Mineral chemistry and geothermo-barometry based on amphibole of alkali gabbro dykes of Zarigan, northeast of Bafq

Many mafic dykes, with the Early Paleozoic age, have intruded into Zarigan granitoid pluton and its host sedimentary units in the northeast of Bafq city. Petrographycal studies show these dykes are alkaline gabbro to monzogabbro with medium to fine grain intergranular to granular textures. Major minerals include clinopyroxene, amphibole and plagioclase and minor minerals are a few amounts of biotite, olivine, alkali feldspar, and nepheline. Amphiboles are calcic and belong to kaersutite-potasic kaersutite type. Geothermo-barometry calculations, based on amphibole mineral, show the prevailing pressure and temperature of kaersutites crystallization at 6.3-8.2 Kbar and 1040-1140 °C. According to geochemical composition, kaersutites are in the range of alkaline amphiboles, so that they are derived from mantle and are related to intercontinental extensional tectonic environment. Based on these evidences, minerals have been crystallized from the magmas originated from asthenospheric upwelling during Paleo-Tethys early rifting and associated with Posht-e-Badam block basement tension faults function.