HIMALAYAN TECTONOSTRATIGRAPHIC ZONES FROM NEPAL TO PAKISTAN

Indian plate rocks in Kumaun and Nepal have traditionally been divided into orogen-parallel tectonostratigraphic zones separated by major fault zones which are from south to north the Subhimalaya, Main Boundary thrust (MBT), Lesser Himalaya, Main Central thrust (MCT), Higher Himalayan crystallines (HHC), South Tibetan Fault system (STFS), and Tibetan Tethys. Each contains distinctive stratigraphic and structural characteristics and each extends westward to the Chamba-Zanskar region. A one-to-one extrapolation farther west across Pakistan has not been successful due to: a) the absence of any fault with demonstrated displacement comparable to the MCT; b) a westward decrease in post-Paleocene shortening of the Indian plate from >600 km in Nepal to ca. 200 km in Pakistan; c) strong late Paleozoic and Late Cretaceous deformation which thinned or eliminated Tethyan shelf deposition; d) offset of tectonostratigraphic zones in eastern Pakistan along the north-trending Jhelum-Balakot shear; and e) the presence of the Kohistan fault which was active in the Eocene and Oligocene and which truncates the northern margin of the Indian plate. It has no counterpart in Nepal.

The Subhimalaya, MBT, and Lesser Himalaya are recognized in Pakistan but the Subhimalaya contains rock with Lesser Himalayan affinities and both the Sub- and Lesser Himalaya contain rock with Tethyan affinities. The closest analog to the MCT is the Khairabad fault which is younger and shows less displacement. North of the Khairabad fault the Pakistani hinterland contains a lower Proterozoic to Mesozoic depositional sequence which includes lower Proterozoic Lesser Himalayan Ulleri-type granitic rock, upper Proterozoic Higher Himalayan kyanite- and sillimanite-grade schist and gneiss, and Tethyan fossiliferous Paleozoic and Mesozoic platform deposits. The rocks are not in fault contact therefore the HHC, STFS, and Tibetan Tethys cannot be extrapolated to Pakistan. A possible scenario is that major displacement was transferred from the Kohistan fault to the MCT in early Miocene which then propagated westward in the middle Miocene to form the Khairabad fault. Because of decreased total shortening, the rocks in Pakistan could represent a stratigraphic link between the disparate Lesser, Higher and Tethyan stratigraphy of Kumaun and Nepal.