Collaborative Research: Australia Down Under: Quantification of Rates and Amount of Continental Subduction During Neogene Arc-continent Collision on Timor

Brigham Young University, Provo UT

Investigators

Abstract

The objective of this project is to test whether arc-continent collision events modify overall convergence rates, with the island of Timor as test-case. The mountainous island of Timor exposes a tectono-stratigraphic section of a typical arc-continent collision, with elements from the overriding Asian oceanic/arc plate, a wedge of high pressure/low temperature metamorphic rocks and an underlying deformed Australian continental passive margin sedimentary sequence. An accurate geologic map of the Island, which describes the distribution of rock types and structures, will be produced that will form the basis for balanced structural cross-sections, which, in turn, will be used to quantify how much the sedimentary rocks once deposited on the margin have been telescoped during collision. The magnitude of shortening should correlate with the amount of continental crust that has been subducted. Paleomagnetic analysis is used to determine paleolatitude, rotation, and age of strata. High- to low-temperature thermochronologic data will document the magnitude, variability, and timing of exhumation. Shortly after the recognition of plate tectonics, the Wilson cycle was introduced in order to describe the creation and demise of ocean basins. The original four stages ? continental rifting, seafloor spreading and formation of ocean basins, closure of ocean basins by subduction of oceanic lithosphere, and continent-continent collision - still form a fundamental basis for our understanding of tectonic processes. Arc-continent collision marks the ultimate demise of an intra-oceanic subduction zone and is a common phenomenon during ocean closure. It is usually assumed that significant underthrusting of continental material under an oceanic island arc is inhibited by buoyancy but the magnitude of continental subduction remains unconstrained. This project will provide an estimate for the magnitude of continental crust that has been subducted, results that would have important implications for mantle chemistry and dynamics. The project involves a significant collaboration with researchers from Norway, Swiss, Australia, and Indonesia as well as training of U.S. and international students.