Amphibole mineral chemistry and geothermobarometry of the emplacement depth of Touyeh- Darvar pluton, Southwest of Damghan, Semnan

Touyeh- Darvar granitoid pluton is situated in 50 Km SW of Damghan in Semnan province in the eastern Alborz zone. This pluton has intruded into the early Paleozoic rock units (Barout, Zaygun and Lalun Formations). Based on the field observations and petrographic studies, the pluton composed of monzonite, quartz monzonite and monzodiorite. Mineralogically, the pluton consists of plagioclase, alkali feldspar, quartz±biotite±amphibole. It’s accessory minerals include ilmenite, magnetite, zircon, apatite, titanite and chalcopyrite and sericite, epidote, calcite, and chlorite are it’s secondary minerals. The Amphiboles of the Touyeh- Darvar rocks are low pressure calcic type with ferro-hornblende composition and igneous origin. Application of the geothermobarometry methods yielded temperature ranges of 650–730°C and pressures less than 2 Kb for stopping of exchange and final equilibrium of amphibole in the pluton that corresponds to less than 5 km depths for emplacement depth of the pluton. Existence of fine grained hyper-solvous to sub-solvous reaction textures (Perthitic, myrmekitic, graphic and granophyric) in the rocks of pluton and the lack of apparent contact metamorphism around it indicate diapiric ascend and emplacement of the pluton in a relatively cool and solid state in shallow depths of the crust. The Veins of mineral deposits such as Fe-Mn oxide-hydroxides, fluorite, barite, lead and zinc in the pluton host rocks are the obvious evidence for these states