TECTONIC EVOLUTION OF THE SERAM TROUGH, INDONESIA

摘要

The Seram Trough is located in the northern part of the Banda Arc-Australian collision zone in eastern Indonesia and is currently the site of contraction between the Bird's Head and Seram. It has been interpreted as a subductibn trench, an intracontinental thrust zone and foredeep, and a zone of strike-slip faulting. Recently acquired 2D seismic lines help interpret its tectonic evolution. Folding in the Early Pliocene formed an anticlinorium between Misool and the Onin Peninsula of Irian Jaya. A newly recognised Pliocene angular unconformity truncates sediments as old as Middle Jurassic and is an ancient topographic surface with significant relief. It was later folded and now dips south towards the trough where it is covered by up to 3 km of sediments. Initial tilting of the unconformity surface was accompanied by deposition of a transgressive sequence which can be traced into the trough. This is overlain by two sequences which prograde towards the trough. These show progressive rotation of the unconformity surface, gravitational displacement of sediments into the trough, and thrusting which continues to the present day. Contraction occurred in the trough from the Early Pliocene and is younger than the previously suggested Late Miocene age. Thrust faults in the trough deform sediments deposited above the unconformity and detach at the unconformity surface. On Seram thrust faults repeat Mesozoic-Miocene sequences and probably detach at their contact with metamorphic basement. The detachment surface must cut through the Mesozoic-Miocene sequence between Seram and the trough. This work suggests the Seram Trough is not a subduction trench but a foredeep produced in response to loading by the developing fold and thrust belt of Seram, with an associated peripheral bulge to the north. The Seram Trough is interpreted to be a very young zone of thrusting within the Australian continental margin.