Allende陨石富深绿辉石—钙长石—尖晶石难熔包体的岩石学和矿物化学特征:熔融和蚀变证据

Petrography and mineral chemistry of fassaite-anorthite-spinel-rich refractory inclusion from Allende meteorite:evidence for melting and alteration

对Allende陨石中一块富深绿辉石-钙长石-尖晶石难熔包体进行了岩石学和矿物化学研究.包体近似球形（半径～3 mm）,边部为钙长石和方钠石（MgO=1.04％ ～2.69％;FeO＜ 1.57％）组成的矿物圈层（厚度～ 200 μm）,内部主要矿物有深绿辉石（Al203 =7.63％ ～16.08％; TiO2=1.73％～4.48％）、钙长石（MgO ＜0.41％;Na2O ＜0.14％）和尖晶石（FeO ＜1.70％）.包体中残留黄长石（（A）k70～ 85,Na2O ＜0.22％）,颗粒较小（＜10 μm）,大部分都被蚀变成为钙铝榴石、钙镁橄榄石和氯硅铝钙石（MgO=5.07％～8.04％; FeO＜0.31％）.包体规则的外形不可能由气—固凝聚形成,而可能是由熔融重结晶形成.黄长石含量较少以及残余黄长石非常富镁说明包体可能经历过蚀变作用,且方钠石与氯硅铝钙石的产状和成分差异说明包体可能经历了两次不同的蚀变事件.

The petrography and mineral chemistry of a fassaite-anorthite-spinel-rich refractory inclusion from Allende meteorite has been studied.The inclusion is nearly spherical （radius as 3 mm）.The rim of the inclusion has a mineral layer （200 μm thick） which consists of anorthite and sodalite （MgO =1.04％ ～ 2.69％ ; FeO ＜ 1.57％）.Inside the inclusion,primary minerals include fassaite （Al2O3 =7.63％ ～ 16.08％ ; TiO2 =1.73％ ～ 4.48％）,anorthite （MgO ＜ 0.41％ ; Na2O ＜ 0.14％） and spinel （FeO ＜ 1.70％）.The residual melilite （（A）k7o～85,Na2O ＜0.22％） has fine grain （＜ 10 μm） and most of the melilite are replaced by grossular,monticellite and wadalite （MgO =5.07％ ～ 8.04％ ; FeO ＜ 0.31％）.The regular shape of the inclusion is not likely formed by gas-solid condensed process but probably due to melting and recrystallized.The rare appearance of melilite and the residual melilite characterized by Mg-rich indicate that the inclusion had suffered alteration.Furthermore,the differences between sodalite and wadalite in mineral texture and chemical composition suggest that the inclusion had experienced two different alteration events.