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

通过对高压和超高压变质岩的详细岩石学和矿物学研究，得出了以下具有代表性的结论：(1)Dissakite是尿安石的镁衍生替代物。铬闪石产于苏鲁超高压变质带中国石榴石二辉橄榄岩中。该矿物是俯冲超镁铁质岩中锶和稀土元素的重要储集体，在地壳与上地幔物质相互作用中起着重要作用。(2)对苏鲁超高压变质带中国榴辉岩及其组成矿物进行了锶同位素分析。榴辉岩的锶同位素分带结构和估算的87Sr/86Sr初始比值清楚地指示了超高压变质岩在折返阶段广泛的变质流体迁移和同位素均一化。(3)三巴川变质带贝西地区的石榴石橄榄岩记录了早期低温水化反应和后期近绝热压力升高的P-T轨迹，表明楔状地幔橄榄岩向下俯冲至100公里。(4)在构造研究的基础上，提出了三巴川变质带中榴辉岩和非榴辉岩单元。含绿泥质变质岩的物相分析证实，两个单元在峰期变质阶段的压差较大，为1 GPa.这一事实清楚地表明了两个单元之间存在构造不连续，并在岩石学上支持了桑巴加瓦带大规模推覆构造的观点。

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.