The Kohistan Sequences: Crust and Mantle of an Obducted Island Arc
Abstract
The Kohistan sequence outcrops in the western part of the western Himalayan syntaxis. It is a thick pile (3040 km) of metamorphosed magmatic, volcanic and sedimentary rocks. It is composed of six main units i.e. from bottom to top:
- the southern amphibolitlc belt with basal ultramafics,
- the "pyroxene granulite" belt (10-15 km thick),
- the northern amphibolitic belt, intruded by various dioritic bodies,
- a metasedimentary oceanic series (Kalam series), - a volcanic calc-alkaline series (Utror Volcanics), up to 6-8 km thick,
- an upper detrital series (Yasin group, Lower Cretaceous).
This sequence is interpreted as a complete cross-section of a mature island arc formed by subduction during Mesozoic in the southern part of the Neotethys and obducted onto the Indian plate in Upper Cretaceous times.
References
Asrarullah, Ahmad, Z. and Abbas, S., 1979. Ophiolites in Pakistan. In Geodynamics of Pakistan: Abul Farah and Kees DeJong edit. Geol. Survey of Pakistan, Quetta, 181-192.
Bard, J.P., Jan, M. Q., Maluski, H., Matte, Ph. and Proust, F., 1979. Position et extension de la "ceinture" metamorphique a facies schistes bleus dans 1'Nimalayn du Pakistan Nord. 7e R. Ann. Sc. Terre. Lyon, p. 29.
Casnedi, R., Desio, A., Forcella, F., Nicoletti, M. and Petrocianni, C., 1978. Absolute age of some granitoid rocks between Hindu Raj and Gilgit River. Rend. Acc. Naz. Lincei Ser. VIII, 641, 2041 210.
Desio, A., 1974. Geological Reconnaissance in the Middle Indus Valley between Chilas and Besham Quila. Bull. Soc. Geol. Ital. 93, 345-368.
Desio, A, 1975. Some geological notes and problems on Chitral Valley (N.W. Pakistan) Rendiconti del. Classe di Sci. fis mat e natur. Acc. Naz. Lincel. Ser. VIII, vol. LVIII, fasc. 4.
Desio, A., 1978, One the Geology of the Desoai Plateau (Kashmid. htm. Atti Della Accadenia Nazionale dei Lincci, ser. VIII, vol. XV, Sezione IIa.
Desio, A., Prernoli Silvs, I. and Rossi-Ronchetti, C., 1977. On the Cretaceous outcrop in the Chumarkhan and Laspur valleys, Gilgit Chitral, N.W. Pakistan. Riv. Ital. Paleont. v. 83, no 3, 56- 578, trav. 15-16, Milano, 1977.
Franke, W., Gansser, A. and Tromrnsdorff, V., 1977. Geological observations in the Ladakh Area (Himalayas) a preliminary report. Schweiz. mineral. pettog. Mitt., 57, 89-113.
Gansser, A., 1964. Geology of the Himalayas. Interscience, Publ. J. Wiley and Son, London 289 p.
Gansser, A., 1980. The significance of the Himalayan Suture Zone. Tectono-physics, vol. 62, no 1/2, 13-35.
Jan, M.Q., 1979. Petrography of the Jijal Complex, Kohistan. Geological Bulletin University of Peshawar (Special Issue), 11(1), 31-50.
Jan, M.Q., 1979b. Petrography of the Amphibolites of Swat and Kohistan. Geological Bulletin University of Peshawar (Special Issue), 11(l), 51-64.
Jan, M.Q., 1979c. Petrography of Pyroxene Granulites from Northern Swat and Kohistan. Geological Bulletin University of Peshawar (Special Issue), 11(1), 65-87.
Jan., M.Q., 1979d. Petrography of Quartz Diorites to the South of Kalam Swat. Geological Bulletin University of Peshawar (Special Issue), 11(l), 89-97.
Jan, M.Q., and Mian, Ihsanullah, 1971. Preliminary geology and petrography of Swat Kohistan. Geol. Bun, Univ. of Peshawar., 6(1), 1-32.
Jan, M.Q., and Kempe, D R.C., 1973. The Petrology of the basic and intermediate rocks of upper Swat, Pakistan. Geol. Mag. 110, 285-300.
Mattauer, M., Proust, F., Tspponnier, P., and Cassaigneau, C., 1978. Ophiolites, obductions et technique globale dans I'Est de I'Afghanistan. C.R. Acad. Sc. Paris, t. 287, 983485.
Rossi - Ronchetti, C., 1965. Rudiste e Narinee de! Cretaceo di Yasin (Pakistan nord-occidentale). Desio's Itals. Exoed. Karakorum Hindu Kush. Scient , Reports IV, Paleont, Zool. Botany, v. 1, 229-272.
Tahirkheli, R A. K. and Jan, M.Q., 1979. Preliminary Geological map of Kohistan and adjoining areas. In Geology of Kohistan. Geol. Bull. Univ. Peshawar (Special Issue), 11(1).
Tahirkheli, R A. K., Mattauer, M., Proust, F., and Tapponier P., 1979. The India Eurasia suture zone in Northern Pakistan: some new data for an interpretation at plate scale. In Geodynamics of Pakistan: A. Farah and K.A. DeJong edit. Geol. Surv of Pakistan, 125-130.
