Permalink : http://hdl.handle.net/2115/36724

Geologic structure of western Nepal has two tectonic systems, one being the Himalayan gneiss zone and its klippes of allochthonous nature and the other being the Midland meta-sediment zone of autochthonous or parautochthonous nature; the former is thrust over the latter along a salient tectonic zone called the Main Central Thrust zone. The Himalayan geneisses composed of high grade metamorphic rocks of the Barrovian type have a monotonous structure dipping gently northward. Meanwhile, the Chakhure-Mabu crystallines, which make up a klippe on the Midland meta-sediments, have been derived from the root of the Himalayan gneisses in the north. It is considered that the Jajarkot crystallines also form another klippe derived from the Main Central thrust zone in the north. The Midland meta-sediments show an anticlinorium structure composed of a thick sequence of platform-type sediments and are divided into five formations. The lower part of them is composed of the calcareous Ila Formation with stromatolite and the quartzite-rich Dali Formation, both of which are respectively correlative with the upper calcareous Subgroup and the middle siliceous Subgroup of the Midland meta-sediment Group of central Nepal. The Midland meta-sediments of western Nepal is considered to range in age from Riphean to Eocambrian despite of a possibility that the upper part would be of Palaeozoic in age. The Main Central Thrust zone is a profound tectonic zone characterized by intensely mylonitized rocks accompanied with characteristically blastomylonitic "augen" gneiss and garnet-mica-chlorite phyllitic schist. Geology and tectonics of western Nepal are correlated very well with those of eastern Kumaun of India immediately adjacent to the west.