L群普通球粒陨石母体的冲击变质历史

天体之间的冲击碰撞在太阳系的形成和演化过程中占有重要的地位。月球和太阳系内主要天体在39亿年前发生了高频率的天体撞击事件，即：月球灾变事件。小行星在太阳系演化过程中经历的最主要地质作用就是冲击变质，而陨石则记录了小行星在不同时期发生的冲击碰撞事件。普通球粒陨石是最常见的陨石类型，本项目将重点研究L群普通球粒陨石，寻找冲击熔融脉中的高压矿物相，特别是涂氏磷钙石，利用电子显微镜、电子探针、拉曼光谱仪、和背散射电子衍射仪来确定熔融脉所经历的高温高压条件。在此基础上进一步利用CAMECA 1280 大型离子探针测定冲击熔融脉和陨石主体中磷酸盐的U-Pb和Pb-Pb年龄，限定L群普通球粒陨石的母体经历过的冲击碰撞历史和发生的时间。本项目试图要解决的科学问题是：L群普通球粒陨石经历了多少次有影响力的冲击变质过程？冲击碰撞发生在什么时间？L群普通球粒陨石的母体有没有经历过类似月球灾变事件的冲击变质历史？

Impact events have played an important role in the formation and evolution of planets and small bodies of the solar system. The Moon was subjected to intense post-accretionary bombardment between about 4.0 and 3.8 billion years ago, and there is evidence for a short and intense late heavy bombardment (LHB) period, around 3.85±0.05 Ga. If a LHB occurred on the Moon, the other planets, including asteroids, must have been subjected to an impact flux at least as intense. Chondrites are the most abundant meteorites derived from the main-belt asteroids. They usually contain numerous shock-induced melt veins. In this study, we will use the ion microprobe to measure U-Pb and Pb-Pb ages of tuite, a high pressure phase of phosphates found in shock-induced melt veins of L chondrites. The ultimate goal of this project is to seek the evidence of LHB on the L-chondrite parent body.