The Paris meteorite, the least altered CM chondrite so far

摘要: The Paris chondrite provides an excellent opportunity to study CM chondrules and refractory inclusions in a more pristine state than currently possible from other CMs, investigate the earliest stages of aqueous alteration captured within single bulk composition. It was found effects former colonial mining engineer may have been observed fall. texture, mineralogy, petrography, magnetic properties chemical isotopic compositions are consistent with classification as CM2 chondrite. There ˜45 vol.% high-temperature components mainly Type I (with olivine mostly Fa0-2, mean Fa0.9) granular textures because low mesostasis abundances. II contain Fa7 Fa76. These dominantly IIA, but there IIAB IIB chondrules, II(A)B minor highly ferroan olivine, IIA(C) augite only pyroxene. amoeboid aggregates (AOAs) fine-grained spinel-rich Ca-Al-rich (CAIs). CAI phases formed sequence hibonite, perovskite, grossite, spinel, gehlenite, anorthite, diopside/fassaite forsterite. most embedded which also occurs massive nodules. Refractory metal nuggets many platinum group element abundances (PGE) decrease following condensation sequences their host phases. Mn-Cr isotope measurements mineral separates define regression line slope 53Mn/55Mn = (5.76 ± 0.76) × 106. If we interpret Cr systematics dating components, particularly age is 4566.44 0.66 Myr, close puts new constraints on early evolution solar system. Eleven individual samples O mixing that passes through CO3 falls indicates very fresh sample, variation explained by local differences extent alteration. anhydrous precursor CM2s CO3-like, two groups differed CMs accreted higher proportion water. has little matrix (˜47%, plus 8% fine grained rims) less altered chondrites. Chondrule silicates (except mesostasis), phases, submicron forsterite amorphous silicate all well preserved freshest domains, abundant (metal stage 1 Palmer Lauretta (2011)). Metal sulfide correspond least heated or equilibrated chondrites, Category A Kimura et al. (2011). composition tochilinite-cronstedtite intergrowths gives PCP index ˜2.9. Cronstedtite zones whereas normal petrologic subtype 2.6-2.0 based S/SiO2 ∑FeO/SiO2 ratios (Rubin al., 2007), cronstedtite destroyed CI chondritic volatile abundances, interactions between occurred during alteration, modifying zones. trapped Ne contents, primitive organic compounds, material CMs. gradational contacts domains different degree scale ˜1 cm, clasts, suggesting water-limited style no significant metamorphic reheating.