Oxygen Isotopes in the Minerals of Unequilibrated Chondrites

P.I.s建议使用加州大学洛杉矶分校的Cameca 1270离子探针和岩石学技术来确定不平衡球粒陨石中存在的导电相磁铁矿中的三种o同位素，以获得与以下相关的详细成分数据：(1)导致球粒陨石形成的星云过程；(2)形成太阳星云的主要O储集层的组成；(3)母体发生的低变质作用。在接下来的一年里，P.I.s将研究不平衡碳质（CV）和普通（H， L， LL）球粒陨石中磁铁矿的形成。对许多CV球粒陨石薄片的P.I.s检查表明，磁铁矿在球粒中相对常见。P.I.s将使用离子探针来确定这些磁铁矿在氧3同位素图上的成分，相对于其他CV矿物，这些矿物描述了一条混合线，从18O值-40%沿着0.94的斜率延伸到这条线与陆地分馏线的交叉点。私家侦探们希望回答的一个关键问题是，这些磁铁矿是在太阳星云中形成的，还是在CV母体氧化过程中形成的。P.I.s的第二个项目将是检查一些不平衡的普通球粒陨石中磁铁矿-碳化物组合中磁铁矿中的三种O同位素。Krot在加州大学洛杉矶分校发现了许多这样的组合。这些氧化/还原组合的来源尚不清楚；同样，可能的地点是太阳星云和母体。精确的o同位素数据将对地点和氧化磁铁矿中铁的物质的性质提供重要的限制。

9418520 Wasson The P.I.s propose to use the UCLA Cameca 1270 ion-microprobe and petrographic techniques to determine the three O-isotopes in the conducting phase magnetite present in unequilibrated chondritic meteorites in order to obtain detailed compositional data that relate to: (1) the nebular processes that led to the formation of the chondrites; (2) the compositions of major O reservoirs that contributed to the solar nebula; and (3) low-grade metamorphic processes that occurred in parent bodies. During the next year the P.I.s will study the formation of the magnetite in unequilibrated carbonaceous (CV) and ordinary (H, L, LL) chondrites. The P.I.s examination of many thin sections of CV chondrites shows that magnetite is relatively common in chondrules. The P.I.s will use the ion microprobe to determine the compositions of these magnetites on the oxygen 3-isotope diagram relative to other CV minerals that describe a mixing line extending from 18O values -40% along a slope of 0.94 almost to the intersection of this line with the terrestrial fractionation line. A key question the P.I.s hope to answer is whether this magnetite formed in the solar nebula or during the oxidation of the CV parent body. The P.I.s' second project will be to examine the three O isotopes in magnetite present in magnetite-carbide assemblages in some unequilibrated ordinary chondrites. Krot discovered a number of these assemblages while at UCLA. The origin of these oxidized/reduced assemblages is not known; again, the possible locales are the solar nebula and the parent body. Precise O-isotope data will provide important constraints both on the locale and on the nature of the agent that oxidized the Fe of the magnetite.