¹B.Sutter et al. (>10)
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2022JE007387]
¹Jacobs Technology, NASA Johnson Space Center, Houston, TX, USA
Publishes by arrangement with JohnWiley & Sons

Results from the Sample Analysis at Mars (SAM)-evolved gas analyzer (EGA) on board the Mars Science Laboratory Curiosity rover constrained the alteration history and habitability potential of rocks sampled across the Siccar Point unconformity in Gale crater.
The Glasgow member (Gm) mudstone just below the unconformity had evidence of acid sulfate or Si-poor brine alteration of Fe-smectite to Fe amorphous phases, leaching loss of Fe-Mg-sulfate and exchange of unfractionated sulfur 34S (δ34S=2±7‰) with enriched 34S (20±5‰, V-CDT). Carbon abundances did not significantly change (322-661 μgC/g) consistent with carbon stabilization by amorphous Al- and Fe-hydroxide phases. The Gm mudstone had no detectable oxychlorine and extremely low nitrate. Nitrate (0.06 wt.% NO3), oxychlorine (0.13 wt% ClO4), high C (1472 μg C/g), and low Fe/Mg-sulfate concentration (0.24 wt.% SO3) depleted in 34S (δ34S = -27‰ ± 7), were detected in the Stimson formation (Sf) eolian sandstone above the unconformity. Redox disequilibrium through the detections of iron sulfide and sulfate supported limited aqueous processes in the Sf sandstone. Si-poor brines or acidic fluids altered the Gm mudstone just below the unconformity but did not alter underlying Gm mudstones further from the contact. Chemical differences between the Sf and Gm rocks suggested that fluid interaction was minimal between the Sf and Gm rocks. These results suggested that the Gm rocks were altered by subsurface fluids after the Sf placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations.

¹Michael P. Lucas,¹Nicholas Dygert,²Jialong Ren,²Marc A. Hesse,²Nathaniel R. Miller,¹Harry Y. McSween
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13930]
¹Department of Earth & Planetary Sciences, University of Tennessee, 1621 Cumberland Ave., 602 Strong Hall, Knoxville, Tennessee, 37996 USA
²Department of Geological Sciences, University of Texas at Austin, 2275 Speedway Stop C9000, Austin, Texas, 78712 USA
Published by arrangement with John Wiley & Sons

Primitive achondrites of the acapulcoite–lodranite clan (ALC) are residues of partial melting that displays a continuum of thermal metamorphism and partial melting most likely set by burial depth within an internally heated, primordial acapulcoite–lodranite parent body (ALPB). New major and trace element data from eight ALC meteorites and the application of several thermometric methods suggest that the ALPB was affected by partial differentiation disrupted by rapid cooling from peak, magmatic temperatures. Application of rare earth element-in-two-pyroxene thermometry recovers temperatures of 1125–1250 °C for lodranites, while two-pyroxene solvus and Ca-in-olivine thermometry recover lower temperatures for ALC meteorites (941–1114 °C and 686–850 °C, respectively). Major and trace element disequilibrium in acapulcoite and transitional groups provides evidence for cryptic melt infiltration and melt rock reaction within these layers of the ALPB. From lodranites, we determined rapid cooling rates of ~1 to ~26 °C yr−1 from peak temperatures, consistent with collisional fragmentation of the parent body during differentiation. After this initial period of rapid cooling, cooling rates decreased by two to four orders of magnitude through Ca-in-olivine closure temperatures (~750 °C). We hypothesize that the primordial ALPB possessed an onion shell-type layered structure that was disrupted by collisional breakup during partial differentiation. Thermal modeling suggests that ALC samples originate from ~300 m to ~10 km radius collisional fragments that cooled rapidly over time scales of several to ~20,000 yr, then reaccreted to form a slower cooling, second-generation rubble-pile asteroid. The source of ALC meteorites is a second-generation (or later) rubble-pile body of S-type spectral class located near the Jupiter 3:1 mean motion resonance in the Main Belt of asteroids.