Allan Hills 76005 Polymict Eucrite Pairing Group: Curatorial and Scientific Update on a Jointly Curated Meteorite

Allan Hills 76005 (or 765) was collected by the joint US-Japan field search for meteorites in 1976-77. It was described in detail as "pale gray in color and consists of finely divided macrocrystalline pyroxene-rich matrix that contains abundant clastic fragments: (1) Clasts of white, plagioclase-rich rocks. (2) Medium-gray, partly devitrified, cryptocrystalline. (3) Monomineralic fragments and grains of pyroxene, plagioclases, oxide minerals, sulfides, and metal. In overall appearance it is very similar to some lunar breccias." Subsequent studies found a great diversity of basaltic clast textures and compositions, and therefore it is best classified as a polymict eucrite. Samples from the 1976-77, 77-78, and 78-79 field seasons (76, 77, and 78 prefixes) were split between US and Japan (NIPR). The US specimens are currently at NASA-JSC, Smithsonian Institution, or the Field Museum in Chicago. After this initial finding of ALH 76005, the next year s team recovered one additional mass ALH 77302, and then four additional masses were found during the third season ALH 78040 and ALH 78132, 78158 and 78165. The joint US-Japan collection effort ended after three years and the US began collecting in the Trans-Antarctic Mountains with the 1979-80 and subsequent field seasons. ALH 79017 and ALH 80102 were recovered in these first two years, and then in 1981-82 field season, 6 additional masses were recovered from the Allan Hills. Of course it took some time to establish pairing of all of these specimens, but altogether the samples comprise 4292.4 g of material. Here will be summarized the scientific findings as well as some curatorial details of how specimens have been subdivided and allocated for study. A detailed summary is also presented on the NASA-JSC curation webpage for the HED meteorite compendium

Allan Hills 76005 polymict eucrite pairing group: curatorial and scientific update on a jointly curated meteorite.

第2回極域科学シンポジウム/第34回南極隕石シンポジウム 11月17日（木） 国立国語研究所 2階講

Volatile Element Depletion of the Moon The Roles of Pre-Cursors, Post-Impact Disk Dynamics, and Core Formation

The compositional and isotopic similarity of Earths primitive upper mantle (PUM) and the Moon has bolstered the idea that the Moon was derived from the proto-Earth, but the Moons inventory of volatile lithophile elements Na, K, Rb and Cs are lower than in Earths PUM by a factor of 4 to 5. The abundances of fourteen other volatile elements exhibit siderophile behavior (volatile siderophile elements or VSE; P, As, Cu, Ag, Sb, Ga, Ge, Bi, Pb, Zn, Sn, Cd, In, and Tl) that could be used to evaluate whether the Moon was derived from the proto-Earth, and whether their depletion can be attributed to volatility or core formation. In this study, newly available core-mantle partitioning data are used, together with bulk Moon compositions, protolunar disk dynamics modelling to test the hypothesis that the Moon was derived from PUM-like material. At lunar core formation conditions, As, Sb, Ag, Ge, Bi, Sn are siderophile, whereas P, Cu, Ga, Pb, Zn, Cd, In and Tl are all weakly siderophile or lithophile. Most of the VSE can be explained by a combination of known processes pre-cursor volatile depletion, melt-gas dynamics and equilibria in the protolunar disk, and core formation. Explaining this whole group of volatile elements may require a combination of mixing and separation of the newly formed Moon from remnant gas rich in the highest volatility VSEs. This large group of volatile elements informs a wide temperature range and offers a powerful test of melt-gas segregation mechanisms in the protolunar disk and lunar formation hypotheses

Siderophile Element Depletion in the Angrite Parent Body (APB) Mantle: Due to Core Formation?

The origin of angrites has evaded scientists due in part to unusual mineralogy, oxidized character, and small numbers of samples. Increased interest in the origin of angrites has stemmed from the recovery of approximately 10 new angrites in the past decade. These new samples have allowed meteoriticists to recognize that angrites are compositionally diverse, old, and record very early differentiation. Also, a magma ocean has been proposed to have been involved in APB early differentiation, but this remains untested for siderophile elements which are commonly cited as one of the main lines of evidence for magma oceans on the early Earth, Moon, Mars and eucrite parent body (e.g., [6]). And recent suggestions that angrites may or may not be from Mercury have also peaked interest in these achondrites. Given all of this background, a detailed understanding of the early differentiation process is desired. Previous efforts at examining siderophile element (SE) concentrations with respect to core formation processes in the APB have not resulted in any definite conclusions regarding segregation of a metallic core. The goal of this study is to summarize what is known about SE concentrations in the suite, estimate depletions of SE compared to chondrites, and apply metal/silicate experimental partition coefficients to assess whether the APB had a core

Assessment of Volatile Depletion Mechanisms for the Moon - Pre-Cursors, Giant Impact, Core Formation, Post-Impact Loss

The volatile element depletions in the Moon have been recognized for decades. Multiple explanations have been debated, and arguments have become more quantitative, in large part due to new elemental partitioning and isotopic data. Depletions in pre-cursor materials and due to post-accretion degassing have been evaluated using isotopic data. Partitioning of many volatile elements into metallic cores can now be evaluated for many volatile siderophile elements (VSE). Here is presented an evaluation of the role of core formation for 12 volatile siderophile elements for which partitioning data is now available. Examination of all 12 elements at once allows recognition of general trends, without undue focus on one element. Ga, Ge, Zn, Sn, As, Sb, Cd, Ag, Bi, P, In, Cu are all moderately to highly volatile, and will be discussed in their order of volatility as gauged by their 50 percent condensation temperature

Overview of Carbonaceous Chondrites in the US Antarctic Meteorite Collection: Implications for Understanding Bennu and Ryugu

Spectral studies of the target asteroids of the OSIRIS-REx and Hayabusa2 missions - Bennu and Ryugu - have included comparisons to several samples from the US Antarctic meteorite collection including MET 00639 (CM2), MET 01072 (CM2), ALH 83100 (CM1/2), and LAP 02277 (CM1). The fact that these four samples provide insight into understanding these asteroids leads one to wonder what carbonaceous chondrites (CCs) are represented in the US collection and are there others that might also be helpful for comparison? Here is an overview of the CCs in the collection (n=930) and a demonstration of the great diversity of samples available as a resource to these missions

Experimentation to Understand Planet and Proto-Planet Formation

Experimental petrology has placed constraints on a wide variety of nebular and planet formation processes such as chondrule formation, CAI (Calcium-Aluminum-rich Inclusions) crystallization, asteroid magmatism, mantle melting, core formation, element partitioning related to radiogenic isotopes and heat production. Although great progress has been made, there remain several key problems where more data are required to constrain modelling, both empirical and thermodynamics-based. Here I will focus on several areas with implications for meteoritics and planetary science, including systems of low fO2 (Oxygen fugacity), constructing models that include both metal and silicate for mantle melting and differentiation, high pressure phase equilibria relevant to full range of silicate mantles, and core-mantle equilibria where H and O are specified, and their effects are measured

Re-Evaluation of HSE DATA in Light of High P-T Partitioning Data: Late Chondritic Addition to Inner Solar System Bodies Not Always Required for HSE

Studies of terrestrial peridotite and martian and achondritic meteorites have led to the conclusion that addition of chondritic material to growing planets or planetesimals, after core formation, occurred on Earth, Moon, Mars, asteroid 4 Vesta, and the parent body of the angritic meteorites. One study even proposed that this was a common process in the final stages of growth. These conclusions are based al-most entirely on the 8 highly siderophile elements (HSE; Re, Au, Pt, Pd, Rh, Ru, Ir, Os), which have been used to argue for late accretion of chondritic material to the Earth after core formation was complete. This idea was originally proposed because the D(metal/silicate) values for the HSE are very high (greater than 10,000), yet their concentration in the terrestrial mantle is too high to be consistent with such high Ds. The HSE in the terrestrial mantle also are present in chondritic relative abundances and hence require similar Ds if this was the result of core-mantle equilibration. The conclusion that late chondritic additions are required for all five of these bodies is based on the chondritic relative abundances of the HSE, as well as their elevated concentrations in the samples. An easy solution is to call upon addition of chondritic material to the mantle of each body, just after core formation; however, in practice this means similar additions of chondritic materials to each body just after core formation which ranges from approximately 4-5 Ma after T(sub 0) for 4 Vesta and the angrites, to 10-25 Ma for Mars, to 35 to 60 Ma for Moon and perhaps the Earth. Since the work of there has been a realization that high PT conditions can lower the partition coefficients of many siderophile elements, indicating that high PT conditions (magma ocean stage) can potentially explain elevated siderophile element abundances. However, detailed high PT partitioning data have been lacking for many of the HSE to evaluate whether such ideas are viable for all four bodies. Re-cent partitioning studies have covered P, T, fO2, and compositional ranges that allow values to be predicted at conditions relevant to these five inner solar system bodies. Because the D(HSE) metal/silicate are lowered substantially at higher PT conditions and natural com-positions (FeNi metallic liquids and peridotites) it is natural to re-examine the role of core formation on the HSE patterns in a variety of inner solar system bodies. Here I will discuss other processes (including high PT core formation for Mars, Moon and Earth) that can produce the observed HSE patterns, and demonstrate that there are viable hypotheses other than the "one size fits all" hypothesis of late chondritic additions

Siderophile Element Constraints on the Conditions of Core Formation in Mars

Siderophile element concentrations in planetary basalts and mantle samples have been used to estimate conditions of core formation for many years and have included applications to Earth, Moon, Mars and asteroid 4 Vesta [1]. For Earth, we have samples of mantle and a diverse collection of mantle melts which have provided a mature understanding of the how to reconstruct the concentration of siderophile elements in mantle materials, from only concentrations in surficial basalt (e.g., [2]). This approach has led to the consensus views that Earth underwent an early magma ocean stage to pressures of 40-50 GPa (e.g., [3,4]), Moon melted extensively and formed a small (approx. 2 mass %) metallic core [5], and 4 Vesta contains a metallic core that is approximately 18 mass % [6,7]. Based on new data from newly found meteorites, robotic spacecraft, and experimental partitioning studies, [8] showed that eight siderophile elements (Ni, Co, Mo, W, Ga, P, V and Cr) are consistent with equilibration of a 20 mass% S-rich metallic core with the mantle at pressures of 14 +/- 3 GPa. We aim to test this rather simple scenario with additional analyses of meteorites for a wide range of siderophile elements, and application of new experimental data for the volatile siderophile and highly siderophile elements

Opaque Assemblages in CK and CV Carbonaceous Chondrites

CK carbonaceous chondrites are the only group of carbonaceous chondrites that exhibit thermal metamorphism. As a result, CKs display features of metamorphism such as silicate darkening, recrystallization and shock veins. Calcium Aluminum Inclusions and Fe-Ni metal are rare. CV carbonaceous chondrites are unequilibrated and have two subgroups; oxidized and reduced. The CV and CK carbonaceous chondrite groups have been compared to each other often because of petrographic similarities, such as overlapping oxygen isotopic ratios. Scientists have suggested the two groups of carbonaceous chondrites formed from the same parent body and CKs are equilibrated CV chondrites [1, 2]. The oxidized CV group has been most closely related to CKs. This study examines the petrology and mineralogy of CKs and CVs focusing on opaque minerals found in the meteorites. Using the oxide, metal and sulfide assemblages, constraints can be placed on the temperature and oxygen fugacity at which the meteorites equilibrated. The temperature and oxygen fugacity of the CK and CV chondrites can be compared in order to help define their formation history