Possible impact-induced refractory-lithophile fractionations in EL chondrites
Possible impact-induced refractory-lithophile fractionations in EL chondrites
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EL 球粒陨石中可能由撞击引起的难熔亲石分馏
DOI：
10.1016/j.gca.2008.12.002
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发表时间：
2009
影响因子：
5
通讯作者：
J. Wasson
中科院分区：
文献类型：
--
作者：
A. Rubin;H. Huber;J. Wasson
文献资料表明，在大多数球粒陨石群中的耐火-亲石元素相对于CI球粒陨石是未分馏的;主要例外是EL球粒陨石群，其观察到的福尔斯（均为6型）在Ca和轻稀土元素中亏损。与此相反，文献数据和我们新的INAA数据EL 3 PCA 91020，EL 3 MAC 88136和EL 4 Grein 002显示，这些样品的一些重复几乎平坦的稀土元素模式（不像那些EL 6陨石），其他重复表现出分馏的稀土元素模式类似的EL 6陨石。岩相学检查表明，许多EL 6（和一些EL 3和EL 4）榴辉岩是冲击熔融角砾岩或含有冲击熔融部分。我们认为，形成这些角砾岩和产生熔体的相同撞击过程是造成所观察到的耐火亲石元素中大量成分分馏的原因，即，从最初未平衡的EL 3材料制备EL 6沸石。当大量的撞击热沉积时，斜长石和/或顽火辉石中的主要稀土载体--钙铝榴石（CaS）可能已经被熔融，然后被搬运了相当远的距离（> 10 cm）。EL 6方解石代表贫REE（特别是LREE）和Ca的残体。与EL陨石的情况不同，我们对ALH 84170、EET 87746和SAH 97096（均为EH 3）的新INAA数据显示出一些分散性，但与具有均匀耐火-亲石丰度的EH组一致。
Literature data show that refractory-lithophile elements in most chondrite groups are unfractionated relative to CI chondrites; the principal exception is the EL-chondrite group whose observed falls (all of which are type 6) are depleted in Ca and light REE. In contrast, literature data and our new INAA data on EL3 PCA 91020, EL3 MAC 88136 and EL4 Grein 002 show that some replicates of these samples have nearly flat REE patterns (unlike those of EL6 chondrites); other replicates exhibit fractionated REE patterns similar to those of EL6 chondrites. Petrographic examination shows that many EL6 (and some EL3 and EL4) chondrites are impact-melt breccias or contain impact-melted portions. We suggest that the same impact processes that formed these breccias and produced melt are responsible for the observed bulk compositional fractionations in refractory-lithophile elements, i.e., EL6 chondrites were produced from initially unequilibrated EL3 material. When large amounts of impact heat were deposited, plagioclase and/or oldhamite (CaS) (the major REE carriers in enstatite chondrites) may have been melted and then transported appreciable (>10cm) distances. EL6 chondrites represent the residuum that is depleted in REE (particularly in LREE) and Ca. Unlike the case for EL chondrites, our new INAA data on ALH 84170, EET 87746 and SAH 97096 (all EH3) show some scatter but are consistent with the EH group having uniform refractory-lithophile abundances.
DOI：
10.1029/88eo00188
发表时间：
1988-05
期刊：
Eos, Transactions American Geophysical Union
影响因子：
--
作者：
C. Goodrich
通讯作者：
C. Goodrich