Comparison of the LEW88516 and ALHA77005 martian meteorites: Similar but distinct
Comparison of the LEW88516 and ALHA77005 martian meteorites: Similar but distinct
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LEW88516 和 ALHA77005 火星陨石的比较：相似但不同
DOI：
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发表时间：
1994
期刊：
影响因子：
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通讯作者：
D. Garrison
中科院分区：
文献类型：
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作者：
A. Treiman;G. Mckay;D. Bogard;D. Mittlefehldt;Ming‐Sheng Wang;L. Keller;M. Lipschutz;M. Lindstrom;D. Garrison
从矿物和整体成分来看，刘易斯崖（LEW）88516陨石与ALHA 77005火星陨石非常相似。这两颗陨石没有配对，因为它们的矿物成分不同，它们是在相距500公里的冰原上发现的，有不同的陨石来源，它们在陆地上的居住年龄也不同。LEW 88516中的矿物包括：橄榄石、辉石（低钙和高钙）和斜长岩;以及次要矿物铬铁矿、白磷铁矿、钛铁矿和磁黄铁矿。LEW 88516中的矿物颗粒范围可达几毫米。从纹理上看，陨石是复杂的，橄榄石和铬铁矿嵌在辉石中，间隙玄武岩纹理区域和富含玻璃（冲击）细脉。橄榄石成分范围从Fo（sub 64）到Fo（sub 70），（平均值）Fo（sub 67）），比ALHA 77005（Fo（sub 69）至Fo（sub 73））更多的亚铁烷和更多的变化。辉石组成介于En（sub 77）Wo（sub 4）和En（sub 65）Wo（sub 15）之间，在En（sub 63）Wo（sub 9）和En（sub 53）Wo（sub 33）附近的簇中，平均镁含量高于ALHA 77005，变化也更大。LEW 88516的冲击特性从弱变形到完全熔化。通过电子探针分析、仪器中子活化和放射化学中子活化的模式重组进行的大量化学分析证实，LEW 88516与ALHA 77005的关系比其他已知的火星陨石更密切。关键元素丰度比是典型的火星陨石，因为它是非磁性稀土模式。LEW 88516和ALHA 77005的化学成分之间的差异与其组成矿物比例的轻微差异一致，而不是基本的岩石成因差异。LEW 88516中的稀有气体丰度与ALHA 77005中的丰度一样，显示出捕获（冲击注入）气体中Ar-40和Ar-129的适度过量。与其他ALHA 77005和shergottite火星陨石（EETA 79001除外）一样，LEW 88516的惰性气体同位素丰度与暴露于宇宙射线的时间一致，为2.5-3 Ma。没有对宇宙射线产生实质性的屏蔽作用，这表明LEW 88516在这段时间里是一个直径不超过几厘米的物体。
By mineral and bulk compositions, the Lewis Cliff (LEW) 88516 meteorite is quite similar to the ALHA77005 martian meteorite. These two meteorites are not paired because their mineral compositions are distinct, they were found 500 km apart in ice fields with different sources for meteorites, and their terrestrial residence ages are different. Minerals in LEW88516 include: olivine, pyroxenes (low- and high-Ca), and maskelynite (ater plagioclase); and the minor minerals chromite, whitlockite, ilmenite, and pyrrhotite. Mineral grains in LEW88516 range up to a few mm. Texturally, the meteorite is complex, with regions of olivine and chromite poikilitically enclosed in pyroxene, regions of interstitial basaltic texture, and glass-rich (shock) veinlets. Olivine compositions range from Fo(sub 64) to Fo(sub 70), (avg. Fo(sub 67)), more ferroan and with more variation than in ALHA77005 (Fo(sub 69) to Fo(sub 73)). Pyroxene compositions fall between En(sub 77)Wo(sub 4) and En(sub 65)Wo(sub 15) and in clusters near En(sub 63)Wo(sub 9) and En(sub 53)Wo(sub 33), on average more magnesian and with more variation than in ALHA77005. Shock features in LEW88516 range from weak deformation through complete melting. Bulk chemical analyses by modal recombination of electron microprobe analyses, instrumental neutron activation, and radiochemical neutron activation confirm that LEW88516 is more closely related to ALHA77005 than to other known martian meteorites. Key element abundance ratios are typical of martian meteorites, as is it nonchondritic rare earth pattern. Differences between the chemical compositions of LEW88516 and ALHA77005 are consistent with slight differences in the proportions of their constituent minerals and not from fundamental petrogenetic differences. Noble gas abundances in LEW88516, like those in ALHA77005, show modest excesses of Ar-40 and Xe-129 from trapped (shock-implanted) gas. As with other ALHA77005 and the shergottite martian meteorites (except EETA79001), noble gas isotope abundances in LEW88516 are consistent with exposure to cosmic rays for 2.5-3 Ma. The absence of substantial effects of shielding from cosmic rays suggest LEW88516 spent this time as an object no larger than a few cm in diameter.