¹D. Tirsch, ^2,3J.L. Bishop, ¹J. Yoigt, ⁴L.L. Tornabene, ⁵G. Erkeling, ^1,6R. Jaumann
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.05.006]
¹Institute of Planetary Research, German Aerospace Center (DLR), Rutherfordstrasse 2, 12489 Berlin, Germany
²Carl Sagan Center, The SETI Institute, Mountain View, CA 94043, USA
³Exobiology Branch, NASA-Ames Research Center, Moffett Field, CA 94035, USA
⁴University of Western Ontario, London, ON, Canada
⁵German National Library of Science and Technology (TIB), Leibniz Information Centre for Science and Technology, Hannover, Germany
⁶Institute of Geological Sciences, Freie Universitaet Berlin, 12249 Berlin, Germany
Copyright Elsevier

We analyze the emplacement chronology and aqueous alteration history of distinctive mineral assemblages and related geomorphic units near Hashir and Bradbury impact craters located within the Libya Montes, which are part of the southern rim of the Isidis Basin on Mars. We derive our results from a spectro-morphological mapping project that combines spectral detections from CRISM near-infrared imagery with geomorphology and topography from HRSC, CTX, and HiRISE imagery. Through this combination of data sets, we were able to use the morphology associated with specific mineral detections to extrapolate the possible extent of the units hosting these compositions. We characterize multiple units consistent with formation through volcanic, impact, hydrothermal, lacustrine and evaporative processes. Altered pyroxene-bearing basement rocks are unconformably overlain by an olivine-rich unit, which is in turn covered by a pyroxene-bearing capping unit. Aqueously altered outcrops identified here include nontronite, saponite, beidellite, opal, and dolomite. The diversity of mineral assemblages suggests that the nature of aqueous alteration at Libya Montes varied in space and time. This mineralogy together with geologic features shows a transition from Noachian aged impact-induced hydrothermal alteration and the alteration of Noachian bedrock by neutral to slightly basic waters via Hesperian aged volcanic emplacements and evaporative processes in lacustrine environments followed by Amazonian resurfacing in the form of aeolian erosion.

^1,2,3Qing-Feng Mei, ^1,2,3Jin-Hui Yang, ^1,2Yue-Heng Yang
Journal of Analytical Atomic Spectroscopy 33, 569-577 Link to Article [DOI:
10.1039/C8JA00024G]
¹State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Institutions of Earth Science, Chinese Academy of Sciences, Beijing 100029, China
³ University of Chinese Academy of Sciences, Beijing 100049, China

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¹K. K. Larsen, ¹D. Wielandt, ¹M. Bizzarro
Journal of Analytical Atomic Spectroscopy 33, 613-628 Link to Article [DOI:
10.1039/C7JA00392G]
¹Centre for Star and Planet Formation, Natural History Museum of Denmark, University of Copenhagen, Denmark

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¹Quinn R. Shollenberger, ¹Jan Render, ¹Gregory A. Brennecka
Earth and Planetary Science Letters 495, 12-23 Link to Article [https://doi.org/10.1016/j.epsl.2018.05.007]
¹Institut für Planetologie, University of Münster, Wilhelm-Klemm-Straße 10, Münster, 48149 Germany
Copyright Elsevier

The oldest dated solids in our Solar System, calcium–aluminum-rich inclusions (CAIs), contain isotopic anomalies in a whole suite of elements relative to later formed Solar System materials. Previous work has reported differences in the proportions of nucleosynthetic components between CAIs and terrestrial rocks as a function of mass. However, the nucleosynthetic fingerprint of the CAI-forming region is still lacking significant data in the heavier mass range (A > 154). Therefore, we present the first erbium (Er) and ytterbium (Yb) isotopic data along with hafnium (Hf) isotopic compositions in a wide variety of CAIs derived from a variety of CV and CK chondrites. This work presents new methods for Er and Yb isotopic investigation that were explored using both thermal ionization mass spectrometry (TIMS) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). Relative to terrestrial rock standards, CAIs—regardless of host rock, petrologic or chemical classification—have uniform and resolvable Er, Yb, and Hf isotopic compositions. The CAI isotopic patterns correspond to r-process deficits (or s-process excesses) relative to terrestrial values of 9 ppm for Er, 18 ppm for Yb, and 17 ppm for Hf. This new Er, Yb, and Hf data help complete the nucleosynthetic fingerprint of the CAI-forming region, further highlighting the systematic difference between the CAIs and later formed bulk planetary bodies. Such a systematic difference between CAIs and terrestrial rocks cannot be caused by different amounts of any known single presolar phase but is likely the result of a well-mixed reservoir made of diverse stellar sources.

^1,2Ritesh Kumar Mishra
Current Science 114, 1510-1519 Link to Article [doi: 10.18520/cs/v114/i07/1510-1519]
¹Center for Isotope Cosmochemistry and Geochronology, Astromaterials Research and Exploration Science Division, EISD-XI,
NASA-Johnson Space Center, 2101, NASA Parkway, Houston, TX 77058, USA
²Oak Ridge National Laboratory Associated Universities, Tennessee 37830, Kentucky, USA

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¹E Terán Bobadilla, ²J H Abundis Patiño, ³C Añorve Solano, ³C R Moraila Valenzuela,⁴F Ortega Gutierrez
Astronomy & Geophysics 59, 2.30-2.31 Link to Article [https://doi.org/10.1093/astrogeo/aty084]
¹Facultad de Ciencias Físico Matemáticas, Universidad Autónoma de Sinaloa, Mexico.
²Electrical and Computing Engineering, Technical University of Munich, Germany.
³Facultad de Ciencias de la Tierra y del Espacio, Universidad Autónoma de Sinaloa, Mexico.
⁴Instituto de Geología, Universidad Nacional Autónoma de México, Ciudad Universitaria, Delegación Coyoacán, Mexico.

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^1,2P. Bonnand, ^1,3A. N. Halliday
Nature Geoscience (in Press) Link to Article [doi:10.1038/s41561-018-0128-2]
¹Department of Earth Sciences, University of Oxford, Oxford, UK
²Laboratoire Magmas et Volcans, Université Clermont Auvergne, CNRS, Clermont-Ferrand, France
³The Earth Institute, Columbia University, New York, NY, USA

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¹Yuki Hibiya et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.04.031]
¹Department of Earth and Planetary Science, University of Tokyo, Hongo 7-3-1, Bunkyo, Tokyo 113-0033, Japan
Copyright Elsevier

Northwest Africa (NWA) 6704 is a unique achondrite characterized by a near-chondritic major element composition with a remarkably intact igneous texture. To investigate the origin of this unique achondrite, we have conducted a combined petrologic, chemical, and 187Re–187Os, O, and Ti isotopic study. The meteorite consists of orthopyroxene megacrysts (En55-57Wo3-4Fs40-42; Fe/Mn = 1.4) up to 1.7 cm in length with finer interstices of olivine (Fa50-53; Fe/Mn = 1.1–2.1), chromite (Cr# ∼ 0.94), awaruite, sulfides, plagioclase (Ab92An5Or3) and merrillite. The results of morphology, lattice orientation analysis, and mineral chemistry indicate that orthopyroxene megacrysts were originally hollow dendrites that most likely crystallized under high super-saturation and super-cooling conditions (1–102°C/hr), whereas the other phases crystallized between branches of the dendrites in the order of awaruite, chromite → olivine → merrillite → plagioclase. In spite of the inferred high super-saturation, the remarkably large size of orthopyroxene can be explained as a result of crystallization from a melt containing a limited number of nuclei that are preserved as orthopyroxene megacryst cores having high Mg# or including vermicular olivine. The Re–Os isotope data for bulk and metal fractions yield an isochron age of 4576 ± 250 Ma, consistent with only limited open system behavior of highly siderophile elements (HSE) since formation. The bulk chemical composition is characterized by broadly chondritic absolute abundances and only weakly fractionated chondrite-normalized patterns for HSE and rare earth elements (REE), together with substantial depletion of highly volatile elements relative to chondrites. The HSE and REE characteristics indicate that the parental melt and its protolith had not undergone significant segregation of metals, sulfides, or silicate minerals. These combined results suggest that a chondritic precursor to NWA 6704 was heated well above its liquidus temperature so that highly volatile elements were lost and the generated melt initially contained few nuclei of relict orthopyroxene, but the melting and subsequent crystallization took place on a timescale too short to allow magmatic differentiation. Such rapid melting and crystallization might occur as a result of impact on an undifferentiated asteroid. The O–Ti isotope systematics (Δ17O = −1.052 ± 0.002, 1 SD; ε50Ti = 2.28 ± 0.23, 2 SD) indicate that the NWA 6704 parent body sampled the same isotopic reservoirs in the solar nebula as the carbonaceous chondrite parent bodies. This is consistent with carbonaceous chondrite-like refractory element abundances and oxygen fugacity (FMQ = −2.6) in NWA 6704. Yet, the Si/Mg ratio of NWA 6704 is remarkably higher than those of carbonaceous chondrites, suggesting significant nebular fractionation of forsterite in its provenance.

^1,2C.K. Shearer, ³S. Messenger, ²Z.D. Sharp, ¹P.V. Burger,^3,4 A.N. Nguyen, ³F.M. McCubbin 
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.04.034]
¹Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico 87131
²Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131
³NASA Johnson Space Center, Mailcode XI, 2101 NASA Parkway, Houston, Texas 77058
⁴Jacobs, NASA Johnson Space Center, Houston, Texas 77058
Copyright Elsevier

The δ37Cl from different generations of apatite in martian meteorite Chassigny has a range of ≈10‰ and is almost as great as measurements made on all martian meteorites (≈14‰). This range represents the mixing of distinct Cl isotope reservoirs during the formation of Chassigny: (1) an isotopically light-Cl mantle reservoir (δ37Cl=-4 to -6‰) that exhibits limited variability and (2) an isotopically heavy Cl crustal reservoir (δ37Cl>0) that exhibits significant variability. The mantle component documented in Chassigny melt inclusions that host a solar noble gas composition are derived from pristine, martian mantle. The incompatible element depleted and enriched shergottite sources as defined by radiogenic isotope systematics and trace element concentration ratios have very similar Cl isotopic signatures and suggest that both are derived from the martian mantle. The enrichment of isotopically heavy Cl in the crust resulted from protracted loss of 35Cl to space that started early in the history of Mars. The Cl isotopic signature of the martian mantle is different from the Earth, Moon, and many primitive meteorites (δ37Cl=0), suggesting that these differences represent distinct Cl sources in the solar nebula. The low δ37Cl source represents the primordial Solar System composition from which Mars accreted. The higher δ37Cl values observed for the Earth, Moon, and many chondrites are not primordial, rather they represent the later incorporation of 37Cl-enriched HCl-hydrates into accreting material.

¹Shaolin Li, ^2,3Weibiao Hsu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13110]
¹Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
²School of Astronomy and Space Sciences, Nanjing University, Nanjing, China
³Space Science Institute, Macau University of Science and Technology, Macau, China
Published by arrangement with John Wiley & Sons

The disruption of the L chondrite parent body (LCPB) at ~470 Ma is currently the best‐documented catastrophic celestial impact event, based on the large number of L chondritic materials associated with this event. Uranium‐lead (U‐Pb) dating of apatite and its high‐pressure decomposition product, tuite, in the Sixiangkou L6 chondrite provides a temporal link to this event. The U‐Pb system of phosphates adjacent to shock melt veins was altered to varying degrees and the discordance of the U‐Pb system correlates closely with the extent of apatite decomposition. This suggests that the U‐Pb system of apatite could be substantially disturbed by high‐temperature pulse during shock compression from natural impacts, at least on the scale of mineral grains. Although many L chondrites can be temporally related to the catastrophic LCPB impact event, the shock conditions experienced by each individual meteorite vary. This could be due to the different geologic settings of these meteorites on their parent body. The shock pressure and duration derived from most meteorites may only reflect local shock features rather than the impact conditions, although they could provide lower limits to the impact conditions. The Sixiangkou shock duration (~4 s), estimated from high‐pressure transformation kinetics, provides a lower limit to the high‐pressure pulse of the LCPB disruption impact. Combined with available literature data of L chondrites associated with this impact event, our results suggest that the LCPB suffered a catastrophic collision with a large projectile (with a diameter of at least 18–22 km) at a low impact velocity (5–6 km s⁻¹). This is consistent with astronomical estimates based on the dynamical evolution of L chondritic asteroids.