Mud Volcanoes, Shale Diapirs, Wrench Faults,
and Melanges in Accretionary Complexes,
Eastern Indonesia.,
A. J. Barber , S. Tjokrosapoetro , T. R. Charlton
B. AAPG Bulletin Volume 70, Issue 11. (November),
C. Pages 1729 - 1741 (1986)
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Di Timor, Indonesia timur, di mana tepian utara benua Australia bertumbukan dengan busur Banda (northern margin of the Australian continent is colliding with the Banda Arc), sedimen tepian benua Australia terlibat di dalam baji imbrikasi (imbricate wedge), yang melewati utara pada jalur lipatan depan daratan dan sesarnaik (foreland fold and thrust belt).
Pemetaan lapangan di Timor telah menunjukkan bahwa lempung bersisik (scaly clays) mengandung blok berbentuk tidak teratur atau phacoidal dengan panjang hingga beberapa meter dan terdiri dari berbagai satuan batuan, yang berasal dari unit stratigrafi lokal. Terjadi dalam tiga lingkungan: (1) bersama patahan transpresi (wrench faults), (2) sebagai
diapirs serpih yang memotong silang (crosscutting), dan terkait dengan gunung lumpur (mud volcano).
Sebuah model diusulkan menghubungkan fenomena ini. Serpih menjadi overpressure sebagai akibat dari overthrusting; overpressure ini dilepaskan bersama patahan geser vertikal, yang menembus unit overthrusthing; serpih overpressured mengandung blok unit konsolidasi meningkat pada zona sesar sebagai diapirs serpih dan keluarnya air, minyak, dan gas membangun mud volcano di permukaan.
Endapan melange berkembang sangat luas di Timor, disebut Lempung bersisik Bobonaro (Bobonaro scaly Clay), yang telah ditafsirkan oleh Audley-Charles dan peneliti berikutnya sebagai (olistostrom). Studi kami menafsirkan Bobonaro scaly Clay sebagai produk dari diapirisme serpih.
Diapir serpih kemungkinan akan dihasilkan di mana pun ketika air-sedimen yang jenuh terlibat ke dalam kompleks akresi (accretionary complexes). Namun, diapir telah terjadi di kompleks akresi purba (ancient accretionary complexes) tidak dicatat. Meskipun melanges, biasanya ditafsirkan sebagai olistostromes, umumnya dilaporkan.
Kriteria yang diusulkan dimana produk-produk diapirisme serpih mungkin dikenali, termasuk:
(1) bentuk tubuh diapir;
(2) hubungannya dengan batuan di sekitarnya;
(3) sifat dari matriks dan blok-block tertutup;
(4) bentuk-bentuk blok dan hubungannya dengan susunan matrik, dan
(5) pengaruh dari deformasi.
Pentingnya diapirism serpih dalam pembentukan melanges belum sepenuhnya dihargai, dan produk dari diapirism serpih merupakan komponen utama kompleks akresi purba dan masa kini.
In Timor, eastern Indonesia, where the northern margin of the Australian continent is colliding with the Banda Arc, Australian continental margin sediments are being incorporated into an imbricate wedge, which passes northward into a foreland fold and thrust belt.
Field mapping in Timor has shown that scaly clays, containing irregularly shaped or phacoidal blocks (up to several meters long) and composed of a wide range of lithologies derived from local stratigraphic units, occur in three environments: along wrench faults, as crosscutting shale diapirs, and associated with mud volcanoes.
A model is proposed linking these phenomena. Shales become overpressured as a result of overthrusting; this overpressure is released along vertical wrench faults, which cut through the ove thrust units; overpressured shales containing blocks of consolidated units rise along the
fault zones as shale diapirs; and escaping water, oil, and gas construct mud volcanoes at the surface.
An extensive melange deposit in Timor, the Bobonaro Scaly Clay, has been interpreted by Audley-Charles and subsequent workers as an olistostrome. Our study interprets the Bobonaro Scaly Clay as the product of shale diapirism.
Shale diapirs are likely to be generated wherever water-saturated sediments are incorporated into accretionary complexes. Diapirs have not, however, been recorded as occurring in ancient accretionary complexes, although melanges, usually interpreted as olistostromes, are commonly reported.
Criteria are proposed by which the products of shale diapirism might be recognized, including:
(1) shape of the diapiric body;
(2) its relationship to the surrounding rocks;
(3) nature of the matrix and of the enclosed blocks;
(4) shapes of the blocks and their relationship to he matrix; and
(5) effects of deformation.
The importance of shale diapirism in the formation of melanges has not been fully appreciated, and the products of shale diapirism constitute a major component of ancient and present-day accretionary complexes.