Tectonic history of Sumba Island, Indonesia, since the Late Cretaceous and its rapid escape into the forearc in the Miocene

The island of Sumba lies within the Sunda-Banda forearc and contains volcanic, plutonic and volcaniclastic rocks that record a history of are volcanism extending from Late Cretaceous (similar to 80 Ma or earlier) to Oligocene (similar to 31 Ma) time. During the Late Cretaceous, Sumba formed part of a Great Indonesian Volcanic Are system near southeastern Eurasia. Between Late Cretaceous and Early Miocene time, Sumba remained part of that are system, which ceased to be volcanically active by similar to 31 Ma. During the Late Miocene (similar to 18 Ma), Sumba, as part of the relict are system, was situated near the present site of Alor and Wetar. At similar to 16 Ma, Sumba was torn from the relict are and began to move at a velocity of similar to 50 mm/yr in a west-south-westerly direction. Volcanism along the modern Bands Are soon followed. By similar to7 Ma, Sumba finally came to rest, after having moved similar to 450 km into the forearc. We interpret the rapid motion of Sumba into the forearc as a discrete block to have been a response to the collision between Australia and Indonesia in the area of Timer. The Savu Basin possibly originated as an arc-crestal rift which then opened behind Sumba as the latter moved westward. Over the past 16 My. more than 3 km of sediment have been deposited in the Savu Basin by erosion from the surrounding islands. Sumba stopped moving to the west-south-west at similar to7 Ma after reaching approximately its present location. Since then, the island has ceased to be a discrete tectonic fragment and has behaved as an integral part of the forearc. During the past similar to7 My, compressional tectonics within the forearc has led to elevation of the rocks exposed on Sumba by as much as 4 km. (C) 2001 Elsevier Science B.V.. All rights reserved.