Characteristics of tectono-magmatic alkali gabbros in northern Fathabad, Zarand (NW Kerman): based on the pyroxene mineral chemistry

Fathabad area is located in northwest of the city of Zarand (Kerman province) in the Posht-e-Badam block of the central Iran structural zone. The Ordovician–Silurian gabbroic stocks have intruded into volcanic-sedimentary rocks of the Rizu series. The gabbros are mainly composed of clinopyroxene, kaersutite, plagioclase and biotite. Electron microprobe analyses demonstrate that the clinopyroxenes are aluminous diopside with alkaline-to-peralkaline affinity. Thermobarometry studies reveal a temperature ranging between 1121°C to 1184°C for the formation of clinopyroxene, in which the pressure varies from 6 to 11 kb. The chemical composition of clinopyroxene grains exhibit their association with oceanic island basalts that are related to intraplate rift environments. It seems that the Fathabad alkalic gabbroic stocks are related to the Ordovician–Silurian Paleo-Tethys rifting events that were emplaced during the back-arc extension in the northern margin of the Gondwana supercontinent.