مسير PTT سنگهاي دگرگونه مال خوي ، نمونه اي از يك مسير نرمال در جهت عقربه ساعت

PTt Path in Metamorphic Rocks in the North of Khoy Region: A Case of a Clockwise Normal Route

Metamorphic rocks in the Khoy region are restricted by obducted ophiolites to the southwest and sedimentary rocks of Precambrian-Paleozoic to the northeast. The Qom Formation (Oligocene-Miocene) with basal conglomerate transgressively overlies all these rocks. The metamorphic rocks consist of both metasediments and metabasits. The metasediments are micaschist, garnet-staurolite schist and garnetstaurolite sillimanite schist with some meta arkose, marble and quartzite, where metabasits are greenschist and amphibolite with basalt and gabbroic protolith and their origin of tholeitic and calc-alkaline magma type. Geotermobarometry based on equivalence of minerals stability and their paragenises in these rocks and microprobe analysis by several different ways indicate that metamorphism occurred in temperature (450°C to 680°c`) with 5.5 - 7.5 kb pressure. In the margin of the minerals, pressures decrease considerably (<2kb) where temperature decrease is insignificant. The PTt path in these metamorphics was normal. The MFG line passes over the triple junction of Al2SiO5 polymorphs and the average geothermal gradient during metamorphism was between 27 °c to 30 °c per kilometer, which is more concordant with collision zones. It is concluded that the thickening of the crust produced metamorphism in this area when the Arabian plate collided with Azarbayjan plate during post Cretaceous (probably Eocene).