The genesis of zonal texture of chromites from the Qingshuiquan serpentinite in East Kunlun Mountains

Abstract: The ultrabasic rocks in the Qingshuiquan area of Eastern Kunlun Mountains have been altered into serpentinite, in which the zonal texture of some chromites provides important information concerning the alteration and evolutionary process of the rocks. The result of electron microprobe analysis shows that the girdle of chromite is composed of three parts, i.e., alumo-chromite, ferri-chromite and chrome-magnetite, from core to rim, respectively, and all of them were wrapped in chlorite. From the alumo-chromite to the ferri-chromite, the Cr2O3, Al2O3, MgO and Mg# values decrease, while the Fe2O3, FeO, TiO2 as well as Cr# and YFe values increase. The authors hold that, along with the serpentinization and regional metamorphism as well as hydrothermal fluid activity, the chromite went through a process in which the temperature was decreasing and the oxygen fugacity was increasing. And then the zonal texture was formed. This process corresponded to another one during which the host rock of the chromite moved upward from the mantle to the crust, accompanied by metamorphism.