Geology of a part of the Kohistan terrane between Gilgit and Chilas, northern areas, Pakistan
Abstract
More than 4000 Km2 area of the Kohistan terrane, exposed between Gilgit and Chilas, is mapped and described in this paper. A variety of plutonic and metamorphosed volcanic and sedimentary rocks are encountered in the mapped area, which have been classified into Kamila amphibolite, Chilas complex, Kohistan batholith and Jaglot Group. The Jaglot Group, comprising a succession of mesediments and metavolcanics, is divided into three stratigraphic units, which, from base to top, include Gilgit Formation [~l km thick succession of schists, paragneisses, calc-silicates and amphibolites (some derived from the pillowed basalts)], Gashu-Confluence Volcanics (>0.5km thick volcaniclastics and massive to pillowed basalts) and Thelichi Formation (comprising a volcanic basal part, overlain by > 1 km thick turbidites with a thick marble unit in the middle). The rocks of the Jaglot Group are regionally metamorphosed in amphibolite- and greenschist facies; the highest grade is depicted by the occurrence of silliminite in the pargneisses of the Gilgit Formation. A pair of crusted-scale anticline (the Gilgit anticline) and syncline (Jaglot syncline) control the structure of the area. These, together with their parasitic folds, repeat the stratigraphy of the area several times. The Jaglot Group is regionally correlated with the succession of metasediments and metavolcanics exposed along the Northern Suture (i.e., Yasin Group Sediments and Chalt Volcanics) and is considered to have been deposited in an oceanic basin (probably of a back-arc affinity) on the basis of the predominance of turbidites in the metasediments and pillowed basalts in the volcanics.
References
Ahmed, Z. Hussain, S. & Awan, A., 1977. Petrology of Thelichi area, Gilgit Agency. Geol. Bull. Panjab University, 14, 27-38.
Bard, J. P., Maluski, H., Matte, P. & Proust, F., 1980. The Kohistan sequence: Crust and mantle of an obducted island arc. Geol. Bull. Univ. Peshawar, 13, 87-93.
Coward, M. P., Windley, B. F., Broughton, R. D., Luff, I. W., Petterson, M. G., Pudsey, C. G., Rex, D. C. & Khan, M. A., 1986. Collision tectonics in the NW Himalayas. In: Collision Tectonics (M. P. Coward & A. C. Ries, eds.). Geol. Soc. London, spec. Pub., 19, 203-219.
Coward, M. P., Butler, R. W. H., Khan, M. A. & Knippe, R. J., 1987. The tectonic history of Kohistan and its implications for Himalayan structure. Jour. Geol. Soc. London, 144, 377-391.
Desio, A., 1964. Tectonic relationship between the Karakoram, Pamir and Hidukush. Report XXII Sess. India, Intern, Geol. Congr. New Delhi, Il, 192-213.
Desio, A., 1978. On the geology of Deosai plateau (Kashmir), Mem. Accad. Naz. Lincei, 15, 1-19.
Desio, A., 1979. Geological evolution of the Karakoram. In: Geodynamics of Pakistan (A. Farah, A. & K. A. DeJong, eds.). Geol. Surv. Pakistan, 111-124.
Ghazanfar, M., Chaudhry, M. N. & Hussain, M., 1991. Geology and petrotectonics of southeast Kohistan, northwest Himalaya, Pakistan. Kashmir Jour. Geol., 8 & 9, 67-9.
Hanson, C. R., 1989. The northern suture in the Shigar valley, Baltistan, northern Pakistan. Geol. Soc. Am. Spec. Paper, 232, 32-215.Hayden, H. H., 1916. Notes on the geology of Chitral, Gilgit and Pamirs. Rec. Geol. Surv. India, 45, 271-335.
Ivanac, J. F., Traves, D. M. & King, D., 1956. The geology of the NW portion of the Gilgit Agency. Rec. Geol. Surv. Pakistan, Quetta, 3,1-27.
Jan, M. Q. & Howie, R. A., 1981. The mineralogy and geochemistry of the metamorphosed basic and ultrabasic rocks of the Jijal complex, Kohistan, N. W. Pakistan. Jour. Petrol., 22, 85-126.
Jan, M. Q., Asif, M. & Tahirkheli, T. & Kamal, M., 1981. Tectonic subdivision of the granitic rocks of northern Pakistan. Geol. Bull. Univ. Peshawar, 14, 159.182.
Jan, M. Q. Parvez, M. K., Khattak, M. U. K & Windley, B. E., 1984. The Chilas stratiform complex: field and mineralogical aspects. Geol. Bull. Univ. Peshawar, 17, 153-169.
Jan, M. Q. & Windley, B. E., 1990. Chromium spinel silicate chemistry in ultramafic rocks of the Jijal complex, Northeast Pakistan, Jour. Petrology, 31, 667-715.
Khan, M. A., 1988. Petrology and structure of the Chilas ultramafic-mafic complex, Kohistan Arc, NW Himalayas. Unpubl. Ph. D. Thesis. Univ. London.
Khan, M.A. & Coward, M. P., 1990. Entrapment of an intra-oceanic island arc in collision tectonics: a review of the structural history of the Kohistan arc, NW Himalaya. In: Geology and geodynamic evolution of the Himalayan collision zone (K. K. Sharma, ed.) Phys. & Chem. Earth, 17, 1-18.
Khan, M. A., Jan, M. Q., Windley, B. F., Tarney, J. & Thirlwall, M. F., 1989. The Chilas ultramafic-mafic igneous comp of the Kohistan Island arc in the Himalaya of north Pakistan. Geol. Soc. Amer. Spec. Paper 232, 75-94.
Khan, M. A. & Jan, M. Q., 1992. Some fundamental field and petrographic aspects of the Chilas mafic-ultramafic complex, Kohistan arc, Northern Pakistan. Acta Mineral. Pakistanica, 6, 126-147.
Khan, M. A, Jan, M. Q. & Weaver, B. L., 1993. Evolution of the lower arc crust in Kohistan, N. Pakistan: temporal arc magmatism through early, mature and intra-arc rift stages. In: Himalayan Tectonics (P. J. Treloar & M. P. Searle, eds.), Spec. Publ. Geol. Soc. London, 74, 123-138.
Khan, T., Latif, M., Khan, N.A. & Shah, S. H., 1989. Geology and petrography of the rock outcrops in Shinghai gah and Kiner gah Gilgit-Chilas districts Northern areas of Pakistan. Geol. Surv. Pakistan, Inf. Release, 446.
Khan, T., Khan, M. A. &Jan, M. Q., 1993. Kohistan, a Collage of island arc and back-arc basin assemblages in the Himalaya of N. Pakistan. Geol. Soc. Amer. Abstracts with Programs, A-122.
Khan, T., Khan, M. A. & Jan, M. Q., 1994. High-grade schists and paragneisses in the Kohistan island arc terrane. Jour. Res. Geol. Japan (in press).
Miller, D. J., Loucks, R. R., & Ashraf, M., 1991. Platinum group elements mineralization in the Jijal layered mafic-ultramafic complex, Pakistani Himalayas. Economic Geol., 86, 1093-1102.
Petterson, M. G., 1984. The structure, petrology and geochemistry of the Kohistan batholith, Gilgit, N. Pakistan. Unpubl. Ph. D. Thesis, Leicester University, U. K.
Petterson, M. G. & Windley, B. F., 1985. Rb-Sr dating of the Kohistan arc batholith in the Trans-Himalayan of the North Pakistan and tectonic implications. Earth Planet. Sci. Lett., 74. 45-57.
Petterson, M. G. & Windley, B. F., 1991. Changing source regions of magmas and crustal growth in the Tran-Himalayas: Evidence from the Chalt volcanics and Kohistan batholith, Kohistan, N. Pakistan. Earth Planet. Sci. Lett., 102, 326-341.
Pudsey, C.J., 1986. The Northern Suture, Pakistan: margin of a Cretaceous island 123, 405-423.
Pudsey, C. J., Coward, M. P., Luff, l. W., Shackleton, M., Windley, B. F. & Jan, M.Q., 1985. The collision zone between the Kohistan arc and the Asian plate in NW Pakistan. Trans. R. Soc. Edinbrough 76, 464-479.
Pudsey, C J., Schroeder, R. & Skelton, PN., 1986. Cretaceous (Aptian-Albian) age for the island arc volcanics, Kohistan. In: Recent researches in geology. Palaeontology, stratigraphy and structure of the western Himalayas. Hindustani Publishing co. Delhi, 150-168.
Sullivan, M. A, Windley, B. F., Saunders, A. D, Haynes, J. R. & Rex, D. C., 1993. A palaeo-geographic reconstruction of the Dir Group: evidence for magmatic arc migration within Kohistaní N. Pakistan. In: Himalayan Tectonics (P. J. Treloar & M. P. Searle eds.). Geol. Soc. London, Spec. Pub., 74, 139-160.
Tahirkheli, R. A. K., 1982. Geology of Himalaya, Karakoram and Hindukush in Pakistan. Geol. Bull. Univ. Peshawar, 15, 54pp.
Tahirkheli, R. A.K. & Jan, M. Q., 1979. Geology of Kohistan, Karakoram, Himalaya, Northern Pakistan. Geol. Bull. Univ. Peshawar, 11, Spec. Issue. (in pocket map).
Tahirkheli, R. A. K., Mattaure, M., Proust, F., & Tapponnier, P., 1979. The India-Eurasia suture in northern Pakistan: synthesis and interpretation of data on plate scale. In: Geodynamics of Pakistan (A. Farah, A. & K. A. DeJong, eds.). Geol. Surv. Pakistan, 125-130.
Treloar, P. J., Rex, F. C, Guise, P. G., Coward, M. P., Searle, M. P., Windley, B. F., Petterson, 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 suturing, deformation, metamorphism and uplift. Tectonics 8, 881-909.
Wadia, D. N., 1932. Note on the geology of Nanga Parbat and adjoining portions of Chilas, Gilgit District. Rec. Geol. Surv. India, Calcutta, 66, 212-234.
