Elements circulation within the earth deduced from the mineralogical and petrological studies of eclogites

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The following representative conclusions were drawn from our detailed petrological and mineralogical works on high-pressure and ultrahigh-pressure metamorphic rocks.(1)Dissakisite is a Mg-derivative substitution of allanite. Cr203-dissakisite occurs in a garnet-lherzolite from the Su-Lu ultrahigh-pressure metamorphic belt, China. This mineral is an important reservoir of Sr and REE hi subducting ultramafic rocks, and plays a significant role in the material interaction between the crust and upper mantle.(2)Sr-isotopic analyses were done on eclogites and their constituent minerals from the Su-Lu ultrahigh-pressure metamorphic belt, China. The Sr-isotopic zonal structure of zoisite and the estimated 87Sr/86Sr initial ratios clearly indicate widespread metamorphic fluid migration and isotopic homogenization during exhumation stage of the ultrahigh-pressure metamorphic rocks.(3)Garnet-peridotites from the Bessi area in the Sanbagawa metamorphic belt record the P-T path with early stage of low-temperature hydrous reaction and subsequent stage of nearly adiabatic pressure increase up to 3-4 GPa, showing subduction of wedge mantle peridotites down to 100 km in depth.(4)The eclogite and non-eclogite units are proposed in the Sanbagawa metamorphic belt mainly based upon the tectonic research. Large pressure gap of 1 GPa at peak metamorphic stage between the two units was confirmed by the phase analyses of chloritoid-bearing metamorphic rocks. This fact clearly indicates the presence of tectonic discontinuity between the two units and petrologically supports the idea of large-scale nappe structure hi the Sanbagawa belt.