¹D. Ray,¹R. R. Mahajan,¹A. D. Shukla,²T. K. Goswami,³S. Chakraborty
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12875]
¹Physical Research Laboratory, Ahmedabad, India
²Department of Applied Geology, Dibrugarh University, Assam, India
³Department of Chemistry, University of California, San Diego, California, USA
Published by arrangement with John Wiley & Sons

A single piece of meteorite fell on Kamargaon village in the state of Assam in India on November 13, 2015. Based on mineralogical, chemical, and oxygen isotope data, Kamargaon is classified as an L-chondrite. Homogeneous olivine (Fa: 25 ± 0.7) and low-Ca pyroxene (Fs: 21 ± 0.4) compositions with percent mean deviation of <2, further suggest that Kamargaon is a coarsely equilibrated, petrologic type 6 chondrite. Kamargaon is thermally metamorphosed with an estimated peak metamorphic temperature of ~800 °C as determined by two-pyroxene thermometry. Shock metamorphism studies suggest that this meteorite include portions of different shock stages, e.g., S3 and S4 (Stöffler et al. 1991); however, local presence of quenched metal-sulfide melt within shock veins/pockets suggest disequilibrium melting and relatively higher shock stage of up to S5 (Bennett and McSween 1996). Based on noble gas isotopes, the cosmic-ray exposure age is estimated as 7.03 ± 1.60 Ma and nitrogen isotope composition (δ15N = 18‰) also correspond well with the L-chondrite group. The He-U, Th, and K-Ar yield younger ages (170 ± 25 Ma 684 ± 93, respectively) and are discordant. A loss of He during the resetting event is implied by the lower He-U and Th age. Elemental ratios of trapped Ar, Kr, and Xe can be explained through the presence of a normal Q noble gas component. Relatively low activity of 26Al (39 dpm/kg) and the absence of 60Co activity suggest a likely low shielding depth and envisage a small preatmospheric size of the meteoroid (<10 cm in radius). The Kr isotopic ratios (82Kr/84Kr) further argue that the meteorite was derived from a shallow depth.

¹Carey Legett IV, ²Brittany N. Pritchett, ¹Andrew S. Elwood Madden, ³Charity M. Phillips-Lander, ¹Megan E. Elwood Madden
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2017.06.031]
¹University of Oklahoma, School of Geology and Geophysics, Norman OK 73019
²Oklahoma Geological Survey, Norman, OK 73019
³School of Geology and Geophysics, University of Oklahoma Norman, OK 73019
Copyright Elsevier

Perchlorate salts and the ferric sulfate mineral jarosite have been detected at multiple locations on Mars by both landed instruments and orbiting spectrometers. Many perchlorate brines have eutectic temperatures < 250 K, and may exist as metastable or stable liquids for extended time periods, even under current Mars surface conditions. Therefore, jarosite-bearing rocks and sediments may have been altered by perchlorate brines. Here we measured jarosite dissolution rates in 2 M sodium perchlorate brine as well as dilute water at 298 K to determine the effects of perchlorate anions on jarosite dissolution rates and potential reaction products. We developed a simple method for determining aqueous iron concentrations in high salinity perchlorate solutions using ultraviolet-visible spectrophotometry that eliminates the risk of rapid oxidation reactions during analyses. Jarosite dissolution rates in 2 M perchlorate brine determined by iron release rate (2.87 × 10−12 ± 0.85 × 10−12 mol m−2 s−1) were slightly slower than the jarosite dissolution rate measured in ultrapure (18.2 MΩ/cm) water (5.06 × 10−12 mol m−2 s−1) using identical methods. No additional secondary phases were observed in XRD analyses of the reaction products. The observed decrease in dissolution rate may be due to lower activity of water (ɑH2O = 0.9) in the 2 M NaClO4 brine compared with ultrapure water (ɑH2O = 1). This suggests that the perchlorate anion does not facilitate iron release, unlike chloride anions which accelerated Fe release rates in previously reported jarosite and hematite dissolution experiments. Since dissolution rates are slower in perchlorate-rich solutions, jarosite is expected to persist longer in perchlorate brines than in dilute waters or chloride-rich brines. Therefore, if perchlorate brines dominate aqueous fluids on the surface of Mars, jarosite may remain preserved over extended periods of time, despite active aqueous processes.