A study of the early solar system through systematic analysis of Antarctic meteorites

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The oxygen isotopic ratios of terrestrial materials plot along a mass-dependent line of δ^<17>O=0.52×δ^<18>O in the δ^<17>O-δ^<18>O space, whereas those of extraterrestrial materials such as meteorites plot off the mass-dependent line depending on the types of meteorites. The extraterrestrial materials can be divided into mass-dependent and mass-independent groups. This reflects the occurrence of the processes that induced isotopic heterogeneity in the early solar system. Thus, the oxygen isotopic signatures of meteorites give an essential key to understand the early solar system processes. More than 13,000 meteorites have been found from Antarctica during the recent expeditions by National Polar Research Institute, most of them are yet to be analyzed for oxygen isotopic ratios.In the present study, we have analyzed the oxygen isotopic ratios of the following types of Antarctic meteorites : CO3(ALH-77003,ALH-77307,A-881632,Y-791717,Y-81020,Y-82050), CM2(B-7904,Y-791198,Y-82054,Y-86720,CK5-6(A-881551,Y-82102, Ureilite(A-881931,Y-74123,Y-790981,Y-791538), Diogenite(Y-74013), Eucrite(Y-790266,Y-791195,Y-791826,Y-791960,A-880702,A-880761,A-881388), EH6(Y-793225,Y-8414). In addition to the above Antarctic meteorites, some recent falls and finds from various places have also been analyzed. They include meteorites from Towada, Hiroshima, Mars (SNCs), and North West Africa(NWA-series). Most of the samples analyzed plot in the regions of known meteorite groups by Clayton (1993), but some plot in a new and unkown region. These meteorites need further studies for chemical, mineralogical and petrological examinations.During the course of this study, we have determined precise δ^<17>O and δ^<18>O values of the international standard materials such as VSMOW,SLAP,NBS28 quartz, NBS30 biotite, UWG2 garnet, San Carlos olivine, etc. This gave a basis for reporting the oxygen isotopic ratios of meteorites in the SMOW scale.