The Geology of the Lower Part of Indus Kohistan (Swat), West Pakistan

Abstract

An area of over 450 square miles in Indus Kohistan, Swat, has been mapped and the detailed petrography of the rocks is presented. The area investigated is bounded by latitudes 35° '15' to the north, and 34° 45' to the south, by the Indus River to the east, and by the drainage divide of the Indus and Swat Rivers to the west. The predominant rocks in the southeast and south belong to the Lower Swat-Buner Schistose Group (Siluro-Devonian or possibly Ordovician). The Schistose Group is commonly represented by low grade quartzites, quartz-mica schists, amphibolites, marbles, calcareous schists, phyllitic schists, graphitic schists, and greenschists. These were intruded by ultramafic rocks (pyroxenites and dunites near Jijal; serpentinites near Alpurai, Jijal etc.) during the earlier phases of the Himalayan orogeny (middle to late Cretaceous). During later orogenic phases (early Tertiary), the area was. intruded by the abundant Swat Granites and Granite Gneisses (generaiiy leucocratic, two feldspar-bearing rocks) andpegmatites, and minor gneissic granodiorites near Shang and Dubair. These events were followed by overthrusting of the (?Precambrian) Upper Swat Hornblendic Group which covers the northern and northwestern part of the investigated area. The Hornblendic Group is represented mostly by diorites, metadiorites, hyper-sthene gabbros, and garnet-amphibole gneisses.