GRV 051523:一块新的灶神星陨石

Grove Mountains(GRV)051523是一块新发现的钙长辉长无球粒陨石,主要由粗粒辉石(62.9 vol%)和长石(34.2 vol%)以及少量不透明矿物(2.7vol%)组成,含很少量的二氧化硅晶屑和细粒富铁橄榄石(Fa75)。粗粒辉石包括易变辉石和普通辉石,两者均普遍具有出熔现象,出熔的晶片大部分宽1-3μm。不透明矿物为铬铁矿、钛铁矿和硫化物。该陨石受到强烈的撞击并角砾化,形成冲击熔脉。粗粒辉石晶体普遍存在微粒状或细针状铬铁矿,并具有定向分布特征,可能也与强烈的冲击变质有关。不同产状的辉石成分均一,表明该陨石经历过强烈的热变质,使其矿物化学组成基本达到平衡,因此将其岩石类型划分为5-6型。GRV 051523的发现为了解灶神星的物质组成、岩浆分异、以及多阶段撞击和热变质历史提供了新材料。

GRV 051523: A NEW HED METEORITE

Grove Mountains(GRV) 051523 is a new eucrite,consisting mainly of coarsegrained pyroxene(62.9vol%) and plagioclase(34.2vol%) with less abundant opaque minerals(2.7vol%) and minor silica and tiny FeO-rich olivine(Fa75).Coarse-grained pyroxenes show exsolution of augite lamellae in pigeonite or vice versa.Width of most exsolution lamella in pyroxenes is 1—3μm.The opaque minerals are chromite,ilmenite and sulfides.The meteorite was heavily shocked,producing breccia and melt veins.Coarse-grained pyroxenes commonly contain abundant tiny or needle-like chromite inclusions with orientation,probably due to heavy shock events.Homogeneous compositions of pyroxenes of various occurrences indicate that GRV 051523 experienced intense thermal metamorphism in the parent asteroid Vesta,and it is classified as Type 5—6.This new eucrite will have additional constraints on chemical composition,magmatic differentiation,multi-stage shock and thermal history of Vesta.