Petrology,Mineralogy and Geochemisty of Antarctic Mesosiderite GRV 020175:Implications for Its Complex Formation History  

作　　者：WANG Linyan HSU Weibiao MA Changqian 

机构地区：[1]Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China [2]Purple Mountain Observatory, Nanjing 210008, China

出　　处：《Acta Geologica Sinica(English Edition)》2010年第3期528-542,共15页地质学报（英文版）

基　　金：The sample of GRV 020175 was provided by the Polar Research Institute of China;supported by China Ministry of Science and Technology(Grant No. 2005DKA21406);the National Natural Science Foundation of China(Grant Nos.10621303 and 40773046);the Minor Planet Foundation of China.

摘　　要：GRV 020175 is an Antarctic mesosiderite,containing about 43 vol%silicates and 57 vol% metal.Metal occurs in a variety of textures from irregular large masses,to veins penetrating silicates, and to matrix fine grains.The metallic portion contains kamacite,troilite and minor taenite.Terrestrial weathering is evident as partial replacement of the metal and troilite veins by Fe oxides.Silicate phases exhibit a porphyritic texture with pyroxene,plagioclase,minor silica and rare olivine phenocrysts embedded in a fine-grained groundmass.The matrix is ophitic and consists mainly of pyroxene and plagioclase grains.Some orthopyroxene phenocrysts occur as euhedral crystals with chemical zoning from a magnesian core to a ferroan overgrowth;others are characterized by many fine inclusions of plagioclase composition.Pigeonite has almost inverted to its orthopyroxene host with augite lamellae, enclosed by more magnesian rims.Olivine occurs as subhedral crystals,surrounded by a necklace of tiny chromite grains（about 2-3μm）.Plagioclase has a heterogeneous composition without zoning. Pyroxene geothermometry of GRV 020175 gives a peak metamorphic temperature（～1000℃） and a closure temperature（～875℃）.Molar Fe/Mn ratios（19-32） of pyroxenes are consistent with mesosiderite pyroxenes（16-35） and most plagioclase compositions（An_（87.5_96.6）） are within the range of mesosiderite plagioclase grains（An_（88-95））.Olivine composition（Fo_（53.8）） is only slightly lower than the range of olivine compositions in mesosiderites（Fo_（55-90））.All petrographic characteristics and chemical compositions of GRV 020175 are consistent with those of mesosiderite and based on its matrix texture and relatively abundant plagioclase,it can be further classified as a type 3A mesosiderite.Mineralogical, penological,and geochemical studies of GRV 020175 imply a complex formation history starting as rapid crystallization from a magma in a lava flow on the surface or as a shallow intrusion.Following primary iGRV 020175 is an Antarctic mesosiderite,containing about 43 vol%silicates and 57 vol% metal.Metal occurs in a variety of textures from irregular large masses,to veins penetrating silicates, and to matrix fine grains.The metallic portion contains kamacite,troilite and minor taenite.Terrestrial weathering is evident as partial replacement of the metal and troilite veins by Fe oxides.Silicate phases exhibit a porphyritic texture with pyroxene,plagioclase,minor silica and rare olivine phenocrysts embedded in a fine-grained groundmass.The matrix is ophitic and consists mainly of pyroxene and plagioclase grains.Some orthopyroxene phenocrysts occur as euhedral crystals with chemical zoning from a magnesian core to a ferroan overgrowth;others are characterized by many fine inclusions of plagioclase composition.Pigeonite has almost inverted to its orthopyroxene host with augite lamellae, enclosed by more magnesian rims.Olivine occurs as subhedral crystals,surrounded by a necklace of tiny chromite grains（about 2-3μm）.Plagioclase has a heterogeneous composition without zoning. Pyroxene geothermometry of GRV 020175 gives a peak metamorphic temperature（～1000℃） and a closure temperature（～875℃）.Molar Fe/Mn ratios（19-32） of pyroxenes are consistent with mesosiderite pyroxenes（16-35） and most plagioclase compositions（An_（87.5_96.6）） are within the range of mesosiderite plagioclase grains（An_（88-95））.Olivine composition（Fo_（53.8）） is only slightly lower than the range of olivine compositions in mesosiderites（Fo_（55-90））.All petrographic characteristics and chemical compositions of GRV 020175 are consistent with those of mesosiderite and based on its matrix texture and relatively abundant plagioclase,it can be further classified as a type 3A mesosiderite.Mineralogical, penological,and geochemical studies of GRV 020175 imply a complex formation history starting as rapid crystallization from a magma in a lava flow on the surface or as a shallow intrusion.Following primary i

关 键 词：mesosiderite metal-silicate mixing thermal metamorphism formation history ANTARCTICA 

分 类 号：P[天文地球]