Geochemistry of serpentinized peridotites from the Indus suture ophiolite in Swat, NW Pakistan
Abstract
The Swat valley ophiolite predominantly consists of ultramafic rocks, which occur as lensoidal masses along the Main Mantle Thrust (MMT) between the Kohistan island arc and Indian plate. On the basis of their petrographic characteristics and modal mineralogy (abundant serpentine + subordinate amounts of bastitised orthopyroxene + variable proportions of olivine + accessory amounts of clinopyroxene + trace to accessory amounts of partly altered chrome spinel), most of the ultramafic rocks can be classified as spinel-, clinopyroxene-bearing harzburgite. Consistent with these mineralogical features, the mentioned rocks contain low to very low amounts of basaltic (Al2O3 and TiO2), low concentration of the moderately incompatible (V, Sc, Zn and Ga) and high levels of moderately compatible to highly compatible components (Fe, Mn, Cr, Co, Ni and Mg). These major, minor and trace element geochemical characteristics suggest that the studied ultramafic rocks largely represent a residue of the upper mantle left after partial melting. A detailed comparison with residual rocks from elsewhere in the world shows that, prior to emplacement during the Cretaceous-Tertiary collision between the Indian plate and the Kohistan arc along the MMT, the source region of the studied rocks had suffered an intermediate degree (15 to .30 %) of partial melting.
References
Arif, M., 1994. Studies of ultramafic rocks from Swat, northwestern Pakistan: implications for the genesis of emerald and nickeliferous phases. Unpubl. Ph.D. thesis, Univ. Leicester, UK.
Arif, M, & Jan, M. Q., 1993. Chemistry of chromite and associated phases from the Shangla ultramafic body in the Indus suture zone of Pakistan. In: Himalayan Tectonics (M. P. Searle & P.J. Treloar, eds.). Geol. Soc. London Spec, publ., 74, 101-112.
Arif, M. & Moon, C. J., 1994. Occurrence, chemistry and genesis of the nickel-rich phases in the ultramafic rocks from Swat, northwestern Pakistan. Geol. Bull. Univ. Peshawar, 27, 29-41.
Arif, M. & Moon, C. J., 1996. Textural and chemical characteristics of olivine and pyroxenes in the ultramafic rocks from the Indus suture zone in Swat, NW Pakistan: Implications for petrogenesis and alteration. Schweiz. Mineral. Petrog, Mitt., 76, 47-56.
Arif, M. & Moon, C. J., 1999. Geochemistry of magnesite-rich rocks from the Indus suture in Swat, NW Pakistan. Geol. Bull. Punjab. Univ., 33/ 34, 111-118.
Ashraf, M., Loucks, R. R. & Awan, M. A., 1989. Serpentinization of cumulate ultramafites and development of heazlewoodite-pentlandite-awaruitemagnetite and pentlandite-chalcopyritepyrrhotite-pyrite associations in Alpurai and Kishora, Swat, Pakistan. Kashmir J Geol, 6/7, 1-22.
Barbieri, M., Caggianelli, A., Di Florio, M. R. & Lorenzoni, S., 1994. Palgiogranites and gabbroic rocks from the Mingora ophiolitic melange, Swat valley, NW Frontier Province, Pakistan. Min. Mag.
, 553-566,
Beccaluva, L., Macciotta, G., Piccardo, G. B. & Zeda, O., 1984. Petrology of lherzolitic rocks from the northern Apennine ophiolites. Lithos, 17, 299-316.
Cann, J.R., 1970. Rb, Sr, Y, zr, Nb in some ocean-floor basaltic rocks. Earth Plan. Sci. Lett. 10, 7-11.
Chaudhry, M.N. & Ashraf, M., 1986. Petrology of the ultramafic from Shangla-Alpurai-Malam Jabba area, Swat. Kashmir J. Geol., 4, 15-32.
Coleman, R. G., 1977. Ophiolites. Springer Verlag, New York,
Coward, M.P., Windley, B.F., Broughton, R.D., Luff, I.W., Petterson, M.G., Pudesy, C.J., Rex, D.C. & Asif, K.M., 1986. Collision tectonics in the NW Himalaya. In: Collision Tectonics (M.P. Coward & A, Ries, eds.). Geol. Soc. spec. Publ.,19, 203-219.
Dick, H.J. B., 1977. Partial melting in the Josephine peridotite I, the effect on mineral composition and its consequences for geobarometry and geothermometry Am. J. Earth sci., 277, 801-832.
Dick, H.J.B., Fisher, R.L. & Bryan, W.B., 1984. Mineralogic variability of the uppermost mantle along mid-ocean ridges. Earth Plan, Sci. Lett., 69, 10.
DiPietro, J. A., & Lawrence, R.D., 1991. Himalayan structure and metamorphism south of the Main Mantle thrust, lower Swat, Pakistan. J. Met. Geol., 9, 481495.
England, R.N. & Davies, H.L., 1973. Mineralogy of ultramafic cumulates and tectonites from eastern Papua. Earth Plan. Sci. Lett., 17, 416-425.
Frey, EA., Suen, C.J. & Stockman, H.W., 1985. The Ronda high temperature peridotite, geochemistry and petrogenesis. Geochim. Cosmoch. Acta, 49 2469-2491.
Hartmann, G. & Wedepohl, K.H., 1993. The composition of peridotite tectonites from the Ivrea complex, northern Italy: residues from melt extraction. Geochim. Cosmoch. Acta, 57, 1761-1782.
Ishiwatari, A., 1985. Igneous petrogenesis of the Yakuno ophiolite (Japan) in the context of the diversity of ophiolites, Contrib. Mineral. Petrol., 89, 155-167.
Jaques, A.L. & Chappell, B. 1980. Petrology and trace element geochemistry of the Papuan ultramafic belt. Contrib. Mineral. Petrol., 75, 55-70.
Jaques, A.L. & Green, D. H., 1980. Anhydrous melting of peridotites at 0-15 kb pressure and the genesis of tholeiitic basalts. Contrib. Mineral. Petrol., 73, 287-310.
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. Geol. Bull, Univ. Peshawar, 17, 127-144.
Komor, S.C., Eithon, D. & Casey, J. F., 1985. Serpentinization of cumulate ultramafic rocks from the North Arm Mountain Massif of the Bay of Island, ophiolite, Geochim. Cosmoch. Acta, 49, 2331-2338.
Labotka, T.C. & Albee, A.L., 1979. Serpentinization of the Belvidere Mountain ultramafic body, Vermont, mass balance and reaction at the metasomatic front. Canad. Mineral. 17, 831-845.
Lawrence, R.D., Kazmi, A.H. & Snee, L. W., 1989. Geological setting of the emerald deposits. In: Emeralds of Pakistan (A.H. Kazmi L.W. Snee, eds.). Geol. Surv. Pak., Quetta, 13-38.
Loubet, M., & Allègre, C.J., 1979. Trace element studies in the Alpine type peridotites of the Beni-Bouchera (Morocco). Geochem. Jour, 13, 69-75.
Loubet, M. & Allègre, C.J., 1982 Trace elements in orogeneic Iherzolites reveal the complex history of the upper mantle. Nature, 298, 809-814.
Michael, P.J. & Bonatti, E., 1985. Peridotite composition from the North Atlantic: regional and tectonic implications for partial melting, Earth Plan. Sci. Lett., 73, 91-104.
Mysen, B.O. & Kushiro, I., 1977. Compositional variation of coexisting phases with degree of melting of peridotite in the upper mantle. Am. Mineral., 62, 843-865.
Ottonello, G., Ernst, W.G. & Jordon, J. L., 1984a, Rare earth and 3d transitional element geochemistry of peridotitic rocks. I, Peridotites from the western Alps. J. Petrol., 25, 343-372.
Ottonello, G., Jordon, J.L. & Piccardo, G. B., 1984b. Rare earth and 3d transitional element geochemistry of peridotitic rocks. II, Ligurian peridotites and associated basalts. J. Petrol., 25, 373-393.
Tahirkheli, R.A.K., Mattauer, M., Proust, F. & Tapponier, P., 1979. The India-Eurasia suture zone in northern Pakistan, synthesis and interpretation of recent data on plate scale. In: Geodynamics of Pakistan (A. Farah, & K.A. DeJong, eds.). Geol. Surv. Pak., Quetta, 125-130.
Treloar, P.J. & Rex, D.C., 1990. Cooling and uplift histories of the crystalline thrust stack of the Indian plate internal zones west of Nanaga Parbat, Pakistan Himalaya, Tectonophysics, 180, 32-349.
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.A., 1989, K-Ar and At-Ar geochronology of the Himalayan collision in NW Pakistan, constraints on the timing of suturing, deformation, metamorphism and uplift. Tectonics, 8, 881-909.
