Petrography of Sandstone of Molasse Deposits (Rawalpindi Group) and their tectonic setting from Khairi-Murat Area, Potwar Sub-basin, Pakistan

Abstract

Potwar sub-basin is a fault-bounded basin, developed due to the collision of Indian and Eurasian plates. In Khairi Murat area (northeastern part of Potwar sub-basin) Late Eocene (Kuldana Formation) to Recent clastic rock units are exposed at the surface. The Murree Formation is exposed on limbs of Khairi Murat anticline, while the Kamlial Formation is exposed along Dhurnal back thrust. The petrographic studies of sandstones of Murree and Kamlial Formations in Khairi-Murat area indicate that the detritus of the rocks were derived from the rising Himalayas. The provenance study of the sandstones of Rawalpindi Group reveals that the source rocks were mainly derived from low-grade metamorphic and plutonic rocks. The sandstones of Rawalpindi Group contain heavy minerals like tourmaline, epidote, garnet, chlorite, rutile, hornblende and zircon. This complex heavy detritus also indicate that the sediments were derived from igneous and metamorphic source. Tectonically the area is highly disturbed due to Himalayan orogeny. The main faults in the area are the Khairi Murat reverse fault and Dhurnal back thrust. The field and petrographic investigations reveals the effects of Himalayan uplifting and thrusting on sedimentation in the area. The rock fragments and modal composition of the clastic rocks indicates different stages of Himalayan tectonics.