Study of garnet-amphibolite and garnet mica schist from the Faryab complex with an approach to field data, petrography and chemistry of constituent minerals

Garnet amphibolite and garnet micaschists of the Faryab complex, located in the southeast of the Sanandaj-Sirjan zone, are exposed immediately under the peridotites and sometimes a few meters away from the peridotites of this region with fault boundaries. Some garnet amphibolites mainly include poikiloblasts of garnet and amphibole, plagioclase, quartz, secondary minerals of epidote, biotite, chlorite, as well as oxide minerals of, magnetite, ilmenite, titanite and apatite mineral. Garnet micaschists include the main minerals garnet, amphibole, muscovite, epidote, plagioclase, quartz, and secondary minerals biotite, chlorite, rutile, apatite, titanite, and ilmenite. Considering the chemistry of garnet poikiloblasts and the chemistry of amphiboles, temperatures of 505 to 708°C and average pressures of 6.7 to 8.6 kbar (upper amphibolite facies) for garnet amphibolites and temperatures 450 to 650°C and average pressures of 6.7 to 7.2 kbar (lower amphibolite facies) have been determined for garnet micaschists. Accordingly, garnet amphibolites show the highest metamorphic degree, while garnet micaschists show a lower metamorphic degree. Such a situation indicates a type of geothermal gradient. Geochemically, garnet amphibolites can be classified in two groups. Group I, which together with garnet micaschists have the geochemical characteristics of sedimentary rocks, while garnet amphibolites of group II show the typical characteristics of basalts. The Faryab metamorphic complex next to the ophiolitic remnants of the region may indicate the evolution of this ophiolitic complex in a Neotethys accretion-subduction position during the Upper Cretaceous.