Mineralogy and Mineral Chemistry of the Amphibolite Belt and Main Mantle Thrust Rocks from Gantar Area, Allai Kohistan, North Pakistan
Abstract
Petrographic and mineralogical studies are performed for the Kohistan island arc, MMT melange zone and Indian plate lithologies at Gantar village and in its surroundings, in Alai Kohistan, Hazara. Petrographic studies reveal that locally, the Kohistan island arc lithology is exclusively comprised of amphibolites and epidote amphibolites with certain patches of hornblende pegmatites. The MMT melange zone includes greenschist and blueschist whereas the Indian plate sequence is made up of a variety of schistose rocks and siliceous marble. Petrography and mineral chemistry indicate that amphibolites have an igneous parentage and have undergone successive metamorphic episodes of amphibolite facies, epidote-amphibolite facies and greenschist facies, in a temperature range of 530<=500oC and a pressure range of 6-<= 4.5 kb, whereas the MMT melange zone rocks show signatures of amphibolite facies, blueschist facies (7kb) and greenschist facies matamorphic episodes. The hornblende pegmatite patches in amphibolites are interpreted as products of low pressure metasomatism, on the basis of lower VIAl content in hornblende as compared to that in amphibolites. Small outcrops of metagabbro and metanorite found in the area are regarded as part of the island arc system, on the basis of their clinopyroxene chemistry. Structural, petrographic and “minera-chemical” features indicate a subduction-obduction related petrogenesis for these rocks.
References
Ahmed, I., Hamidullah, S. & Jehan, N., 1990. Petrology of the Shewa-Shabazgarhi complex, Mardan, North Pakistan. Geol. Bull. Univ. Peshawar 23, 135-159.
Ashraf, M., Chaudhry, M.N. & Hussain, S.S., 1980. General geology and economic significance of the Lahor granite and rocks of southern ophiolite belt in Alai Kohistan area. Geol. Bull. Univ. Peshawar 13, 207-213.
Bard, J. P., 1983. Metamorphic evolution of an obducted island arc: example of the Kohistan sequence (Pakistan) in the Himalayan collided range. Geol. Bull. Univ. Peshawar 16, 105-184.
Baig, M. S., 1989. New occurrences of blucschist from Shin-Kamer and Marin areas of Allai Kohistan, northwest Himalaya, Pakistan. Kashmir Jour. Geol. 6 & 7, 103-108.
Brown, E. Fl., 1977. The crossite content of Ca-amphibole as a guide to pressure of metamorphism. J. Petrol. 18, 53-72.
Coward, M. P., Jan, M. Q., Rex, D, Tarney, J., Thirlwall, M., & Windley, B.F., 1982. Geotectonic framework of the Himalayas of N. Pakistan. J. Geol. Soc. London 139, 299-308.
Deer, W.A., Howie, R.A., & Zussman, J., 1966. An introduction to rock-forming minerals. Longman, London, 528p.
Desio, A. & Shams, F. A., 1980. The age of blucschists and the Indus Kohistan suture line, North-west Pakistan. Acad. Naz. Dei Lincci 8, 74-79.
Hamidullah, S., Haq, I., Jehanzeb, & Khan, F., 1977. Mineralogy and petrology of the Shergarh Sar complex, Allai Kohistan Hazara. Unpubl. M.Sc. Thesis., Univ. Peshawar.
Hamidullah, S., Hussain, I. & Reuber, 1., 1990. Petrochemistry of the amplibolite belt rocks at Mahak and its surrounding. Geol. Bull. Univ. Peshawar 23, 27-43.
Higgens, W. M., 1971. Cataclasite rocks. USGS Prof. Paper No. 687.
Jan, M. Q., 1979. Petrology of the obductcd mafic and ultramafic metamorphites from the southern part of the Kohistan island arc sequence. Geol. Bull. Univ. Peshawar 13, 95-107.
Jan, M. Q., 1988. Geochemistry of amphibolites from the southern part of Kohistan arc, N. Pakistan, Min. Mag. 52, 147-159.
Jan, M. Q., 1990. Petrology and geochemistry of southern amphibolites of the Kohistan arc, N. Pakistan. Phys. Chem. Earth 17, 71-92.
Kazmi, A.H., Lawrence, R.D., Dawood, H., Snee, L. W. & Hussain, S.S., 1984. Geology of the Indus suture zone in the Mingora- Shangla area of Swat, N. Pakistan. Geol. Bull. Univ. Peshawar 17, 127-144.
Laird, J. & Albee, AL., 1981b. Pressure, temperature, and time indicators in mafic schist: Their application to reconstructing the polymetamorphic history of Vermont. Amer. J. Sci. 281, 127-175.
Leake B. E., 1978. Nomenclature of amphiboles. Canadian Mineral. 16, 501-520.
LeBas, M. J., 1962. The role of aluminum in igneous clinopyroxenes with relation to their parentage. Amer. Jour. Sci. 260, 267-288.
Leterrier, J., Maury, R. C., Thonon, P., Girard, D. & Marchal, M., 1982. Identification of the magmatic affinities of paleovolcanic series. Earth Planet. Sci. Lett. 59, 139-154.
Majid, M., & Shah, M. T., 1985. Mineralogy of the blueschist metagraywacke from the Shergarh Sar area, Allai Kohistan, N. Pakistan. Geol. Bull. Univ. Peshawar 18, 41-52.
Miyashiro, A., 1973. Metamorphism and Metamorphic Belts. George Allen & Unwin, London.
Morimoto, N. and others. 1988. Nomenclature of Pyroxenes. Am. Mineral. 73, 1123-1133.
Papike, J. J., 1982. Pyroxene mineralogy of the moon and meteorites. In: Reviews in Mineralogy, Pyroxenes (C. T. Prewitt, ed.). Sp. Publ. Mineral. Soc. Am. 7, 495-525.
Plyusnina, L. P., 1982. Geothermometry and geobarometry of plagioclase-hornblende bearing assemblages. Contrib. Mineral. Petrol. 80, 140-146.
Shah, M. T., 1986. Petrochemistry of Shergarh Sar complex Alai Kohistan, N. Pakistan. Unpub. M. Phil. Thesis, Univ. Peshawar.
Shah, M. T., Majid, M. & Hamidullah, S., (in press). Petrochemistry of amplibolites from Shergarh Sar area, Allai Kohistan, N. Pakistan. Kashmir Jour. Geol. 9.
Tahirkheli, R. A. K., 1979. Geology of Kohistan and adjoining Eurasian and Indo-Pakistan continents, Pakistan. Geol. Bull. Univ. Peshawar 11, 1-30.
Tahirkheli, R. A. K, Mattauer, M., Proust, F. & Tapponnicr, P., 1979. The India-Eurasia suture zone in northern Pakistan. Some new data for interpretation at plate scale. In: Geodynamics of Pakistan (A. Farah & K. A. DeJong eds.). Geol. Surv. Pakistan, 125-130.
Velde. B, 1965. Phengite micas: synthesis, stability and natural occurrence. Amer. Jour. Sci. 263, 886-913.
Yousafzai, I. J., Bangash, M. A, Shah, A. A. & Ahmad, B., 1976. Petrography of the ultramafic and related rocks of Pashto and Barai area, North-East of Shergarh Sar, Allai Kohistan, Hazara. Unpub. M.Sc. Thesis, Univ. Peshawar.
Zahid, M., 1991. Petrology and geochemistry of the melange zone and southern amphibolite belt rocks from Gantar area, Allai Kohistan, Hazara, N. Pakistan. Unpub. M.Phil. Thesis, Univ. Peshawar.
