VARIATION IN FORE-ARC BASIN DEVELOPMENT ALONG THE SUNDA ARC, INDONESIA

The present forearc basin configuration along the Sunda Are initially appears to have been controlled by extension and differential subsiden ce of basement blocks in response to the late Eocene collision of Indi a with Asia. The late Oligocene increase in convergence between the So uth-east Asian and Indian Plates associated with a new pulse of subduc tion, resulted in basement uplift and the formation of a regional unco nformity that can be recognized along the entire Sunda Are. From the e arly to late Miocene, the Sumba and Savu forearc sectors along the eas tern Sunda Are may have been characterized by forearc extension.Submar ine fan deposition on the arcward side of the evolving accretionary pr ism represents the first phase in forearc basin deposition. These fans were subsequently covered by basin and slope sediments derived from t he evolving magmatic are. Structural response to increased late Miocen e compression varied along strike of the Sunda Are. North of Pall, Lom bok and Sumbawa, the incipient collision between Australia and the wes tern Panda Are caused back-are thrusting and basin inversion. Towards the south of Java, an increase in both the size of the accretionary pr ism and convergence rates resulted in uplift and large scale folding o f the outer forearc basin strata. Along the west coast of Sumatra, inc reased compression resulted in uplift along the inner side of the fore arc along older transcurrent faults. Uplift of West Sumatra was follow ed by the deposition of a westward prograding sequence of terrigenous sediments that resulted in the development of a broad shelf. Initial f orearc basin subsidence relates to the age of the subducting oceanic l ithosphere, on top of which the basin is situated. Along the western S unda Are, both fexural loading of the evolving accretionary prism, and across are strike-slip faulting represent additional factors that res ult in forearc subsidence. (C) 1997 Elsevier Science Ltd. All rights r eserved.