Our detailed mineralogical, elemental, and isotopic study of the Miller Range (MIL) 07687 meteorite showed that, although this meteorite has affinities to CO chondrites, it also exhibits sufficient differences to warrant classification as an ungrouped carbonaceous chondrite. The most notable feature of MIL 07687 is the presence of two distinct matrix lithologies that result from highly localized aqueous alteration. One of these lithologies is Fe‐rich and exhibits evidence for interaction with water, including the presence of fibrous (dendritic) ferrihydrite. The other lithology, which is Fe‐poor, appears to represent relatively unaltered protolith material. MIL 07687 has presolar grain abundances consistent with those observed in other modestly altered carbonaceous chondrites: the overall abundance of O‐rich presolar grains is 137 ± 3 ppm and the overall abundance of SiC grains is 71 ± 11 ppm. However, there is a large difference in the observed O‐rich and SiC grain number densities between altered and unaltered areas, reflecting partial destruction of presolar grains (both O‐ and C‐rich grains) due to the aqueous alteration experienced by MIL 07687 under highly oxidizing conditions. Detailed coordinated NanoSIMS‐TEM analysis of a large hotspot composed of an isotopically normal core surrounded by a rim composed of ¹⁷O‐rich grains is consistent with either original condensation of the core and surrounding grains in the same parent AGB star, or with grain accretion in the ISM or solar nebula.

中文翻译：

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独特的碳质球粒陨石Miller系列07687中的二次加工效果

我们对Miller Range（MIL）07687陨石进行的详细矿物学，元素学和同位素研究表明，尽管该陨石与CO球粒陨石具有亲和力，但它也表现出足够的差异以确保将其分类为未分组的碳质球粒陨石。MIL 07687的最显着特征是存在两种不同的基质岩性，这是由于高度局部的水蚀作用引起的。这些岩性之一是富铁的，并显示出与水相互作用的证据，包括存在纤维状（树枝状）亚铁水合物。另一种是贫铁的岩性似乎代表了相对不变的原岩材料。MIL 07687具有与其他温和改变的碳质球粒陨石中观察到的一致的太阳前谷物丰度：富含O的太阳前晶粒的总丰度为137±3 ppm，而SiC晶粒的总丰度为71±11 ppm。但是，在改变和未改变的区域之间，观察到的富O和SiC晶粒数密度存在很大差异，反映出MIL 07687经历了含水变化，导致前太阳晶粒（富含O和C的晶粒）被部分破坏。高氧化条件。NanoSIMS-TEM的详细协调分析，由一个热点组成，该热点由同位素法线核心包围，边缘由以下元素组成：反映了由于MIL 07687在高氧化条件下经历的水相变化，导致前太阳晶粒（富含O和C的晶粒）被部分破坏。对大热点的详细协调的NanoSIMS-TEM分析，该热点由同位素法线核心和由以下组成的边沿包围 反映了由于MIL 07687在高氧化条件下经历的水相变化，导致前太阳晶粒（富含O和C的晶粒）被部分破坏。对大热点的详细协调的NanoSIMS-TEM分析，该热点由同位素法线核心和由以下组成的边沿包围¹⁷富含O的颗粒与同一颗母AGB恒星中核心和周围颗粒的原始凝结或与ISM或太阳星云中的颗粒积聚相一致。