Petrology and geochemistry of gabbros from the Muslim Bagh Ophiolite: implications for their petrogenesis and tectonic setting
Keywords:
Muslim Bagh Ophiolite; Gabbros; Petrology; Geochemistry; Petrogenesis; Tectonic settingAbstract
The Muslim Bagh ophiolite has almost a complete ophiolite sequence with thick mantle section and comparatively less well-developed crustal section. The crustal part of the ophiolite occupiesan area of about 130 km2, having both ultramafic cumulates; dunite, wherlite and pyroxenite and mafic cumulates or gabbros. The gabbros are olivine gabbro, pyroxene gabbro and hornblende gabbro. They are distinguished into cumulates and non-cumulates. Geochemical features indicate that they are tholeiitic and are formed in an arc-related tectonic setting. On NMORB normalized pattern of gabbros the HFS-elements (P, Zr, Sm, Ti, and Y) show a flat pattern parallel to NMORB. In contrast, the LIL-elements (Rb, Ba, Th, Sr) are relatively more enriched than NMORB. The enrichment of LIL-elements over the HFS-elements and the depletion of Nb relative to other HFS-elements suggest involvement of subduction component in the depleted mantle source, and suggest that they are formed in a supra-subduction zone tectonic setting.
References
Ahmed, Z., Abbas, S.G., 1979. The Muslim Bagh Ophiolites. In: Farah, A., DeJong, K.A. (Eds.), Geodynamics of Pakistan. Geological Survey of Pakistan, Quetta, 243-250.
Asrarullah, Ahmad, Z., Abbas, S.G., 1979. Ophiolites in Pakistan: An introduction. In: Farah, A., DeJong, K.A. (Eds.), Geodynamics of Pakistan. Geological Survey of Pakistan, Quetta, 181-192.
Beard, J.S., 1986. Characteristic mineralogy of arc related cumulate gabbros: implications for the tectonic setting of gabbroic plutons and for andesite genesis. Geology, 14, 848-851.
Bedard, J. H., 1991. Cumulate recycling and crustal evolution in the Bay of Islands ophiolite. Journal of Geology, 99, 225-249.
Bilgrami, S.A., 1964. Mineralogy and petrology of the central part of the Hindu Bagh Igneous complex, Hindu bagh Mining District, Zhob Valley. West Pakistan Geological Survey Records, 10, 28.
Cox, K.G., Bell, J.D., Pankhurst, R.J., 1979. The Interpretation of Igneous Rocks. Allen and Unwin, London.
Humphris, S.E., Thompson, G., 1978. Trace element mobility during hydrothermal alteration of oceanic basalts. Geochimica et Cosmochimica Acta, 42, 127-136.
Jenner, G.A., Dunning, G.R., Malpas, J., Brown, M., Brace, T., 1991. Bay of Islands and Little Port complexes, revisited: age, geochemical and isotopic evidence confirm suprasubduction zone origin. Canadian Journal of Earth Sciences, 28, 135-162.
Khan, M., Kerr, A.C., Mahmood, K., 2007. Formation and tectonic evolution of the Cretaceous–Jurassic Muslim Bagh ophiolitic complex, Pakistan: Implications for the composite tectonic setting of ophiolites. Journal of Asian Earth Sciences, 31, 112-127.
Kretz, A., 1983. Symbols for rock forming minerals. American Mineralogist, 68, 277-279.
Mahmood, K., Boudier, F., Gnos, E., Monié, P., Nicolas, A. 1995. 40Ar / 39Ar dating of the emplacement of the Muslim Bagh ophiolite, Pakistan. Tectonophysics, 250, 169-181.
Mahmood, K., Khan. M. 1999. Structural characteristics of Gabbroic rocks from Saplai Tor Ghar Massif, Muslim Bagh ophiolite, Pakistan. Acta Mineralogica Pakistanica, 10, 27-36.
Nicolas, A., 1989. Structures of Ophiolites and Dynamics of Oceanic Lithosphere. Kluwer, Dordrecht.
Pearce, J.A., 1996. A user's guide to basalt discrimination diagrams. In: Bailes, A. H., Christiansen, E.H., Galley, A.G., Jenner, G.A., Keith, Jeffrey, D., Kerrich, R., Lentz, David, R., Lesher, C.M., Lucas, Stephen B., Ludden, J.N., Pearce, J.A., Peloquin, S.A., Stern, R.A., Stone, W.E., Syme, E.C., Swinden, H.S., Wyman, D.A., (Eds.), Trace element geochemistry of volcanic rocks; applications for massive sulphide exploration, Short Course Notes-Geological Association of Canada, 12, 79-113.
Pearce, J.A., Cann, J.R., 1973. Tectonic setting of basic volcanic rocks determined using trace element analysis. Earth and Planetary Science Letters, 19, 290-300.
Pearce, J.A., Lippard, S.J., Roberts, S., 1984. Characteristics and Tectonic significance of supra-subduction ophiolites. In: Kokelaar, B.P., Howels, M.F. (Eds.), Marginal Basin Geology. Geological Society London Special Publications, 16, 77-94.
Penrose Conference, 1972. Penrose field conference on ophiolites, Geotimes, 17, 24-25.
Saunders, A.D., Tarney, J., 1991. Back-arc basins. In: Floyd, P. (Ed.), Ocean Basalts. Blackie, London, 219-263.
Siddiqui, R.H., Aziz, A., Mengal, J.M., Hoshino, K., Sawada, Y., 1996. Geology, Petrochemistry and Tectonic Evolution of Muslim Bagh Ophiolite Complex Balochistan, Pakistan. Geologica; Geoscience Laboratories, Geological Survey of Pakistan, 3, 11-46.
Staudigel, H., 2003. Hydrothermal alteration processes in the oceanic crust. In: Holland, H.D., Turekian, K.K., (Eds.), Treatise on geochemistry, 3, 511-535.
Sun, S.-S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: Implications for mantle com In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins. Geological Society Special Publication, 42, 313-345.
Van Vloten, R., 1967, Geology and chromite deposits of the Nisai area, Hindu Bagh mining district, West Pakistan. Geological Survey of Pakistan, 2, 32.
Winchester, J.A., Floyd P.A., 1976. Geochemical magma type discrimination: Application to altered and metamorphosed igneous rocks. Earth and Planetary Science Letters, 28, 459469.
Wood, D.A., 1980. The application of a Th-Hf-Ta diagram to problems of tectono-magmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the British Tertiary volcanic province. Earth and Planetary Science Letters, 50 (1), 11-30.
