| The Sulu-Dabie orogenic belt is the world's largest known UHP metamorphic belt, formed by the subduction of the Yang plate to the North China plate. The study area is located in the northern part of the second largest rock mass (No.8 rock mass)in the middle of the Sulu UHP-high pressure metamorphic block in Rizhao City,Shandong Province. This paper analyzes the characteristics of the whole rock and the main elements and the trace elements of the sample. What' more,it discuss the causes.The samples collected are clino-pyroxenite, garnet pyroxenite and containing garnet pyroxenite . The main mineral compositions are clinopyroxene, garnet,hornblende, and the secondary minerals are ilmenite, magnetite, chlorite and spinel.Clinopyroxene is diopside. Fe-Ca-garnet end member in garnet is high and amphibole is magnesiohornblende. Spinel particle size less than 0.1mm with low Cr content, often associated with iron minerals.The evolution of rock can be divided into three stages, the first stage of metamorphism process, mineral are not preserved well, so no pressure or temperature can be calculated, mineral assemblages may be clinopyroxene + hornblende + quartz or clinopyroxene + biotite + quartz; The second stage of the peak metamorphism process, mineral assemblage may be omphacite + garnet + coesite + kyanite or omphacite +garnet and . Using Ravna G.P.Brery thermometer and pressure gauge,pressure 0.78 ?0.94Gpa,temperature 836 to 930?; the third stage is retrograde metamorphism, mineral assemblages may be: actinolite + albite, etc. Using Schmidt pressure gauge and Ravna thermometer to calculate the pressure of 0.51Gpa,temperature 624 ?670 ? .In this paper, Theriak/Domno software NCFMASH(Na2O-CaO,FeO-MgO- Al2O3 - SiO2 - H2O) system was used to calculate the garnet pyroxenite profile,the temperature range of 565?840 ?,the pressure range of 0.38?0.66GPaPomegranate pyroxenite and containing garnet pyroxenite belong to the basic rock, pyroxene belongs to intermediate rocks. The results showed that the aluminum element is high while sodium and potassium elements are poor. Rittman index were 0.05, which belong to calc-alki-line-series. And the consolidation index (SI) was 48.83?59.77, which was close to the consolidation index of the original basaltic magma.The samples of the rare earth chondrite meteorite normalized map of the same distribution, the left side is slightly up and the right is slightly down. Light rare earth element (LREE) is slightly rich while heavy rare earth element (HREE) is depletion, L / H ratio shows that there are fractionation phenomenon and pyroxene fractions is the most significant. The distribution of trace elements is the same as that of the primitive mantle standardized distribution. High field strength elements slightly are enriched and phosphorus is strongly depleted that proved the origin of the mantle depletion. Large ion lithophile elements such as Pb, Ba and Sr compared with the mid-ocean ridge basalts is strongly enrich. According to these data, The main element is modeled by TiO2 — FeOT / MgO diagram and the double-logarithmic discriminant diagram of the basaltic tectonic environment of the trace elements is analyzed. The comprehensive analysis shows that the tectonic environment of the protolith formation is the convergence arc island environment. |
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