LATE CRETACEOUS ARC-CONTINENT COLLISION IN WESTERN PAKISTAN AND IMPLICATIONS FOR HIMALAYAN OROGENY

The timing and nature of the Himalayan collision in western Pakistan is relatively poorly established. Certain aspects of the geochemical evidences for the Muslim Bagh Ophiolite have led us to question the existing ideas argues that the ophiolites of eastern Afghanistan and northwestern Pakistan are result of obduction caused by closure of Tethys. Our work integrates field, remote sensing and geochemical data and presents new model for collision of Indian plate in Western Pakistan.

ASTER imagery is used for mapping the ophiolites. The Short-Wave Infrared (SWIR) bands provided spectral information about the lithology and structure. This normalized using a log residual algorithm and is spatially sharpened and transformed using principal components analyses (PCA) and minimum noise fraction (MNF) transformation techniques for classification. Our geochemical data indicate that Muslim Bagh ophiolite formed the forearc basement of an oceanic island arc that collided with the Indian continent during the Late Cretaceous to Paleocene. The arc basement was modified by a series of mafic sills and dikes intruded into the ophiolitic ultramafic section. These diabases show typical subduction related trace element patterns on N-MORB-normalized diagram. The large ion lithophile are enriched relative to light rare earth elements and are enriched relative to the high field strength elements and show associated Nb depletions suggesting chemical affinities with arc-related rocks. Furthermore the spinal composition of Muslim Bagh Ophiolite shows calcalkaline and boninite magmas.

This arc related sill/dike event may be associated with subduction of an oceanic ridge during closure of part of the Tethys. Based on reinterpretation of previously published geochemistry, age and sedimentation data we propose presence of an island arc system which collided with Indian plate around 68 Ma before India's final terminal collision with Eurasia.