K. Mohammadiha; M. Sabzehie; M. Ghahraie pour; J. Radfar
Abstract
A large widespread outcrop of granitoid - mylonitic gabbros complexes is observed in northeastern part of Serow, NW Iran. Those rocks were considered as Precambrian gneiss and metamorphic rocks (Haghipour and Aghanabati, 1977), or alternatively, a complex of acidic to basic igneous rocks which have undergone ...
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A large widespread outcrop of granitoid - mylonitic gabbros complexes is observed in northeastern part of Serow, NW Iran. Those rocks were considered as Precambrian gneiss and metamorphic rocks (Haghipour and Aghanabati, 1977), or alternatively, a complex of acidic to basic igneous rocks which have undergone intense deformation and dynamic metamorphism by shearing (Mohammadiha, 2000; Mohammadi Torkabad, 2001). The basic mylonitic rocks in the studied area are simply composed of plagioclase, hornblende, actinolite, chlorite, and epidote. They display minor remains of primary pyroxenes which are largely replaced by amphibole. Feldspars have been altered to epidote, and secondary plagioclase (more sodic) and roughly sericite. There are some gabbros with clastic and lentiform fabric which were not affected by dynamic deformation in the shear zone. Cataclastic flow, micro fracturing, dislocation creep, recovery, diffusion creep, grain boundary sliding and pressure dissolution are the dominant deformation mechanisms influenced the complexes. The consequent structures are foliation, lineation, undoluse extinction, porphyroclasts with core-mantle structure, micro fractures parallel and unparallel with brecciation, mechanical twining, mica fish structure, banded differentiated structure and kinked foliation. We conclude that the whole observed evidences demonstrate a major dynamic deformation in a brecciated zone in the studied area.
K. Mohammadiha; M. Sabzehie; M. Ghahraei pour; A. Kosari Torbehbar
Abstract
Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole ...
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Located in the NW Iran, in Sanadaj-Sirjan metamorphic belt, the studied area mainly comprises of metamorphic and varied acidic-basic igneous originated rocks. Basic metamorphic rocks have been chemically controlled by two main metamorphic processes including metasomatism and dynamic deformation. Amphibole and plagioclase are of the most significant minerals occurring in the rocks. Here we represent the chemical variations of those metamorphic minerals in relation to their host rocks and prograde metamorphism. Mineral chemistry analyses of amphibole minerals reveal an increase in Al2O3, TiO2 and a decrease in MgO, MnO during mylonitization of gabbroic rocks. Affected by metasomatism, the Al2O3 and Na2O contents of amphiboles have been also increased. CaO content of plagioclase has declined; in contrast, Al2O3 and Na2O have raised during mylonitization and metasomatism processes. These variations are overally ruled by chemical composition of the intruded pluton, pressure-temperature condition, oxygen fugacity and occurrence of equilibrant phases. Increasing Al and Na brings about tschermakite substitution in the deformed amphiboles and edinite substitution in the metasomatized rocks respectively.