^1,2Noël Chaumard,^1,3Bertrand Devouard
¹Laboratoire Magmas et Volcans, CNRS UMR 6524, Université Blaise Pascal, OPGC-IRD, Clermont-Ferrand Cedex, France
²Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Universités, Muséum national d’histoire naturelle, UPMC Univ. Paris 06, UMR CNRS 7590, IRD UMR 206, Paris Cedex 5, France
³Aix-Marseille Université, CNRS, IRD, Aix en Provence, France

CK chondrites are the only group of carbonaceous chondrites with petrologic types ranging from 3 to 6. It is commonly reported than ~15 vol% of CK4–6 samples are composed of chondrules. The modal abundance of chondrules estimated here for 18 CK3–6 (including five CK3s) ranges from zero (totally recrystallized) to 50.5%. Although almost all chemically re-equilibrated with the host matrix, we recognized in CK3s and Tanezrouft (Tnz) 057 (CK4) up to 85% of chondrules as former type I chondrules. Mean diameters of chondrules range from 0.22 to 1.05 mm for Karoonda (CK4) and Tnz 057 (CK4), respectively. Up to ~60% of chondrules in CK3–4 are surrounded by igneous rims (from ~20 μm to 2 mm width). Zoned olivines were found in unequilibrated chondrules from DaG 431 (CK3-an), NWA 4724 (CK3.8), NWA 4423 (CK3.9), and Tnz 057 (CK4). We modeled Fe/Mg interdiffusion profiles measured in zoned olivines to evaluate the peak metamorphic temperatures and time scales of the CK parent body metamorphism, and proposed a two-stage diffusion process in order to account for the position of inflection points situated within chondrules. Time scales inferred from Fe/Mg interdiffusion in olivine from unequilibrated chondrules are on the order of tens to a hundred thousand years (from 50 to 70,000 years for peak metamorphic temperatures of 1140 and 920 K, respectively). These durations are longer than what is commonly accepted for shock metamorphism and shorter than what is required for nuclide decay. Using the concept of a continuous CV–CK metamorphic series, which is reinforced by this study, we estimated peak metamorphic temperatures

Reference
Chaumard N, Devouard B (2016) Chondrules in CK carbonaceous chondrites and thermal history of the CV–CK parent body. Meteoritics&Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12599]
Published by arrangement with John Wiley&Sons

¹Allan H. Treiman et al. (>10)*
¹Lunar and Planetary Institute, Houston, TX, USA
*Find the extensive, full author and affiliation list on the publishers website

The Windjana drill sample, a sandstone of the Dillinger member (Kimberley formation, Gale Crater, Mars), was analyzed by CheMin X-ray diffraction (XRD) in the MSL Curiosity rover. From Rietveld refinements of its XRD pattern, Windjana contains: sanidine (21% weight, ~Or95); augite (20%); magnetite (12%); pigeonite; olivine; plagioclase; amorphous and smectitic material (~25%); and percent-levels of others including ilmenite, fluorapatite, and bassanite. From mass balance on the APXS chemical analysis, the amorphous material is Fe-rich with nearly no other cations — like ferrihydrite. The Windjana sample shows little alteration, and was likely cemented by its magnetite and ferrihydrite. From ChemCam LIBS chemical analyses, Windjana is representative of the Dillinger and Mt. Remarkable members of the Kimberley formation. LIBS data suggest that the Kimberley sediments include at least three chemical components. The most K-rich targets have 5.6% K2O, ~1.8 times that of Windjana, implying a sediment component with >40% sanidine, e.g., a trachyte. A second component is rich in mafic minerals, with little feldspar (like a shergottite). A third component is richer in plagioclase and in Na2O, and is likely to be basaltic. The K-rich sediment component is consistent with APXS and ChemCam observations of K-rich rocks elsewhere in Gale Crater. The source of this sediment component was likely volcanic. The presence of sediment from many igneous sources, in concert with Curiosity’s identifications of other igneous materials (e.g., mugearite), implies that the northern rim of Gale Crater exposes a diverse igneous complex, at least as diverse as found in similar-age terranes on Earth.

Reference
Treiman AH et al. (2016) Mineralogy, Provenance, and Diagenesis of a Potassic Basaltic Sandstone on Mars: CheMin X-ray Diffraction of the Windjana Sample (Kimberley Area, Gale Crater). Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2015JE004932]

Published by arrangement with John Wiley&Sons