EVIDENCE OF RAPID TECTONIC UPLIFT IN EAST NEW BRITAIN, PAPUA NEW GUINEA

We present evidence of rapid uplift along the eastern coast of New Britain, Papua New Guinea (PNG) based upon U/Th dating of uplifted Holocene coral reefs. New Britain is one of a group of islands making up the nation of PNG in the western Pacific Ocean and resides on the South Bismarck plate. The western portion of the South Bismarck plate is colliding with and overriding the northern Australian plate margin; the eastern portion is overriding the Solomon Sea plate. The western portion of the South Bismarck plate includes the island of New Guinea and the Huon Gulf. On the island of New Guinea, the Huon-Finisterre Mountains and uplifted Huon Peninsula result from the collision. To the east, the Solomon Sea plate is subducting rapidly beneath the New Britain Trench and this subduction is thought to be responsible for the active volcanism on the island of New Britain, particularly along the northern coast. Although uplift rates of the nearby Huon Peninsula are well constrained (~2-3 m/ka; Chappell et al., 1996) and the horizontal component of plate motion is described in Wallace et al. (2004), little is known about vertical motion along the eastern margin of New Britain. Based upon sea-level curves for Papua New Guinea (Lambeck and Chappell, 2001), present sample elevations, and preliminary estimates of paleowater depth (~<2 m) of two in-situ Porites lutea corals dated at 8.6 +/-0.1 ka (δ²³⁴U_i 148.2) and 9.0+/-0.2 ka (δ²³⁴U_i 147.6), we calculate a minimum mean uplift rate of 2 m/ka for east coast of New Britain. The fact that the uplift rate on at least part of New Britain, well east of the zone of continental collision, is similar to those rates measured on the Huon Peninsula raises major questions concerning the driving mechanism for uplift of New Britain.