ENERGY CONSIDERATIONS FOR THE ARABIAN, INDO-AUSTRALIAN, AND ASIAN COLLISIONAL SYSTEMS OF NEOTETHYS

Plate reconstruction models suggest that the northern edge of the Indian subcontinent contacted the subduction system bordering the southern margin of the Asian continent sometime between 50 and 40 Ma. After 40 Ma India continued its northward drift relative to Asia at a slower rate accompanied by a pronounced anticlockwise rotation resulting in approximately 1200 km of indention into the Asian continental mass. Similarly, Arabia-Eurasia convergence continued after Neotethyn-ocean closure at approximately 10 Ma, all of that coincident with Afro-Arabian divergence in the Red Sea, which began at about 25 Ma. The indention, compressional tectonism, and uplift that resulted from the continent-continent convergence in both regions required a large energy source that is commonly attributed to slab-pull forces. But local slab pull forces, along with associated forces of trench suction, slab roll back and slab suction, cease to be factors once the buoyant continental mass encounters the subduction system. For various reasons, other sources such as ridge push and plate momentum can be discounted as well. This leaves an apparent paradox, especially acute in the Indian case, where the energy needed to drive the post-subduction indention over a time period in excess of 40 million years appears to be locally absent. Less severe, but nonetheless baffling, is the question of how Arabia can be flanked on one side by an expanding ocean and on the other by a compressional mountain belt, also in the apparent absence of local driving forces. The energy question can be easily addressed by considering global, as opposed to local forces. The Arabian and Indo-Australian plates, which include the two large continental masses, together form a large body of lithosphere that has behaved more or less rigidly over the considered time period. The two plates have behaved as a large beam, spanning nearly half the circumference of the globe that rotated anti-clockwise in response to strong forces originating at the descending slabs along its northwest margin from modern-day Burma to Java. Ample far-field energy was available to create the Himalayan and Zagros collisional belts in this case. At the same time, the continental lithosphere of Anotolia was pulled to the west, and that of Asia to the south and east following slab rollback at their respective subduction systems. In this regard it is better to drop the concept of forceful indention of India and Arabia as a driving force for extrusion. Rather slab rollback/suction drives extrusion, allowing room for indention.