摘要
介绍了各类陨石氧同位素组成的特点 ,对陨石氧同位素组成的主要成因观点进行了评述 ,结合地球的原始物质组成 ,讨论了陨石氧同位素组成的地球科学意义。
Oxygen isotopic compositions of meteorites and some hypotheses on it's origin are reviewed. The following viewes about oxygen isotopic composition origin of chondrites and Earth are proposed: (1) Because of no clear that how much matters from out of solar system mixed into original solar nebular, the nebular may be taken for homogeneous oxygen isotopic composition. (2) The mass dependent isotope fractionations occured by evaporation and gasification in early solar nebular, so that nebular became nebular gas with heterogeneous oxygen isotopic composition. In inner field of nebular(near original sun), the evaporation and gasification were stronger, and difference oxygen isotopic sources formed in difference position of nebular with varying temperature and pressure. (3) Some of nebular gas may undergo chemical reactions in which non mass dependent oxygen isotope fractionations occured, and its oxygen isotope possessed δ 17 O=δ 18 O Then these nebular underwent condensation and formed many types of condensate, and these condensates can suffer aqueous alterations, melts, recondensation and accretion, finally the bodies for different chondrite group formed. (4) The thermal metamorphism or partial melting can lead to a second mass dependent oxygen isotope fractionation of the chondritic bodies. (5) Because those chemical reaction caused non mass dependent oxygen isotope fractionation occur under lower temperature and higher oxygen fugacity, the enstatite chondrites did not show appearance of no mass dependent oxygen isotope fractionation. (6) A few years ago the authors suggested that the 96% of primitive Earth was composed of quasi enstatite chondrite planetesimal and quasi enstatite achondrite planetesimal in previous paper. It can be seen from the δ 17 O δ 18 O plot of this paper that oxygen isotopic composition of Earth is similar to that of enstatite chondrite,which indicites that the authors's point on primitive Earth's composition is reasonable.
出处
《地球科学进展》
CAS
CSCD
2000年第5期534-540,共7页
Advances in Earth Science
基金
国家自然科学基金项目!"高温高压下的熔体与流体混溶和分离研究"(编号 :49772 111)