Zhang, Ping1, Miller,As.Prof Meghan1
1Australian National University, Canberra, Australia
The active arc-continent collision in the Banda Arc is a result of convergence of the Indo-Australian plate with the Eurasian plate in Southeast Asia. There, the subduction of the Cretaceous to Jurassic age Indian Ocean lithosphere along the Sunda Arc transitions to the recent arc-continent collision at the Banda arc while the NW Australian continental margin and the active volcanic arc converge. Such complicated convergent tectonics leads to pronounced structural heterogeneity and complexity of both vertical and lateral extents along to the convergent margin. Therefore, understanding detailed knowledge of deep structure in the area is key to unravelling the dynamic processes that occur. In this study, we image detailed crustal and uppermost mantle structure utilizing ~4-years of broadband seismic data recently collected in the Timor-Leste and Nusa Tenggara Timor region of Indonesia. We apply three techniques, ambient noise tomography, teleseismic P-wave receiver function and coda autocorrelation, to resolve a 3-D Vs model and Moho structure. Our tomographic images show low-velocity anomalies (<30 km) beneath the outer arc island of Timor related to the underthrusted Gondwana Sequence from the incoming Australian plate, which are vertically offset by the high-velocity backstop of the Banda forearc terrane. The structure progressively changes along strike, reflecting different collisional stages developed as a result of the oblique convergence and incoming plate heterogeneity. At greater depth, we detect seismically fast lithospheric mantle (>30 km) and the arc-ward dipping Moho beneath Timor, both interpreted to be from the incoming Australian plate. Our findings provide direct seismic structural evidence of the subducted Australian continental margin at lithospheric depths beneath the Banda Arc collision zone.
Ping Zhang is a PhD student, working with As. Prof. Meghan Miller, at The Australian National University. Her PhD focuses on understanding the Banda Arc-Australian Continent collision through 3-D seismic imaging, based on a new seismic experiment carried out from March 2014 to August 2019.