Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury
Reclassification of four aubrites as enstatite chondrite impact melts: Potential geochemical analogs for Mercury
复制标题
将四种赤辉石重新分类为顽辉石球粒陨石冲击熔体：汞的潜在地球化学类似物
DOI：
10.1111/maps.13252
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发表时间：
2019
影响因子：
2.2
通讯作者：
B. Turrin
中科院分区：
文献类型：
--
作者：
A. Udry;Z. Wilbur;R. R. Rahib;F. McCubbin;Kathleen E. Vander Kaaden;T. Mccoy;K. Ziegler;J. Gross;C. DeFelice;L. Combs;B. Turrin
我们目前的岩石学和同位素数据西北非洲（NWA）4799，NWA 7809，NWA 7214，和NWA 11071陨石，这是以前被归类为Aubrites。这四种陨石含有31 - 56体积%的等粒、近端元顽火辉石、铁、镍金属、斜长石、陆地蚀变产物和硫化物，如硫陨硫、硫镍银矿、硅铝石、奥铜银矿和卡斯韦尔银矿。顽火辉石的等颗粒结构和顽火辉石周围金属的存在表明，这些岩石不是通过像奥辉岩一样的火成岩过程形成的，而是通过撞击过程形成的。此外，存在陆前风化金属（7.1-14体积%），与顽火辉石相比无差异模态丰度，存在石墨，不存在透辉石和镁橄榄石，硫铁矿中Ti含量低，Fe、Ni金属中Si含量高，表明这些岩石是通过对顽火辉石而非奥辉岩母体的冲击熔融形成的。这些陨石的形成与EHa顽火辉石球粒陨石母体具有相似的性质的母体建议由他们的矿物学。根据39 Ar-40 Ar年龄，这些母体经历了至少4.5 Ga（NWA 11071）到至少4.2 Ga（NWA 4799）的撞击事件，表明太阳系的这个区域在其历史早期受到了严重的轰击。通过将NWA顽火辉石球粒陨石撞击熔体与水星进行比较，我们推断，鉴于它们的金属丰度高，它们代表了这颗行星的不完美的岩石学类似物，但它们可以代表水星上元素的行为和地球化学亲和力的重要地球化学类似物。此外，顽火辉石球粒陨石撞击熔体代表了理解高温过程和水星撞击过程的重要岩石学模拟，因为它们具有相似的矿物学、富铁金属和贫FeO硅酸盐丰度以及低氧逸度。
We present petrologic and isotopic data on Northwest Africa (NWA) 4799, NWA 7809, NWA 7214, and NWA 11071 meteorites, which were previously classified as aubrites. These four meteorites contain between 31 and 56 vol% of equigranular, nearly endmember enstatite, Fe,Ni metal, plagioclase, terrestrial alteration products, and sulfides, such as troilite, niningerite, daubréelite, oldhamite, and caswellsilverite. The equigranular texture of the enstatite and the presence of the metal surrounding enstatite indicate that these rocks were not formed through igneous processes like the aubrites, but rather by impact processes. In addition, the presence of pre‐terrestrially weathered metal (7.1–14 vol%), undifferentiated modal abundances compared to enstatite chondrites, presence of graphite, absence of diopside and forsterite, low Ti in troilite, and high Si in Fe,Ni metals suggest that these rocks formed through impact melting on chondritic and not aubritic parent bodies. Formation of these meteorites on a parent body with similar properties to the EHa enstatite chondrite parent body is suggested by their mineralogy. These parent bodies have undergone impact events from at least 4.5 Ga (NWA 11071) until at least 4.2 Ga (NWA 4799) according to 39Ar‐40Ar ages, indicating that this region of the solar system was heavily bombarded early in its history. By comparing NWA enstatite chondrite impact melts to Mercury, we infer that they represent imperfect petrological analogs to this planet given their high metal abundances, but they could represent important geochemical analogs for the behavior and geochemical affinities of elements on Mercury. Furthermore, the enstatite chondrite impact melts represent an important petrological analog for understanding high‐temperature processes and impact processes on Mercury, due to their similar mineralogies, Fe‐metal‐rich and FeO‐poor silicate abundances, and low oxygen fugacity.