AN UNUSUAL MANTLE MINERAL ASSEMBLEGE FROM CORE-MANTLE BOUNDARY

An unusual mineral assemblage discovered in ophiolitic chromitite from the Yarlung Zangbo ophiolite belt, Tibet. It includes more than 100 species (or subspecies) mineral, such as: native element, alloy, oxide (arsenide) and silicate. An important mineral assemblage, consisting of Fe, FeO, FexSiy, SiO2 and Si, has been found from the chromitite sample. According to recent experimental date this assemblage is similar to results of reaction between liquid iron of Earth°¯s outer core and silicates at the base of the lower mantle (Knittle and Jeanloz, 1991), formed in D" layer between the outer core and the lower mantle. The existence of these ultrahigh-pressure minerals implies that the deep mantle activity of ophiolite might have affected the Earth°¯s outer core. The chemical reaction between the outer and the lower mantle might have happened. Ultrahigh pressure minerals formed in D" layer and brought up to the upper mantle by mantle plume generated within D" lager. The mineral assemblage of ophiolitic mantle has great significance in mineralogy and geodynamics and documents that the experiment mad by Knittle and Jeanloz to be important. Key word: core-mantle boundary, ophiolite, chromitite, alloy, lower mantle