DEFORMASI KOMPLEKS DI PULAU SIMEULUE, SUMATRA: INTERAKSI ANTARA STRUKTUR DAN DIAPIRISME

Sonny Aribowo; Lina Handayani; Nugroho D. Hananto; Karit L. Gaol; Syuhada Syuhada; Titi Anggono

doi:10.14203/risetgeotam2014.v24.89

DEFORMASI KOMPLEKS DI PULAU SIMEULUE, SUMATRA: INTERAKSI ANTARA STRUKTUR DAN DIAPIRISME

Sonny Aribowo, Lina Handayani, Nugroho D. Hananto, Karit L. Gaol, Syuhada Syuhada, Titi Anggono

Abstract

The accretionary prism complex has unique morphological characteristic as a result of deformation and sedimentation processes that develop in the area. Simeulue Island is one example of the islands in the accretionary complex. Geological study was arranged to map geological structure and morphology of Simeulue Island by satellite images interpretation and field survey. We use Landsat TM 5, Landsat 8 and Aster-GDEM imageries for morphology and structural geology interpretation. The collision in the deformation front has generally developed reverse and thrust faults in the Simeulue Island. The north-northeast blocks tend to be higher than the south-southwest blocks. Based on imagery interpretation, the dominant thrusts are the trenchward-vergence thrusts. Measurement of structural features and folds reconstruction indicated the existence of the out-of-sequence thrusts, which might activated the arcward-vergence thrust. This arcward-vergence thrust could be interpreted as a backthrust fault of a backstop mechanism in the inner accretionary prism. The thrusts might be correlated to the mud diapirisms that were also found in some locations in the island. The finding of thrusts and mud diapirism traces concurred to the theory that the mélange complexes in subduction zones were formed through mud diapirism that facilitated by backthrust faults.

ABSTRAK

Kompleks prisma akresi memiliki karakteristik morfologi yang unik sebagai hasil dari proses deformasi dan sedimentasi yang berkembang di daerah tersebut. Pulau Simeulue merupakan salah satu contoh pulau yang terbentuk pada prisma akresi. Studi geologi dilakukan untuk menggambarkan keadaan struktur geologi yang terbentuk di Pulau Simeulue yang berhubungan dengan mekanisme pembentukan sesar-sesar anjak pada prisma akresi, pembentukan kompleks batuan bancuh dan mekanisme kubah lumpur. Morfologi dan struktur geologi Pulau Simeulue dipetakan melalui interpretasi citra dan survey lapangan. Citra yang digunakan dalam studi ini adalah citra Landsat TM5, Landsat 8 dan Aster-GDEM. Tumbukan di bagian muka deformasi mengakibatkan berkembangnya struktur berupa sesar-sesar naik dan anjak dimana di bagian utara-timurlaut cenderung lebih naik daripada bagian selatan-baratdaya. Berdasarkan hasil interpretasi citra, sesar-sesar yang berkembang tersebut umumnya merupakan sesar-sesar anjak berarah palung (trenchward-vergence thrusts). Berdasarkan hasil pengukuran fitur struktur di lapangan dan rekonstruksi lipatan di Pulau Simeulue, perkembangan struktur anjak juga terjadi secara out-of-sequence yang mengakibat-kan teraktifkannya sesar anjak berarah busur (arcward-vergence thrusts). Sesar anjak berarah palung dapat diinterpretasikan sebagai backthrust fault dari sebuah mekanisme backstop di bagian belakang prisma akresi. Sesar-sesar anjak ini dapat dikaitkan dengan keberadaan kubah lumpur (mud diapir) yang jejaknya juga ditemukan di beberapa lokasi di Pulau Simeulue. Hal-hal tersebut mendukung teori bahwa kompleks batuan mélange di Pulau Simeulue terbentuk melalui proses mud diapirism yang muncul melalui sesar-sesar anjak.

Keywords

Simeulue Island, mélange complex, accretionary prism, backthrust faults, mud diapir, subduction complex.

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DOI: http://dx.doi.org/10.14203/risetgeotam2014.v24.89