Showing 4 results for Basalt
Volume 8, Issue 3 (2-2009)
Abstract
The Javaherdasht basalts have considerable outcrops in the north part of Alborz mountains in the east of Guilan province.The petrographical, geochemical and isotopical evidence is indicative of the contamination of the basalts with continental crust. The petrographical evidence such as corosion gulf and crenated margins in pyroxene phenocrysts and chemical composition difference between clinopyroxene phenocrysts margins with matrix clinopyroxenes suggest of crustal contamination and nonequilibrium due to the change of matrix composition as compared with pre-existed phenocrysts in rock .The depletion in elements such as Zr, Nb,TiO2 ,P2O5 and enrichment of LIL elements,high ratios of Pb/Nd and Ba/Nd,low content of Zr/Nb,Y/Nb,Ce/Pb, positive correlation between SiO2 and 87 Sr/86Sr and positive correlatian between MgO and Nd are geochemical and isotopical evidences of crustal contamination of these basalts. Our studies show that these basalts have a clear elemental equilibrium with lower and middle crust rocks and that they have been contaminated with them.
Faribourz Masoudi, Roghieh Doroozi,
Volume 13, Issue 4 (2-2014)
Abstract
In the northern hillside of Central Alborz, in south Marzanabad, there are outcrops of basic volcanic rocks which attributed to Cretaceous time .In this study, effective processes on evolution of these volcanic rocks are surveyed to add on our knowledge about Mesozoic magmatisim in Central Alborz. Based on petrographical and geochemical studies, south Marzanabad basic rocks could be classified into 2 groups of basalt and andesite basalt. Geochemical diagrams imply that the magma nature is alkaline and generated in intracontinetal extensional environment. Microscopic studies, mineral chemical composition and the observed trends in geochemical diagrams of whole rocks, all are inline with fractional crystallization as a main magmatic process. Fractionation began with crystallization of olivine and pyroxene and minor plagioclase in basalts and continued with crystallization of clinopyroxene and plagioclase in andesite basalt. In addition to petrographical, mineralogical and chemical evidences, the occurrence of fractional crystallization process is confirmed by the geochemical modeling with Melts software which also let us to reconstruct the condition of fractionation process. Based on the fractional crystallization modeling in south Marzanabad basic volcanic rocks, basalts are generated by 40 percent of fractional crystallization from primary magma. Basaltic andesites also produced after the fractionation of basalts, during 70 percent fractional crystallization from the same magma. Olivine thermobarometric studies also confirm the accuracy of data which is obtained by the Melts software.
Mehraj Aghazadeh, Adel Sarkhoshi, ,
Volume 16, Issue 41 (5-2015)
Abstract
In the North of Bam city there were extensive volcanism and outcrops are basic and felsic volcanic rocks that crosscut by various dykes The volcanic rocks have sub alkaline and calc-alkaline to shoshonitic characteristic, however dykes are alkaline and potassic in nature. In the spider diagram all samples show enrichment in the LILEs and depletion and troughs in the HFSs elements that coincide with subduction related and upper crust rocks features. The studied samples represent enrichment in the LREE with various (La/Yb)N ratio and rhyolites show clear trough in Eu. According to geochemical features, studied rocks generated from different sources. Trachy andesy basalts and trachy andesites formed from 1-10% partial melting of metasomatized spinal lherzolite source. Dacitic magma generated from partial melting of mafic source in the lower crust while rhyolites formed from partial melting of metagreywacke source. The olivine basaltic and basaltic dykes generated from less than 1% and 3-5% partial melting of metasomatized garnet- spinel- bearing lherzolitic mantle source, respectively. Eocene volcanism in the Bam area has been occurred during subduction of Neo-Tethys oceanic crust beneath central Iran in the continental volcanic arc tectonic setting.
Volume 18, Issue 57 (1-2004)
Abstract
Ab-e-garm village situated 85km to sw of Ghazvin, and the studied area located somewhere around. From geographical point of view this area is the Soltanieh mountains continuation in Kabudar Ahang geological quadrangle. Lower Cretaceous igneous rocks in this area consist of: spilitic basalt, alkali olivine basalt, basalt, mugearite and trachy-basalt, which would be seen as lava and tuff, and their intrusives are mostly, microgabbro, pyroxene hornblende gabbro and mela gabbro. These igneous rocks are of alkaline series. Good correlations and continuous trends of main element oxides vs. silica in chemical variation diagrams, confirm genetic relationship between different facies. Comparison of geochemical data and petrography of these rocks shows that seperation of OL, PX and magnetite caused parent magma differentiation, ended into formation of different terms from it. With respect to continental rifts abundances between small continent boundaries in Iran in lower Cretaceous time, it is possible that the lower Cretaceous igneous rocks of Ab-e-garm area be related to these rifts or back arc zone of oceanic crust subduction between these small continents, however,to distinguish exact history of Ab-e-garm area we do need much more data at this time.
