Petrology
Mehdi Rezaei-Kahkhaei; Dariush Esmaeily; Hanieh Sahraei
Abstract
Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve ...
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Neshveh volcanic rocks located in the NW Saveh are parts of the Uromeyeh-Dokhtar magmatic arc. The rocks are mainly basalt, basaltic andesite, andesite and trachyandesite in composition. Petrographical studies represent some evidences for the lack of equilibrium between crystals and magma, such as sieve texture, two generation of fresh and altered plagioclase, reaction rim, corrosion and rounding of phenocrysts. Major and trace element diagrams show, although crystal differentiation was effective in the evolution of the study rocks, the scatter and unusual trends, which are observed in some diagrams in comparing with fractionation trend, reflect magma mixing and contamination were also important during magma generation. Inconsonance and high variations in Sr concentrations together with binary diagrams of Nb/Y-Nb and Rb-Zr/Rb reveal magma mixing role in the evolution of Neshveh volcanic rocks. Considering the above facts, we can conclude that magma mixing and magmatic differentiation were the important processes in formation of the Neshveh volcanic rocks. As well as, the incorporation of new magmatic pulse(s) with differentiation magma is the most effective mechanism for the evolution of volcanic rocks from the study area.
M. Sheibi; D. Esmaeily; J. Luc Bouchez
Abstract
The Lower Cretaceous Shir-Kuh granitic batholith in central Iran intruded to the sandstones and shales of Nayband-Shemshak Formation. The batholith consists of three main granodioritic, monzogranitic and leucogranitic units. The anisotropy of magnetic susceptibility technique (AMS) was used for distinguishing ...
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The Lower Cretaceous Shir-Kuh granitic batholith in central Iran intruded to the sandstones and shales of Nayband-Shemshak Formation. The batholith consists of three main granodioritic, monzogranitic and leucogranitic units. The anisotropy of magnetic susceptibility technique (AMS) was used for distinguishing relative chronology between emplacements of the magma batches in Shir-Kuh batholith. The rather low susceptibility magnitudes (Km<400mSI) call for the dominance of biotite as magnetic carriers, considered as typical of the so-called paramagnetic granites and there is a first-order correlation between magnetic susceptibility and rock-type. The various magnetic data (magnetic lineation and foliation maps, K, P and T parameters), complemented by field and microstractural observations, allow us to propose that the two main feeders of the batholith represent tension gashes that formed at the base of the brittle crust and served as conduits for the magma. The progressive differentiation of magmas associated with petrographic zoning of the Shir-Kuh Batholith is therefore viewed as progressive opening and infilling of the En echelon gashes more or less parallel to the regional dextral shear zone. The filling started with granodiorites, followed with monzogranites and ended with leucogranites and resulted in the construction of the batholith.