Major and Trace Element Variations in the Lavas of Shergarh Sar Area and Their Significance with Respect to the Kohistan Tectonic Anomaly
Abstract
A belt of dark-green volcanics along with serpentinite, peridotiie, pyroxenite and greenschist marks the spatial disposition of the Indus suture zone in Allai Kohistan of Hazara division. Major and trace element analyses of selected lava samples are used to investigate geochemical variations in the Shergarh Sar Pashtu village section of the volcanic belt. The lavas are mostly glassy but occasionally show phenocrysts of plagioclase, clinopyroxene and, very rarely, brown hornblende. On the basis of normative mineralogy, two compositional groups, e.g. olivine tholeiite and quartz tholeiite, are identified. Fractionation control of the observed phenocrysts over the major and trace element distribution in the lava$ is established through the solutions of chemical data in the C.M.A.S. model and conventional two-dimensional plots. The major and trace element constraints of the studied lavas are corresponding more closely to tholeiites developed in the island arc type environments and substantiate, through a chemical comparison, the assumed prevalence of such structure(s) in the Tethys ocean before the complete closure as proposed in the tectonic models of the Himalayan development.
References
Andrew-Speed, C.P. & Brookfield, M.E., 1982. Middle Palaeozoic to Cenozoic geology and tectonic evolution of the north western Himalaya. Tectonophysics 82, 253-275.
Bard, J.P., 1983. Metamorphic evolution of an abducted island arc: Example of the Kohistan sequence (Pakistan) in the Himalayan collided range. Geol. Bull. Univ. Peshawar 16, 105-1 84.
Brooks, C.K., 1976. The Fe203 /FeO ratio of basalt analyses: an appeal for a standardized procedure. Bull. Geol. Soc. Denmark 25, 117-119.
Brown, G.M. & Schairer, J.F., 1967. Melting relations of some calc-alkaline volcanic rocks. Yb. Carnegie Instn. Wash, 66, 460-467.
Cam, J.R., 1969. Spilites from the Carlsberg Ridge. Jour. Petrol. 10, 1-19.
Carmichael, I.S.E., 1964. The petrology of Thingmdi, a Tertiary volcano in eastern Iceland. Amer. Mineral. 52, 181 5 - 4 1.
Coward, Map., Jan, M.Q., Rex, D. Tarney, J., Thirlwall, M. & WindIey, B.F., 1982. Geotectonic Framework of the Himalayas of N. Pakistan. Jour. Geol. Soc. London 139, 299-308.
Cox, K.G., Bell, J.D. & Pankhurst. R.J., 1979. The Interpretation of Igneous Rocks. Allen and Unwin, London.
Engel, A.E.J., Engel, C.G.I. & Havens, R.G., 1965. Chemical characteristics of oceanic basalt and the upper mantle. Bull. Geol. Soc. Amer. 76, 719-734.
Frey, F.A., Green, D.H. & Roy, S.D., 1978. Integrated models of basalt petrogenesis. A study of quartz tholeiites to olivine melilites from south eastern Australia utilizing geochemical and experimental petrological data. Jour. Petrol. 19, 463-513.
Fyfe, W.S., 1976. Hydrosphere and continental crust: growing or shrinking ? Geosci. Can. 3, 82-83.
Green, D.H., 1976. Experimental studies on a modal upper mantle composition at high pressure under water saturated and water undersaturated conditions. Can. Mineral. 14, 255-268.
Hallberg, J.A. & Williams., 1372. Archean mafic and ultramafic rock associations in the Eastern Gold-fields regions, Western Australia. Earth. Planet. Sci. Letters 15, 191250.
lrvine, T.N. & Baragar, W.R.A., 197 1. A guide to the classification of the common volcanic rocks. Can. Jour. Earth Sci. 8, 523-4.9.
Jan, M.Q., 1980. Petrology of the obductcd mafic and ultramafic motamorphitcs from the southern part of the Kohistan island arc sequence. Geol. Bull, Univ. Peshawar 13, 95-107.
Jan, M.Q., & Asif. M., 1983. Geochemistry of tonalites and (Quartz) diorites of the Kohistan Ladakh (Trans Himalayan) granite belt in Swat, N.W. Pakistan. In "Granite of Himalaya, Karakorum and Hindukush" (F.A. Shams, ed.), Inst, of Geol. Punjab Univ. Lahore, Pakistan,
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, Northern Pakistan. GeoI. Bull. Univ. Peshawar 17, 127-143.
Klootwijk, C., Sharrna, M.L., Gergan, J., Tirkey, B., Shah, S.K. & Agarwal, V., 1979. The extent of greater India, II. paleomagnctic data from the Ladakh intrusives at Kargil north western Himalayas. Earth Planet, Sci. Letters 44, 47-44.
Kuao, H., 1959. Origin of Cenozoic petrographic provinces of Japan and surrounding areas. BuI1. volcanol. Ser. 11, 37-76.
Lensch, G., 1980. Major element chemistry of the ophiolites in north-eastern Iran. In 'ophiolites' (Panayiotou, A. ed.). Int. Ophiolite Symp, Cyprus, 398-401.
Majid, M. and Paracha, F.A., 1980. Calc-alkaline magmatism at destructive plate margin in Kohistan, northern Pakistan. Geol. Bull. Univ. Peshawar 13, 109-120.
Majid, M., Shah, M.T., Latif, A., Aurangzeb & Karnal, M., 1981. Major element abundance in the Kalam lavas. Geol. Bull. Univ. Peshawar 14, 46-62.
Melson, W.T., Thompson. G. & Van Andel. T.H., 1968. Volcanism and metamorphism in the mid-Atlantic ridge, 22"N. Latitude. Jour. Geophys. Res. 73, 5925-41.
Miyashiro, A., 1974. Volcanic rock series in island arcs and active continental margin. Amer. Jour. Sci. 274, 321-355.
Mullen, E.D., 1983. MnOITi02j P20s a minor element discriminant for basaltic rocks of oceanic environments and its implications for petrogenesis, Earth Planet. Sci. Letters 52, 53-62.
Pearce, J.A., 1975. Basalt geochemistry used to investigate past tectonic environments on Cyprus. Tectonophysics 25, 41-67.
Roeder, P.H. & Emslie, R.F., 1970. Olivine-liquid equilibrium. Contrib. Mineral. Petrol. 29, 275-89.
Schwarzer, R.R. $ Rogers, J.J.W., 1974. A world-wide comparison of alkali olivine basalts and their differentiation trends. Earth Planet. Sci. Letters 23, 286-296.
Shah, M.T., 1985. Petrochemistry of the Shergarh Sar Complex, Allai Kohistan. Unpubl. M. Phil. thesis, Univ. Peshawar.
Streckeisen, A., 1979. Classification and nomenclature of volcanic rocks, lamprophyres, carbonatite. and melilitic rocks. Recommendations and suggestions of the IUGS sub-commission on the systematics of igneous rocks. Geology 7, 331-335.
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., Mattaucr, M., Proust, I?. & Tapponnier, 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 eds.). G.S.P. Quetta, 125-130.
Virdi, N.S., 1981. Presence of parallel metamorphic belt in the northwest Himalayas-Discussion. Tectonophysics 72, 141-146.
Wood, D.A., 1978. Major and trace element variations in the Tertiary lavas of eastern Iceland and their significance with respect to the Iceland geochemical anomaly. Jour. Petrol. 19, 393-436.
