Inherited lithospheric structures control arc-continent collisional heterogeneity

Abstract:

From west to east along the Sunda-Banda arc in SE Asia, convergence of the Indo-Australian plate transitions from subduction of oceanic lithosphere to arc-continent collision. This region of eastern Indonesia and Timor-Leste provides an opportunity for unraveling the processes that occur during collision between a continent and a volcanic arc, and can be viewed as the temporal transition of this process along strike. We have collected a range of complementary geological and geophysical data to place constraints on the geometry and history of arc-continent collision. Utilizing ~4 years of new broadband seismic data we image the structure of the crust through to the uppermost mantle. Ambient noise tomography of the lithosphere shows velocity anomalies along strike and across the arc that are attributed to the inherited structure of the incoming and colliding Australian plate. The pattern of anomalies at depth resemble the system of salients and embayments that are present offshore western Australia, which were formed during the rifting of east Gondwana. Previously identified changes in the geochemistry of volcanic material from lead isotope anomalies from the inner arc islands correlate with the newly identified velocity structures representing the underthrusted and subducted Indo-Australian plate. Reconstruction of uplift from river profiles from the outer (non-volcanic) arc islands suggests rapid uplift at the far ends of the islands of Timor and western Sumba, inferred to be associated with the incoming and collided plate structure. Altogether, we suggest that the tectonic evolution of this region is defined by the inherited structure of the Gondwana rifted continental margin of the incoming plate. Therefore, the initial template of plate structure controls eventual orogenesis.