

Early Cretaceous accretionary complex(es)

Late Cretaceous forearc sediments

Gondwanan microcontinental fragment

Sumba

Karangsambung

Early Cretaceouscontinental arc

Sundaland units

'Sundaland'

Tethyan and Gondwanan units

'Tethys' ocean

Karangsambung-Bantimala Trench

Early Cretaceous accretionary complexes

500 km

Site of UHPM/VHPMrocks (P > 20 kbar)

Arc volcano

Trend of complex

?

Late Cretaceous forearc basins

Ciletuh

Oceanward migration of magmatic front

Accretionary complex of offscapedoceanic material (OPS) resulting fromprolonged Mesozoic subduction of

Mesozoic ophiolite

Early Cretaceous

Microcontinentalfragment

Late CretaceousTre

nch

Manghalihat

Late Cretaceous island arc

Mengkoka

Pompangeo

Fig. 11 Paleotectonic reconstruction of theeast Sundaland margin in the Late Cretaceous.Present-day outlines of parts of Kalimantan,Sumatra, Java, Sumba and Sulawesi are shownfor reference. For explanation see text.


LATE EARLY CRETACEOUS: COLLISIONOF A GONDWANAN CONTINENTAL FRAGMENT

At ca 120±115 Ma, a Proterozoic±PaleozoicGondwanan continental fragement collided withthe eastern part of the subduction zone. Rem-nants of the unmetamorphosed Jurassic supra-crustal sedimentary cover of this fragmentinclude the Paremba, Nanaka, Tetambahu andMeluhu Fms in southwest, central and southeastSulawesi. These rocks are probably similar tothose parental to the low-grade Pompangeo,Bantimala and Latimodjong schists, with whichthey are presently interthrust.

Further evidence of a Gondwanan continentalfragment underlying at least parts of the Sula-wesi region is provided by geochemical charac-teristics of the extensive Late Miocene±Pliocenemagmatic rocks in west central Sulawesi. Iso-topic, major and trace element data indicatethat the parental rocks of the Miocene meltswere Late Proterozoic±early Paleozoic Go-ndwanan continental crustal and mantle litho-spheric assemblages, possibly similar to thosepresently found on the northern margin of theAustralian Plate (Bergman et al. 1996). Igneousand metamorphic rocks of this Paleozoic conti-nental basement may crop out over large areasin the Mengkoka Mountains of the SoutheastArm (Rusmana et al. 1993). Until further de-tailed ®eld and petrological research and radio-metric dating is conducted, however, the statusof these rocks remains uncertain. Other geologicprovinces in the central Indonesian region withancient continental basement or metamorphicrocks of continental origin include the Pater-noster Platform in the Java Sea (Hutchison1989) and Sumba (Hamilton 1979; Hutchison1989; Wensink 1989). On the basis of paleo-magnetism, petrological similarities and theunusual occurrence of radiolarian chert atop aschistose basement, the Mutis±Lolotoi Complexin Timor has been correlated with crystallineschists in both southwest Sulawesi and south-east Kalimantan (Haile et al. 1979; Barber1981). On the basis of geophysical data, Rich-ardson & Blundell (1996) also postulated that anallochthonous microcontinental fragment of un-certain provenance constitutes a major part ofthe Timor collision complex.

LATE EARLY CRETACEOUS: METAMORPHISMOF THE REGIONAL SCHISTS

Underthrusting of the northern margin of thecontinental fragment resulted in the recrystalli-zation of the supracrustal sediments (now thePompangeo, Latimodjong and Bantimala schists)to greenschist, blueschist and epidote amphibo-lite grade. This coincided with the retrogradeoverprint on the VHP tectonic blocks, which mayhave been uplifted from mantle depths tomid-crustal levels, and incorporated into the ac-cretionary complexes, by entrainment in ser-pentinite diapirs.

The origin of the garnet peridotites of centralSulawesi is unclear. They may represent mate-rial entrained in a mantle diapir at the margin ofthe continental fragment, when it rifted from theAustralian craton, or relics of mantle wedge, oroceanic mantle subducted along with the regionalschists and VHPM rocks. The latter may be un-likely in view of the `high' peak temperaturesrecorded in most of the garnet peridotites.

EARLY LATE CRETACEOUS: EXHUMATION OF THEREGIONAL SCHISTS AND VHP TECTONIC BLOCKS

Termination of under¯ow by collision and buoy-ancy of the continental fragment facilitated rapiduplift of the stranded, recrystallized accretionarycomplexes along with the, presumably older,VHP tectonic blocks in Sulawesi and south-east Kalimantan. Exhumation of the low-gradeschists must have been relatively rapid sincethey are unconformably overlain in southwestand central Sulawesi by Cenomanian chert.

Collision of the continental fragment may havealso initiated the north-directed overthrustingand emplacement of the Meratus and Bobaris(forearc) ophiolites in southeast Kalimantan.

LATE CRETACEOUS: OCEANWARD MIGRATIONOF SUBDUCTION TRENCH

The collision of a continental fragment with theSunda subduction system in the late Early Cre-taceous would have necessitated outboard,oceanward migration of the subduction zone tofacilitate continuing plate convergence. In thisway the former lower plate (the stranded andpartially recrystallized continental fragment) wastransferred to the upper plate, and both themagmatic front and forearc basin migrated� 200±300 km southwards. Late Cretaceous vol-


canics of the Alino Gp are the remnants of the arcactivity in southeast Kalimantan; the ¯ysch suc-cessions of the Late Cretaceous Tinombo,Marada, Latimodjong, Balangbaru and Karang-sambung Fms, all of which were deposited di-rectly onto uplifted Early Cretaceous schists,may represent parts of the forearc basin (Fig. 11).

EOCENE±OLIGOCENE: ROTATION OF SUNDALANDAND DISPERSAL OF ACCRETIONARY COMPLEXES

Rotation of the continental edi®ce of southeastSundaland counterclockwise by approximately45° in the Eocene±Oligocene resulted in the dis-persal of sections of the accretionary complexesby sinistral strike±slip faulting related to in-creasingly oblique convergence. The opening ofsmall marginal basins in the central Indonesianregion (North and South Makassar, Bali andFlores Basins, and Gulf of Bone), throughout theTertiary would have further dispersed the frag-ments to their present positions.

ACKNOWLEDGEMENTS

This paper bene®ted greatly from reviews byJ. G. Liou, S. Maruyama and A. Ishiwatari.Fieldwork in Indonesia would not have beenpossible without the ®nancial support of theUniversity of London Consortium for GeologicalResearch in Southeast Asia, the AIST of Japan.We acknowledge the invaluable logistic supportand advice from, and discussion with geologistsof the Geological Research and DevelopmentCentre (GRDC), and Indonesian Institute ofSciences (LIPI), Bandung, particularly R. Su-kamto and T. O. Simandjuntak of GRDCand J. Sopaheluwakan, I. Zulkarnain andA. Kadarusman of LIPI.

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