Phlogopite-Amphibole-Pyroxenite Xenoliths in Langao,Shaanxi Province,China:evidence for Mantle Metasomatism |
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摘 要: |
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关 键 词: | 金云母 闪石 辉岩 包体 表生交代变质作用 陕西 |
Phlogopite-amphibole-pyroxenite xenoliths in Langao, Shaanxi Province, China: Evidence for mantle metasomatism |
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Authors: | Xueyi Xu Yuehua Huang Linqi Xia Zuchun Xia |
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Institution: | (1) Xi’an Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, 710054 Xi’an;(2) Northwest University, 710069 Xi’an |
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Abstract: | Phlogopite-amphibole-pyroxenite xenoliths contained in the alkali basic-ultrabasic subvolcanic complex in Langao, Shaanxi
Province, are composed of diopside, Ti-rich pargasite, phlogopite apatite, sphene and ilmenite, which have subsolidus metamorphism-deformation
textures such as triple-points, cataclastic boundaries and kink-bands. Mineral chemical characteristics show that the diposide,
Ti-rich paragasite and phlogopite are derived from the mantle and are the products of mantle metasomatism. Compared with normal
mantle-derived spinel-lherzolites, the xenoliths are enriched in TiO2, Fe2O3, CaO, Na2O and K2O, with apparent depletion in MgO. Chondrite-normalized REE patterns and primordial-mantle normalized trace elements data
show that they are enriched in REE (especially LREE) and incompatible trace elements. The petrographic, mineralogical and
petrochemical characteristics indicate that the xenoliths are metasomatized mantle xenoliths, which offers the evidence for
mantle metasomatism and represents the anomalous mantle beneath the Early Paleozoic rift in northern Daba Mountains. The agents
of mantle metasomatism are probably derived from the rising of mantle hot plumes. The processes of metasomatism varied from
limited-range fluid metasomatism in deep mantle (>90 km) to pervasive metasomatism of silicate melt.
This project was financially supported by the National Natural Science Foundation of China (No. 49402035). |
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Keywords: | phlogopite-amphibole-pyroxenite xenolith mantle metasomatism Langao Shaanxi Province |
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