非洲西北部独特的无球粒陨石11042：探索L球粒陨石母体的熔化和分裂
Unique achondrite Northwest Africa 11042: Exploring the melting and breakup of the L Chondrite parent body
摘要：
西北非洲（NWA）11042是一个严重冲击无球粒陨石与中等粒度的堆积结构。其橄榄石和辉石组成、氧同位素组成和铬同位素组成与L球粒陨石一致。Sm-Nd法测得其结晶年龄为4100 ± 160 Ma。岩石中的震积矿物软质岩的Ar-Ar年龄为484.0 ± 1.5Ma。这一年龄大致与L球粒陨石母体的破碎事件相吻合，该事件在许多L球粒陨石的冲击年龄和化石L球粒铬铁矿的陆地记录中很明显。NWA 11042显示亲铁元素的大量贫化（<0.01倍CI），表明复杂的火成岩历史，涉及在L球粒陨石母体上提取Fe-Ni-S液体。由于其相对年轻的结晶年龄，这种火成岩过程的热源最有可能是撞击。由于它的矿物学、岩石学和O同位素与未分组的无球粒陨石NWA 4284（这项工作）相似，这两颗陨石很可能是配对的，来自同一母体。
英文摘要：
Northwest Africa (NWA) 11042 is a heavily shocked achondrite with medium-grained cumulate textures. Its olivine and pyroxene compositions, oxygen isotopic composition, and chromium isotopic composition are consistent with L chondrites. Sm-Nd dating of its primary phases shows a crystallization age of 4100 +/- 160 Ma. Ar-Ar dating of its shocked mineral maskelynite reveals an age of 484.0 +/- 1.5 Ma. This age coincides roughly with the breakup event of the L chondrite parent body evident in the shock ages of many L chondrites and the terrestrial record of fossil L chondritic chromite. NWA 11042 shows large depletions in siderophile elements (<0.01 times CI) suggestive of a complex igneous history involving extraction of a Fe-Ni-S liquid on the L chondrite parent body. Due to its relatively young crystallization age, the heat source for such an igneous process is most likely impact. Because its mineralogy, petrology, and O isotopes are similar to the ungrouped achondrite NWA 4284 (this work), the two meteorites are likely paired and derived from the same parent body.
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