COLLISION FACTORY IN THE OROGENIC BELTS OF SOUTHERN EURASIA; LARGE SCALE COMPARISON

A global view at the orogenic belts of Southern Eurasia shows a striking widening toward the east. This geometry mimics the V-shape of the original Paleotethys and Tethys oceans. However the classical “zipper” closure cannot account for the finite geometry. In order to explore this difference, we observe the mechanisms of present-day opening and closure of basins in SE Asia. The different stages all controlled by the consequence of a long lasting subduction which firstly creates marginal basins floored with oceanic crust, and later closes these basins when it is perturbed. The processes of shortening are all illustrated in SE Asia, from the subduction blocking to reversal (e.g. Philippines or Timor), subduction of the back arc basin (e.g. Celebes), transfer to the opposite margin (Makassar) and subduction of the entire basin (NW Borneo). These examples display progressively more advanced phases of collision tectonics with characteristic structural, metamorphic, and magmatic features, prior to the impending Australia-Eurasia continental collision in the future.

In this “collision factory” of the modern SE Asia, basin collapse, ophiolite emplacement, arc collisions, microcontinental accretion and subduction, and crustal shortening have been taking place during the last 45 my. as a complex orogenic prelude to a final continent-continent collision. The mechanisms of these discrete geological phenomena, their imprint on the rock record, the subduction zone geodynamics involved, and the tectonic settings of different crustal and lithospheric entities can still be determined because of the wealth of geophysical, geological, and marine geology data.

If the still visible Neogene or active propagators respects the opening of the large paleo-oceanic domains, they fail to explain the width of the orogenic belts which involves larger continental blocks. It is thus possible that there is a relation between the width of the ocean and that of the crustal blocks, and that the transmission of the extensional strain goes far into the margins, following the increase of the mechanical thickness of the lithosphere.