R Dabiri; M.H Emami; H Mollaei; M Ghaffari; M Vosougi Abedini; N Rashidnejad Omran
Abstract
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. ...
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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.
Monireh Kheirkhah; M. H. Emami
Abstract
At the farthest end of NW Iran, the Quaternary basalts crop out in Azerbaijan province, located in Alpine – Himalaya belt and highly pleatue of Iran-Turkish, eastern Anatolian. The Quaternary volcanic units of NW Azerbaijan cover a broad compositional range from basalts, basaltic andesite, trachy ...
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At the farthest end of NW Iran, the Quaternary basalts crop out in Azerbaijan province, located in Alpine – Himalaya belt and highly pleatue of Iran-Turkish, eastern Anatolian. The Quaternary volcanic units of NW Azerbaijan cover a broad compositional range from basalts, basaltic andesite, trachy andesite to trachyte. These rocks are erupted from deep tension, strike-slip faults in a pull a part basin and volcanic centers. Source of primary magmas and crustal contamination processes have certainly contributed to the understanding of the origin of basaltic rocks. Based on field area, petrography and petrology studies, 10 samples were selected for 143Nd/144Nd and 87Sr/86Sr measurements. The obtained results were correlated with other isotopic data of similar Quaternary basaltic rocks from Turkey. Isotopic study indicates that all of these rocks are derived from mantle and plot in Bulk Earth field and mantle array. The basaltic rocks in the northern area are derived from a depleted mantle and those from the southern area shows contamination by crust.
