Post-collision isostatic readjustment in the Southern Banda Arc

Abstract

Summary The collision between the Australian continent and island arcs marginal to SE Asia is currently taking place in the Banda Arc region, with some of the most intense deformation on, and around, the island of Timor. From Late Miocene to Mid-Pliocene times the area was dominated by a compressional tectonic regime which resulted in the emplacement from the N of large thrust sheets on the deformed Australian continental margin. During the last 3 Ma, however, compression seems to have been unimportant in the islands and vertical movements, both positive and negative; have been commonplace and rapid. Considerable departures from isostatic equilibrium are suggested by gravity surveys in the region and in some cases the sign of the isostatic anomalies accords well with the observed sense of vertical movement. In other areas, such as Northern Timor and the inner (volcanic) arc, uplift is occurring where the the gravity data suggest that there should be subsidence. A possible explanation is that a contribution to the high gravity values is made by a cold, and therefore dense, subducted slab which is now sinking independently after rupture near the continental margin. Because of the rupture, the sinking slab no longer exerts a downward pull on the overlying lithosphere which has thus been freed to rebound isostatically.