Document Type : Original Research Paper
Authors
1 Assistant professor, Faculty of Earth Science, Shahrood University of Technology, Shahrood, Iran
2 Professor, School of Geology, College of Science, University of Tehran, Tehran, Iran
3 Professor, University of Toulouse, Toulouse, France
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 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.
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