¹L. V. Forman,¹N. E. Timms,¹P. A. Bland,^1,2L. Daly,¹G. K. Benedix,³P. W. Trimby
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13380]
¹Space Science & Technology Centre, School of Earth & Planetary Sciences, Curtin University, GPO Box U1987, Perth, WesternAustralia 6845, Australia
²School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
³Oxford Instruments Nanoanalysis, High Wycombe HP12 3SE, UK
Published by arrangement with John Wiley & Sons

Meteoritic matrices are commonly classified by their modal mineralogy, alteration,and shock levels. Other “textural” characteristics are not generally considered inclassification schemes, yet could carry important information about their genesis andevolution. Terrestrial rocks are routinely described by grain morphology, which has led tomorphology-driven classifications, and identification of controlling processes. This paperinvestigates three CV chondrites—Allende (CV3.2oxA), Kaba (CV3.0oxB), and Vigarano(CV3.3red)—to determine the morphologic signature of olivine matrix grains. 2D grain sizeand shape, and crystallographic preferred orientations (CPOs) are quantified via electronbackscatter diffraction mapping. Allende contains the largest and most elongate olivinegrains, while Vigarano contains the least elongate, and Kaba contains the smallest grains.Weak but notable CPOs exist in some regions proximal to chondrules and one region distalto chondrules, and CPO geometries reveal a weak flattening of the matrix grains against theedge of chondrules within Allende. Kaba contains the least plastically deformed grains, andAllende contains the most plastically deformed grains. We tentatively infer that morphologyis controlled by the characteristics of the available population of accreting grains, andaqueous and thermal alteration of the parent body. The extent of overall finite deformationis likely dictated by the location of the sample with respect to compression, the localizedenvironment of the matrix with respect to surrounding material, and the post deformationtemperature to induce grain annealing. Our systematic, quantitative process forcharacterizing meteorite matrices has the potential to provide a framework for comparisonwithin and across meteorite classes, to help resolve how parent body processing differedacross and between chondritic asteroids.

¹Paula Lindgren,²Lydia Hallis,³Fredrik S. Hage,²Martin R. Lee,⁴John Parnell,¹Anders Plan,⁵Alistair Doye,⁵Ian MacLaren
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13381]
¹Department of Geology, Lund University, S€olvegatan 12, 223 62 Lund, Sweden
²School of Geographical & Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
³SuperSTEM Laboratory, SciTech Daresbury Campus, Daresbury WA4 4AD, UK
⁴School of Geosciences, University of Aberdeen, Aberdeen AB24 3UE, UK
⁵School of Physics & Astronomy, University of Glasgow, Glasgow G12 8QQ, UK
Published by arrangement with John Wiley & Sons

A carbon-rich melt fragment from the Gardnos impact structure has been studied for a better understanding of the preservation and structural form(s) of carbon that have been processed by impact melting. The carbon was analyzed in situ in its original petrographic context within the melt fragment, using high-resolution techniques including focused ion beam-transmission electron microscopy and electron energy loss spectroscopy. Results show that the carbon is largely uniform and has a nanocrystalline grain size. The Gardnos carbon has a graphitic structure but with a large c/a ratio indicating disorder. The disorder could be a result of rapid heating to high temperatures during impact, followed by rapid cooling, with not enough time to crystallize into highly ordered graphite. However, temperature distribution during impact is extremely heterogenous, and the disordered Gardnos carbon could also represent material that avoided extreme temperatures, and thus, it was preserved. Understanding the structure of carbon during terrestrial impacts is important to help determine if the history of carbon within extraterrestrial samples is impact related. Furthermore, the degree of preservation of carbon during impact is key for locating and detecting organic compounds in extraterrestrial samples. This example from Gardnos, together with previous studies, shows that not all carbon is lost to oxidation during impact but that impact melting can encapsulate and preserve carbon where it is available.

¹Saya Kagami,¹Makiko K. Haba,¹Tetsuya Yokoyama,^2,3Tomohiro Usui,⁴Richard C. Greenwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13382]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Ookayama, Tokyo 152-8551, Japan2Earth-Life Science Institute, Tokyo
²Institute of Technology, Ookayama, Tokyo 152-8550, Japan
³Department of Solar System Sciences, ISAS, JAXA, Sagamihara, Kanagawa 252-5210, Japan
⁴Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, UK
Published by arrangement with John Wiley & Sons

We report the results of a detailed study of the basaltic eucrite Northwest Africa(NWA) 7188, including its mineralogical and bulk geochemical characteristics, oxygenisotopic composition, and147,146Sm-143,142Nd mineral isochron ages. The texture andchemical composition of pyroxene and plagioclase demonstrate that NWA 7188 is amonomict eucrite with a metamorphic grade of type 4. The oxygen isotopic compositionand the Fe/Mn ratios of pyroxene confirmed that NWA 7188 belongs to the howardite–eucrite–diogenite meteorite suite, generally considered to originate from asteroid 4 Vesta.Whole-rock TiO2, La, and Hf concentrations and a CI chondrite-normalized rare earthelement pattern are in good agreement with those of representative Stannern-group eucrites.The147,146Sm-143,142Nd isochrons for NWA 7188 yielded ages of 4582190 and 4554+17/19 Ma, respectively. The closure temperature of the Sm-Nd system for different fractionsof NWA 7188 was estimated to be>865°C, suggesting that the Sm-Nd decay system haseither been resistant to reheating at~800°C during the global metamorphism or onlypartially reset. Therefore, the146Sm-142Nd age of NWA 7188 corresponds to the period ofinitial crystallization of basaltic magmas and/or global metamorphism on the parent body,and is unlikely to reflect Sm-Nd disturbance by late reheating and impact events. In eithercase, NWA 7188 is a rare Stannern-group eucrite that preserves the chronologicalinformation regarding the initial crustal evolution of Vesta.