Synthesis of Ophiolitic Mélanges along the Indus Suture Zone in Northern Pakistan

The Indus suture zone in northern Pakistan consists of discontinuous, strongly imbricated, ophiolitic bodies. One such large ophiolite body, the Dargai ophiolite stretches for a distance of 30 km and is clearly dismembered and consists dominantly of ultramafic rocks, mafic cumulates, and dolerite dikes. Petrographic data indicate that the rocks have experienced low-grade metamorphism (chlorite-greenschist facies).

Emplacement of this and other ophiolite has been considered to be related to collision of Kohistan and India but the timing of this collision is poorly constrained. Some have suggested that the Kohistan island arc collided with Asia along the Shyok suture (on the north side of Kohistan) between 75 Ma and 94 Ma. This hypotheses has been called into question and another model is suggested where Kohistan collided first with India near equator and then this combined block collided with Asia. A perhaps even larger question is: Could the collision of India with Kohistan have preceded collision between Kohistan and Asia?

In southern Tibet recently three terranes are identified with intraoceanic island arc affinities (Zedong, Dazhuqu and Bainang). Paleomagnetic studies show that ophiolitic rocks of the Dazhuqu block were generated at equatorial or low northern latitudes. These observations suggest that there was an oceanic island-arc system extending from western Pakistan to southern Tibet that collided with India in low northern latitudes. To test this hypotheses we are focusing on the Indus Suture Zone in northern Pakistan. We are using remote sensing techniques to distinguish the ophiolitic mélanges, identify the faults and are developing a tectonic synthesis of the Kohistan-Indian plate collision.