The formation and aqueous alteration of CM2 chondrites and their relationship to CO3 chondrites: A fresh isotopic (O, Cd, Cr, Si, Te, Ti, and Zn) perspective from the Winchcombe <scp>CM2</scp> fall

As part of an integrated consortium study, we have undertaken O, Cd, Cr, Si, Te, Ti, and Zn whole rock isotopic measurements the Winchcombe CM2 meteorite. δ66Zn values determined for two aliquots are +0.29 ± 0.05‰ (2SD) +0.45 (2SD). The difference between these analyses likely reflects sample heterogeneity. isotope compositions show excellent agreement with published data. δ114Cd a single aliquot is 0.04‰ (2SD), which close to previous result Murchison. δ130Te three gave indistinguishable results, mean value +0.62 0.01‰ essentially identical CM2s. ε53Cr ε54Cr 0.319 0.029 (2SE) 0.775 0.067 (2SE), respectively. Based on its Cr composition, plots other chondrites. ε50Ti ε46Ti 3.21 0.09 0.46 0.08 respectively, in line recently data δ30Si composition −0.50 0.06‰ (2SD, n = 11) from obtained In conformity petrographic observations, oxygen both bulk micromilled fractions clearly demonstrate that parent body experienced extensive aqueous alteration. style alteration exhibited by consistent relatively closed system processes. Analysis different within broadly support view that, while lithologies individual meteorite can be highly variable, each characterized predominant type. Mixing regolith environment form cataclastic matrix supported analysis Winchcombe. Previously unpublished 12 chondrites, when combined data, define well-constrained regression slope 0.77. more limited linear trend at isotopically heavy, aqueously altered, end 0.77 array. array intersects field CO3 falls, indicating unaltered precursor material CMs was falls. Our earlier suggestions main differences CO3s CM2s reflect differing amounts water ice co-accreted into their respective bodies, being high case low CO3s. small Si CM CO meteorites explained proportions versus refractory silicates. COs may also respect Ti isotopes; however, further required test this possibility. relationship chondrites revealed our supports emerging snow protoplanetary disks marks important zone planetesimal accretion.