TY - JOUR ID - 43953 TI - Investigation of Magmatic Processes in the Quaternary Volcanism in NW of Ahar: a Geochemical and Isotopic Study JO - Scientific Quarterly Journal of Geosciences JA - GSJ LA - en SN - 1023-7429 AU - Dabiri, R AU - Emami, M.H AU - Mollaei, H AU - Ghaffari, M AU - Vosougi Abedini, M AU - Rashidnejad Omran, N AD - Assistant Professor, Department of Geology, Mashhad Branch, Islamic Azad University, Mashhad, Iran AD - Associate Professor, Department of Geology, Islamic Azad University, Islamshahr Branch, Tehran, Iran AD - Associate Professor, Department of Geology, Islamic Azad University, Science and Research Branch, Tehran, Iran AD - Assistant Professor, Department of Geology, Tarbiat Modares University, Tehran, Iran Y1 - 2014 PY - 2014 VL - 23 IS - 90 SP - 55 EP - 62 KW - Quaternary KW - Geochemistry KW - Isotopic study KW - Fractional Crystallization KW - Crustal contamination KW - NW Iran KW - Ahar DO - 10.22071/gsj.2014.43953 N2 - Quaternary volcanic rocks are widely developed in NW of Ahar, NW Iran. Based on geochemical data, these rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and trachyandesites. The major- and trace-element chemistry indicates that the lavas are dominantly alkaline in character. The studied rocks display microlithic porphyritic texture with phenocrysts of olivine, clinopyroxene, and plagioclase ± amphibole ± biotite. Major and trace element abundances vary along continuous trends of increasing SiO2, Al2O3, K2O, Na2O, Ba and Rb decreasing CaO, Fe2O3* and Cr with decreasing MgO.The volcanic rocks in this area are characterized by the LILE and LREE enrichments and negative HFSE anomalies. The Sr and Nd isotopic ratios vary from 0.704463 to 0.704921and from 0.512649 to 0.512774, respectively.CaO/Al2O3 ratios versus MgO, La/Sm ratios versus Rb and Ba and Zr versus Th suggest that that fractional crystallization was a major process during the evolution of magmas. AFC modeling and isotopic data as well as microscopic evidence, clearly indicate that crustal contamination accompanied by the fractional crystallization played an important role in petrogenesis of the trachyandesites. Also, geochemical and isotopic compositions indicate that magma mixing was not essential process in the evolution of Ahar magmas. Alkali basaltswith high 143Nd/144Nd ratio, low 87Sr/86Sr ratio and high MgO, Ni and Cr contents indicate that they crystallized from relatively primitive magmas. REE modelling and Trace element ratios indicate that the alkali baslats were derived by small degrees (~1-3%) of partial melting from the spinel lherzolite. UR - http://www.gsjournal.ir/article_43953.html L1 - http://www.gsjournal.ir/article_43953_f4e9dca3bdcbe122c319d589cbdb84e3.pdf ER -