HIMALAYAN AND ZAGROS FORELAND BASINS: PLATE TECTONIC PARALLELS, STRUCTURAL VARIETIES AND IMPLICATIONS FOR HYDROCARBON PROSPECTIVITY

The tectonics of both Himalaya and Zagros is related to the Wilson Cycle of the opening (in the Permian) and closing (in the Eocene) of the Neo-Tethys, and the subsequent collision of the Arabian and Indian plates with Central Iran-Tibet margin of Asia. Yet, the resulting foreland basins are drastically different in terms of hydrocarbon prospectivity. Using data from structural cross sections, paleotectonic reconstructions and petroleum systems, this paper compares and contrasts these two ‘sister' foreland basins. Subduction of the Neo-Tethyan oceanic floor beneath the Asian active margin gave rise to the magmatic arcs of the Trans-Himalayan belt in southern Tibet and the Urmieh-Dokhtar belt in Central Iran. Post-collisional convergence in each orogen produced a thrust-folded wedge with a thickness increasing toward the hinterland. Faster motion of the Indian plate has resulted in a high-energy orogen characterized by higher uplift rates and a thick-skinned tectonic deformation in which the Indian crystalline basement has been reactivated within the core of the Himalayan orogen. The presence of a mobile salt layer at Precambrian-Phanerozoic interface has produced a basement-cover detached deformation style in Zagros. While the Himalayan foreland basin to the south of the Main Boundary Thrust rests on the Indian Precambrian crust, the Zagros foreland basin was superimposed on the Paleozoic-Mesozoic Tethyan (passive margin) sediments. The poly-phase basin in front of Zagros provided a suitable habitat for the development of multiple petroleum systems. Furthermore, the occurrence of evaporite layers both at the base (Cambrian) and on top (Miocene) of the Phanerozoic succession in the Zagros basin not only sealed and protected the whole basin but also created salt anticlines with suitable structures for petroleum traps. The Himalayan foreland basin has not proven to be petroliferous, although a petroleum system possibly exists in the clastic sediments overridden by the Main Boundary Thrust. In some respects, Zagros may represent the initial development of the Himalaya.