^1,2Y. Li,^1,3A. Mei,^1,2W. Hsu,⁴S. Li
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2023JE008124]
¹Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing, China
²CAS Center for Excellence in Comparative Planetology, Hefei, China
³School of Astronomy and Space Sciences, University of Science and Technology of China, Hefei, China
⁴Astronomical Research Center, Shanghai Science & Technology Museum, Shanghai, China
Published by arrangement with John Wiley & Sons

Ca-phosphates in Campo del Cielo (CdC) and Nantan were comprehensively studied to provide insights into the thermal histories of the IAB main group (MG) and related irons. In CdC, apatite grains are characterized by (a) close intergrowth with troilite/graphite in border area between silicate and metal in most cases and (b) near-flat rare earth elemental patterns (LaN/YbN = 0.6–0.7). This indicates they were formed during a metal-silicate mixing event at a relatively high temperature. Combining with petrographic textures, we suggest that the replacement of high-Ca pyroxene by low-Ca pyroxene at ∼950–1,000°C could release Ca and facilitate the formation of apatite grains. In the Nantan nodule, Ca-phosphates do not share a similar origin with those in CdC, as indicated by their different mineral chemistries and mineral associations. Ca-phosphates and associated silicates could crystallize from a P-C-S-rich metallic melt with the oxidation of lithophile elements. Combining all analyses from CdC and Nantan yielded a SIMS Pb-Pb isochron age of 4,558 ± 56 Ma. Considering that all the IAB-MG irons experienced a rapid high-temperature cooling process, the age of 4,558 ± 56 Ma provides another line of evidence that the parent body of IAB-MG and related irons experienced metal-silicate mixing in first 50 Myr of solar system. The previously reported Ar-Ar ages of ≤4.47 Ga could be related to the late reheating process(es). The degrees of late shock heating may vary from specimen to specimen.

¹Eng, A.M. et al. (>10)
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2023JE008033]
¹Western Washington University, Bellingham, WA, USA
Published by arrangement with John Wiley & Sons

Since leaving Vera Rubin ridge (VRr), the Mars Science Laboratory Curiosity rover has traversed though the phyllosilicate-bearing region, Glen Torridon, and the overlying Mg-sulfate-bearing strata, with excursions onto the Greenheugh Pediment and Amapari Marker Band. Each of these distinct geologic units were investigated using Curiosity’s Mast Camera (Mastcam) multispectral instrument which is sensitive to iron-bearing phases and some hydrated minerals. We used Mastcam spectra, in combination with chemical data from Chemistry and Mineralogy, Alpha Particle X-ray Spectrometer, and Chemistry and Camera instruments, to assess the variability of rock spectra and interpret the mineralogy and diagenesis in the clay-sulfate transition and surrounding regions. We identify four new classes of rock spectra since leaving VRr; two are inherent to dusty and pyroxene-rich surfaces on the Amapari Marker Band; one is associated with the relatively young, basaltic, Greenheugh Pediment; and the last indicates areas subjected to intense aqueous alteration with an amorphous Fe-sulfate component, primarily in the clay-sulfate transition region. To constrain the Mg-sulfate detection capabilities of Mastcam and aid in the analyses of multispectral data, we also measured the spectral response of mixtures with phyllosilicates, hydrated Mg-sulfate, and basalt in the laboratory. We find that hydrated Mg-sulfates are easily masked by other materials, requiring ≥90 wt.% of hydrated Mg-sulfate to exhibit a hydration signature in Mastcam spectra, which places constraints on the abundance of hydrated Mg-sulfates along the traverse. Together, these results imply significant compositional changes along the traverse since leaving VRr, and they support the hypothesis of wet-dry cycles in the clay-sulfate transition.