OXYGEN ISOTOPIC COMPOSITIONS OF METEORITES AND IT'S SIGNIFICANCE
Received date: 2000-01-17
Revised date: 2000-02-23
Online published: 2000-10-01
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 possessedδ17O=δ18O.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 theδ17O-δ18O 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.
Key words： Meteorite; Oxygen isotope; Original Earth composition.
HOU Wei, XIE Hong-sen . OXYGEN ISOTOPIC COMPOSITIONS OF METEORITES AND IT'S SIGNIFICANCE[J]. Advances in Earth Science, 2000 , 15(5) : 534 -540 . DOI: 10.11867/j.issn.1001-8166.2000.05.0534
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