Surface uplift history of the incipient Banda arc-continent collision: Geology and synorogenic foraminifera of Rote and Savu Islands, Indonesia

摘要

Field mapping and analysis of foraminifera from synorogenic pelagic units of Rote and Savu Islands, Indonesia reveals high rates of surface uplift of the incipient Banda arc-continent collision during the past 1.8 myr. New geological maps of these islands document accretion to the Banda forearc of Triassic through Tertiary sedimentary cover units from the down-going Australian continental margin. Foraminifera-rich synorogenic deposits of the Batu Putih Formation unconformably overlie these accreted units. We use paleodepth versus time estimates from benthic and planktic foraminifera's to measure long-term surface uplift rates for the accretionary wedge. Although strong currents in the region cause some problems with reworking. several distinctive species have been found. Synorogenic deposits in Savu and Rote yield foraminifer's of biozone Neogene (N) 18 to N22 (5.6-1.0 myr) that were deposited at estimated depths of around 3000 m. These deposits are unconfomrably overlain by uplifted coral terraces. The highest coral terraces in Savu are >300 m above sea level and perhaps as old as 0.8 myr. In Rote the highest coral terrace is 200 above sea level and similar to 0.2 myr old. These data indicate that collision of the Australian continental margin with the Banda Arc, which initiated much earlier in Timor, has propagated westward towards Rote where it is in the initial stages of accretionary wedge emergence. Collision of the Scott Plateau propagated SE from Sumba (2-3 Ma) to Savu (1.0-0.5 Ma) and then to Rote (0.2 Ma). Average rates of surface uplift of the Batu Putih Formation pelagic deposits during the past 2 myr in Rote and Savu are similar to 1.5 and 23 mm/a, respectively. The rise of these islands is clogging the Indo-Pacific seaway.