^1,2,3Y. Li,^3,4A. E. Rubin,¹W. Hsu,⁴K. Ziegler
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006360]
¹Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
²Macau University of Science and Technology, Macau, China
³Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA
⁴Maine Mineral and Gem Museum, Bethel, ME, USA
⁵Institute of Meteoritics, University of New Mexico, Albuquerque, NM, USA
Published by arrangement with John Wiley & Sons

The NWA 11004 ordinary chondrite (OC) can provide insights into the complex petrogenetic processes of the early solar system. Although originally classified as an L7 chondrite, it is reclassified as LL based on kamacite Ni (4.9 ± 0.3 wt.%) and Co (3.6 ± 0.5 wt.%) and bulk O‐isotopic composition (δ¹⁷O = 3.76‰; δ¹⁸O = 5.39‰). NWA 11004 is characterized by (1) the occurrence of 3‐ to 5‐mm‐sized poikilitic pyroxene, (2) scattered low‐Ca pyroxene data in a TiO₂ versus Al₂O₃ diagram, (3) relatively magnesian olivine and low‐Ca pyroxene (Fa_25.4, Fs_21.3), (4) low abundances of high‐Ca pyroxene, plagioclase, troilite and Ca‐phosphate, and (5) low rare earth element contents in low‐Ca pyroxene. The geochemical features of olivine and low‐Ca pyroxene in NWA 11004 differ from literature data for grains that crystallized from a melt in an OC impact melt breccia. We suggest that in NWA 11004, a plagioclase‐phosphate high‐Ca pyroxene‐troilite melt migrated away during partial melting. Some high‐Ca pyroxene grains crystallized from the residual melt, as indicated by a positive linear trend in a TiO₂ versus Al₂O₃ diagram. Whereas poikilitic low‐Ca pyroxene in NWA 11004 exhibits undulose‐to‐weak mosaic extinction, the olivine chadacrysts exhibit sharp optical extinction; this implies that NWA 11004 experienced a late‐stage shock event (S4) followed by annealing. The Ca‐phosphate ²⁰⁷Pb/²⁰⁶Pb age of 4546 ± 34 Ma most likely dates this late‐stage shock event. We suggest that the presence of type 7 OC in the early solar system may be attributable to impacts on warm chondritic asteroids that were initially heated by the decay of ²⁶Al.

¹T. S. Peretyazhko,¹S. J. Ralston,¹B. Sutter,²D. W. Ming
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2019JE006220]
¹Jacobs, NASA Johnson Space Center, Houston, TX, USA
²NASA Johnson Space Center, Houston, TX, USA
Published by arrangement with John Wiley & Sons

Ancient aquatic environments in Yellowknife Bay, Gale crater, Mars, could create favorable conditions for adsorption of chlorine compounds (perchlorate and chloride) on Fe (III) (hydr)oxides present in the Sheepbed mudstone, such as akaganeite and ferrihydrite. In this work, 5.2 mM ClO4− and 1.7 to 12 mM Cl− were adsorbed onto ferrihydrite and 5.2 mM ClO4− was adsorbed onto akaganeite at ultraacidic (pH 2–2.5), acidic (pH 3.8–4.5), and near‐neutral (pH 6.2–7.7) pH. Samples were characterized by evolved gas analysis and compared to the data collected for the Cumberland sample from the Sheepbed mudstone. Evolved gas analysis showed that ferrihydrite with 0.5–1 wt.% ClO4− adsorbed under ultraacidic and acidic conditions had a well‐resolved O2 peak at 306 °C due to the thermal decomposition of adsorbed ClO4−. All akaganeite samples with 0.5 wt.% adsorbed ClO4− had a weak peak at 312 °C tentatively assigned to decomposing perchlorate. Evolved gas analysis demonstrated that 0.5–2 wt.% Cl− adsorbed on ferrihydrite at ultraacidic and acidic pH was the main contributor to HCl evolved at >470 °C. Comparison with martian observations indicated that the temperature of the O2 peak originating from ClO4− adsorbed on ferrihydrite matched well with the thermal evolution of O2 from the Cumberland. Evolved HCl originating from Cl− adsorbed on ferrihydrite was within the temperature range of the high‐temperature HCl release from Cumberland (~770 °C). These observations suggest that ferrihydrite containing adsorbed ClO4− and Cl− could exist in the mudstone. Experimental results are consistent with adsorption at acidic pH < 4 environments through postdepositional water‐rock interactions of ferrihydrite with acid‐sulfate groundwater containing dissolved chloride and perchlorate.