摘要
Detailed in situ LM-ICPMS researches on the composite xenoliths from Yingfengling volcano of Leizhou Peninsula, South China, indicate that most incompatible trace elements of clino- pyroxenes in composite xenoliths decrease spatially from pyroxenites to distal lherzolites, and com- patible elements and HREE increase steeply. The increasing and decreasing rate is distinct for dif- ferent trace elements, which give rise to element chromatographic fractionation within metasomatized lherzolites. The element chromatographic fractionation result actually from the difference in element diffusive rate in melts or fluids percolating through wall-rock lherzolites. Based on element variation profiles in composite xenoliths this study indicates that Sr, Nb, La and Ce have the highest diffusive mobility, MREE-HREE are moderate, and Zr, Hf, Ti, Ga and Sc are very low in most cases. Higher diffusive rates of LREE than HREE would enlarge the REE fractionation of metasomatized peridotites, and lower diffusive rate of Zr, Hf and Ti relative to neighbor REEs with similar incompatibility would cause the relative depletion of these elements in metasomatized peridotites. Trace elements com- monly have a higher diffusive rate in fluid-rich infiltrating melt, which will weaken element chroma- tographic fractionation during the metasomatism. The range of mantle metasomatism caused by sili- cate melt intrusion is very limited, generally within tens of centimeters wide. The width of metasoma- tized wall-rock peridotites near the pyroxenite or horblendite veins was strictly controlled by both melt volume and chemical characteristics.
Detailed in situ LM-ICPMS researches on the composite xenoliths from Yingfengling volcano of Leizhou Peninsula, South China, indicate that most incompatible trace elements of clino- pyroxenes in composite xenoliths decrease spatially from pyroxenites to distal lherzolites, and com- patible elements and HREE increase steeply. The increasing and decreasing rate is distinct for dif- ferent trace elements, which give rise to element chromatographic fractionation within metasomatized lherzolites. The element chromatographic fractionation result actually from the difference in element diffusive rate in melts or fluids percolating through wall-rock lherzolites. Based on element variation profiles in composite xenoliths this study indicates that Sr, Nb, La and Ce have the highest diffusive mobility, MREE-HREE are moderate, and Zr, Hf, Ti, Ga and Sc are very low in most cases. Higher diffusive rates of LREE than HREE would enlarge the REE fractionation of metasomatized peridotites, and lower diffusive rate of Zr, Hf and Ti relative to neighbor REEs with similar incompatibility would cause the relative depletion of these elements in metasomatized peridotites. Trace elements com- monly have a higher diffusive rate in fluid-rich infiltrating melt, which will weaken element chroma- tographic fractionation during the metasomatism. The range of mantle metasomatism caused by sili- cate melt intrusion is very limited, generally within tens of centimeters wide. The width of metasoma- tized wall-rock peridotites near the pyroxenite or horblendite veins was strictly controlled by both melt volume and chemical characteristics.
基金
This study was supported by the Innovation Project of the National Natural Science Foundation of China(Grant No.40221301)
the National Natural Science Foundation of China(Grant Nos.40372087 and 40132010)
Australian Research Council Grants(to S.Y.O'Reilly).
