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Jurnal Geologi Indonesia, Vol. 5 No. 3 September 2010: 197-207 Indonesian Landforms and Plate Tectonics H. TH. VERSTAPPEN The International Institute for Geo-Information Science and Earth Observation (ITC), Enschede, the Netherlands, Mozartlaan 188, 7522HS ABSTRACT The horizontal con¿guration and vertical dimension of the landforms occurring in the tectonically unstaEle parts of ,ndonesia were resulted in the ¿rst place from plate tectonics. 0ost of them date from the 4uaternary and endogenous forces are ongoing. Three maMor plates ± the northward moving ,ndo- Australian 3late, the south-eastward moving SE-Asian 3late and the westward moving 3aci¿c 3late - meet at a plate triple-Munction situated in the south of 1ew Guinea‘s Bird‘s Head. The narrow 1orth-0oluccan plate is interposed Eetween the Asia and 3aci¿c. ,t tapers out northward in the 3hilippine 0oEile Belt and is gradually disappearing. The greatest relief amplitudes occur near the plate Eoundaries: deep ocean trenches are associated with subduction zones and mountain ranges with collision belts. The landforms of the more stable areas of the plates date back to a more remote past and, where emerged, have a more subdued relief that is in the ¿rst place related to the resistance of the rocNs to humid tropical weathering Rising mountain ranges and emerging island arcs are suEMected to rapid humid-tropical river erosions and mass movements. The erosion products accumulate in adMacent sedimentary Easins where their increasing weight causes suE- sidence Ey gravity and isostatic compensations. /iving and raised coral reefs, volcanoes, and fault scarps are important geomorphic indicators of active plate tectonics. Compartmental faults may strongly affect island arcs stretching perpendicular to the plate movement. This is the case on Java. Transcurrent faults and related pull-apart basins are a leading factor where plates meet at an angle, such as on Sumatra. The most complicated situation exists near the triple-Munction and in the 0oluccas. 0odern research methods, such as GPS measurements of plate movements and absolute dating of volcanic outbursts and raised coral reefs are important tools. The mega-landforms resulting from the collision of India with the Asian continent, around 50.0 my. ago, and the ¿nal collision of Australia with the 3aci¿c, aEout 5.0 my. ago, also had an important impact on geomorphologic processes and the natural environment of SE-Asia through changes of the monsoonal wind system in the region and of the oceanic thermo-haline circulation in eastern ,ndonesia Eetween the 3aci¿c and the ,ndian ocean. ,n addition the landforms of the region were, of course, affected Ey the 4uaternary gloEal climatic fiuctuations and sea level changes. Keywords: mega landforms, morphostructures, plate tectonics, Indonesia SARI Kon›gurasi horisontal dan dimensi vertikal bentang alam terjadi di wilayah-wilayah Indonesia, yang secara tektonik tidak stabil terutama sebagai akibat dari pergerakan lempeng tektonik. Sebagian Eesar Eentang alam terseEut Eerumur .uarter dan dipengaruhi oleh gaya-gaya endogen. Tiga lempeng utama yaitu Lempeng Indo-Australia yang bergerak ke utara, Lempeng Asia Tenggara yang bergerak ke tenggara, dan Lempeng Pasi›k yang bergerak ke arah barat, bertemu pada satu simpang tiga (triple junction) yang terletak di selatan Kepala Burung, Papua. Lempeng Maluku Utara yang sempit menyisip antara Asia dan Pasi›k, Lempeng ini miring ke utara pada sabuk Filipina yang mobil dan berangsur menghilang. Amplitudo relief yang terbesar terjadi dekat batas-batas lempeng: parit laut dalam yang berasosiasi dengan zona subduksi dan MDMaran pegunungan dengan sabuk tumbukan. Bentang alam daerah-daerah yang lebih stabil terdapat pada lempeng yang berumur jauh lebih tua dan tempat pemunculannya mempunyai relief yang lebih mudah berubah. Hal ini berkaitan dengan resistensi batuan terhadap pelapukan tropis lembab. -DMaran pegunungan dan busur kepulauan yang Naskah diterima 30 Juli 2010, revisi kesatu: 04 Agustus 2010, revisi kedua: 31 Agustus 2010, revisi terakhir: 02 September 2010 197 198 Jurnal Geologi Indonesia, Vol. 5 No. 3 September 2010: 197-207 terbentuk, mengalami erosi yang cepat oleh sungai tropis lembab dan gerakan tanah. Produk erosi menumpuN di ceNungan sedimen yang terdeNat. 3eningNatan penyeEaran dan NeteEalan sedimen tersebut menyebabkan terjadinya terban oleh gravitasi dan kompensasi isostatik. Terumbu karang yang hidup dan tumEuh, gunung Eerapi dan gawir sesar merupaNan indiNator geomor¿N penting lempeng tektonik aktif. Bagian-bagian sesar mungkin sangat mempengaruhi busur kepulauan yang meregang tegak lurus terhadap pergerakan lempeng. Kasus ini terjadi di Pulau Jawa. Sesar mendatar dan cekungan-cekungan tarikan adalah faktor penciri adanya pertemuan lempeng yang menyudut satu sama lain, seperti halnya di Sumatra. Situasi paling rumit ditemukan di dekat persimpangan-tiga (triple junction) dan di Maluku. Metode penelitian modern, seperti pengukuran pergerakan lempeng dengan GPS dan pentarikhan absolut produk gunung api dan tumbuhnya terumbu karang merupakan cara yang penting. Mega-bentang alam akibat benturan India dengan Benua Asia, sekitar 50 jtl., dan akhir tumbukan Australia dengan Pasi›k, sekitar 5 jtl., juga memiliki dampak penting pada proses geomorfologi dan lingkungan alam di Asia Tenggara melalui perubahan sistem angin musiman di wilayah dan sirkulasi termo-haline samudera di Indonesia timur antara Pasi›k dan Samudra Hindia. Selain itu bentang alam wilayah ini, tentu saja, dipengaruhi oleh fiuktuasi iklim global Kuarter dan perubahan permukaan air laut. Kata kunci: mega bentang alam, struktur morfo, tektonik lempeng, Indonesia INTRODUCTION patterns of swamps and other characteristics of alluvial plains, coastal con¿guration, etc. The landforms of ,ndonesia and adMacent areas The three most important plates affecting the are strongly related to 4uaternary 3late tectonics. Indonesian region are the SE-Asian Plate, the Indo- This applies especially to the volcanic- and non- Australian 3late, and the 3aci¿c 3late. They can Ee volcanic island arcs of the archipelago (Hamilton, subdivided into a number of smaller Plates and meet 1979; Hall and Blundell, 1996; Gupta, 2003). at a triple Munction situated south of 1ew Guinea‘s Their spatial distribution reveals the location of Bird‘s Head. ,n addition, the narrow 1orth 0oluccan suEduction- and collision zones caused Ey the Plate is interposed in the north between the Sulawesi lateral movement of a number of tectonic Plates. Sea Plate, an oceanic associate of the SE-Asian Plate, Most of these subduction- and collision zones are and the Philippine Sea Plate, a forerunner of the active and characterized Ey great suE-marine and 3aci¿c 3late. They Eoth suEduct under the 1orth- suE-aerial relief amplitudes that have strongly Moluccan Plate (Kreemer et al., 2000). This plate increased during the 4uaternary. Emerged island tapers out northward in the 3hilippine 0oEile Belt arcs and rising mountain ranges are suEMected to that extends up to Taiwan. (Figure 1) Active subduc- intense humid-tropical weathering processes, river tion zones form deep trenches with important nega- erosion and mass movements. The erosion prod- tive gravity anomalies. The three main ones are the ucts accumulate in adMacent sedimentary Easins trough situated south of the Sunda Arc and curving where their increasing weight causes subsidence up northward to the east of the Banda Arc, and the Ey gravity and isostatic compensation. The relief troughs occurring respectively to the east and west of amplitude of the Plates is much less and the land- the 1orth 0oluccan 3late / 3hilippine 0oEile Belt. forms of their emerged parts around the Sunda- and Active volcanism is associated with belts of Sahul/ Arafura shelves indicate an advanced stage ongoing Plate subduction. The longest row is that of development related to geological events of a connected with the subduction of the northward more remote past. The landforms in these parts of moving Indian Ocean Plate in Sumatra, Java, Nusa the country now refiect differences in resistance Tenggara and the SE-Moluccas. The volcanic activ- of the rocks to humid tropical weathering in the ity of this row is extinct only on the islands of Alor ¿rst place. Several geomorphic indicators exist for and Wetar, where Timor, an outpost of the Austra- detecting zones of neo-tectonics in the lowlands. lian continent, collides with it. Active volcanism They include drainage anomalies, distriEutional also accompanies the subduction zones situated Indonesian Landforms and Plate Tectonics (H. Th. Verstappen) 199 1000 E 110 0E 1200 E 1300 E 1400 E 1500 E nch N re u T ky Ryu 0 0 20 N ch 20 N n Tre P h PHILIPPINE SEA PLATE PHILI PI E MO LE BELiT a il Tre ch l i p n M n la n p i i n n SOUTH CHINA P N BI e Bo T SEA PLATE r e n c h na aria 10 0N M 10 0N PACIFIC PLATE SULU SEA PLATE N- O UC S M L CA SE S AIN PL TE -AA SULAWESI SEA PLATE Kalimantan CAROLINE PLATE uS am ALTPE 0 Sunda 0 0 tra 0 Belt S t u rren n nscu d Tra a Tr New Guinea enc h Triple Junction Jawa Jav Shelf 10 0S a Tre Sahul - arafura 100 S nch INDO - AUSTRALIAN PLATE 1000 E 110 0E 1200 E 1300 E 1400 E 1500 E Legend: Plate movement direction Figure 1. The plate-tectonic con›guration of Indonesia and surroundings (Katili, 1980). at both sides of the North Moluccan Plate, in the left-lateral Sorong - Koor fault zone stretching from 0inahasa and northern Halmahera respectively. the north coast of New Guinea to the Moluccas, These two volcanic arcs continue in the two paral- and the left-lateral Philippine fault zone that can be lel and closely spaced rows of active volcanoes in traced from northern Luzon up to Halmahera. The the 3hilippine 0oEile Belt (-avelosa, 1994). 9ol- Semangko zone is the scene of a number of pull- canism is extinct in western Sulawesi because the apart basins with related volcanic phenomena. The northward moving Australian 3late ElocNed 3aci¿c Sorong - .oor fault strongly affects the 0amEeramo suEduction already in the Tertiary.
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