Geochemistry and petrogenesis of metavolcanic rocks in Gawuch and Drosh formations, Chitral, northern Pakistan
Abstract
Metavolcanic rocks constitute an important lithology in the study area. It occurs as two stratigraphic entities i.e., Gawuch and Drosh Formations. The Metavolcanic of the Gawuch formation are both porphyritic and very fine-grained. The porphyretic volcanics vary from fresh to highly altered and are commonly dissected by quartz and calcite veins. Volcanic rocks of Drosh Formation are massive to weakly foliated, fine-grained and commonly altered. The detailed geochemistry, mainly based on major and trace element, suggests that the metavolcanic rocks of the Gawuch formation are calc-alkaline, and those of Drosh Formation are tholeiitic in character. It is, therefore, suggested that the two groups of metvolcanics, despite difference in their petrological character, originated with a strongly subduction component.
References
Bard, J.P., Maluski, H., Matte, P.H. & Proust, F., 1980. The Kohistan sequence; Crust and mantle of an obducted island arc. Geol. Bull. Univ. Peshawar, 13, 87-93.
Holm, P.E., 1986. The geochemical finger prints of different tectonomagmatic environments using hydromagmatophile element abundances of tholeiitic basalts and basaltic andesites. Chem. Geol. 51, 303-323.
Irvine, T.N, & Bargar, W.R.A., 1971. A guide to the chemical classification of the common volcanic rocks. Canad. J. Sci., 8, 523-548.
Meschede, M., 1986. A method of discriminating between different type of mid-Ocean ridge basalts and continental tholeiites with the Nb-zr-Y diagram. Chem. Geol., 56, 207-218.
Khan, T., Khan, M.A. & Jan, M.Q., 1994. Geology of a part of the Kohistan terrain between Gilgit and Chilas, northern areas, Pakistan. Geological Bulletin University of Peshawar, 27, 99-112.
Pearce, J.A. & Cam, J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analyses. Earth Planet. Sci. Lett., 19, 290-300.
Pearce, J.A. & Norry, M.J., 1979. Petrogenetic implications of Ti, Zr, Y and Nb variations in volcanic rocks. Contrib. Mineral. Petrol., 9, 33-47.
Petterson, M.G. & Windley, B., 1986. Petrology and Geochemical evolution of arc-batholith, Gilgit, N. Pakistan. Geol. Bull. Univ. Peshawar, 19, 121-149.
Petterson, M.G. & Windley, B., 1991. Changing source regions of magmas and crustal growth in the Trans-Himalayas:
