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.

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

钾和其他中等挥发性元素亏损是类地行星普遍的全岩化学成分特征之一,能用来示踪不同的亏损过程。球粒陨石是组成行星的前体物质,研究球粒陨石中钾同位素的亏损和分异机制,对于太阳系物质或行星的起源、形成和演化具有十分重要的意义。

Potassium elemental and isotope systematics were investigated for a suite of central European tektites from three strewn sub-fields in Czech Republic and possible parent sedimentary materials from the vicinity of the Ries impact structure in SE Germany, supplemented by data for several other impact-related materials (bediasites, Ivory Coast tektites, Libyan Desert Glass). This is paralleled by computation of potential K loss and attendant isotope fractionation for physico-chemical conditions typical for formation of tektite precursor melts. These theoretical calculations indicate a <0.1% loss of K from tektite precursor melts up to 2,500 K and <0.002% change in the K-41/K-39 ratio even for a small sphere of 0.002 m at 2,500 K, precluding any significant K loss and isotope fractionation. Numerical modelling also indicates that differential velocities between surrounding gas and liquid are not sufficient to remove the gaseous boundary layer, such that the partial pressure of potassium developed around the molten moldavite beads impedes further evaporation and also contributes to back-condensation of the already evaporated potassium.Central European tektites (moldavites) are enriched in K compared to the assumed sedimentary sources from the wider Ries area whereby the latter materials do not exceed 2.9 wt.% K2O compared to 2.5-4.1 wt.% K2O in moldavites. The apparent K enrichment in moldavites may be explained by a yet unaccounted process during formation of tektite precursor melts and/or unidentified source, such as volcanoclastic deposits that were produced by large Mid-Miocene volcanic centers in the Pannonian Basin. The K isotope compositions of tektites are more variable than those of sediments from the wider Ries area but they largely overlap (delta K-41 from -0.78 +/- 0.03 parts per thousand to -0.13 +/- 0.03 parts per thousand versus -0.72 +/- 0.03 parts per thousand to -0.28 +/- 0.02 parts per thousand, respectively). These ranges mimic K-41/K-39 variations reported for igneous and sedimentary portions of the upper difference among the three investigated strewn sub-fields, depending on their respective distance from the impact. In detail, moldavites from the closest strewn sub-field in the Cheb Basin show predominantly heavy K isotope compositions and those from the farthest strewn sub-field in Western Moravia are uniformly isotopically light. The origin of this difference may reflect lithological heterogeneity of the target area.Potassium contents in bediasites and Ivory Coast tektites range between 1.3 and 1.8 wt.% K2O and their corresponding delta K-41 values vary from -0.57 +/- 0.02 parts per thousand to -0.41 +/- 0.03 parts per thousand. Both ranges are significantly narrower than those observed for moldavites. When compared to data for possible sedimentary precursors in the Chesapeake Bay and Bosumtwi impact structure, respectively, it is apparent that these tektites were neither depleted nor enriched in potassium. The extent of their K isotope fractionation relative to plausible sources remains unconstrained. The Libyan Desert Glass displays invariant delta K-41 of similar to-0.57 +/- 0.06%0 at <= 0.01 wt.% K2O. Given the silica-rich nature of LDG , the lack of possible parent materials, no further constraints can be placed at present to further resolve the source material or reveal details of LDG formation process. (C) 2021 Elsevier Ltd. All rights reserved.

Studies of the new growth and re-distribution of Cu-rich phases in chondrites of different petrologic subtypes can potentially provide insights into post-accretionary parent-body processes. We present a systematic study of the distribution of Cu-rich phases and metallic Cu in Ornans-like carbonaceous chondrites (CO3) that underwent little aqueous alteration or shock (most with shock stages of S1) but exhibit a range of thermal metamorphism (subtype 3.0-3.7). A comparison to ordinary chondrites (OCs), which have undergone a larger range of shock levels, allows us to constrain the relative roles of radiogenic and shock heating in the origin of Cu distribution in chondrites. We found that the Cu content of Ni-rich metal and calculated bulk Cu content of CO3 chondrites (based on mass-balance calculations) show an increase from CO3.0 to CO3.2 chondrites. We speculate that some unidentified phases in the matrix account for a significant portion (nearly-100 ppm) of the Cu budget in bulk samples of CO3.0 chondrites, while Ni-rich metal is the main Cu-carrier for CO3.2-3.7 chondrites. Within CO3.2-3.7 chondrites, Cu and Ni contents of Ni-rich metal are positively correlated, showing a systematic decrease from lower to higher subtype (-0.41 wt% Cu and-45.0 wt% Ni in CO3.2 Kainsaz;-0.28 wt% Cu and-38.8 wt% Ni in CO3.7 Isna). Metallic Cu grains were found in every sample of CO3.2-3.7 chondrites, but not in any CO3.0-3.1 chondrites. Metallic Cu is: (1) present at metallic-Fe-Ni-pyrrhotite interfaces; (2) associated with fine irregular pyrrhotite grains in Nirich-metal-pyrrhotite nodules; (3) associated with fizzed pyrrhotite (fine-grained mixtures of irregularly shaped metal grains surrounded by pyrrhotite); (4) present at the edges of metallic Fe-Ni grains; and (5) present as isolated grains. In some metallic-Cu-bearing mineral assemblages, pyrrhotite has higher Cu concentrations than adjacent Ni-rich metal and shows a drop in Cu concentration at the interface between metallic Cu and Cu-rich pyrrhotite. This implies that the precipitation of metallic Cu grains could be related to the local Cu enrichment of pyrrhotite. We consider that radiogenic heating is mainly responsible for the formation of opaque phases in CO chondrites based on the relatively slow metallographic cooling rate (-0.1-5 degrees C/Ma), the increasing uniformity of Ni contents in Ni-rich metal with increasing CO subtype (44.3 +/- 17.3 wt% in CO3.00 to 38.8 +/- 3.4 wt% in CO3.7 chondrite), and the relatively narrow range of pyrrhotite metal/sulfur ratios (-0.976-0.999). Metal/sulfur ratios of pyrrhotite grains in most CO3.2-3.7 chondrites (mean =-0.986-0.997; except Lance) are slightly higher than those in CO3.0-3.1 chondrites (mean =-0.981-0.987; except Y-81020), possibly indicative of a release and re-mobilization of sulfur during progressive heating as previously reported for type-3 chondrites. In this regard, we suggest most metallic Cu grains in CO3 chondrites may have precipitated from Cu-rich pyrrhotite due to sulfidation of Fe-Ni metal during parent-body thermal metamorphism. Locally, a few metallic Cu grains associated with fizzed pyrrhotite could have formed during transient shock-heating. Both thermal and shock metamorphism could be responsible for the formation of metallic Cu. Although the systematic decrease in the Ni contents of Ni-rich metal from subtype-3.2 to subtype-3.8 also occurs in OCs, the average Cu contents of Ni-rich metal grains are indistinguishable among type-3 OCs of different subtypes.The paucity of metallic Cu in weakly shocked type-3 OCs could be related to: (1) the relatively low-bulk Cu contents of OCs, and/or (2) the relatively rapid metallographic cooling rates at <500-600 degrees C (-1-10 degrees C/Ma for LL chondrites), possibly resulting from early disturbance of OC parent bodies. The intergrowth of metallic Cu and irregular pyrrhotite more commonly occurs in shocked type-4 to type-6 OCs than in CO3 chondrites. This could be due to S in type-4 to type-6 OCs being more mobilized due to shock heating than in unshocked CO3 chondrites. We predict that some other groups of carbonaceous chondrites (e.g., CI and CM) are less likely to produce metallic Cu due to the: (1) relatively low amount of metallic Fe-Ni; (2) relatively low parent-body temperatures of-100-300 degrees C; (3) high mobility of Cu in solution for aqueously altered samples; and (4) the short heating duration for metamorphosed samples.

The alkali element K is moderately volatile and fluid mobile; thus, it can be influenced by both primary processes (evaporation and recondensation) in the solar nebula and secondary processes (thermal and aqueous alteration) in the parent body. Since these primary and secondary processes would induce different isotopic fractionations, K isotopes could become a potential tracer to distinguish them. Using recently developed methods with improved precision (0.05 parts per thousand, 95% confidence interval), we systematically measured the K isotopic compositions and major/trace elemental compositions of chondritic components (18 chondrules, 3 CAIs, 2 matrices, and 5 bulks) in the carbonaceous chondrite fall Allende. Among all the components analyzed in this study, CAIs, which formed initially under high-temperature conditions in the solar nebula and were dominated by nominally K-free refractory minerals, have the highest K2O content (average 0.53 wt%) and have K isotope compositions most enriched in heavy isotopes (delta K-41: -0.30 to -0.25 parts per thousand). Such an observation is consistent with previous petrologic studies that show CAIs in Allende have undergone alkali enrichment during metasomatism. In contrast, chondrules contain lower K2O content (0.003-0.17 wt%) and generally lighter K isotope compositions (delta K-41: -0.87 parts per thousand to -0.24 parts per thousand). The matrix and bulks are nearly identical in K2O content and K isotope compositions (0.02-0.05 wt%; delta K-41: -0.62 to - 0.46 parts per thousand), which are, as expected, right in the middle of CAIs and chondrules. This strongly indicates that most of the chondritic components of Allende suffered aqueous alteration and their K isotopic compositions are the ramification of Allende parent-body processing instead of primary nebular signatures. Nevertheless, we propose the small K isotope fractionations observed (< 1 parts per thousand) among Allende components are likely similar to the overall range of K isotopic fractionation that occurred in nebular environment. Furthermore, the K isotope compositions seen in the components of Allende in this study are consistent with MC-ICP-MS analyses of the components in ordinary chondrites, which also show an absence of large (10 parts per thousand) isotope fractionations. This is not expected as evaporation experiments in nebular conditions suggest there should be large K isotopic fractionations. Nevertheless, possible nebular processes such as chondrules back exchanging with ambient gas when they formed could explain this lack of large K isotopic variation.