geotektonik jawa_2010_2011

8/4/2019 GEOTEKTONIK JAWA_2010_2011

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FAKULTAS ILMU DAN TEKNOLOGI KEBUMIANPROGRAM STUDI MAGISTER GEOLOGI

INSTITUT TEKNOLOGI BANDUNG

2011

Oleh : Kelompok 3

Kurnia Setiawan Widana 22010002

Adi Gunawan Muhammad 22010003

Tatik Handayani 22010010


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Hall, R., 2002, Cenozoic geological and plate tectonic evaluation of SE Asia and SW Pacific, :computer based reconstruction, model and animation, Journal of Asian Earth Sciences, vol 20 p. 353-451

E. Lschen , C. Mller , H. Kopp , M. Engels , R. Lutz , L. Planert, A. Shulgin , Y.S. Djajadihardja ,2010 , Structure, evolution and tectonic activity of the eastern Sunda forearc, Indonesia,from marineseismic investigations, Tectonophysisc, 124951, Article in Press

Referensi

H. Kopp, D. Hindle , D. Klaeschen , O. Oncken , C. Reichert , D. Scholl, 2009, Anatomy of the westernJava plate interface from depth-migrated seismic images, Earth and Planetary Science Letters vol.

288 ,p. 399407

Ian Metcalfe, 2011, Tectonic framework and Phanerozoic evolution of Sundaland, GondwanaResearch vol.19, p. 321

Hall, R., and Morley, C.K., 2004, Sundaland Basins, Geophysical Monograph Series 149, ContinentOcean Interactions Within East Asian Marginal Seas, American Geophysical Union

Hall, R., Clement, B., Smyth, H. R., 2009, Sundaland: Basement Character, Structure and PlateTectonic, Proceeding, Indonesian Petroleum Assocciation, Thirty-ThirdAnnual Convention andExhibition, Indonesia.

Smyth, H.R., Hamilton, P.J., Hall, R., Kinny, P.D., 2007, The Deep Crust Beneath Island Arcs: Inherited

Zircons Reveal a Gondwana Continental Fragment Beneath East Java, Indonesia, Earth andPlanetary Science Letters 258 (2007) 269282


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J.M. Whittaker , R.D. Mller, M. Sdrolias, C. Heine., 2007. Sunda-Java trench kinematics, slab

window formation and overriding plate deformation since the Cretaceous, Earth and Planetary ScienceLetters , vol 255 ,p 445457

Referensi

A. Shulgin,H. Kopp,C. Mueller,L. Planert,E. Lueschen,E. R. Fluehand Y. Djajadihardja, 2011,Structural architecture of oceanic plateau subduction offshore Eastern Java and the potentialimplications for geohazards, Geophysical Journal International vol. 184, p 1228

Clement, B., Hall, R., Smyth, H. R.,, Cottam M.A.,, 2009. Thrusting of a volcanic arc: a newstructural model for Java , Petroleum Geoscience, vol. 15 , p. 159174

Smyth, H. R.,, Hall, R., Nichols, G.J., 2008. Cenozoic volcanic arc history of East Java, Indonesia:The stratigraphic record of eruptions on an active continental margin , The Geological Society of

AmericaSpecial Paper 436, p.199 - 222


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IAN MTCLAFE 2011ABSTRAK

Sundaland comprises a heterogeneous collage of continental blocks derived from the IndiaAusmargin of eastern Gondwana and assembled by the closure of multiple Tethyan and back-arc ocnow represented by suture zones. The continental core of Sundaland comprises a western Sibuand an eastern IndochinaEast Malaya block with an island arc terrane, the Sukhothai Island Arcomprising the Linchang, Sukhothai and Chanthaburi blocks sandwiched between. This island athe margin of IndochinaEast Malaya, and then separated by back-arc spreading in the PermianJinghong, NanUttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Palae

represented to the west by the ChangningMenglian, Chiang Mai/Inthanon and BentongRaubThe West Sumatra block, and possibly the West Burma block, rifted and separated from Gondwwith Indochina and East Malaya in the Devonian and were accreted to the Sundaland core in thWest Burma is now considered to be probably Cathaysian in nature and similar to West Sumatrit was separated by opening of the Andaman Sea basin. South West Borneo and/or East Java-are now tentatively identified as the missing Argoland which must have separated from NW Au

the Jurassic and these were accreted to SE Sundaland in the Cretaceous. Revised palaeogeogrreconstructions illustrating the tectonic and palaeogeographic evolution of Sundaland and adjacare presented.


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Hall, 2002


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5. ConclusionsThe Phanerozoic evolution of Sundaland and adjacent regions of SEAsia involved the rifting and separation of three collages ofcontinental terranes (probably as elongate slivers) from easternGondwana and the successive opening and closure of three ocean

basins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys.The Palaeo-Tethys is represented in Sundaland by the Inthanon(Chiang Mai), Chanthaburi (cryptic) and BentongRaub Suture Zones.The Sukhothai Island Arc System, including the Linchang,Sukhothai and Chanthaburi Terranes is identified between theSibumasu and IndochinaEast Malaya terranes in Sundaland andwas constructed on the margin of IndochinaEast Malaya andseparated by back-arc spreading in the Permian. The Jinghong, Nan

Uttaradit and Sra Kaeo Sutures represent the closed back-arc ocean.The West Sumatra and West Burma blocks rifted and separatedfrom Gondwana, along with Indochina and East Malaya in theDevonian and formed a composite terrane Cathaysialand withSouth China in the Permian.In the Late PermianEarly Triassic, West Sumatra and West Burmawere translated westwards to their positions outboard of Sibumasu bystrike-slip translation at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates.The continental micro-blocks that rifted and separated fromGondwana in the Jurassic are here identified as East Java, Bawean,Paternoster, West Sulawesi, Mangkalihat and SW Borneo. The EastJava, Bawean, Paternoster, West Sulawesi, Mangkalihat compriseArgoland, derived from the Exmouth Plateau region of westernAustralia, and SW Borneo comprises the Banda block derived from the

Banda embayment region of western Australia. These were accretedto SE Sundaland in the Late Cretaceous.


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ABSTRAKNewly pre-stack depth-migrated seismic images resolve the structural details of the western

plate interface. The structural segmentation of the forearc into discrete mechanical domainsdistinct deformation styles. Approximately 2/3 of the trench sediment fill is detached and incfrontal prism imbricates, while the floor sequence is underthrust beneath the dcollement. Whowever, differs markedly from margins such as Nankai or Barbados, where a uniform, contidcollement reflector has been imaged. In our study area, the plate interface reveals a spatinonlinear pattern characterized by the morphological relief of subducted seamounts and thic

average patches of underthrust sediment. The underthrust sediment is associated with a lodetermined from wide-angle data. Active underplating is not resolved, but likely contributes tthe large bivergent wedge that constitutes the forearc high. Our profile is located 100 km weJava tsunami earthquake. The heterogeneous dcollement zone regulates the friction behasubduction environment where the earthquake occurred. The alternating pattern of enhancecontact zones associated with oceanic basement relief and weak material patches of undertinfluences seismic coupling and possibly contributed to the heterogeneous slip distribution.

images resolve a steeply dipping splay fault, which originates at the dcollement and terminfloor and which potentially contributes to tsunami generation during co-seismic activity. 2009 Elsevier B.V. All


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Koop, 2009


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4. ConclusionsThe re-processed and newly pre-stack depth-migrated profileacross the western Java margin images the structural segmentation ofthe forearc and provides an account of the kinematic evolution of thesubduction complex. The complex plate interface is characterized bylocal morphologic structure and underthrust sediment patches, whichlikely influence the frictional properties of the shallow megathrustzone. Compared to other dcollement zones in large accretionarysystems (e.g. Barbados (Westbrook et al., 1988), Cascadia (Adam et al.,2004) or Nankai (Bangs et al., 2004)), the Java case shows a nonuniformcharacter of irregular thickness (Figs. 2 and 3). Unlike for the

well-studied Barbados or Nankai margins, for which a remarkableimaging quality has been documented (e.g. Bangs et al., 1999, 2009),the western Java data are not sufficient to quantify physical propertychanges along the dcollement. The seismic images of the spatiallyvariable, nonlinear pattern of the dcollement zone, however, supportthe inference that differential friction along this margin segment mayinfluence earthquake seismogenesis. The splay fault system, which

serves as a mechanical boundary between the inner and outerwedges, potentially transfers slip to the seafloor (Kame et al., 2003).This thrust fault connects to the dcollement at a depth ofapproximately 12 km, rising to the seafloor where it reaches itssteepest slope, thus potentially causing significant vertical displacementof the seafloor as often associated with tsunami generation. The

2006 tsunami earthquake occurred 100 km east of our line andunderscores the persistent seismic and tsunamigenic hazard of this


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Hall & Morley, 2004

Geografi PaparanSunda


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Hall, 2009


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Clements et al 2009


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Awang Satyana, 2007

Analisis struktur Pulau Jawa


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(Smyth et al, 2007)


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Macpherson & Hall, 1999


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(Smyth et al, 2007)


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(Smyth et al, 2008)


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(Smyth et al, 2008)


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(Smyth et al, 2008)

KS

JH


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S i fi P S l K d d R b


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Southern Mountains Zone Kendeng Zone Rembang Zone

Smyth et.al., 2005

Stratigrafi zona Pegunungan Selatan, Kendeng dan Rembang


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(Smyth et al, 2008)

a record of a cycle of arc activity from initiation in the middle


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a record of a cycle of arc activity from initiation in the middleEocene (ca. 42 Ma) to termination in the early Miocene(ca. 20 Ma). The Kendeng Basin, directly behind the SouthernMountains Arc, contains >6 km of volcaniclastic and sedimentaryrocks. The basin is not a typical backarc basin, and its subsidencehistory is linked to volcanic activity within the SouthernMountains Arc.

The fi nal stage of volcanic activity in the Southern MountainsArc is marked by the Semilir Eruption (ca. 20 Ma), whichdistributed ash over a wide area and may be comparable to thePleistocene eruption of Toba in Sumatra. Following this phase ofmajor eruptions, there was a lull in volcanic activity during themiddle Miocene, followed by resumption in arc activity to thenorth of the Southern Mountains Arc, along the axis of the modern

Sunda Arc during the late Miocene. The mechanisms thatresulted in the decline in volcanism, and northward movement inarc axis, are not yet understood and show that our understandingof arcs is still incomplete.The stratigraphic record of volcanic arcs can provide insightsinto the character of the deep crust. The entire East Java regionwas previously thought to be underlain by Cretaceous arc andophiolitic fragments, but Archean to Cambrian zircons within

acidic products of the Southern Mountains Arc point to theoccurrence of a continental crust of Gondwanan character andwestern Australian origin beneath the old arc. This continentalfragment is thought to have collided with Sundaland during theCretaceous and is interpreted to have terminated the Cretaceousphase of subduction. The extent of this fragment is not knownbut may be traceable into Sulawesi. The use of inherited zircons

to determine the character of the deep crust may be applicable inother arcs.


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ABSTRACT: Java is part of a volcanic island arc situated in the Indonesianarchipelago at the southern margin of the Eurasian Plate. Sundaland continentalcrust, accreted to Eurasia by the Early Mesozoic, now underlies the shallow seas tothe north of Java where there has been considerable petroleum exploration. Java hasan apparently simple structure in which the eastwest physiographic zones identifiedby van Bemmelen broadly correspond to structural zones. In the north there is the

margin of the Sunda Shelf and, in southern Java, there are Cenozoic volcanic arcrocks produced by spatially and temporally discrete episodes of subduction-relatedvolcanism. Between the Sunda Shelf and the volcanic rocks are Cenozoic depocentresof different ages containing sedimentary and volcanic material derived fromnorth and south. This simplicity is complicated by structures inherited from theoldest period of subduction identified beneath Java, in the Cretaceous, by extensionrelated to development of the volcanic arcs, by extension related to development ofthe Makassar Straits, by late Cenozoic contraction, and by cross-arc extensionalfaults which are active today. Based on field observations in different parts of Java,we suggest that major thrusting in southern Java has been overlooked. The thrustinghas displaced some of the Early Cenozoic volcanic arc rocks northwards by 50 kmor more. We suggest Java can be separated into three distinct structural sectors thatbroadly correspond to the regions of West, Central and East Java. Central Javadisplays the deepest structural levels of a series of north-directed thrusts, andCretaceous basement is exposed; the overthrust volcanic arc has been largely

removed by erosion. In West and East Java the overthrust volcanic arc is stillpreserved. In West Java the arc is now thrust onto the shelf sequences that formedon the Sundaland continental margin. In East Java the volcanic arc is thrust onto athick volcanic/sedimentary sequence formed north of the arc in a flexural basin duelargely to volcanic arc loading. All the components required for a petroleum systemare present. This hypothesis is yet to be tested by seismic studies and drilling, but, ifcorrect, there may be unexplored petroleum systems in south Java that are worthinvestigating.

Clements et al 2009


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Clements et al 2009


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Clements et al 2009


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fragment with the JavaMeratus subduction system, subduction


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g y ,ceased and there was a passive margin south of Java until theEocene (Fig. 10). In the Middle Eocene, subduction resumedand a new arc developed south of the Sunda Shelf. The load ofvolcanoes contributed to the development of a flexural basinbetween the arc and the shelf that was between 50 km and100 km wide, and followed the shelf edge running ENE the

length of Java. From the Late Eocene to Early Miocene thebasin was supplied with quartz-rich clastic sediments by riversdraining the Sunda Shelf in West and Central Java, withsubordinate amounts of volcanic debris supplied from the arcvolcanoes, which were largely submarine and non-explosive. InEast Java, volcanoes were emergent earlier and erupted explosivelyand supplied greater amounts of volcanic debris to the

basin to the north. Arc activity ceased for a period in the EarlyMiocene and resumed again in the Late Miocene at a locationnorth of the site of the Palaeogene arc. At some time betweenthe Early Miocene and Pliocene, the Palaeogene sequence wasthrust northwards, by more than 50 km in West Java, but withprobably much smaller displacements in East Java. Java can beseparated into three structural sectors of West, Central and EastJava. Central Java displays the deepest structural levels of

thrusting and Cretaceous basement is exposed; the overthrustvolcanic arc has been largely removed by erosion but may bepresent to the south of Java. In West and East Java theoverthrust volcanic arc is still preserved. In West Java the arc isnow thrust onto the shelf sequences that formed on theSundaland continental margin. Northward thrusting of thePalaeogene volcanic arc rocks of the Southern Mountains

offers a simpler explanation than autochthonous models for stratigraphicand structural relationships in southern Java. Overthrusting


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Setiadji et al, 2006


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Setiadji et al, 2006 vide Budiman et al, 2000

suggest two orogenic events during the Neogene, i.e.,


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in Upper Miocene and Plio-Pleistocene. These compressiveevents created a major backthrust (the Barabis-Kendeng thrust) which can be traced from the SundaStrait eastwards across Java (Simandjuntak and Barber,1996).The main structural features of Java are shown onFigure 2 and are summarized as follows. Besides thebackarc thrust of Barabis-Kendeng fault, there are threemain strike-slip faults found in Java. In western Java,the still active NE-SW Cimandiri fault crosscuts the

whole of west Java. Another strike-slip fault, namely theCitandui fault, occurs in western Java and trends NWSE.This old and inactive fault was interpreted fromgravity data (Untung and Sato, 1978). The third systemoccurs in central Java, namely the Central Java fault as aNE-SW left-lateral strike-slip fault which crosscuts the

whole island (Simandjuntak and Barber, 1996). The 27 May 2006 earthquakYogyakarta regionand killed almost 5,000 people is likely to be associatedwith this fault system. On the Java Sea part, there aremany petroleum sub basins and basement highs controlledby NE structures. Meanwhile, the Sunda Strait has been

experiencing crustal opening since 2 Ma and related volcanicactivit since 1 Ma Nishimura et al. 1986 .

al, 2006

of island arc magmas in Java is illustrated in Figure 12.The main magma source in Java is considered partial


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The main magma source in Java is considered partialmelting of mantle wedge, triggered by hydrous fluidsreleased from the dehydrated slabs. In many places partialmelting occurred at several different depths producingdouble volcanic chains. The primary magma compositionis basalt, with K2O contents increasing to the deeper meltingpoint (backarc-side). During migration to upper

crustal levels, the primary parental basalts are modified byfractional crystallization, accumulation, and crustal assimilation.The presence of adakitic rocks that occur erraticallyamong other normal island arc rocks but systematically occur only

in central and east Java demonstrates thatanother type of primary magma is present in eastern Java.This magma has an original intermediate composition andis generated by partial melting of basaltic source ratherthan mantle peridotite. There are still two possible sources

of adakitic magmas in eastern Java: a hot subductedoceanic plate and/or basalt underplate. The clues for thefirst option come from the geodynamic reconstruction ofJava (Hall, 2002) that suggested the presence of an activespreading center between Indian and Australian plates andbeing subducted somewhere in eastern part of Java islandsince the initiation of Java trench 50 to 40 Ma (Fig. 13).This model implies the presence of relatively young (hot)basalt being subducted at Java trench even for todays

standard (


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Abstract H.R. Smyth et al 2007Inherited zircons in Cenozoic sedimentary and igneous rocks of East Javarange in age from Archean to Cenozoic. Thedistribution of zircons reveals two different basement types at depth. Theigneous rocks of the Early Cenozoic arc, found along thesoutheast coast, contain only Archean to Cambrian zircons. In contrast,clastic rocks of north and west of East Java containCretaceous zircons, which are not found in the arc rocks to the south. Thepresence of Cretaceous zircons supports previousinterpretations that much of East Java is underlain by arc and ophioliticrocks, accreted to the Southeast Asian margin duringCretaceous subduction. However, such accreted material cannot accountfor the older zircons. The age populations of Archean toCambrian zircons in the arc rocks are similar to Gondwana crust. We

interpret the East Java Early Cenozoic arc to be underlain by acontinental fragment of Gondwana origin and not Cretaceous material aspreviously suggested. Melts rising through the crust,feeding the Early Cenozoic arc, picked up the ancient zircons throughassimilation or partial melting. We suggest a WesternAustralian origin for the fragment, which rifted from Australia during theMesozoic and collided with Southeast Asia, resulting inthe termination of Cretaceous subduction. Continental crust was thereforepresent at depth beneath the arc in south Java whenCenozoic subduction began in the Eocene.

2007 Elsevier B.V. All rights reserved


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Smyth et.al., 2007


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Smyth et.al., 2007

Perbandingan data set umurmineral zirkon (CambrianArchaean) Jawa Timurdengan Perth Basin dan North

Borneo


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Hall 2008 dimodifikasi dari Smyth et.al., 2007


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Smyth et.al., 2007


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Smyth et.al., 2007

P b k


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Penampang tumbukanfragmen benua terhadapsundaland

Smyth et.al., 2007


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7. ConclusionsThis is the first firm evidence of a Gondwana continentalfragment in this part of Southeast Asia. Prior tothis study little was known about the character of thecrust beneath much of Java and in particular nothing was

known about the crust beneath the Paleogene arc. Thecontinental fragment beneath the Southern Mountains ofEast Java was identified by the distribution of ancientzircons in the Cenozoic igneous and sedimentary rocks.UPb dating of zircons from East Java has alloweddistinct basement types to be mapped. In the north and

west there is Cretaceous accreted arc and ophioliticmaterial and in the south along the Southern MountainsArc there is compelling evidence for a fragment ofGondwana continental crust. The rising Cenozoic meltsfeeding the Southern Mountains Arc mixed with thecontinental crust and picked up ancient zircons throughassimilation or partial melting. This fragment could be

large and may extend beneath Sulawesi.The zircons dated in southeast Java are very similarin age to those of the Gondwana terranes of India andAustralia. Mesozoic reconstructions of the region showa history of Mesozoic rifting of Gondwana fragmentsfrom northwest Australia and this is thought to be theultimate source of the zircons in the igneous and sedimentaryrocks of East Java.


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(Whitaker et al, 2007)


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4. Conclusions (whitaker 2007)Upper plate strain expected for Sundaland back-arcregions fromreconstructed trench-normal plate motions of

the Sundaland core and margin correlate well with knownupper plate strain regimes. The three types of upper platemotion to affect the Sundaland margin since 80 Ma are:(1) A consistently advancing upper plate correspondsto compression in the overriding back-arc, causedby the collision between the down-going Indian

plate and the advancing Sundaland plate,(2) An advancing upper plate, where the Sundalandmargin advances more rapidly than the Sundalandcore, correlates with extension in the upper plate e.g.southern Andaman Sea, Sumatra and Java at 3015 Ma, 3515, and 4515 Ma, respectively. The

only mechanism for the margin to advance fasterthan the core is pulling by subduction hinge rollback,(3) Uniform upper plate retreat correlates withextension in the upper plate in two cases, Javanesecrustal extension 6050 Ma, and spreading in theAndaman Sea 150 Ma.


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Abstrak Metclafe, 2011Sundaland comprises a heterogeneous collage of continental blocks derived from the IndiaAustralian

margin of eastern Gondwana and assembled by the closure of multiple Tethyan and back-arc ocean basinsnow represented by suture zones. The continental core of Sundaland comprises a western Sibumasu blockand an eastern IndochinaEast Malaya block with an island arc terrane, the Sukhothai Island Arc System,comprising the Linchang, Sukhothai and Chanthaburi blocks sandwiched between. This island arc formed onthe margin of IndochinaEast Malaya, and then separated by back-arc spreading in the Permian. TheJinghong, NanUttaradit and Sra Kaeo Sutures represent this closed back-arc basin. The Palaeo-Tethys isrepresented to the west by the ChangningMenglian, Chiang Mai/Inthanon and BentongRaub Suture Zones.

The West Sumatra block, and possibly the West Burma block, rifted and separated from Gondwana, alongwith Indochina and East Malaya in the Devonian and were accreted to the Sundaland core in the Triassic.West Burma is now considered to be probably Cathaysian in nature and similar to West Sumatra, from whichit was separated by opening of the Andaman Sea basin. South West Borneo and/or East Java-West Sulawesiare now tentatively identified as the missing Argoland which must have separated from NW Australia inthe Jurassic and these were accreted to SE Sundaland in the Cretaceous. Revised palaeogeographicreconstructions illustrating the tectonic and palaeogeographic evolution of Sundaland and adjacent regionsare presented.


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(Metclafe, 2006)


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(metclafe 2006)


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(metclafe 2011)


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(metclafe, 2011)


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5. ConclusionsThe Phanerozoic evolution of Sundaland and adjacent regions of SE


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Asia involved the rifting and separation of three collages ofcontinental terranes (probably as elongate slivers) from easternGondwana and the successive opening and closure of three oceanbasins, the Palaeo-Tethys, Meso-Tethys and Ceno-Tethys.The Palaeo-Tethys is represented in Sundaland by the Inthanon

(Chiang Mai), Chanthaburi (cryptic) and BentongRaub Suture Zones.The Sukhothai Island Arc System, including the Linchang,Sukhothai and Chanthaburi Terranes is identified between theSibumasu and IndochinaEast Malaya terranes in Sundaland andwas constructed on the margin of IndochinaEast Malaya andseparated by back-arc spreading in the Permian. The Jinghong, NanUttaradit and Sra Kaeo Sutures represent the closed back-arc ocean.The West Sumatra and West Burma blocks rifted and separated

from Gondwana, along with Indochina and East Malaya in theDevonian and formed a composite terrane Cathaysialand withSouth China in the Permian.In the Late PermianEarly Triassic, West Sumatra and West Burmawere translated westwards to their positions outboard of Sibumasu bystrike-slip translation at the zone of convergence between the Meso-Tethys and Palaeo-Pacific plates.

The continental micro-blocks that rifted and separated fromGondwana in the Jurassic are here identified as East Java, Bawean,Paternoster, West Sulawesi, Mangkalihat and SW Borneo. The EastJava, Bawean, Paternoster, West Sulawesi, Mangkalihat compriseArgoland, derived from the Exmouth Plateau region of westernAustralia, and SW Borneo comprises the Banda block derived from theBanda embayment region of western Australia. These were accretedto SE Sundaland in the Late Cretaceous.


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Hall, 2008

Borneoand West Sulawesi (Parkinson et al., 1998). However,


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outboard of this ophiolitic zone, East Java and West Sulawesi(Fig. 8) are interpreted to be underlain in part by Archean continentcrust. Geochemistry (Elburg et al., 2003) and zircondating (Smyth et al., 2007; van Leeuwen et al., 2007) indicate

that underlying crust formed part of a block rifted from thewest Australian margin (Fig. 9). It is not possible to excludethe possibility that zircons are recycled from clastic sedimentsderived from Archeancrust, as is the case for parts of westAustralia, but these would presumably rest on Precambrian

basement, and relatively few Proterozoic zircons have beenfound in East Java. At present, bearing in mind that fewzircongeochronological studies have been carried out in Indonesia,arrival of a block of Archean continental crust is the simplestexplanation for the zircon ages, geochemistry and LateCretaceoustermination of subduction at the Sundaland activemargin. Thus, following collision of this block, Sundaland hadthe form shown in Fig. 7 at the beginning of the Cenozoic

nown a ou e e ec o ese o er p a eboundaries on the intraplate stress field in


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the region. Wecompile the first extensive stress datasetfor Southeast Asia, containing 275 ADquality (177 AC) horizontal

stress orientations, consisting of 72 stressindicators from earthquakes (locatedmostly on the periphery ofthe plate), 202 stress indicators frombreakouts and drilling-induced fracturesand one hydraulic fracture test

within 14 provinces in the plate interior.This data reveals that a variable stresspattern exists throughoutSoutheast Asia that is largely inconsistentwith the Sunda plate's approximately ESEabsolute motion

direction. The present-day maximumhorizontal stress in Thailand, Vietnam andthe Malay Basin ispredominately northsouth, consistent withthe radiating stress patterns arising fromthe eastern Himalayansyntaxis. However, the present-day


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Luschen et al 2010


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The subduction of the Indo-Australian plate along the Java Trenchis active since the late Oligocene (e.g. Hamilton, 1979). The overridingplate is continental including Sumatra and western Java (Kopp et al.,2001) and the basement below the forearc basin offshore Bali and

Lombok is probably rifted crust of continental character in transitionto oceanic character at Sumbawa and further east (Banda Sea) (Vander Werff, 1996).The convergence rate increased from 5 cm/a to7 cm/a during the last 10 Ma (7.3 cm/a today according to the globalvelocity model MORVEL, DeMets et al., 2010) and is almostperpendicular to the Java Trench, in contrast to oblique convergence

offshore Sumatra, where plate motion is partitioned into thrust andstrike-slip movements. The volcanism of the island arc was initiatedduring the Pliocene and changes from an intermediate compositionon East Java to a mafic composition on Sumbawa, which documents atransition from a continental to an oceanic overriding upper plate(Hamilton, 1988). The present-day configuration of plate boundariesin South-East Asia shows a quite complex history of interaction of thePacific, the Indo-Australian and the Eurasian plate. Reconstructions

and modelling by Hall (2002, with a comprehensive literature list)and Hall and Smyth (2008) suggest major plate reorganisations at 45,25 and 5 Ma.


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Since about 1500 km of oceanic plate have been subductedalready, a continued process as described may have formed thebasement of the outer arc high, the forearc basin as well as thebasement of the island arc east of Java, composed of ophiolite sheetsand napes as described e.g.

These blank zones justabove the basement are a widespread phenomenon in our study area.The involved fluids may originate from dewatering of subductedoceanic sediments pervading the basin basement. In this case it seemsto be a continuing process, instead of a cyclic one as observedfrequently in the Barbados accretionary prism (Deville et al., 2006). Asimilar situation is known as the catastrophic East Java mud volcano(Davies et al., 2008). Since most of the oceanic sediments of the Argo

Abyssal Plain are subducted (and partly recycled within the outer archigh), the amount of subducted seawater must be relatively high6. ConclusionsSeismic images of unprecedented resolution and depth penetrationhave been collected during cruise SO190 in the eastern Sundaforearc at the transition from an oceanic-island arc subduction regime to a continental-island arc collision regime in the western Banda arc


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SUMMARYThe region offshore Eastern Java represents one of the few places where the early stage ofoceanic plateau subduction is occurring. We study the little investigated Roo Rise oceanicplateau on the Indian plate, subducting beneath Eurasia. The presence of the abnormal bathyme

features entering the trench has a strong effect on the evolution of the subduction system,and causes additional challenges on the assessment of geohazard risks. We present integratedresults of a refraction/wide-angle reflection tomography, gravity modelling, and multichannelreflection seismic imaging using data acquired in 2006 south of Java near 113E. Thecomposite structural model reveals the previously unresolved deep geometry of the oceanicplateau and the subduction zone. The oceanic plateau crust is on average 15 km thick andcovers an area of about 100 000 km2.Within our profile the Roo Rise crustal thickness rangesbetween 18 and 12 km. The upper oceanic crust shows high degree of fracturing, suggestingheavy faulting. The forearc crust has an average thickness of 14 km, with a sharp increase to33 km towards Java, as revealed by gravity modelling. The complex geometry of the backstopsuggests two possible models for the structural formation within this segment of the margin:either accumulation of the Roo Rise crustal fragments above the backstop or alternativelyuplift of the backstop caused by basal accumulation of crustal fragments. The subducting

plateau is affecting the stress field within the accretionary complex and the backstop edge,which favours the initiation of large, potentially tsunamogenic earthquakes such as the 1994Mw = 7.8 tsunamogenic event


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4 CONCLUSIONThe summary of our results is shown in Fig. 9. In the 113E segmentof the Java trench, we observe the approach of the oceanicplateau Roo Rise to the trench and the effects it causes on the local


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plateau Roo Rise to the trench, and the effects it causes on the localsubduction regime.The Roo Rise is characterized by variable crustal thickness rangingfrom 18 to 12 km and shallowing towards Java. It extends laterallyfor at least 70 km within our profile (Fig. 2). Based on thebathymetric data and its link to the presence of a deep compensating

crustal root, the thickened oceanic plateau crust with an averagethickness of about 15 km is expected to cover an area of approximately100 000 km2 (200 km 500 km) offshore Central-EasternJava. The transition to normal oceanic crust is not well defined,but the plateau can extend into the subduction system up to 60 kmnorthward from the trench.The structure of the upper crust of the incoming oceanic plateshows a high degree of fracturing in its top section. This fracturing isclearly visible in the high-resolution bathymetry and MCS transect

down to 2 km below the top of the crust (Fig. 8). It is possible thatthe crust is cut by faults even to a greater depth, as indicated bythe low mantle velocities that require fluid percolation (Carlson &Miller 2003), and by an increased level of shallow crustal seismicity(Abercrombie et al. 2001; Bilek & Engdahl 2007).Within our profiles, we do not recover any direct evidence for thepresence of the bathymetric features on the oceanic plate currentlypresent below the accretionary prism. Depth variations of the basementobserved on the trench-parallel profile, may serve as evidence

for bathymetric features associated to the RooRise.Gravity modelling requires a sharp crustal thickness increasebelow Java. As the region is not covered with seismic data, we canonly speculate on the origin of this crustal structure. The thick crustcan be a part of the Gondwana revenue as suggested by Smyth et al.(2007).The approach of the Roo Rise to the trench has strong effects onthe local seismicity setting. The geohazard risks should be reconsideredas this segment of the margin has an increased probabilityfor tsunamogenic earthquakes.


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Kesimpulan


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Kesimpulan

Kapur Akhir

Penunjaman Lempeng Benua Australian dengan Sundaland

Di sebelah timur Jawa terjadi tumbukan mikrokontinen Godwana danberakhirnya jalur subduksi Kapur

Paleogen

Eosen Tengah penunjaman di selatan Jawa mulai aktif lagi, dengan ditandaiadanya busur vulkanik di Jawa dengan arah Barat Timur

Terbentuk cekungan flexural di Tengah Jawa antara lain CekunganCimandiri, Cekungan Karangsambung dan Cekungan Kendeng


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Neogen

Penunjaman terus berlanjut

Pusat vulkanik bergeser ke arah utara

Pengisian cekungan

Batuan Dasar, berdasarkan penentuan umur mineral zirkon

Jawa Barat bagian Utara = Kerak kontinen Sundaland

Jawa Barat bagian Selatan = Melange dari busur akresi

Jawa Timur bagian Utara = Melange dari busur akresi

Jawa Timur bagian Selatan = Mikrokontinen Godwana

Selamat Tinggal


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Selamat Tinggal

TerimaKasih


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geotektonik jawa_2010_2011

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