Primitive achondrites, representing 'transitional' samples between chondrites and differentiated achon-drites, provide a great opportunity to decode the thermal histories of planetesimals in the early solar sys-tem. In this work, we report a comprehensive study of petrography, mineralogy, O-Cr isotopes and 53Mn-53Cr systematics of four ungrouped primitive achondrites, Northwest Africa (NWA) 12869, NWA 3250, NWA 11112, and Tafassasset. High resolution X-ray tomographic microscopy (HR-XTM) observa-tions yield the 3D spatial distributions of metal, sulfide, and plagioclase, providing the direct petrologic evidence for incipient melting. In NWA 12869, NWA 3250, and NWA 11112, only FeNi-FeS eutectic melt-ing occurs, with small fractions of metal and sulfide melt and amalgamate sporadically. As for Tafassasset, in addition to common metal and sulfide melt, plagioclase (+/- pyroxene) extensively melts and intercon-nects to form networks, with the generation of basaltic melts. The 53Mn-53Cr systematics in NWA 12869 [initial 53Mn/55Mn of (3.24 +/- 0.32) x 10-6] and Tafassasset [initial 53Mn/55Mn of (3.48 +/- 0.20) x 10-6] are determined with mineral separates and bulk samples. When anchored to the D'Orbigny angrite, NWA 12869 has a 53Mn-53Cr age of 4563.4 +/- 0.6 Ma, while Tafassasset has an age of 4563.8 +/- 0.4 Ma. The Mn-Cr ages of NWA 12869 and Tafassasset record the time of incipient melting within their parent bod-ies.Considering that NWA 12869, NWA 3250, and NWA 11112 exhibit the same olivine-dominated (47- 69 vol%) mineral assemblages with recrystallized textures and a great similarity in mineral chemistry (olivine: Fa35-38; pyroxene: Fs27-30Wo3.0-3.5; plagioclase: An47-50; chromite: Cr#: 74-76; Mg#: 14.0- 14.6), oxygen fugacity (IW-2 to IW-1), as well as 54Cr nucleosynthetic anomalies (e54Cr: 1.01 +/- 0.09 to 1.44 +/- 0.18) and oxygen isotopes (D17O:-1.72 to-1.78 +/- 0.05 parts per thousand), we first classify them into a new grou-plet of primitive achondrites, different from Tafassasset. This grouplet does not share a parent body with CR chondrites, but rather derives from incipient melting of a carbonaceous chondrite parent body which formed in a nebular reservoir physically close to that sampled by CR chondrites. More chondrite, differ-entiated achondrite, and/or iron samples associated with this new grouplet would provide further con-straints on the rate and onset time of accretion, as well as the interior structure of the planetesimal in the outer solar system.(c) 2023 Elsevier Ltd. All rights reserved.

In December 2020, Chang'E-5 (CE-5), China's first lunar sample return mission, successfully collected samples totaling 1731 g from the northern Oceanus Procellarum. The landing site was located in a young mare plain, a great distance from those of Apollo and Luna missions. These young mare basalts bear critical scientific significance as they could shed light on the nature of the lunar interior (composition and structure) as well as the recent volcanism on the Moon. In this article, we investigated a CE-5 basalt sample (CE5C0000YJYX065) using a combination of state-of-art techniques, including high resolution X-ray tomographic microscopy (HR-XTM), energy dispersive X-ray spectroscopy (EDS)-based scanning electron microscope (SEM), and electron probe microanalysis (EPMA) to reveal its 3D petrology and minerology. Our results show that this sample has a fine-to medium-grained subophitic texture, with sparse olivine phenocrysts setting in the groundmass of pyroxene, plagioclase, ilmenite and trace amounts of other phases. It has an extremely high ilmenite modal abundance (17.8 vol%) and contains a significant amount (0.5 vol%) of Ca-phosphate grains. The mineral chemistry is in excellent agreement with that of Apollo and Luna high-Ti basalts. The major phase pyroxenes also display strong chemical zoning with compositions following the trends observed in Apollo high-Ti basalts. Based on current data, we came to the conclusion that CE5C0000YJYX065 is a high-Ti mare basalt with a rare earth element (REE) enriched signature. This provides a rigid ground-truth for the geological context at the CE-5 landing site and clarifies the ambiguity inferred from remote sensing surveys.(c) 2021 Science China Press. Published by Elsevier B.V. and Science China Press. All rights reserved.

The many unique characteristics of CB chondrites have resulted in the impact hypothesis becoming the favoured model for their formation. Here, we further investigate the formation mechanisms of CB chondrites by analysing the elemental and K isotope compositions of chondrules and bulk fractions from the CBa chondrite Gujba. Similar to previous work, the refrac-tory element ratios in the Gujba chondrules show evidence of a differentiated precursor, with the Nb/Ta, Zr/Hf, Sc/Th and Zr/Th ratios showing fractionation relative to other chondrites. In addition, the bulk fractions, and to a lesser extent the chon-drules with attached matrix and metals, display significantly more refractory element fractionation and a large enrichment in light REEs. Based on EDS elemental mapping and comparisons with previous studies, the most likely source of this highly fractionated material appears to be the small amount of heterogeneously distributed interstitial fine-grained material within Gujba. These large refractory element fractionations (i.e., Nb/Ta, Zr/Hf, Sc/Th Zr/Th, and LREE/HREE) are best explained by a significant partial melting process such as crustal formation. Nevertheless, the mechanism of patrial melting cannot be conclusively determined with the data available here. The K isotopic compositions of the Gujba chondrules analyzed here range from -2.24 parts per thousand to -0.41 parts per thousand in delta K-41, whereas the bulk analyses show delta K-41 values of -0.81% to -0.72 parts per thousand. This range of chondrule K isotope compositions is significantly larger, and extends to much lighter compositions, compared to all other chondrites measured so far by bulk ICP-MS. In addition, the Gujba chondrules display a clear negative correlation of K iso-topic composition with K concentration, with the chondrules showing the lightest K isotope compositions having the highest K concentrations. This distinctive correlation indicates that evaporation was likely the dominant process affecting the K iso-topic variation observed in the Gujba chondrules. Nevertheless, the extremely light delta K-41 values seen in the most K-rich chon-drules (which are lighter than any other early solar system material so far measured) indicate that incomplete condensation likely took place before evaporation. As such, we propose a two-stage model to explain the formation of chondrules in Gujba, with Stage 1 characterized by incomplete condensation of vaporized material with an average isotopic fractionation factor (a) of 0.9984 (when using the most K enriched chondrule to constrain the model), and Stage 2 representing partial evaporation in a vapor plume with an average a range of 0.9976 to 0.9990. Using these a values we calculate an approximate vapor saturation index value of 0.935 for condensation and between 0.903 and 0.960 for evaporation. This formation process requiring both condensation and evaporation for CB chondrules is consistent with an impact generated vapor plume and further expands our understanding of CB chondrite formation. (C) 2022 Published by Elsevier Ltd.

钾是个中等挥发性元素，可用来揭示早期太阳星云中挥发分的亏损机制和分馏机制。本项目利用国际上最新的高精度MC-ICP-MS钾同位素分析技术，按照任务书计划，在钾同位素研究方面取得了重要进展：1)完成了大量碳质球粒陨石和普通球粒陨石全岩的高精度钾同位素研究，发现它们的钾同位素呈二分性分布，且钾同位素成分与陨石的化学类型、岩石类型、冲击变质类型、风化级别及宇宙射线暴露年龄没有明显的相关性，不符合单阶段部分蒸发或冷凝机制；2)完成了碳质球粒陨石中各组分(球粒、难熔包体和基质)的高精度钾同位素研究，发现球粒的钾同位素成分是星云过程和母体过程综合叠加的结果；3)完成了全世界不同散落区的冲击玻璃(Tektite)样品的高精度钾同位素研究，并与上陆壳源岩进行对比，发现中等挥发性元素钾在冲击玻璃形成过程中不发生丢失，同位素不发生分馏，与理论计算和数值模拟结果一致。.此外，本项目还对我国返回的嫦娥五号首批月球样品开展了岩相学、矿物学和同位素研究，发现了一块较为少见的高钛月海玄武岩岩屑，为研究月球年轻地质活动提供了重要证据；对小行星样品开展了岩石学、矿物学以及年代学研究，为太阳系早期小行星熔融、冲击和裂解历史提供了重要见解。

2020年12月,我国首次月球采样返回任务——嫦娥五号,在月球正面的风暴洋北部一举成功返回了1731 g样品.嫦娥五号着陆区位于年轻的月海平原,远离美国Apollo和苏联Luna任务采样点.这些年轻的月海玄武岩对于揭示月球内部的成分和结构以及

2020年12月,我国首次月球采样返回任务——嫦娥五号,在月球正面的风暴洋北部一举成功返回了1731 g样品.嫦娥五号着陆区位于年轻的月海平原,远离美国Apollo和苏联Luna任务采样点.这些年轻的月海玄武岩对于揭示月球内部的成分和结构以及火山活动历史具有十分重要的科学意义.本文利用高分辨率显微CT、扫描电子显微镜、电子探针等技术对编号为CE5C0000YJYX065的嫦娥五号岩屑样品开展了详细的岩石学、矿物学和三维层析成像研究.结果表明,该样品具有细粒至中粒次辉绿结构,少量橄榄石斑晶分布在由辉石、斜长石、钛铁矿和其他副矿物组成的基质中.样品含有极高丰度的钛铁矿（17.8vol.%）,并富含磷酸盐矿物（0.5 vol.%）.主要组成矿物的化学成分和演化趋势与Apollo和Luna任务返回的高钛玄武岩高度一致.多项证据表明,不同于目前已报道的嫦娥五号中钛和低钛月海玄武岩类型。CE5C0000YJYX065是一种富集稀土元素的高钛月海玄武岩,由此证明嫦娥五号着陆区发生了多次火山活动,其能量来源可能来自放射性元素的衰变.

钙长辉长无球粒陨石(Eucrite)是Howardite-Eucrite-Diogenite(HED)族陨石的重要成员,也是研究灶神星壳演化历史的重要对象。本文研究了多个玄武质Eucrite样品中主要的SiO2相——普通石英和鳞石英的成因,进而讨论其对Eucrite陨石热演化