Geochemistry of Sabzevar regional metamorphic rocks, northern Central Iranian Microcontinent Blocks (CIM)

Abstract

HP/LT metabasite rocks can preserve some evidences of tectonic and geochemical processes of a subduction zone. Sabzevar Ophiolite and metabasites which are located at the north of Central Iranian Microcontinent Block (CIM) have preserved such evidences. The metabasites are fossil oceanic crust of Neotethys-related basin. Metabasites are composed of glaucophane schist, amphibolite and greenschist. Major and trace element contents of the rocks indicate that blueschist and amphibolite protoliths were MORB basalts. Rare earth elements show presence of two MORB types, N- and E-MORB. ΣREE is 132-246 (ppm) and 617-744 (ppm) for the N- MORB and E-MORB basalts, respectively.  La/Yb ratio is ranging from 0.43-0.79 for N-MORB and 8.7 and 1.1 for E-MORB. The Mg# ranges are between 0.24-0.27, 0.23-0.24, 0.42 and 0.38 for glaucophane schist, garnet amphibolite, amphibolite and chlorite schist, respectively, which indicates a weak fractional crystallization in the original magma. High pressure rocks were formed due to northward subduction of Neotethys-branch of Sabzevar basin between CIM and Eurasia since Upper Cretaceous to Eocene. 

Keywords


[1] McCall G.J.H., ''The geotectonic history of Makran and Adjacent areas of southern Iran'', Journal of Asian Earth Sciences. 15 (1977) 517-531.

[2] Stöcklin J., ''Possible ancient continental margins in Iran. In: C.A., Burk and C.L., Drake. The geology of continental margins'', New York Springer, (1974) 837-887.

[3] Babazadeh S.A., De Wever P., ''Radiolarian Cretaceous age of Soulabest radiolarites in ophiolite suite of eastern Iran''. Bulletin de la Société géologique de France, 175 (2004) 121-129.

[4] Shojaat B., Hassanipak A.A., Mobasher K., Ghazi A.M., ''Petrology, geochemistry and tectonics of the Sabzevar ophiolite, North Central Iran'', Journal of Asian Earth Sciences. 21, (2003) 1053-1067.

[5] Nasrabady M., Rossetti F., Theye T., Vignaroli, G., ''Metamorphic history and geodynamic significance of the Early Cretaceous Sabzevar granulites (Sabzevar structural zone, NE Iran)''. Solid Earth, 2, (2011) 219-243.

[6] Omrani H., Oberhänsli R., Moazzen M., Altenberger U., Lange, M., ''Sabzevar blueschists from North Central Iranian micro-continent: Vestiges of the Neotethys related oceanic crust subduction''. 9th International Eclogite Conference 2011, Mariánské Lázně, Czech Republic.

[7] Mocek B., "Geochemical evidence for arc-type volcanism in the Aegean Sea: the blueschist unit of Siphons, Cyclades (Greece)", Lithos 57 (2001) 263-289.

[8] Volkova N. I., Budanov V. I., "Geochemical discrimination of metabasalt rocks of the Fan-Karategin transitional blueschist/greenschist belt, South Tianshan, Tajikistan: Seamount volcanism and accretionary tectonics'', Lithos 47 (1999) 201-216.

[9] Winchester J. A., Floyd P. A., ''Geochemical discrimination of different magma series and their differentiation products using immobile elements''. Chemical Geology 20 (1977) 325-343.

[10] Pearce J.A., Norry M.J., ''Petrogenetic Implications of Ti, Zr, Y, and Nb Variations in Volcanic Rocks'', Contribution to Mineralogy and Petrology 69 (1979) 33-47.

[11] Hastle A. R., Kerr A. C., Pearce J. A., Mitchell S. F., ''Classification of altered volcanic island arc rocks using immobile trace elements: development of the Th-Co discrimination diagram'', Journal of petrology 48 (2007) 2341-2357.

[12] Pearce J. A., Cann J. A., ''Tectonic setting of basic volcanic rocks determined using trace element analyses'', Earth Planetary Scince Latter 19 (1973) 290-300.

[13] Meschede M., ''A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram'', Chemical Geology 56 (1986) 207-218.

[14] Evenson N. M., Hamilton P. J., O’Nions R. K., ''Rare earth elements in chondritic meteorites'', Geochimica Cosmochimca Act. 42 (1978) 1199-1212.

[15] Cotten J., Le Dez A., Bau M., Caroff M., Maury R. C., Dulski P., Fourcade S., Bohn M., Brousse R., ''Origin of anomalous rare-earth element and yttrium enrichments in subaerially exposed basalts: evidence from French Polynesia'', Chemical Geology 119 (1995.) 115-138.

[16] Razavi S.M.H., Nasrabady M., ''Mineralogy, thermobarometry and tectonic setting interpretation of gneisses from western Soltan Abad (NE Sabzevar)'', Iranian Journal of Crystallography and Mineralogy, issue 2 (2011) 227-240.

[17] Amini S., Fotoohi Rad G., ''Geochemistry and Petrogenesis of Metabasites in Gazik area in east of Birjand'', The 23th Symposium on Geoscience, Tehran, Iran (2004).

[18] Ghazi A.M., Hassanipak A.A., Mahoney J.J., Duncan R.A., ''Geochemical characteristics, 40Ar-39Ar ages and original tectonic setting of the Band-e-Zeyarat/Dar Anar ophiolite, Makran accretionary prism, S.E. Iran'', Tectonophysics 393 (2004) 175-196.

[19] Stöcklin J., ''Structural correlation of the Alpine range between Iran and Central Asia'', Societé Geologie de la France Memoire Hors-Serve 8 (1977) 333-353.

[20] Shafaii Moghadam H., Rahgoshay M., Whitechurch H., ''The Nain-Baft ophiolites: An evidence of back-arc basin spreading in the active margin of the Iranian continent'', European Geophysical :union: Conference 9 (2007) SRef-ID: 1607–7962/gra/EGU2007-A-00791.

[21] Shafaii Moghadam H., Stern R.J., Rahgoshay M., ''The Dehshir ophiolite (central Iran): Geochemical constraints on the origin and evolution of the Inner Zagros ophiolite belt'', Geological Society of America Bulletin 122 (2010) 1516-1547.

[22] Sinton J. M., Detrick R. S., ''Mid-ocean ridge magma chambers'', Journal of Geophysical Research 97 (1992) 197-216.

[23] Babazadeh S.A., ''Cretaceous Radiolarians from Birjand ophiolitic range in Sahlabad province, eastern Iran'', Revue de Paléobiologie, Genève 26 (2007) 89-98.