The determination of peak temperature of eclogites in the west of Tieshiguan area, North Qaidam UHP of Qinghai Province, and its geological significance

Lots of eclogites have been found in the west of Tieshiguan, which has fulfilled the recognition of the ultrahigh pressure metamorphic belt between Yuqia and Xitie Mountain. The Yuqia ultrahigh pressure metamorphic belt extends southeastward for 40 kilometers. On the basis of geological features, petrography and mineralogy of eclogites in the west of Tieshiguan, the authors revealed that ultrahigh pressure metamorphic peak period mineral combination (garnet+omphacite+phengite+rutile) has been preserved. It is obviously of retrograde eclogites as shown by the petrographic analysis. The authors used mineralogical thermometer to measure the temperature of the ultrahigh pressure metamorphic peak period of west Tieshiguan, and the results show that the temperature and the pressure were 694-791℃ and 2.5-2.6GPa respectively. Garnet zoning shows that the temperature decreased from the core area to the edge, whereas the pressure increased from the core area to the mantle area and decreased from the mantle area to the edge, which suggests that eclogite went through a dynamic process of rapid subduction and low speed exhumation.