Document Type : Original Research Paper
Author
Ph.D., Department of Geology, Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran
Abstract
The Intrusive bodies of the Karaj-Taleghan Axis, situated in the Central Alborz zone have lithological compositions including gabbro, monzogabbro, monzodiorite, monzonite andfelsic dikes of alkali feldspar syenite to syenite. Furthermore, they are accompanied by pyroclastic rocks of the Karaj formation, for which Oligocene age is considered. Geological surveys, mineralogical and geochemical studies indicated that the parental magma of this complex had shoshonitic and meta-aluminous nature. Petrological evidence show that fractional crystallization from gabbro to monzonite had main role in genesis of these rocks. Enrichment in LILE) Ba, Rb and Th(and depletion in HFSE (Nb and Ti) in Rare Earth Elements distribution patterns of spider diagrams, indicate an subduction-related environment for formation of these rocks. Also they are enriched in LREE rather than HREE, the characteristics which are usually observed in the rocks from subduction environments and active continental margins. Chemical and petrological studies indicate a common source for these igneous rocks and the main role of fractional crystallization in the evolution of magma, although, minor amounts of assimilation and contamination of magma by crustal rocks occurred. The alkaline magma formed by low degree partial melting of an enriched sub-continental lithospheric garnet-lherzolite mantle. Contribution of both the lithospheric and asthenospheric mantles in petrogenesis of the Karaj-Taleghan basic rocks might be attributed to a tensional geodynamic setting with change in subduction dip in the form of roll back, dominated at the final stage of the subduction of Neotethyan plate beneath Iran in upper Oligocene (Chattian).
Keywords
Abdollah, S. A., Said, A. A. and Visona, D., 1997- New geochemical and petrographic data on the gabbrosyenite suite between Hargeysa and Berbera Shiikh (North Somalia). J. of African Earth ciences, Vol, 23, No.3. pp.303-373.
Annells, R. N., Arthurton, R. S., Bazley, R. A. B., Davies, R. G., Hamedi, M. A. R. and Rahimzadeh, F., 1977- Geological map of Iran, Shakran sheet 6162 Tehran, Geological Survey of Iran, scale 1:100,000.
Bogaerts, M., Scaillet, B., Liégeois, J. P. and Auwera, J. V., 2003- Petrology and geochemistry of the Lyngdal granodiorite (Southern Norway) and the role of fractional crystallization in the genesis of Proterozoic ferro-potassic A-type granites Elsevier Science 124, 149-184.
Boynton, W. V., 1984- Geochemistry of the rare earth elements: Meteorite studies. In: Rare Earth element geochemistry (Ed. Henderson, P.) 63-114. Elsevier, Amsterdam.
Conceicao, R. V. and Green, D. H., 2004- Derivation of potassic (shoshonitic) magmas by decompression melting of phlogopite+pargasite lherzolite. Journal of Geology 72: 209-229.
Conly, A. G., Bernan, J. M., Bellon, H. and Scott, S. D., 2005- Arc to rift transitional volcanism in the Sanata Rosalia Region, Baja California Sur, Maxico. Journal of Geology 72: 303-341.
Cotton, J., Le, Dez A., Bau, M., Caroff, M., Maury, R. C., Dulski, P., Fourcade, S., Bohn, M. and Brousse, R. 1995- Origin of anomalous rare earth element and yttrium enrichments in subaerially exposed basalts, evidence from French Polynesia. Chemical Geology 119: 115-138.
Cox, K. G., Bell, J. D. and Pankhurst, R. J., 1979- The interpretion of igneous rocks. Allen and Uniwin, London.
De La Roche, H., Leterrier, J., Grandclaude, P. and Marchal, M., 1980- A classification of volcanic and plutonic rocks using R1R2-diagram and major element analyses – its relationships with current nomenclature. Chemical Geology 29, 183–210.
Ellam, R. M. and Cox, K.G., 1991- An interpretation of Karoo picrite basalts in terms of interaction between asthenospheric magmas and the mantle lithosphere.
Furman, T., 2007- Geochemistry of East African Rift basalts: An overview, Journal of African Earth Sciences 48, 147-160.
Harker, A., 1909- The natural history of igneous rocks. Methuen and Co. London.
Jiang, Y. H., Jiang, S. Y., Ling, H. F., Zhou, X. R., Rui, X. J. and Yang, W. Z., 2002- Petrology and geochemistry of shoshonitic plutons from the western Kunlun orogenic belt, China: implications for granitoid geneses. Lithos 63: 165-187.
Lopez-Plaza, M., Peinado, M., Lopez-Moro, F. J., Rodriguez-Alonso, M. D., Carnicero, A., Franco, M. P., Gonzalo, J. C. and Navidad, M., 2007- Contrasting mantle sources and processes involved in a peri- Gondwanan terrane: A case study of pre-Variscan mafic intrusives from the autochthon of the Central Iberian Zone. Geological Society of America, Special Papers 423: 297-313.
Pearce, J. A., 1983- Role of the sub-continental lithosphere in magma genesis at active continental margins. In: Continental Basalts and Mantle Xenoliths (Eds. Hawkesworth, C. J. and Norry, M. J.) 230-249. Shiva, Nantwich.
Peccerillo, A. and Taylor, S. R., 1976- Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, northern Turkey. Contribution to Mineralogy and Petrology 58: 68-81.
Rollinson, H., 1993- Using geochemical data, evaluation, presentation, interpretation. Harlow, Longman, London.
Ryerson, F. J. and Watson, E. B., 1987- Rutile saturation in magmas: implications for Ti Nb-Ta depletion in island-arc basalts. Earth and Planetary Science Letters 86: 225-239.
Shand, S. J., 1943- Eruptive rocks, Their genesis, composition, classification, and their relations to ore - deposits. John Wiley and Sons, Inc., New York.
Sun, S. S. and Mc Donough, W. F., 1989- Chemical and isotopic systematic of oceanic basalts: implication for mantle composition and process. In: Magmatism in the ocean basins (Eds. Saunders, A. D. and Norry, M. J.) 42: 313-345. Geological society, London
Thompson, R. N., 1982- British Tertiary volcanic province. Scottish Journal of Geology 18: 49-107.
Thriwall, F. M., Upton, B. J. and Jenkins, C., 1994- Interaction between continental lithosphere and Lceland plume- Sm- Nd- Pb isotope geochemistry of Tertiary basalts, Ne Greenland, Journal of Petrology 35, 839-879.
Wyllie, P. J. and Skine, T., 1982- The formation of mantle phlogopite in subduction zone hybridization. Contribution to Mineralogy and Petrology 79: 375-380.
)