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Achondrites provide an opportunity to examine the igneous processes of differentiated bodies in our solar system. The recent discovery of several silica‐rich achondrites suggests that andesitic crusts were more common among planetesimals than previously thought, though the processes behind their emplacement are not well understood. Here, electron backscatter diffraction (EBSD) is used to investigate the igneous emplacement conditions of Erg Chech 002 (EC 002), a recently discovered ungrouped achondrite representing andesitic magmatism ~2 Myr after the formation of calcium–aluminum‐rich inclusions (CAIs). EBSD analyses of crystallographic preferred orientations (CPOs) for augite and plagioclase feldspar phenocrysts indicate that EC 002 exhibits a weak foliation CPO. Augite misorientation inverse pole figures (mIPF) indicate preferential slip along the (100)[001] system with a distinct shift toward the {0kl}[u0w] system in plastically deformed grains. Our findings support the hypothesis that EC 002 was likely emplaced in the lower regions of a magmatic intrusion. Augite slip signatures suggest that EC 002 crystallization and emplacement were restricted to high temperatures (>800°C) and experienced at least two strain regimes. The distinct shift from a dominant (100)[001] slip system, which corresponds to high temperatures (800–1050°C), to a [0kl][u0w] slip system indicates an increased strain rate due to shock deformation (1–5 GPa) attributed to ejection by hypervelocity impact. [ABSTRACT FROM AUTHOR]

The Mars 2020/Mars Sample Return (MSR) Sample Depot Science Community Workshop was held on September 28 and 30, 2022, to assess the Scientifically‐Return Worthy (SRW) value of the full collection of samples acquired by the rover Perseverance at Jezero Crater, and of a proposed subset of samples to be left as a First Depot at a location within Jezero Crater called Three Forks. The primary outcome of the workshop was that the community is in consensus on the following statement: The proposed set of ten sample tubes that includes seven rock samples, one regolith sample, one atmospheric sample, and one witness tube constitutes a SRW collection that: (1) represents the diversity of the explored region around the landing site, (2) covers partially or fully, in a balanced way, all of the International MSR Objectives and Samples Team scientific objectives that are applicable to Jezero Crater, and (3) the analyses of samples in this First Depot on Earth would be of fundamental importance, providing a substantial improvement in our understanding of Mars. At the conclusion of the meeting, there was overall community support for forming the First Depot as described at the workshop and placing it at the Three Forks site. The community also recognized that the diversity of the Rover Cache (the sample collection that remains on the rover after placing the First Depot) will significantly improve with the samples that are planned to be obtained in the future by the Perseverance rover and that the Rover Cache is the primary target for MSR to return to Earth. [ABSTRACT FROM AUTHOR]

Introduction: The chronology of martian meteorites offers unique insights into volcanism on Mars, and hence the geological and thermal evolution of the martian crust and mantle system. It is thought that depleted shergottites (derived from incompatible trace element-depleted mantle sources) formed from a long-lived volcanic centre over more than 2 billion years [1], and that nakhlite source volcano grew many orders of magnitude slower than comparable systems on Earth [2]. In potential contrast, existing estimates of enriched shergottite crystallization ages have a relatively narrow range from 165 to 225 Ma ([3], and references therein). However, alongside rapid growth in the number of classified samples, increasing petrological diversity of enriched shergottites has been recognized. This includes gabbroic samples interpreted as cumulates [4, 5]. New age data are needed to help test potential magmatic links between petrological types of enriched shergottites, and better understand volcanism at enriched shergottite launch site(s) for samples with linked cosmogenic ray exposure (CRE) ages. Unambiguous interpretation of age data from shergottites has long proven challenging due to secondary processes that include intensive shock metamorphism. However recent advances in nanostructurally-guided U-Pb chronology of baddeleyite (e.g. [6, 7]) have overcome these challenges. Apatite and merrillite also have tremendous potential to record igneous, thermal and shock histories [8]. Here, we combine new U-Th-Pb isotope analyses of accessory minerals in enriched shergottites with recent results to further refine understanding of late Amazonian magmatism on Mars, and highlight the potential of apatite and merrillite to constrain the timing of magmatic emplacement. Methodology: Our group have recently undertaken nanostructurally-guided baddeleyite U-Pb isotope analysis of enriched basaltic to microgabbroic shergottites Tindouf 002, Northwest Africa (NWA) 7257, NWA 8679, Jiddat al Harasis (JaH) 479, NWA 10299, and NWA 12919, along with gabbroic shergottite NWA 6963. The approach follows that of [7], combining SEM imaging and electron backscatter diffraction (EBSD) analysis at the University of Portsmouth, with SIMS U-Pb isotope analysis at the University of Heidelberg (following methods of [9]). Nanostructurallyconstrained apatite and merrillite U-Th-Pb isotope analysis was undertaken by LA-ICP-MS at the University of Portsmouth, targeting three samples with a range of shock-metamorphic conditions: NWA 7257, NWA 5298 and Zagami. Findings: EBSD analysis has revealed that all of the studied samples have a range of baddeleyite nanostructures, including evidence for widespread reversion from high P-T ZrO2 polymorphs. Some samples also retain domains with preserved magmatic twin relationships. None of the baddeleyite analysed by SIMS contains evidence for widespread granularization or recrystallisation, which are the only processes known to lead to resolvable Pb-loss and age resetting in baddeleyite from shergottites [6, 7]. As such, the baddeleyite U-Pb Tera-Wasserburg discordia arrays are interpreted to record the timing of magmatic crystallization for each sample. The relatively narrow range of resulting ages (~185 to 220 Ma) from these samples, including an age of 189 ± 13 (95 % conf.) for gabbroic sample NWA 6963, underlines the close temporal linkage between enriched shergottites of varying petrology and geochemistry. LA-ICP-MS U-Pb isotopic dates from apatite and merrillite in NWA 7257 (164 ± 37 Ma; all 2s) and Zagami (199 ± 34 Ma) are within uncertainty of baddeleyite ages [7, 10]. Combining data with [10] results in an apatite and merrillite age of 194 ± 27 Ma for Zagami. Given the modest closure temperature of apatite to Pb-diffusion (350-570 °C [11]), the results imply a simple thermal history from shortly after formation at the martian surface, and insufficient post-shock heating to drive resolvable Pb mobility. This shows that Ca-phosphates can record the timing of primary magmatic processes in shergottites, despite complex shock histories. In combination, the new results further strengthen interpretations that enriched shergottites formed within a relatively short period (~225 to 170 Ma) in the late Amazonian, and that their volcanic centre(s) was/were relatively complex. Additional CRE ages for enriched shergottites will enable analysis of individual launch sites, and testing of the hypothesis that they record a distinct style of martian volcanism from depleted shergottites and nakhlites. [ABSTRACT FROM AUTHOR]

Davidlloydite, ideally Zn3(AsO4)2(H2O)4, is a new supergene mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia. It occurs as elongated prisms (~10:1 length-to-width ratio) that are flattened on {010}, and up to 100 × 20 × 10 μm in size. The crystals occur as aggregates (up to 500 μm across) of subparallel to slightly diverging prisms lying partly on and partly embedded in fine-grained calcioandyrobertsite. Crystals are prismatic along [001] and flattened on {010}, and show the forms {010} dominant and {100} subsidiary. Davidlloydite is colourless with a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. The cleavage is distinct on {010}, and no parting or twinning was observed. The Mohs hardness is 3-4. Davidlloydite is brittle with an irregular to hackly fracture. The calculated density is 3.661 g cm-3. Optical properties were measured with a Bloss spindle stage for the wavelength 590 nm using a gel filter. The indices of refraction are α = 1.671, β = 1.687, γ = 1.695, all ±0.002; the calculated birefringence is 0.024; 2Vobs = 65.4(6)°, 2Vcalc = 70°; the dispersion is r < v, weak; pleochroism was not observed. Davidlloydite is triclinic, space group P1̅, with a = 5.9756(4), b = 7.6002(5), c = 5.4471(4) Å, α = 84.2892(9), β = 90.4920(9), γ = 87.9958(9)°, V = 245.99(5) Å3, Z = 1 and a:b:c = 0.7861:1:0.7167. The seven strongest lines in the X-ray powder diffraction pattern [listed as d (Å), I, (hkl)] are as follows: 4.620, 100, (011, 1̅10); 7.526, 71, (010); 2.974, 49, (200, 02̅1); 3.253, 40, (021, 120); 2.701, 39, (2̅10, 002, 1̅2̅1); 5.409, 37, (001); 2.810, 37, (210). Chemical analysis by electron microprobe gave AS2O5 43.03, ZnO 37.95, CuO 5.65, H2O(calc) 13.27, sum 99.90 wt.%. The H2O content and the valence state of As were determined by crystal structure analysis. On the basis of 12 anions with H2O = 4 a.p.f.u., the empirical formula is (Zn2.53Cu0.39)∑2.92AS2.03O8(H2O)4. The crystal structure of davidlloydite was solved by direct methods and refined to an R1 index of 1.51% based on 1422 unique observed reflections collected on a three-circle rotating-anode (MoKα radiation) diffractometer equipped with multilayer optics and an APEX-II detector. In the structure of davidlloydite, sheets of comer-sharing (As5+O4) and (ZnO4) tetrahedra are linked by ZnO2(H2O)4 octahedra. The structure is related to that of parahopeite. [ABSTRACT FROM AUTHOR]

Uchucchacuaite, ideally AgMnPb3Sb5S12, was originally reported as orthorhombic, with possible space group Pmmm, P222, or Pmm2, and unit-cell parameters a = 12.67, b = 19.32, and c = 4.38 Å obtained from powder X-ray diffraction data (Moëlo et al. 1984a). Using single-crystal X-ray diffraction, we examined two uchucchacuaite samples, one from the type locality, Uchucchacua, Peru, and the other from Hokkaido, Japan (designated as R100213 and R070760, respectively). Our results show that uchucchacuaite is isostructural with ramdohrite and fizélyite, with monoclinic symmetry (P21/n) and the unit-cell parameters a = 19.3645(11), b = 12.7287(8), c = 8.7571(6) Å, β = 90.059(3)° for R100213 and a = 19.3462(7), b = 12.7251(5), c = 8.7472(3) Å, β = 90.017(2)° for R070760. Both samples are pervasively twinned and the twin refinements yielded the final R1 factors of 0.037 and 0.031 for R100213 and R070760, respectively. The chemical compositions determined from electron microprobe analysis are Ag0.99(Mn0.92Pb0.03Sb0.02 Bi0.01)∑ =0.98Pb3.00Sb5.00S12.00 for R100213 and Ag1.00(Mn0.82Sb0.11Ag0.04 Bi0.02)∑ =0.99Pb2.98Sb5.00S12.00 for R070760. The key structural difference among uchucchacuaite, ramdohrite, and fizélyite lies in the cations occupying the M2 site, which can be expressed with a general structural formula as Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed., where M2+ represents divalent cations with 0 ≤ y ≤ 1/2. From the current list of IMA-defined minerals, we consider M = Cd with y = 0.125 for ramdohrite, M = Pb with y = 0.25 for fizélyite, and M = Mn with y = 0.5 for uchucchacuaite. Associated with the variation in the average M2 cation size from fizélyite (1.078 Å) to ramdohrite (0.955 Å) and uchucchacuaite (0.83 Å) is the significant decrease in the average M2-S bond distance from 2.917 to 2.834, and 2.654 Å, respectively, as well as corresponding variations in the unit-cell b dimension from ~13.23 to 13.06 and 12.73 Å. [ABSTRACT FROM AUTHOR]

Constraining the timing and intensity of Solar System bombardment is critical to understanding planetary formation, evolution and habitability. However, the identification and dating of shockmetamorphic events in the mafic igneous lithologies that dominate planetary materials remains highly challenging, particularly at relatively modest shock pressures. The accessory mineral baddeleyite (monoclinic-ZrO2) is common in these mafic crustal rocks, though the microstructural response of this mineral to shock loading is currently unconstrained. Here we show that baddeleyite yields a predictable sequence of microstructures in the shock pressure range of 5 to ~20 GPa, based on analysis of mafic rocks collected along a well-constrained shock-pressure gradient in the crystalline bedrock of the Sudbury impact structure, Canada. High-resolution electron backscatter diffraction mapping of baddeleyite grains exposed to <20 GPa of shock loading reveals a range of microstructures, including complex orthogonally related crystalline subgrains, amorphous domains, and crystal plastic deformation. Evidence that the observed microstructures are principally controlled by the transition to, and subsequent reversion from, the high-pressure (experimentally constrained to >5 GPa) orthorhombic-ZrO2 polymorph is provided by phase-heritage reconstruction using relationships between reverted monoclinic orientations. Baddeleyite is a sensitive shock barometer and chronometer over low pressure ranges that can augment ongoing studies into the intensity of Solar System bombardment. [ABSTRACT FROM AUTHOR]