细粒富Ca, Al包体W-L边氧同位素和稀土元素组成特征研究

Ca-, Al-rich inclusions (CAIs) in chondrites are the earliest assemblages of the solar nebula, and they contain information of early solar nebula. They are the probe of studying the origin and evolvement of early solar nebula. Some CAIs are often surrounded by thin mono- or bi-mineralic rims known as Wark-Lovering (W-L) rims. W-L rims are composed of the same primary high temperature minerals as CAIs, such as melilite, spinel, pyroxene, hibonite, perovskite, anorthite and olivine. W-L rims offer a record of conditions during the earliest stages of Solar System formation in the inner regions of the solar accretion disk, and its provide a lot of information of both formation process of CAIs and nebula environment. CAIs may be texturally divided into coarse-grained and fine-grained inclusions. Previous studies focused on coarse inclusions for technical analysis. The hibonite-bearing inclusions, fluffy Type As and spinel-pyroxene rich fine-grained inclusions have the bulk compositions following the predicted gas-solid condensation trajectory from a gas of solar composition, and the minerals of them have a small particle size. Traditional methods of data analysis is susceptible to adjacent mineral. The Cameca NanoSIMS 50L has high sensitivity and high spatial resolution, and it can be more accurate determination of isotope and trace element of a smaller particle size minerals from fine-grained inclusions. The study will use Cameca NanoSIMS 50L with high spatial resolution oxygen isotope analysis and rare earth elements, and it analyzed the compositions of oxygen isotopes and rare earth elements in W-L rim from fine-grained inclusions. Analysis conclusion will restrict the formation of W-L rim from fine inclusions and nebula environment of the source region of CAI formation.

球粒陨石中的富Ca, Al包体 (简称CAIs) 形成于太阳星云演化的最初始阶段，保存了星云形成和演化的各种信息。CAI常具有由一种或几种矿物组成的边部(常被称为W-L边)，W-L边的形成演化过程与星云紧密相关，所以其对认识CAI形成演化过程和早期星云环境都具有重要意义。由于分析技术等多方面的原因，以前的研究主要针对粗粒包体。含黑复铝石型、松散A型和富尖晶石-辉石型细粒包体代表了星云从高温-低温连续凝聚的产物，颗粒的粒径一般较小，传统分析方法得到的数据容易受到相邻矿物的影响。新一代纳米粒子探针具有较高的灵敏度和极高的空间分辨率，能够较准确测定细粒包体中较小粒径矿物颗粒的同位素和微量元素组成。本项目拟运用纳米粒子探针高空间分辨的氧同位素和稀土元素分析技术，对上述细粒包体的W-L边开展氧同位素和稀土元素组成特征研究，制约细粒包体W-L边的形成演化过程与包体形成源区星云环境。

CAIs及其W-L边均形成于太阳星云演化的最初始阶段，保存了星云形成和演化的各种信息，是认识早期星云演化的探针。本项目运用电子探针及纳米离子探针高空间分辨的氧同位素分析技术，对CAIs及其W-L边开展矿物岩石学和氧同位素组成特征研究。主要研究成果如下：(1)C#1包体的W-L边具有与包体内部矿物相似的氧同位素组成，表明其形成于同一熔融结晶事件，W-L边形成后与贫16O同位素组成的星云发生了氧同位素交换。C#1包体具有与富Al球粒相似的氧同位素组成特征和形成演化过程。(2) K2-9(FTA)和K2-10(CTA)的氧同位素特征表明，包体和W-L边均形成于富16O同位素组成的源区，当包体发生蚀变时，发生了强烈的氧同位素交换。(3)GRV陨石中，H群和L群受到的冲击变质不同，L群相较于其他化学群明显受到了更强烈的冲击变质，可能与陨石母体表面特征有关。岩石类型与冲击变质也存在紧密联系，5型和6型受到了的冲击变质更强烈。