High Pressure (Eclogite Facies) Metamorphism in the Indian Plate, NW Himalaya, Pakistan
Abstract
A zone of high pressure (eclogite facies) metamorphism, characterized by eclogites with an assemblage of omphacite - garnet - quartz - rutile ± phengite, has been recognized in the higher Himalaya in the Indian Plate of NE Pakistan. This suggests that the Upper Kaghan Nappe is the deepest derived part of the Indian Plate to have been subducted and subsequently uplifted along the whole length of the Himalaya. Mineral chemistry by microprobe analysis suggests that the eclogites formed at temperatures of 650±50oC and pressures of 13-18 kbar, suggesting depth of eclogite formation at 60 km. The eclogites show an incipient decompressional re-equilibration which probably occurred at decreasing temperatures.
References
Bruncl, M. & Kcinast, J.R., 1986. Etude petro-structurale des chcvauchement ductile himalayen sur la transversale de I’Everest- Makalu (Nepitl oriental). Can. J. Earth Sci. 23, 1117-1137.
Burg, J.P., Leyreloup, A., Girardcau, J. & Chen, G.M., 1987. Structure and metamorphism of a tectonically thickened continental crust: the Yalu Tsangpo suture zone (Tibet). Phil. Trans. Royal Soc. London A 321, 67-86.
Chaudhry, M.N. & Ghazanfar, M., 1987. Geology, structure and geomorphology of Upper Kaghan valley, NW Himalaya, Pakistan. Geol. Bull. Punjab Univ. 22, 13-57.
Dewey, J., Cande, S. & Pitman, W.C., 1989. Tectonic evolution of the India/Eurasia collision zone. Edogae geol. Helveticae 82, 717-734.
Droop, G.T.R., Lombardo, B. & Pognante, U., 1990. Formation and distribution of eclogite fcies rocks in the Alps. In: Eclogite facies rocks (D.A. Carswell cd.). Blackie, Glasgow, 225-259.
Ellis, D.J. & Green, D.H., 1979. An experimental study of the effect of Ca upon garnet-clinopyroxene Fc-Mg exchange equilibria. Contrib. Min. Pet. 71, 13-22.
Greco, A., 1969. Tectonics and metamorphism in the western Himalayan syntaxis area (Azad Kashmir, NE Pakistan). Ph.D. thesis, ETII Zurich. 193p.
Greco, A., Martinotti, G., Papritz, K., Ramsay, G. & Rey, R., 1989. The crystalline rocks of the Kaghan Valley (NE Pakistan). Ecolgae geol. Helvcticae 82, 629-653.
Green, T.H. & Hellman, P.L., 1982. Fe-Mg partitioning between coexisting garnet and phengite at high pressure, and comments on a garnet-phengitc geobaroincter. Lithos 15, 253-266.
Heinrich, C.A., 1982. Kyanitc-eclogite to amphibolite facies evolution of hydrous mafic and pelitic rocks, Adula Nappe, central Alps. Contrib. Min. Pct. 81, 30-38.
Holland, T.J.B., 1983. The experimental determination of activities in disordered and short-range ordered jadeitic pyroxenes. Contrib. Min. Pet. 82, 214-220.
Honegger, K., Le Fort, P., Mascle, G. & Zimmerman, J.L., 1989. The blueschists along the Indus Suture Zone in Ladakh, NW Himalaya. Jour. Met. Geol. 7, 57-72.
Hubbard, M.S., 1989. Thermobarometric constraints on the thermal history of the Main Central Thrust Zone and Tibetan Slab, eastern Nepal Himalaya. Jour. Met. Geol. 7, 19-30.
Jan. M.Q., 1991. High-P metamorphic rocks from the Himalaya and their tectonic implication -a review. In: Geology and geodynamic evolution of the Himalayan collision zone (K.K. Sharma, cd.) Phys. Chem. Earth 18, 329-343.
Krogh, E.J., 1988. The garnet-clinopyroxene Fe-Mg geothermometer -a reinterpretation of existing experimental data. Contrib. Min. Pct. 99, 44-48.
Leake, B.E., 1978. Nornenclature of amphiboles. Amcr. Min. 63, 1023-1052.
Le Fort, P., 1986. Metamorphism and magmatism during the Himalayan collision. In: Collision Tectonics (M.P. Coward & A.C. Ries eds.) Geol. Soc. Lond. Spec. Pub. 19, 159-172.
Maruyama, S., Suzuki, K. & Liou, J.G., 1983. Greenschist- amphibolite transition equilibria at low pressure. Jour. Pet. 24, 583-604.
Massonne, H.J. & Schreyer, W., 1987. Phengite geobarometry based on the limiting assemblage with K-feldspar, phlogopite and quartz. Contrib. Min. Pct. 96, 212-224.
Pognante, U. and Lombardo, B., 1989. Metamorphic evolution of the High Himalayan Crystalline in the SE Zanskar, India. Jour. Met. Geol. 7, 9-17.
Pognante, U., Castelli, D., Benna, P., Genovese, G., Oberli, F., Meier, M. & Tonarini, S., 1990. The crystalline units of the High Himalayas in the Lahul-Zanskar region (northwest India): metamorphic-tectonic history and geochronology of the collided and imbricated Indian Plate. ecol. Mag. 127, 101-116.
Rubie, D.C., 1986. The cataclasis of mineral reactions by water and restriction on the presence of aqueous fluid during metamorphism. Min. Mag. 50, 399-415.
Shams, F.A., 1972. Origin of the Shangla buleschist, Swat Himalaya, Pakistan. Geol. Bull. Punjab Univ. 13, 67-70.
Spencer, D.A., Ghazanfar, M. and Chaudhry, M.N., 1991. The Higher Himalayan Crystalline unit, Upper Kaghan Valley, NW Himalaya, Pakistan. Geol. Bull. Univ. Peshawar 24, (in press).
Treloar, P.J., 1989. Imbrication and unroofing of the Himalayan thrust stack of the north Indian Plate, north Pakistan. Geol. Bull. Univ. Peshawar, 22, 25-44.
Treloar, P.J., Rex, D.C., Guise, P.G., Coward, M.P., Searle, M.P., Windley, B.F., Peterson, M.G., Jan, M.Q. & Luff, I.W., 1989. K-Ar and Ar-Ar geochronology of the Himalayan collision in NW Pakistan: constraints on the timing of the suturing, deformation, metamorphism and uplift. Tectonics 8, 881-909.
Winkler, H.G.F., 1974. Petrogenesis of metamorphic rocks. Springer-Verlag, New York, 320p.
