林东陨石的分类与成因探讨

Classification and origin of the Lindong meteorite

林东陨石发现于我国内蒙古地区，被划分为LL5—6型普通球粒陨石角砾岩。本项工作对林东陨石开展了深入的岩石矿物学分析，提出将其重新划分为表土角砾岩的新观点。林东陨石主要由大至厘米级的角砾、以及微米大小的细粒基质两部分构成。不同角砾之间，表现出明显差异的岩石结构，反映了不同程度的热变质，岩石类型变化范围为4-6型。角砾以岩屑为主，还含有残余球粒和粗粒的矿物碎屑。不同岩石类型角砾的橄榄石Fa值（29．7mol％-30．5mol％）、低钙辉石Fs值（24．9mol％-26．1mol％）、以及铁纹石的Co含量（2．38％-2．51％）等，表明这些角砾均为低铁低金属的LL化学群，判断其来自同一小行星母体。林东陨石的细粒基质主要由微米大小的矿物碎屑固结而成，颗粒之间有较多的孔隙，整体较为松散。细粒基质的化学组成与岩石角砾中的矿物颗粒相同，应当是后者的机械粉碎产物。据此推测林东陨石的母体是一颗LL群小行星，表面经历了长期的小天体碰撞，形成各种岩屑和微细矿物晶屑，然后固结成林东陨石表土角砾岩。林东陨石的发现为研究小行星表面的演化历史，以及太阳风辐射等太空风化提供了珍贵样品，并为我国小行星探测提供可供对照的对象。

Lindong meteorite is the first breccia found in Inner Mongolia, classified into LL5-6 ordinary meteorite. The deeply studied petrography and mineral chemistry of Lindong meteorite indicates that it is a regolith breccia. Lindong meteorite mainly consists of lithic, mineral, and relict chondrule clasts set in a fine-grained and loosely compacted matrix. The rock structure shows obvious difference between different clasts, which reflects the different degree of metamorphism, and the diverse clasts could be classified into 4, 5, and 6 petrographic types. Based on the Fa value （29.7 mol% - 30.5 mol%） of olivine, Fs value （24.9 mol% - 26.1 mol%） of low-Ca pyroxene, and Co content （2.38% - 2.51%） of kamacite, the meteorite can be classified into LL chemical group. The loose matrix is formed by consolidation of micron sized mineral debris. The similar mineral chemical compositions between the diverse clasts and the matrix suggest that they should come from the same asteroid and ejected from the surface of the parent asteroid after multiple brecciations. Lindong regolith breccia could record the evolution history of the asteroid surface and solar wind radiation, which is very helpful for studying the evolution history of early solar system.