Geology of Kohistan and Adjacent Eurasian and Indo-Pakistan Continents, Pakistan
Abstract
Kohistan constitutes about 36000 square kilometers of territory located between the Indo-Pakistan and Eurasian Plates, on the northwestern tip of the Himalaya. Earlier, Desio (1964) has differentiated this part as a tectonic zone of Kararkoram. Bulk of Kohistan sequence consists of amphibolites, diorites, meta-norites (pyroxene-granulites) and associated volcanic rocks which are considered to be the crust of an ancient calc-alkaline island arc. This sequence has been obducted on to the Palaeozoic rocks of the Indo-Pakistan continent on the south and subducted under the Eurasian Platform along the northern megashears. The northern megashear along Hini-Chalt-Yasin-Drosh was formerly used to be considered the only extension of the Indus suture west of Nanga Parbat. Recent studies by Tahirkheli et a1. (1976, 77) have brought to light a southern megashear marked by the occurrence of ultramafics and high pressure metamorphic rocks, called Main Mantle Thrust (MMT), which delineates the southern contact of the Kohistan Island arc and the Indo-Pakistan continent. This confirms the bifurcation of the Indus suture into two suture zones, west of Nanga Parbat. In this paper, an attempt has been made to introduce the geology of Kohistan island arc and the adjoining Eurasian and Indo-Pakistan continents.
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