Document Type : Original Research Paper

Authors

1 Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran

2 School of Earth Sciences, Damghan University of Basic Sciences, Damghan, Iran

Abstract

Peridotites (Cpx-bearing harzburgites, lherzolites, wherlites and dunites) associated with pegmatite gabbros, gabbro impregnations, gabbroic-diabasic dikes, pyroxenites and websterites are the main constituents of the mantle sequence in the Nain ophioliote assemblage. Petrographic and geochemical studies indicate that peridotites in the Nain ophiolites are Cpx-bearing harzburgites with Al-rich spinels (Cr#=16.12-41.55) equilibrated at about 1000˚C. Pegmatite gabbros are found as small pockets within peridotites showing deformed clinopyroxenes and plagioclases. Gabbro-diabase dikes, mostly rodingitized, injected into the peridotites without chilled margins. These dikes are geochemically co-genetic with pillow lavas and micro-gabbros of the crustal sequence, but display variable degrees of partial melting. Based on the geochemistry of the mafic rocks and the peridotites, we suggest that Nain ophiolites were developed in a back arc spreading basin.
 

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References
Agard, P., Monie, P., Gerber, W., Omrani, J., Molinaro, M., Meyer, B., Labrousse, L.,Vrielynck, B., Jolivet, L., Yamato, P., 2006- Transient, synobduction exhumation of Zagros blueschists inferred from P-T, deformation, time, and kinematic constraints: Implications for Neotethyan wedge dynamics, Geophys. Res. 111, B11401, doi:10.1029/2005JB004103.
Arai, S., 1994 - Compositional varation of olivine-chromian spinel in Mg-rich magmas as a guide to their residual spinel peridotites, Volcanology and Geothermal Research 59 279-293.
Arai, S., 1994- Characterization of spinel peridotites by olivine-spinel compositional relationships: review and interpretation. Chemical geology, 113 191-204. 
Arvin, M., Robinson, P.T., 1994- The petrogenesis and tectonic setting of lavas from the Baft ophiolitic mélange, southwest of Kerman, Iran. Can, Earth Sciences, 31, 824-834.           
Arvin, M., Shokri, E., 1997- Genesis and eruptive environment of basalts from the Gogher ophiolitic mélange, southwest of Kerman, Iran. Ofioliti, 22, 175-182.
Babaie, H. A., Ghazi, A. M., Babaei, A., La Tour, T.E., Hassanipak, A. A., 2001- Geochemistry of arc volcanic rocks of the Zagros Crush Zone, Neyriz, Iran, Asian Earth Sci, 19, 61-76.
Berberian, M., King, G. C. P., 1981- Towards a paleogeography and tectonic evolution of
Brey,G. P. & Kohler, T.,1990- Geothermobarometry in fourphaselherzolites,II,New thermobarometers,and practicalassessment of existing thermobarometers, Petrol, 31, 1353–1378.
Cannat, M., 1996- How thick is the magmatic crust at slow spreading ridges?, Geophys. Res. 101, 2847-2857.
Coleman, R.J., 1977- Ophiolilte. Springer, New York.
Davoudzadeh, M., 1972-  geology and petrology of the area North of Nain, Central Iran. Rep.No.1.
Dick, H. J. B., Bullen, T., 1984- Chromaian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas. Contributions to Mineralogy and Petrology, 8654-76.  
Ghazi, A. M., Hassanipak, A. A., 2000- Petrology and geochemistry of the Shahr-Babak ophiolite, Central Iran. Geological Survey of America, Special paper, 349, 485-497.
Girardeau, J., Francheteau, J., 1993- Plagioclase-wehrlite and peridotites on the East Pacific Rise (Hess Deep) and the Mid-Atlantic, Ridge (DSDP Site 334): evidence for magma percolation in the oceanic upper mantle. Proc.Ocean Drill. Prog: Sci. Res, 115, 137-149.
Girardeau, J., Monnier, C., Lemee, L., Quatrevaux, F., 2002- The Wuqbah peridotite, central Oman ophiolite: Petrological characteristics of the mantle in a fossil overlapping ridge setting. Marine Geophys. Res. 23, 43-56.
Godard, M., Jousselin, D., Bodinier, J. L., 2000- Relationships between geochemistry and structure beneath paleo-spreading center: a study of the mantle section in the Oman ophiolite. Earth Planet. Sci. Lett. 180, 133-148.
Ionov, D. A., Bodinier, J. L., Mukasa, S. B., Zanetti, A., 2002- Mechanismsand sources of mantle metasomatism: major and trace element conditionsof peridotite xenoliths from Spitzbergen in the context of numerical modeling, Petrol. 43/12.
Iran. Can. J. Earth Sciences 18, 210-265.
Jin, Z.A., Green, H.W., Zhou, Y., 1994- Melt topology in partially molten mantle peridotite during ductile deformation, Nature,372:164-1670.
Kepezhinskas, P. K., Defant M. J., Drummond, M.s., 1995- Na metasomatism in the island-arc mantle by slab melt-peridotite interaction: evidence from mantle xenoliths in the North Kamchatka arc. Journal of Petrology 36 1505-1527.   
Kinzler, R.J., 1997- Melting of mantle peridotite at pressures approachingthe spinel to garnet transition: application to midocean ridge basaltpetrogenesis, Geophys. Res. 102, 853–874.  
Li, C. N., 1992-   Petrology of Igneous Trace Elements. ChinaUniversity of Geosciences Press, Wuhan(in Chinese) .
Meschede, M., 1986- A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram, Chemical Geology, 56 207-218.
Nicolas, A., 1989- Structure of ophiolites and dynamics of oceanic lithosphere, Kluwer Academic publishers.
Nicolas, A., Prinzhofer A., 1983- Cumlative or residual origin for the transition zone in ophiolites., Jurnal of structural evidence, 24 188-206 .
Niu, Y., Hekinian, R., 1997- Basaltic liquids and harzburgitic residues in the Garrett Transform: a case study at fast-spreading ridges, Earth Planet. Sci. Lett. 146, 243-258.
Pearce, J. A ., 1996- A users guide to basalt discrimination diagrams.In: Wyman D. A.(Ed.), Trace Elemant Geochemistry of Volcanic Rocks: Applications for Massive Sulphid Exploration, Short Course Notes-Geol. Assoc.Can., Vol.12pp.79-113. 
Pearce, J. A., Parkinson, I. J., 1993- Trace element models for mantle melting: application to volcanic arc petrogenesis. In: Prichard H.M.,Alabaster T.,Harris N.B., Neary C. R.(Eds.), Magmatic Processes and Plate Tectonics. Geological Society of London, Special Publication, vol.79, pp.373-403.
Sachlleben, T. h. and Seck,H, .A., 1981- Chemical control of Al-solubility in orthopyroxene and its implications on pyroxene geothermometry Contnbutions to Mineralogy and Petrology, 78,157-165.
Saunders, A., Tarney, J., 1991- Back-arc basins. In: Floyd, P.A. (Ed.), Oceanic basalts, Blackie and Son Ltd., 219-263.
Shahabpour, J., 2004- Tectonic evolution of the orogenic belt in the region located between Kerman and Neyriz, Asian Earth Sci. 24 ,405–417.
Shervais, J. W., 1982-  Ti-V plots and the petrogenesis of modern and ophiolitic lavas. Earth Planet.Sci. Lett.59 101-118.  
Taylor, W. R., 1998- An experimental test of some geothermometer and geobarometer formulations for upper mantle peridotites with application to the thermobarometry of fertile lherzolite and garnet websterite. Neues Jahrbuch für Mineralogie, Abhandlungen, 172, 381–408.
Winchester, J. A ., Floyd, P. A., 1977- Geochemical discrimination of different magma series and their differentiation products using immobile elements, Chemical geology, 20325-343.  
Wood, D. A., 1980- The application of a Th-Hf-Ta diagram to problems of tectonomagmatic classification and to establishing the nature of crustal contamination of basaltic lavas of the  British Tertiary volcanic province. Earth Planet. Sci. Lett.,50 11-30.