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Resumen
Zaker volcanic units are located in the western Alborz Zone (northeast of Zanjan). Volcanic rocks of this area are combinations of basalt, andesite and trachy andesite. In these units, pyroxene, plagioclase and rarely olivine crystals are as phenocrysts in a background of fine crystals and glass minerals. Of course, also, some small outcrops of andesite tuff units are observed. These units are metaluminous and are located in ranges from high calcium calc -alkaline to shoshonitic rocks natures. The significant feature of these units is the enrichment of LREE elements relative to HREE. Furthermore, positive anomalies of LILE elements such as Cs, Ba, K and Sr along with negative anomalies of HFSE elements such as Ti, Nb and P are observed in all samples. Negative anomalies of Nb and enrichment of light rare earth elements relative to heavy rare earth elements, represent the subduction zone environments. The formation environments of these units are continental arcs and the primary magma is composed of partial melting of garnet spinel lherzolite with a very small amount of garnet during the melting process. The low ratio of (La / Yb) N (6.79-4.6) in all volcanic units indicates the absence of garnet at the origin or the partial presence of this mineral in the source of the magma. The geochemical characteristics of these units indicate that magma has originated from high horizons of the mantle (probably a lithospheric mantle) and has tolerated some crust contaminations during the ascent.
Citas
Aghanabati, A. (2004) Geology of Iran. Geological Survey of Iran, Tehran (in Persian).
Alavi, M. 1991. Sedimentary and structural characterics of palo-Tethys remnants in northeastern Iran. Geol. Soc. Of Amer. Bull. V. 103, PP. 983-992.
Aldanmaz, E., Koprubasi, N., Gurer, O. F., Kaymakci, N. and Gournaud, A. (2006) Geochemical constraints on the Cenozoic, OIB-type alkaline volcanic rocks of NW Turkey: implications for mantle sources and melting processes. Lithos 86: 50-76.
Allen, M. B., Jackson, J. and Walker, R. (2004) Late Cenozoic reorganization of the Arabia-Eurasia collision and the comparison of short-term and long-term deformation rates. Tectonics 23: 1-16.
Al-Saleh, A. M. and Boyle, A. P. 2001. Neoproterozoic ensialic back-arc spreading in the eastern Arabian Shield: geochemical evidence from the Halaban Ophiolite. African Journal of Earth Sciences. 33 (1), 1-15.
Berberian, F. and Berberian, M. (1981) Tectono-plutonic episodes in Iran. In: H.K., Gupta and F.M., Delany (Eds.): Zagros, Hindukosh, Himalaya geodynamic evolution. American Geophysical Union, Washington 5-32.
Boynton W.V., Ë Cosmochemistry of the rare earth elements; meteorite studies. In: P. Henderson (Editor), The rare earth element geochemistryË, Elsevier, Amsterdam, (1984) 115-1522.
Cox, K. G. Bell, J. D. and Pankhurst, R. J. 1979. The Interpretation of Igneous Rocks. George Allen and Unwin.-
Edward C.M.H., Menzies M.A., Thirlwall M.F., Morrid J.D., Leeman W.P., Harmon R.S., ËThe transition to potassic alkaline volcanism in island arcs: the Ringgite-Beser Complex, East JavaË, Journal of Petrology, 35(1994): 1557-1595.
Hirayama, et al., "Geological Map of Iran 1:100000 Series Sheet Tarom", (1966).
Ionov, D. & Hofmann, A. 1995. Nb-Ta-rich mantle amphiboles and micas: Implications for subduction-related metasomatic trace element fractionations. Earth and Planetary Science Letters, 131(3-4), 341–356.
Irvine, T.N. and Baragar, W.R.A. 1971. A guide to the chemical classification of the common volcanic rocks, Canadian J. Earth Sci., 8, 523-548. Geological Society Special Publica ¬tion, 30: 415-431.
McKenzi D., O'Nions R.K., ËPartial melt distribution from inversion of rare earth element concentratorsË, Journal of Petrology, 32 (1991) 1021-1091.
Nabavi, M. (1977) Geology of Iran. Geological Survey of Iran, Tehran (in Persian).
Peccerillo, A. and Taylor, S.R., 1976. Geochemistry of Eocene calc-alkaline volcanic rocks from the Kastamonu area, Northern Turkey. Contributions to Mineralogy and Petrology, 58(1): 63-81.
Nagudi N., Koberl Ch., Kurat G., ËPetrography and Geochemistry of the sigo granite, Uganda and implications for originË, Journal of African earth Sciences, 36 (2003) 1-14.
Nicholson K. N., Black P. M., Hoskin P. W. O., Smith I. E. M., "Silicic volcanism and back-arc extension related to migration of the Late Cainozoic Astralian-Pacific plate boundary. In: Asiabanha. A., Ghasemi. H. and Meshkin. M., 2009. Paleogene continental-arc type volcanism in NorthQazvin, North Iran", facies analysis and geochemistry. Schweizerbartsche Verlagsbuchhandlung. v. 186/2; (2004) p. 201-214.
Rollinson, H.R. 1993. Using geochemical data: evaluation, presentation, interpretation. Longman Group, UK lst edition. 352p.
Rollinson, H., Ë Using geochemical data: evolution, presentation, interpretationË, Longman Scientific and Technical, (1989) 248.
Sajjona F.G., Maury R.C., Bellon H., Cotten J., Defant M., ËHigh Field Strength Element Enrichment of Pliocene””Pleistocene Island Arc Basalts, Zamboanga Peninsula, Western Mindanao (Philippines)Ë, Journal of petrology, 37 (1996) 693-726.
Saunders A.D., Storey M., Kent R.W., Norry M.J., ËConsequences of plume–lithosphere interactions. In: B.C. Storey, T. Alabaster and R.J. Pankhurst (Editors), Magmatism and the Causes of Continental Break-upË, Geological Society London Special Publication, (1992) 41–60.
Sengor, A. M. C., Altiner, D., Cin, A., Ustaomer, T. and Hsu, K. J. (1988) The Tethyside orogenic collage. In: M. G., Audley-Charles and A., Hallam (Eds.): Gondwana and Tethys. Geological Society and Oxford University Press, Special Publication of the Geological Society 37: 119-181.
Schandl, E. S. and Gorton, M. P. (2002) Application of high field strength elements to discriminate tectonic settings in VMS environments. Economic Geology 97: 629-642
Shand S.J., ËEruptive rocks; their genesis, composition, classification and their relation to ore-depositsË, Hafner Publishing Company, New York, (1947) 448.
Shaw D.M., ËTrace element fractionation during anataxisË, Geochimica et Cosmochimica Acta, 34 (1970) 237-243.
Stampfli, G. M., Marcoux, J. and Baud, A. (1991) Tethyan margins in space and time. Palaeogeography, Palaeoclimatology, Palaeoecology 87: 373-409.
Stocklin, J., Eftekharnezhad, J. "Geological map of Zanjan", (1968) 1:250000 GSI.
Sun S.S., McDonough W.F., ËChemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: A.D. Saunders and M.J. Norry (Editors), Magmatism in the Ocean BasinsË, Geological Society of London (1989) 313–345.
Tepper J.H., Nelson B.K., Bergantz G.W., Irving, A.J.,ËPetrology of the Chilliwack atholith, North Cascades, Washington: generation of calc-alkaline granitoids by melting of mafic lower crust with variable water fugacityË, Contributions to Mineralogy and Petrology, 113 (1993) 333-351.
Wensink, H. and Varekamp, J. C. (1980) Paleomagnetism of basalts from Alborz: Iran part of Asia in the Cretaceous. Tectonophysics 68: 113-129.
Wilson, M. 1989. Igneous petrogenesis: a global tectonic approach, Unwin Hymen, London, 466 pp.
Winchester J.A., Floyd P.A.,ËGeochemical discrimination of different magma series and their differentiation protextures and setting of VMS mineralization in the Pilbara ducts using immobile elementsË, Journal of Chemical Geology 20 (1977) 325-344.
Wood D.A., ËThe 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 provinceË, Earth Planet. Sci. Lett., 50 (1980) 11-30.