Geological Sockly 0/ MaklyJUz - Circum-Pacific Council/or Energy aM Mimral &i0tur:eJ Tectonic Fl'IlI1Iewor/;. aM Energy &i0tur:eJ 0/ tbe Wutem Margin 0/ tbe Pacific BoJin No-"er 27 - Dtamber 2, 1992, KtmIo. Lumpur, MaklyJUz
Neogene tectonics and orogenesis of Indonesia
T.O. SIMANDJUNTAK
Geological Research and Development Center (GRDC) Jalan Diponegoro 57, Bandung, Indonesia
Abstract: The present tectonic conf1guration of the Indonesian archipelago is thought to have been developed during Neogene times, and shows a triple convergence, which is due essentially to interaction of three megaplates: the westward-moving Pacific Plate, the northward-moving Indo-Australian Plate and the south-southeastward-moving Eurasian Plate. The archipelago is built up of at least 5 distinctive crustal elements including 1) Sunda Shield (SE Eurasian Plate) 2) Indian (Oceanic) Plate, 3) Australian Craton 4) Pacific Plate and 5) Transitional Complex. Each unit consists of several distinctive tectonic units. This tectonic convergence was subsequently followed by the development of orogenic belts in most parts of the region, which kinematically can be recognized and divided into 4 types: 1. Sunda Orogeny in western Indonesia due essentially to a back-arc thrusting in Jawa and Nusatenggara, and transpressional movement of the Barisan Fault System in Sumatera. The orogeny gave rise the development of the Southern Mountain Ranges in Jawa and the Barisan Mountain Ranges in Sumatera, which are coincident with the fold and fault belt. In Sumatera the belt shows a typical flower structural setting. 2. Banda Orogeny in Sulawesi and its surroundings due essentially to the development of a Tethyan type convergence together with the transcurrent movement of the Palu-Koro Fault System, which give rise the development of mountain ranges in Sulawesi. 3. Melanesian Orogeny in Irian Jaya and Papua New Guinea and Sahul Platform due to the development of thin-skinned tectonics, causing the development of the Central Irian Jaya Fold and Thrust Belt coincident with the Central Irian Jaya Mountain Ranges. 4. Talaud Orogeny in the northern Maluku region due to the development of double arc collision coupled with the transpressional movement of southern extension of the Philippine Fault System giving rise the development of the imbricated Talaud-Tifore ridge in the form of flower structure, which is partly emerged above sea level.
INTRODUCTION comprehensive information on the geology of the region (Simandjuntak, 1992b). These data give a This paper presents an overview and analysis better understanding on the geological and tectonic of the tectonic development and tectonic setting of history of the achipelago. the Indonesian archipelago particularly from the Up to date information is provided by GRDC, Neogene to present times. Pertamina, Lipi, Lemigas, Marine Geological During the last two decades, since the beginning Institute (MGI) and other domestic and overseas of Pelita I in 1970 (the first five years of national institutions related to earth sciences. development of Indonesia), the geology of the This paper is part of the work carried out in archipelago was intensely and systematically conjunction with the compilation of the geotectonic investigated by both government and private map of Indonesia and the Working Group on institutions. These include geological mapping Geotectonic Map Project of East Asia (WGGM conducted by the Geological Survey of Indonesia CCOP-NW Quadrant Circum Pacific). and Geological Research and Development Center (GRDC), partly in collaboration with the United States Geological Survey (USGS), the British TECTONIC SETTING OF INDONESIA Geological Survey (BGS) United Kingdom, Bureau Based on geological and geophysical data, the of Mineral Resources (BMR) of Australia and JICA Indonesia Archipelago can be divided into at least of Japan. five mega crustal elements, comprising 1) Sunda Exploration for mineral and energy resources Shield (SE Eurasian Plate) in the north-west, 2) by foreign and national companies and geological Indian Ocean Plate in the south and west, 3) and geophysical research by both Indonesian and Australian Craton in the southeast, 4) Pacific Plate foreign earth scientists, has revealed more in the east-northeast and 5) Transitional Complex
Geol. Soc. MalayolUz, Bulletin 33, Novemher 1993; pp. 43-64 44 T.O. SIMANDJUNTAK in the central part of the region (Simandjuntak, Ridge (TTR), Paleogene Western Halmahera 1992a). These crustal elements are tectonically Magmatic Arc (WHMA), Mesozoic Eastern bounded to each other by either active or inactive Halmahera Ophiolite Belt (EHOB), Neogene (reactivated) subduction zones or wrench anqtor Sangihe Volcanic Arc (SVA), Paleogene Sulawesi thrust faults (Figs. 1 and 2). Sea Floor (SSF), Paleozoic Misool and Birds Head Platform (MBHP), Collision Zone of Irian Jaya. Tectonostratigraphy of Indonesia The accretional wedges in the western part of Tectonostratigraphically, on the basis of Sumatera and southern part of Jawa in western lithological association, structures, age anqtor Indonesia may be included in the Transitional biostratigraphy and geophysical data, each crustal Complex. element can be divided into several distinctive Carboniferous metamorphics occurring in most tectonic units (Fig. 3; Simandjuntak, 1992a). of the micro-continents are considered to be the Sunda Shield corresponds to most of western oldest rocks in the Transitional Complex. The Indonesia, including Sumatera, Jawa, Jawa Sea, metamorphic rocks are intruded by Permo-Triassic Kalimantan and part of the South Arm of Sulawesi. granitic rocks with Mesozoic, passive margin, The Sunda Shield can be divided into: a) fore arcs, sedimentary cover rocks. b) volcanic arcs and c) back arcs in Sumatera and The Banda Sea crust, based on identification of Jawa d) platform and e) accreted zone in magnetic reversal ages, heat flow analysis, Kalimantan and f) magmatic arcs in the South bathymetry and onland geology is thought to have Arm of Sulawesi. been formed in Cretaceous times (Lapouille, 1985; Carboniferous meta-flysch sediments are the Lee and McCabe, 1986). oldest rocks recognised in the Sunda Shield. Juxtaposition of the Paleozoic micro-continents However, core samples from east Medan, North with the Cretaceous oceanic crust in the Banda Sumatera were dated as Devonian in age. regions indicates that these continental slices are Indian Ocean is floored by oceanic crust of allochthonous in origin. Cretaceous-Paleogene age with a cover of pelagic The Banda Platform geologically shows sediments. similarities with the South East Kalimantan and Australian Craton is represented by parts of the South Arm of Sulawesi, in especially the its northern margins which occur in Irian Jaya and occurrence of Cretaceous flysch sediments Sahul Platform, and can be divided into 3 distinctive associated with volcanics and Paleogene Volcanics. units, composing a) the Southern Plains of Irian The platform therefore is quite different, both in Jaya, b) the Central Irian Jaya Fold and Thrust age and lithological association, from the other Belt and c) the Birds Head and Neck of Irian Jaya (paleozoic) micro-continents described previously. and Misool. These tectonic units are always bounded by The oldest rocks in Irian Jaya are pelites faults and thrusts from each other. Some of these containing fossils, Graptolites, of Siluro-Ordovician faults may be reactivated at the present time. age. Pacific Ocean with its floor of Mesozoic or Major Structures older oceanic crust and deep sea sedimentary cover. Major or regional scale structures include Transitional Complex is dermed as the region subduction zones and thrusts and steep faults. that is presently tectonically active convergence, Figure 1 shows the present tectonics and structural divergencE¥'rift;ing, faulting (thrusts, wrenchs, block configuration of the Indonesian archipelago. The or extensional faults), and in parts is volcanically development of these structures is related closely and seismically active. The complex is also to the tectonic convergences and tectonic characterised by the presence of Paleozoic divergences during the evolution of the regions from allochthonous terranes juxtaposed with the Mesozoic to present times. surrounding younger autochthonous terranes. The Some of the faults might have reactivated older complex consists of some 17 distinctive units, structures. including accretional zone of the Cretaceous Eastern Sulawesi Ophiolite Belt (ESOB), Paleozoic Banggai Subduction Zones and Thrust Faults Sula Platform (BSP), Paleozoic Tukang-Besi-Buton Active subduction zones include the Jawa Platform (BSP), Paleozoic Mekongga Platform (MP), Trench, the New Guinea Trench and the Philippine Paleozoic Seram-Buru Platform (SBP), Paleozoic Trench. Thrust faults include the Halmahera Obi-Bacan Platform (OBP), Cretaceous Sumba Thrust and Sangme Thrust in the northern Maluku Platform (SP), Timor-Tanimbar-Kai Accretional Sea, North Sulawesi Thrust, .. Asmat Thrust" in Zone, Quaternary Banda Arcs (BA), Cretaceous Irian Jaya and Seram Thrust in central Maluku. Banda Sea Floor (BSF), Paleogene Talaud-Tifore The Flores Thrust of Nusatenggara appears to x W --l a. :E 0 u W --l I- w let ...J Il. Z z o let 0: z U o Z 0'" KALIMANTAN SO 01' .....~ Go., ~..p...... ~ "0 ~~ 01'...... LAUT ARAFURU 10 ... I Figure 2. Distribution of earthquake epicenters in Indonesia. NUMBER OF REGION OF DESTRUCTIVE EARTHQUAKE I. Aceh x. Flores XVIII. Halmahera II. Sumatra Utara XI. Kupang XIX. Ambon III. Sumatra Barat XII. Yamdena XX. Kepala Burung IV. Bengkulu XIII. Sulawesi Selatan XXI. Jayapura V. Lampung XIV. Sulawesi Tenggara XXII. Paniai,lNabire VI. Jawa Barat XV. Sulawesi Tengah (Jayawijaya) XXIII. Wamena VII. Yogya XVI. Sulawesi Utara XXIV. Tarakan VIII. Lasem XVII. Sangir-Talaud XXV. Kalimantan Selatan IX. Bali-Lom~ak UMUR PAPI\RAN SUNDA SAMUDRA HINDIA KOMPLEK TRANSISI KRATON AUSTRALIA SAMUDRA PASIFIK AGE SUIVOA SHIEL 0 INDIAN OC£AN TRANSITIONAL COMPLEX AUSTRALIAN CRATON PACIFIC OCE Art -. M.o.. Sedlm." PeIO,.1 N . ",/o,ie, $,d,,"'"'' KO,. S,dl"". o KO. ,,11,01 .. 1'".,1" ~ P S,d/""",. K ICTu-JC.roll ••",,,. 100 KTo C,.,,,,.,,,,dro ICopur Or'.III. CIII" Mlo M,u _ Ketoll ,omudra - M•• o.ollium J, - S.dI",." Jura J,,,",,,. $,~/".#It'. /II"OI"~ Oe.OIt/~ ~U J ClUJ I, ::>, J. - "",_.,,111 JUt. .... - S.dl",." Jura J Jti,o ..,~ VDklHt/r, Jill"". S,dl",,,.,. ~o _ ",,,,,.1 Jura - .... JI J,,'t/.,I, ,,,,,,,,1,, •• °0Nil) zoo r-- ), - Sod ...... Trio, I-- Yt"._ 3:fJ~,: l:L",'.,t u$:d. °tu - '" T,llI"l. SIlIlm."" ,n - Yulllo,," Trio. ~. - J::''';''''''$~~/:''''' I ~~ R r,/o,,', VO/elm/f' fl. _ Yol""I' Trl .. )1 - Intro,1 Trl .. TI .. ~ ~ .. Ttl.'./~ tIoI~tlltkl ·1 I rrifllll, 'If'''''''''6 )1 - In"oll Trl•• 1:"11 Tt'o,,/~ IIII""/r,, p, - S.dl"". P.,,. pl. _ '.dl",.,. Plr",o Trio. g~1 I ,."""011 S,.'""nl, ~ .:. P P. - Yullionfil p",.. pia - ~~~~~'r :'~'::·T'I~:d, ~ P"",/titt Vtlle.lflt. r"fJ"k h,,,./OIf III"", "be> PI - 1,,',u.1 PUnt P PI - J~~!'''= ~:~'m'It" ~::o ""mltln mlru,'"'' PI - I"tru.' Per", ~ - I-- I:I~ '.""'tIIt 1tt".. /rl'f _0 ~ 300 CPl •• Sedl",." 1C0r ••ft :t... MelO.oI_um ..." ::> M.,orlll, CO/lJottllp,O'" 0 ~U CI .. Iftpru.1 ICatb ... 3 c. _ S.dlm." 1C0rboft S.II"",,,,, c ... ("",/HIIt/"ftltl' C -0 C,,,6o,.II'NJII' S,d,."",." """,,1.,. c c c. - S.dl ...... Korttoft '"!t c (I _ ,,,,,U.' MarbOll C'tlNM/l,,.,,. $,dl",.,." 0 ~N COrHIt"",..II' lit""" • ., 0 0 (I - ,,,tru •• ,KOnOft wtu CorHItIl.tOUl Inrtu,JwJ, J .... - . r- - ~ p,,,. - MoU"on PoI.OIOII D DI - S.dl""" D••• n ~~ PI", PIIIII'OI./~ M,'.m"rpltlr, O,rtllt/Oif SHlI".."" 0. 0" '- I I P,,,,.1I401l"a,, Pal•• loill PI l'o/,,.,,,oIr Pn PII - ~:1!'::on,:~~:,:.-::':. I I "'.'.,..• ,pllie. 400 Plm PI'" - M.H'on Po .....IIlU"' LJ Po/,."I, - /II"OIfttl,plt'~' S MENUMPU MEKAR - CONVERGENCE DIVERGENCE Figure 3. Tectonostratigraphy of the Indonesian region. 48 T.O. SIMANDJUNTAK continue westwards, off-shore, to the north of Bali et al., 1988; GRDC, in press). The double parallel and merges with the Baribis-Kendeng Thrust along sided subduction zones in the North Maluku Sea northern Jawa and then terminates in the Sunda are still active at the present times (GRDC, in Strait at the southern end of the Barisan Fault press). System. In northern Irian, the New Guinea Trench in The Jawa Trench is the surface expression of which the Pacific Plate is being subducted beneath an active subduction zone located off-shore along the northern margin of Australian continent in west Sumatera and stretching to south Jawa and Neogene (Hamilton, 1979; Smith, 1990). This Nusatenggara. It seems the subduction zone may collision is classified as oblique convergence, as be terminated off-shore to the SE of Sumba Island, indicated by the northward-moving Australian on the Sumba Fracture of Audley-Charles (1975). Continent against the westward-moving Pacific In Sumatera the subduction zone can be classified Plate. as an oblique convergence, since the northwards The North Sulawesi Trench is the surface moving Indian Ocean Plate is subducted beneath expression of a subduction zone, where the Eocene the southeastward-moving Eurasian Plate. oceanic crust of the Sulawesi Sea is being subducted In northern Indonesia, active subduction zones beneath the North Arm of Sulawesi in Neogene occur in a smaller scale such as along the Philippine times. The subduction zone seems to have been Trench in which the Philippine Sea Plate is active for a relatively short time. The present day subducted beneath the Halmahera Islands and seismicity however, suggests the subduction zone along the western Talaud-Tifore ridge, in which a might be recently reactivated. slab of oceanic crust of the North Maluku Basin is This subduction together with the Batui Thrust being subducted beneath the Sangihe Islands (Figs. in the East Arm of Sulawesi in the south gave rise 4, 5). The seismicity suggests that this subduction to the development of a double opposing might be continued to the Batul Thrust in the East convergences in the region in Neogene times. The Arm of Sulawesi, in the south, giving rise to the seismicity and the occurrence of terraces of development of the Minahasa-Sangihe arc (Fig. 6; Quaternary coral reefs indicates that this McCaffrey et al., 1983; Simandjuntak, 1986c; Hall subduction might be active at the present time 0 15 30 45 60 75 .1/1 ,.iz 'N ...i 3 :to S" .~ [5 (U•. 1U-U IJ Col&b&~ Trencb Phllipine Trench Figure 4. Seismic reflection profile of western margin of the Maluku Sea Basin (GRDC, in press). NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 49 (Simandjuntak, 1986d). Fault System (BFS) appears to have at one time The Timor Trough-Kai Trough-Seram Trough been activated with a sense of transtensional is the surface expression of collision zones of Tethyan movements as indicated by the presence of elongated type, in which the NW margin of the Australian grabens or fault bounded basins such as the continent underplates the Banda Island Arcs. Lauttawar, Toba, Maninjau, Singkarak and Ranau Audley-Charles et al. (1972) considered that this lakes within the fault zone of the BFS in Sumatera. collision zone was active in Early Tertiary times. The development of the Barisan Mountain At present the collision might be (re)activated Ranges associated with the BFS, however strongly (Cardwell and Isacks, 1978; Hamilton, 1979; Bowin suggests that this fa"ult was dominated by et al., 1980; Katili, 1970; Silver, 1981). transpressional dextral movement. By contrast, the steep faults in eastern Transcurrent Faults Indonesia including the Sorong-North Sula, Sorong The main steep faults include the wrench faults South Sula and Tarera-Aiduna with their western of the Barisan Fault System (BFS) in Sumatera, extension and then merged with the Palu-Koro Fault Palu-Koro Fault System (PKFS) in Sulawesi, System in Sulawesi, are all dominated by sinistral Sorong-Sula Fault System (SSFS) and Tarera transcurrent movement. The occurrence of the Aiduna-Banda Fault System (TABFS) in eastern Poso, Matano and Towuti Lakes within the fault Indonesia. zones of the Palu-Koro-Matano Fault indicates that The Barisan Fault and the Philippine Fault this fault was also at one time developed with a Systems are dextral wrench faults. The Barisan transtensional sinistral movement. 1(11."",1 ... o 1$ ;)0 6 ;0 15 ~o 45 60 W E III •n ~ g :-Go ",'4• 0 'C" . :!- 5 ""'""--- I. 0.. ...::. '9 6 \. • I .. Figure 5, Seismic reflection profile of eastern margins of the Maluku Sea Basin (GRDC, in press). 50 T.O. SIMANDJUNTAK Micro-seismicity analysis and the occurrence of center of triple convergences due to interaction of earthquake hypocenters along the faults and at least 3 megaplates, including the northward thrusts, strongly suggest that most of the faults moving Indo-Australian Plate, the westward &TId thrusts appear to represent older structures moving Pacific Plate and the south-southeastwards that are reactivated at the present time. moving Eurasian Plate. The tectonic evolution ofthe regions is recorded TERTIARY TECTONIC DEVELOPMENT by the development of both tectonic convergences OF INDONESIA and divergences and other tectonic activities. The tectonic convergences in Indonesia consist of several The present complicated nature of the geology, types including Cordilleran-type subduction, in structures and tectonics of the Indonesian which the oceanic crust subducted beneath the archipelago appears to have been developed in the continental margins; Tethyan-type collision, in Neogene times, since the region developed at the which micro-continents underplated the subduction 6 123 124 125 129 130 131 132 -J!. ••• -w.- t • al'li!.~. • DEPTH .,' • (- ~' 0 • ::8 5 o ':.. 0 • 0- .69 km 5 .. ' . o = • + 0 -1\1 •• '. 0 ~ TALAUD 0 • = 70-299 km '+ 0 .. .e, Al +. • 0 4 0} 8 • 0 0 • 0 + > 300 km C • .. 3 0 D 0 E • 2. F + 0 G ij H 0 0 0 0 ~ WA1GEO BANGGAI 0 ~b==? wa 0 8 0 -2 00 ~8 0 0 00 0 ~ -3 0 ~~ 6&, 0 -4 123 124 125 126 127 128 129 130 131 132 Figure 6. Distribution of earthquake epicenters during 1971-1984 in the Sulawesi and Maluku Sea Basins (GRDC, in press). NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 51 complex and island arcs and double arc collision have been repeatedly subjected to either zones. transtensional or transpressional wrench movement The tectonic divergence is characterised by during the history of the fault since the early rifting of the NW margins of the Australian Tertiary times (Fig. 8). continent and then displaced westwards to the The Sunda Orogeny therefore, has been present position in the Banda Sea regions by developed during the dying out or ceassation of the transcurrent-transformal displacement. Tertiary subduction zone, prior to the oceanward migration of the subduction zone and was originated Tertiary Tectonic Convergences in Indonesia by the development of back-arc thrusting along In western Indonesia a cordilleran type northern Jawa and Nusatenggara, and a dextral convergence has occurred repeatedly in Sumatera, transpressional strike-slip movement of the Barisan Jawa and Nusatenggara regions since the late Fault System (BFS) in Sumatera. Paleozoic to present time (Katili, 1971). The In eastern Indonesia the Neogene tectonic Tertiary subduction zone seems to be intermittently convergence appears to be more complicated due to active or reactivated in late Paleogene to early the development of several distinctive types of Neogene and then dying out or ceasing towards the convergences in the south, middle and north parts end of Neogene. of the region. In very late Neogene or early Quaternary the In Irian Jaya and Papua New Guinea the subduction zones migrated oceanwards with Benioff Miocene tectonics convergence is marked by a south zones dipping towards the continent, in which the dipping Benioff zone in which the Pacific Plate Indian Ocean crust subducted beneath the margin underplated the northern margin of the Australian of Sunda Shield (SE Eurasian Plate). Surface Continent (Smith, 1990). During the late stage expression of the subduction zone is now marked and/or subsequently after the ceassation of this by deep trenches off-shore west of Sumatera subduction, the continental margin sequences were stretching continuously to the south, through the thrusted onto the basement of the craton in the Jawa Trench off-shore south of Jawa and terminated thin-skinned tectonics manner. This period of thrust in the zone of discontinuity or the southern end of tectonics was called as the Melanesian Orogeny by the Palu-Koro Fault (Jones, 1969; Katili, 1970; Dow et al. (1986). The thin-skinned tectonics gave Hamilton, 1979; Nishimura et al., 1981) and/or the rise to the imbricated nature and the uplifting of so-called Sumba Fracture (Audley-Charles, 1975) the Central Irian Jaya Fold and Thrust Belt and its in the south-southeast of Sumba Island. continuation to Papua New Guinea eastward. The During the late stage and/or subsequently after belt coincides with the Central Irian Jaya Mountain the ceasing of subduction in Late Neogene, the Ranges with peaks of nearly 6,000 m above sea volcanic belt in Jawa and Nusatenggara was level. At present surface expression of this thrusted over the back-arc basin. Surface expression convergence is marked by a thrust front, which is of this back-arc thrust is now called the Baribis herein called the Asmat Thrust. The thrust bounds Thrust in northern West Jawa and Kendeng Thrust the Southern Plains and the Central Fold and in northern East Jawa (Fig. 7). In Central Jawa Thrust Belt of Irian Jaya (Fig. 9). the thrusts appear to have been disrupted by the The Asmat Thrust continues to the east in the Cimandiri Fault, Citandui Fault and other wrench Papua New Guinea and to the west it appears to faults. For the purposes of the regional description being extended through the Tarera-Aiduna Fault this structure is called Baribis-Kendeng Thrust. and then merges with the Seram-Kai-Timor Trough. Geophysical data show that the Baribis-Kendeng In the southern part of Central Indonesia, the Thrust continues to the east in off-shore to the plate convergence is characteristically marked by north of Bali and to the Flores Thrust, and then the development of a Tethyan collision zone, in terminates in the southern end of the Palu-Koro which the northwest margin of the Australian Fault an : . ." '.. ~BANGKA OROCLINE t.lERATUS TRENCH ":::~~c, 0 "@dr /{1 t... ·· SUNDA WRENCH :=0' / SUNOA J PLATFORM o 100 200 300KM Arcs Baribis - Kendeng Thrust Jowa Sea Jawa TrenCh s Indian ~--_I Ocean Plate ------.-- -- Tertiary Sediments I .....:' \ ,,","" Oceanic Crust BACK ARC THRUSTING Figure 7. Schematic tectonic profile across Jawa Trench. NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 53 PLIO-PLEISTOCENE FOLDS IN SUMATRA: RESULT OF WRENCHING ANTICLINAL AXIS PLATE MOVEMENT FROM FIRST-MOTION EARTHQUAKE STUD:E~ ~ -BAR/SAN OECOSTER,I974, HAMILTON,I972 JlIRENCH FAULT ZONE Barlsan Mentawal Fault System Accreted Cpx Arc (Flower Structure). Trench E w QI'I ....- -:. indian Sumatera . (Sunda Shield) - 1::::::::1 Tertiary Sediments ------ FLOWER STRUCTURE DUE TO WRENCHING Figure 8. Schematic tectonic profile across Sumatera. ~ s N PLATfORM CENTRAL RANGES I , I f-c------THR~xs~E~~~~TS---,;..I~--TH~~:iRSNHAELETS --- I I toE -"UOlO'CS (IP05(O G OA[&CH(O IN e,T[ANA~- ~I~ -INOUAAT[O a c.£AV[D "[SOlO'CS • - I THRUST Stt((TS PA~A[ZOIC' IN IHf[ANAl 111AUsr ~eE".s I l- TttlfuSf ,sHEl-rs OETACHtOJ....e. 'MAUST SHEETS INVOLVING MESOZOIC ------~ ------:-I ; ABove "UOlO'C fAAGe r I 9 PASSIVE-AOO' 8AC"'"Jtusr I I t;!J STNCL'N[.IN ADO' .s(OU(NC[ I .1,(," ~ UNOE'O,.,..EO / FOReLAND / ~ '" ~ PLAlt:'OII_ 8 DASIN TOPOGRAPH'C //r-'" ' '" ~ c: , PRO'ILE \ ~ I.'clii" \ ':s.- " OASEMENT I t-If._DUPL,JI 0' "CSOZQ'IC. PALAEOZOIC C;."'NG ______...... ;:... I - ELEVAllON AeOvE 8(GIONAI- I ~f.S02c,,1C. TftAGET I~ HA"'CIN(i "'All. AfrfD Taf\YIARV CLASl,e oSOIJRC£ 'N 'OO'WAU Figure 9. Schematic tectonic profile across central Irian Jaya. NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 55 During the late stage of this Tethyan type The development of the Minahasa-Sangihe convergence, the orogenic belt appears to be volcanic arc is related closely to this convergence developed due to thin-skinned tectonics in Timor (Simandjuntak, 1988). and the Sahul Platform in Late Neogene times, In the north and northeast, two types of where the continental margin sequences were thrust convergences were developed in Neogene times: i) over the basement complex of the Australian Craton. A cordilleran type convergence occurred in northern This orogenesis gave rise to the development of the Irian indicated by the Pacific Plate under-plating thrust sheet and klippe structure structures in Irian Jaya-Papua New Guinea (Smith, 1990), and Timor, Tanimbar, Kai and Seram Islands (Fig. 10). ii) An arc-arc collision occurred in the northern To the west, this thrust tectonics seem to be part of Maluku Sea. terminated on the eastern end of the J awa Trench, GRDC (Transect VIII, in press) on the basis of or on the Sumba Fracture of Audley-Charles et al. geophysical and onland geological data shows that (1972), or on the southern end of the Palu-Koro at present this convergence seems to be in the form Fault in the off-shore area to the southeast of Sumba of a double-arc collision with two separated Benioff Island. zones dipping westwards beneath the Sangihe Arc In the Banda outer arc, the collision of the and Halmahera Arc respectively. The initial northern margin of the Australian Continent seems framework, an inverted U -shaped subducted oceanic to pre-date the thin-skinned tectonics described crust in this region suggested by Bowin et al. (1980), above, or at the least the thin-skinned tectonics are Hamilton (1979) and Silver et al. (1978), appears to developed during the latest stages of convergences have been greatly disrupted and modified during in Neogene times. the Neogene convergence. Seismicity and Providing a significant amount of the earthquake analyses suggest (Fig. 13) that the displacement of the northern margins of the double parallel-sided collisions are active Australian Continent occurred due to the (reactivated) in the North Maluku Sea (GRDC, in northwards movement of the craton, the initial press). thrust front might be extended to the west into the Simandjuntak (1988) suggested that the presently curving Seram-Kai-Timor Trough in the western subduction continues to the south and joins form of a relatively straight line trending in an the Batui Thrust in the East Arm of Sulawesi and approximately east-west direction in late Neogene then terminates on the Matano-Sula Fault. This times. subduction has initiated the development of the In the northern part of Central Indonesia, the present active volcanoes in the Minahasa-Sangihe Neogene convergence was dominated by a Tethyan Arc. type collision, in which the micro-continents underplated subduction complex and/or island arc Tectonic divergence in eastern Indonesia (Fig. 11). This convergence is evidenced by the The Paleozoic micro-continents occurring in the occurrence of the Eastern Sulawesi Ophiolite Belt Banda regions include the Banggai-Sula Platform that overrides the Banggai-Sula Platform and (BSP), Tukanbesi-Buton Platform (TBP), Mekongga Buton-Mekongga Platform in eastern Sulawesi Platform (MP), Seram-Buru Platform (SBP), Misool (Smith, 1983; Simandjuntak, 1981, 1986a) described Birds Head Platform (MBHP), Obi-Bacan Platform previously. (OBP), and Lucipara Platform (LP). The Sumba The most significant result of this convergence Platform (SP) in the southern-most part of Central is the emplacement of the imbricated ophiolite belt Indonesia is much younger than those mentioned as an obducted slab in eastern Sulawesi above as it contains older than Cretaceous flysch (Simandjuntak, 1986b, 1991). Similar mechanism sediments associated with volcanics. seems to had been taken place in the emplacement These platforms juxtaposed with the adjacent of the Papua New Guinea Ophiolite Belt (Davis, younger terranes. Results of the seismic analysis 1976). show that the platforms are tectonically bounded A double opposing tectonic convergence in with the oceanic crust of the Banda Sea. In eastern northern Sulawesi may have been developed in Sulawesi, the ophiolites of ESOB is underplated by Neogene time during the formation of the the Banggai-Sula, Tukangbesi- Buton and Mekongga northwards dipping collision zone, in which the Platforms (Smith, 1983; Simandjuntak, 1986a; Banggai-Sula Platform under-plated the Eastern Suria-Atmadja et al., 1972). Sulawesi Ophiolite Belt. To the north an early The origin of the micro-continents in the Banda Tertiary convergences with a south-dipping Benioff region eastern Indonesia is not clear and is still zone where the oceanic crust of Sulawesi Sea under discussion. The platforms are generally subducted beneath the North Arm of Sulawesi might regarded as having been detached from Irian in be reactivated in Neogene times (Fig. 12). Cainozoic times and displaced westwards along the 56 T.O. SIMANDJUNTAK Sorong Fault Zone (Visser and Hermes, 1963; in the west adjacent to the newly formed continental Krause, 1965; Hermes, 1968; Gribi, 1973; Hamilton, margin of Papua New Guinea, which marked the 1979; Silver and Moore, 1979; Smith, 1983) or from site of separation of the micro-continents from their north Misool region (Audley-Charles et al., 1972). host Australian Continent. This assumption is based on geological Simandjuntak (1986d), based on recognition of correlation of the micro-continents with the western several hiatuses in the micro-continents, discussed Irian (New Guinea). the tectonic evolution of these platforms. Some of Pigram and Panggabean (1984) suggested that the hiatuses, particularly the Early Jurassic, might the micro-continents in the Banda region were be related to eustatic fall of sea-level superimposed detached from a region in Central Papua New on the tectonic divergence of northern margin of Guinea (Irian), about 141-145 East Longitudes. the Australian Continent. Triassic thermal doming They further speculated that oceanic crust occurring in the northwest margin of the Australian developed during this Triassic rifting is no older Continent appears to have initiated the rifting of than Early Jurassic in the east and Middle Jurassic the regions, followed by slicing up the continental sw NE West Timer .... \ a 0 ••• • . . -~.:.--.!-..-'-- (d) UNIlERPI.A TED FalE-A/lC East Timor I!II BASOOff PLATE" ~ taW£ saF SEDII£NTS o 50 km <,- - " :::- Ipm PERltlNhlWlSSIC SED. ~ f ---"""7"""""'-c----'''"P. § "PIUOZOIC I£TMalPHS. :~[-~'"'" fI~~li~ig~~!'E~E'~ P PRE-PERIIIM SEllEN. al ·9 ~ CRYSTfUltl BASa!EHT m IELES Figure 10. Schematic tectonic profile across Timor Trough, showing the development of thick-skinned tectonic (modified after Harris, 1991). w/-;sn:lI,Y )"AMIJ£SA TAN I M /I" II T II U U (; II ISI.A.fWS STRAITS NV\' Mud Bubuan Mud Comlliu SE volcanism (mobilised Jurassic s't!alesl ------ Zone of u.tlderplaling (pre·t.\ocene) .6.~~~~ o 50 k ... V. E. ~ 6.5" Figure 11. Schematic tectonic profile across Tanibar Trough showing the development of thin-skinned tectonics (Charlton et al., 1991). NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 57 Western Sulow.ul EO$lern Sulawesi M09mo.lc /It;rc Mt.dlan line Oph\olile Bell (WSMA) (ESOB) BanQQar Sula ~j Platform (BSP) I ) \ ¢E X X X X X X X X X X X X X X X X X X X TEHYAN TYPE CONVERGENCE MID - MIOCENE ( a ) Western Sulawesi t.\oomollc Arc (WSMA) ~) Thlckenlno Ophiolite Median line t \ TECTONIC SHORTENING ANO THICKENING PALEOGENE ( b ) W.stern SUIOWHI Moomollc Arc (WSMA). SubduCllon w Complex Imbrlcaled u' Ridoe crul OP.hlolilic Melanoe /" " COROllERAN TYPE CONVERGENCE CRETACEOUS ( c ) Figure 12. Schematic tectonic proflle of Sulawesi. (,. OV ..'l; t?"'l' ~"'l' ~"'l' EAST ARM OF, Paleogen Volcanic Arcs. ~' / SULAWESI ~f?' -J ~f?' ·S lawe,l-Sea crust Late Cretaceous Wasupondo M~lon/ge~ Continental margin se-diment of SSP. Bo lui Collision Zone Iysch sediments {continental margin Ncog ..n Kolokolo .North Sulawesi Trench Sundaland) Melange TOMINI BAY NOR:rH ARM OF SULAWESI sea level N ...... -z Eastern Sulawesi Ophiolile Belt SULAWESI SEA Figure 13. Block diagram showing the development of double subduction in northern Sulawesi. NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 59 margin and the fragments diverged and drifted origin of the Sumba Platform, kinematically, may westwards. Tectonic divergence seems to have been be due to one of the following alternatives: followed by transcurrent displacement of the 1. A continental fragment detached from the SE continental fragments westwards and formation of margin of the Sunda Shield and rifted away to the platforms (micro-continents) in the Banda region the south by transcurrent displacement, prior of eastern Indonesia (Fig. 14). to the development of the Nusatenggara Considering a rate of horizontal movement of Volcanic Arcs in Neogene times. less than 10 cm/year, the continental slabs may 2. A continental slab detached from the SE margin have drifted westwards all the way during Triassic of the Sunda Shield and left at the relatively Early Tertiary until they collided with the nearby its present position during and/or subduction complex and/or island arcs in Middle subsequent after the anti-clockwise rotational Miocene in Eastern Sulawesi and other places in movement of Kalimantan, prior to the the Banda region. The transcurrent movement development of the Nusatenggara Volcanic Arcs along the Sorong-Sula Fault and Tarera-Aiduna in Neogene times. Sula Fault and the other faults might be temporarily 3. A continental slice drifted away to the south by have been much slower or ceased during the history transcurrent displacement subsequent after of their displacement. "rifting" of the SE margin of the Sunda Shield The Sumba Platform is quite distinctive from in the Makasar Strait, prior to the development neighbouring Volcanic Arcs and oceanic crust of of the Nusatenggara Volcanic Arcs. the Indian Ocean and is much younger than the The transcurrent fault appears to have become other micro-continents in the Banda Sea regions. a zone of discontinuity between the western and Simandjuntak (1992c, in press) discussed the origin eastern parts of Indonesia called the Sumba of the Sumba Platform, and geologically correlates Fracture by Audley-Charles (1975). it with Southeast Kalimantan and South Arm of The fault appears to extend northwards through Sulawesi especially during the Cretaceous to the South Arm of Sulawesi to Makasar Strait and Paleogene times. He further suggested that the East Kalimantan. DOUBLE ARC COLLISION COLLISION~LEOGEN ZONE~ ~AND ARC. . PHILIPPINE TRENCH SANGIHE SULAWESI TALAUD-MAYU RIDGE EURASIAN SEA CRATON r I CONTINENTAL CRUST OCEANIC CRUST Figure 14. Block diagram. showing the development of double parallel sided subduction zones in North Maluku Basin. 60 T.O. SIMANDJUNTAK DISCUSSION AND INTERPRETATION northern Jawa were cut and deformed by the Baribis-Kendeng Thrust, hence the Sunda Orogeny On the basis of geological and geophysical data was developed in very late Neogene times. described above, it is obvious that Neogene tectonic To date no evidence for Neogene back-arc convergence in Indonesia has given rise to the thrusting in Sumatera has been recognised. The formation of the archipelago with its complicated Neogene orogeny in this island seems to be confined geology, structures and tectonics. The end-products to dextral transpressional wrenching faulting on of the Neogene convergence is the development of the Barisan Fault System (BFS), due to the oblique very significant mountain building episode of fold convergence in this region. The occurrence of and thrust belts in most of the regions. earthquake hypocenters strongly suggest that at In the following section, the discussion is focused least some segments of the BFS are being on the development of this Neogene Orogenesis in reactivated (Fig. 2; Fitch 1970; Katili, 1971; the Indonesian region, which kinematically can be Kertapati et al., 1992). In the recent earthquakes divided into 4 types: 1) Sunda Orogeny, 2) Banda some of the ponds of sulphuric hot water springs Orogeny, 3) Melanesian Orogeny and 4) Talaud along the BFS, in North and Central Sumatera, Orogeny. were lifted up and ceased, suggesting a transpressional dextral movement of the fault. Sunda Orogeny The significance of the Sunda Orogeny is now Tectonic convergence in western Indonesia, marked by the following tectonic features, most of which is dominated by Cordilleran type collision, them can be readily observed in the outcrops and in appears to have reoccurred since Permian through remote sensing imagery. Mesozoic to present times and subduction zones a. Uplifting of folded and partly faulted rocks of migrated oceanwards with time (Katili, 1970). the Southern Mountain Ranges in Jawa and The subduction and volcanism in Sumatera, also in Nusatenggara to over 3,500 m above sea Jawa and Nusatenggara seem to have temporarily level and the intensely folded and faulted rocks ceased or died out in the Neogene. In this situation, of the Barisan Mountain Ranges in Sumatera in order to accommodate the compressive stress to nearly 4,000 m above sea level, testifying the due to the northward-moving Indo-Australian Plate rapid rising of the regions (or Mountain building). and maintaining an equilibrium isostatics nature b. A tightly folded even partly isoclinally folded of the active margin, the driving force ought to be Miocene back-arc sediments along northern released in the form of back-arc thrusting along Jawa and Nusatenggara and uplifting of northern Jawa and Nusatenggara. deformed Paleogene fore-arc sequences and the In Sumatera, however the situation is different underlying imbricated complex of Cretaceous due to the oblique nature of the convergence, and subduction zones in and along southern Jawa. the Barisan Fault System was (re)activated with Similar structural and tectonic features also dextral transpressional movement. developed in Sumatera. The present geological mapping and geophysical c. The development of flower structures on and survey of western Indonesia by the Geological along the Barisan Fault System in Sumatera. Research and Development Center (GRDC) partly This structure seems to have been magnified in collaboration with the British Geological Survey by the repeatedly reactivation of the Barisan (BGS), geological research by Lemigas, Pertamina Fault System in both transpressional and and private oil companies and also Indonesian transtensional dextral strike-slip movement students reveals actual and comprehensive data prior to the Neogene Sunda Orogeny. confirming the occurrence of the back-arc thrust in d. Deepening of the back-arc basin in the Jawa Jawa, which is herein called the Baribis-Kendeng Sea, Bali Sea and Flores Sea as indicated by Thrust (Fig. 7). This thrust trends E-W parallel the subsiding of the Karimun Jawa High in with the long axis of Jawa and appears to be Jawa Sea. The high appears to have been at terminated at the southern end of the Barisan Fault once emerged above sea level and become the System in the Sunda Strait to the west. To the east source of quartz sandstones of the Paleogene it continues off-shore to the north of Bali to the and Neogene clastics of back-arc sequences in Flores Thrust and terminates in the southern northern Jawa, Madura and Sapudi Islands. extension of the Palu-Koro Fault, off-shore, to the North of Sumba Island (Fig. 8). Seismicity and the Banda Orogeny presence of earthquake hypocenters indicate that The collision of the micro-continents of the the thrusts might being reactivated in most Banggai-Sula, Tukangbesi-Buton and Mekongga segments. Platforms against the Eastern Sulawesi Ophiolite The Mio-Pliocene back-arc sequences in Belt (ESOB) occurred in the Middle Miocene. The PALAEOVENE"VOl.CANIC AR C. ( W SMA I - 160m),r LATE rnETACEOUS TO PALAEOCENE SUBDUCTION ZONE UTURE EASTERN SULAWESI CfHOLITE BELT I E SO B I. z § m z m -I 81 'h. and 0' Juraulc (appr-ox .160myr aQol 'h. norther" _el. 0' '". m Au"rolia lac.d a n.wly lormed oc.on which probably "n~ ,,,. pro'o-'"dlon § Z and prolo·Pocilic oc.on,. Thu. n.w oc.onl were I.poro,.d 'roM 'h. ~, •• g .Iil'.'nll oe.onl 0' N.o-T.,hYI IS.ngor, 19791. _01 ,. .... 'ha'a .. o "1 a Icrlon ~ 01 eonlinonll ondlor mlcroeonlinonll. POrll 01 which "OW b.eomo 'ho IEIC,.. o IP'9ro" a Ponll\loboan. 19841. \ o f5 CO) m Z m en o FUTURE BANDA 'TI Z Tr I ass i c - Ju r as sic MICRO CONTINENT IBMC I 8z men 5> A. ConverQc.nce in Late Cretaceous' to AustraJJan Continent Paleocene in Sulawesi 8. Diver<;lence in northern mar<;lln \ of Australia In Triassic - Juross4c Figure 15. Tectonic divergence of the northern margin of Australia followed by tectonic convergence in Sulawesi regions. 0>...... 62 T.O. SIMANDJUNTAK age of this convergence is indicated by the presence the oceanic crust and/or subduction complexes and/ of Middle Miocene foraminifera in the matrix of or island arcs means the sedimentary pile on the melanges developed during this collision and a Mio continental margin would be thrust over the Pliocene age of the post-orogenic clastics (molasse) continental basement. sediments (Smith, 1983; Simandjuntak, 1980, Similarly, the Tertiary tectonic development of 1986a). The collision is typical of Tethyan type Timor Island was described by Audley-Charles convergence, where the micro continents (1975), Barber and Carter (1977), in Kai-Tanimbar underplated the subduction complex and/or the Island (Charlton et al., 1992), in Seram (Audley island arcs (Simandjuntak, 1986c, 1991). In Timor Charles et al., 1981) and typifies the Tethyan the collision seems to be earlier, considered as collision described by Simandjuntak (1986a) above. Paleogene by Audley-Charles et al. (1972). It was However, the occurrence of an extensive then followed by collision in Tanimbar-Kai and metamorphic complex in the region implies that Seram Island in Neogene times (Fig. 10). the thrusting might be initiated by thick-skinned During late stage and/or subsequent after this tectonics if the metamorphics are part of the convergence the ophiolite belt in eastern Sulawesi basement complex. Considering the metamorphic (ESOB) was imbricated giving rise to the shortening rocks originated as a sedimentary cover, then the and thickened nature of the overriding ophiolite thrusting orogeny in Timor is, kinematically, similar belt. While the continental margin sequences on to that in the Central Irian Jaya Fold and Thrust the underplating platforms were imbricated and Belt. some may be in the form of duplexed stacks due to Dow et al. (1986) concluded that the Melanesian forward migration of the thrust (Fig. 11). Orogeny is the end-product of the oblique tectonic Micro-seismicity, occurrence of earthquake convergence in Irian Jaya in the Late Tertiary. hypocenters and the development of several terraces Subsequently after the ceasing of the Neogene of Quaternary coralreefs in most of the islands, southern-dipping subduction zone off-shore to the suggest that at least partly the thrusts might be north of Irian Jaya-New Guinea (Smith, 1990), the reactivated at present times (McCaffrey et al., 1983; northern margin sequences of the Australian Craton Simandjuntak, 1986a, c; Vita-Vinzi and Hidayat, were thrusted southwards onto the foreland of the 1992). continent. It is called the Asmat Thrust trending The significant of the Banda Orogeny is E-W and bounded on the Southern Plains against evidenced by the development of the following the Central Irian Jaya Fold and Thrust Belt (Fig. 9). structural and tectonics features, most of which are The Asmat Thrust continues to Papua New readily recognized in the field and on remote sensing Guinea in the east. To the west it merges with the imageries. Tarera-Aiduna Fault and terminates in the south a. Uplifting of mountain ranges to over 3,000 m extension of the Palu-Koro Fault further east (Tjia above sea level in Sulawesi and the surrounding and Zakaria, 1974). islands, testifying the rapid rising of the regions. Considering the amounts of the northwards b. Deformed, folded and thrusted of the over-riding displacement of the Australian Craton since the ophiolite belt and the island arcs together with Neogene, the Asmat Thrust might be in a straight the overlying molasse sediments. line through the Kai Trough to Timor Trough in the c. Termination of deposition of non-marine west. molasse sediments due to the uplifting of the The significant physiographical, structural and block fault-originated basins within the collision tectonic features of the Melanesian Orogeny in complex. eastern Indonesia can readily be recognised in the d. During late stage, or subsequent to the orogeny field and remote sensing imageries, including: volcanic arc seems to be shifted, such as Unauna a. The uplifting of the Central Irian Jaya Mountain and Minahasa Sangihe arcs in the northern Ranges to nearly 6,000 m above sea level in a part of Sulawesi Island. relatively short time indicating and testifying to the rapid uplift of the mountain building Melanesian Orogeny phase. Recent geological mapping of northern Irian b. The development of the Central Irian Jaya Fold Jaya conducted by the GRDC in collaboration with and Thrust Belt and its continuation to the BMR of Australia (Dow and Sukamto, 1986) reveals east in Papua New Guinea is essentially due to data, which suggest that the northern margin of the thin-skinned tectonics in northern margins Australia may had been collided with Pacific Plate of the Australian continent. in Tertiary times, prior to the development of thin c. The ceasing of the foreland basin and/or inter skinned tectonics in central Irian Jaya. Subduction sag basin which is now uplifted and forms a flat of such, much thicker, continental margins beneath lying low lands (peneplains) in southern Irian NEOGENE TECTONICS AND OROGENESIS OF INDONESIA 63 Jaya. Paleogene rocks which is originated by the d. The occurrence of Paleozoic metamorphic slabs development of flower structures of the Talaud possibly part of basement complex, may indicate Tifore ridge. that in Timor the development of the thrust c. The shallowing of the North Maluku Basin due sheets and klippe structures was instrumented to the rising of the basement complex. by thick-skinned tectonics. Or alternatively, if d. Shifting of the present active volcanic arc in the metamorphic rocks originated from the Minahasa-Sangihe Volcanic Belt. sedimentary cover rocks, the thrusting orogeny in Timor is instrumented by thin-skinned ACKNOWLEDGEMENTS tectonics similar to that in the Central Irian Jaya Fold and Thrust Belt described previously. Dr. W.J. McCourt of the British Geological Survey (BGS) has read carefully and edited the Talaud Orogeny paper and he also gave valuable suggestions. The Talaud-Tifore ridge in the center of North Maluku Basin is built up of imbricated melange wedges, slices of ophiolites, Late Paleogene volcanics REFERENCES and the overlying Neogene clastics and carbonates. AUOLEY-CHARLES, M.G., 1975. The Sumba fracture: A major The melanges are thrusted upon the Sangihe and discontinuity between Eastern and Western Indonesia. Halmahera arcs in the west and east respectively. Tectonaphysics, 26, 213-228. The melanges are characterised by gravity lows AuoLEY-CHARLES, M.G., CARTER, D.J. AND Mn.soM, J.S., 1972. and shallow seismicity, and may attain thickness Tectonic development of eastern Indonesia in relation to of some 14 km (Cardwell and !sacks., 1978; Gondwanaland dispersal. Nat. Phys. Sci., 39, 35-39. 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