Petrogenesis of opaque assemblages in the Ningqiang carbonaceous chondrite  

作　　者：HSU WeiBiao 

机构地区：[1]Laboratory for Astrochemistry and Planetary Sciences,Purple Mountain Observatory,Nanjing 210008,China

出　　处：《Science China Earth Sciences》2007年第6期886-896,共11页中国科学（地球科学英文版）

基　　金：Supported by the Chinese National Natural Science Foundation for Distinguished Young Scholars (Grant No. 40325009);the One-Hundred-Talent Program of Chinese Academy of Sciences;the Minor Planet Foundation of China

摘　　要：Numerous round to oblate opaque assemblages (OAs) are found in chondrules and matrix of the Ningqiang carbonaceous chondrite. They are mainly composed of Ni-rich metal,magnetite,Fe,Ni-sulfides,with minor amounts of phosphate,phosphoran-olivine,pyroxene and trace amounts of nano-sized platinum-group metal alloys. The mineralogy of Ningqiang OAs is very similar to that of OAs previously reported in Ca,Al-rich inclusions of CV chondrites. Being a rare mineral phase in nature,phosphoran-olivine is thought to form by nonequilibrium reactions between P-bearing molten metal and olivine crystals during rapid cooling. Its occurrence in Ningqiang OAs indicates that the precursor of OAs was locally produced during chondrule formation,rather than directly condensed from the solar nebula as previously thought. The petrographic and mineralogical characteristics of Ningqiang OAs reveal that OAs formed by low temperature alterations of pre-existing homogeneous alloys within chondrules on a planetary body.Numerous round to oblate opaque assemblages (OAs) are found in chondrules and matrix of the Ningqiang carbonaceous chondrite. They are mainly composed of Ni-rich metal, magnetite, Fe, Ni-sulfides, with minor amounts of phosphate, phosphoran-olivine, pyroxene and trace amounts of nano-sized platinum-group metal alloys. The mineralogy of Ningqiang OAs is very similar to that of OAs previously reported in Ca, Al-rich inclusions of CV chondrites. Being a rare mineral phase in nature, phosphoran-olivine is thought to form by nonequilibrium reactions between P-bearing molten metal and olivine crystals during rapid cooling. Its occurrence in Ningqiang OAs indicates that the precursor of OAs was locally produced during chondrule formation, rather than directly condensed from the solar nebula as previously thought. The petrographic and mineralogical characteristics of Ningqiang OAs reveal that OAs formed by low temperature alterations of pre-existing homogeneous alloys within chondrules on a planetary body.

关 键 词：opaque ASSEMBLAGES phosphoran-olivine Ningqiang CARBONACEOUS CHONDRITE PETROGENESIS 

分 类 号：P185.83[天文地球—天文学]