The Higher Himalaya Crystalline Unit, Upper Kaghan Valley, NW Himalaya, Pakistan
Abstract
Kaghan valley, in north Pakistan, provides an unparalleled cross-section of the Indian Plate in the Himalaya, with all of the tectonic units, structural features and metamorphic grades of the Indian Plate exposed in one valley. The Higher Himalaya Crystalline of the NW Himalaya, which crops out in the upper reaches of the valley, is a complex sequence of granites, gneisses, Calc-pelites, metapelites, marbles, amphibolites, quartzites and eclogites. It is bound by two major thrusts: The Main Central Thrust (MCT) to the south and the Main Mantle Thrust (MMT) to the north, which have subsequently led to the exposure of some of the deepest level rocks of the Indian plate during its collision with the Asian plate. A complex deformational history of pre-, syn-, and post- "Himalayan" age is associated with a pre- to syn- deformational upper amphibolite (kyanite to sillimanite) to eclogite facies metamorphism which reached inplaces over 650 oc, as evidenced by minor insitu granitization.
The Higher Himalaya Crystalline of Kaghan Valley is structurally positioned between three major syntaxes: the Hazara - Kashmir Syntaxis (HRS), the Kaghan Syntaxis (KS) and the Nanga Parbat Syntaxis (NPS) which are interpreted as forming due to a change in transport direction. Between the Kaghan Syntaxis and the Nanga Parbat Syntaxis, the Higher Himalaya Crystalline consists of a polyphase, superposed folded domain which produces the Burawai syncline, the Besal anticline and synclines and other large scale features located to the south in Neelum Valley. The fold interference patterns are affected by the extreme ductility of the rocks and caused the rotation of, not only the first fold axis, but also the whole interference structure itself, as seen by the asymmetric shape of a Besal antiform.
A provisional tectonic analysis of the features observed suggest that the first southwestwards-directed phase of nappe transport led to a thickening of the tectonic pile, and that thickening was followed by a northeast-southwest directed deformation. This is in accordance with movements suggested for the formation of the Hazara-Kashmir and the Kaghan syntaxis and leads to the suggestion of a similar model, with a further increment of anticlockwise transport direction change, for the formation of the Nanga Parbat Syntaxis.
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