Abstract CV (Vigarano type) carbonaceous chondrites, comprising Allende‐like ( CV oxA ) and Bali‐like ( CV oxB ) oxidized and reduced ( CV red ) subgroups, experienced differing degrees of fluid‐assisted thermal and shock metamorphism. The abundance and speciation of secondary minerals produced during asteroidal alteration differ among the subgroups: (1) ferroan olivine and diopside–hedenbergite solid solution pyroxenes are common in all CV s; (2) nepheline and sodalite are abundant in CV oxA , rare in CV red , and absent in CV oxB ; (3) phyllosilicates and nearly pure fayalite are common in CV oxB , rare in CV red , and virtually absent in CV oxA ; (4) andradite, magnetite, and Fe‐Ni‐sulfides are common in oxidized CV s, but rare in reduced CV s; the latter contain kirschsteinite instead. Thus, a previously unrecognized correlation exists between meteorite bulk permeabilities and porosities with the speciation of the Ca‐, Fe‐rich silicates (pyroxenes, andradite, kirschsteinite) among the CV ox and CV red meteorites. The extent of secondary mineralization was controlled by the distribution of water ices, permeability, and porosity, which in turn were controlled by impacts on the asteroidal parent body. More intense shock metamorphism in the region where the reduced CV s originated decreased their porosity and permeability while simultaneously expelling intergranular ices and fluids. The mineralogy, petrography, and bulk chemical compositions of both the reduced and oxidized CV chondrites indicate that mobile elements were redistributed between Ca,Al‐rich inclusions, dark inclusions, chondrules, and matrices only locally; there is no evidence for large‐scale (>several cm) fluid transport. Published 53 Mn‐ 53 Cr ages of secondary fayalite in CV , CO , and unequilibrated ordinary chondrites, and carbonates in CI , CM , and CR chondrites are consistent with aqueous alteration initiated by heating of water ice‐bearing asteroids by decay of 26 Al, not shock metamorphism.
Calcium-aluminum–rich inclusions (CAIs) in meteorites carry crucial information about the environmental conditions of the nascent Solar System prior to planet formation. Based on models of 50V–10Be co-production by in-situ irradiation, CAIs are considered to have formed within ~0.1 AU from the proto-Sun. Here, we present vanadium (V) and strontium (Sr) isotopic co-variations in fine- and coarse-grained CAIs and demonstrate that kinetic isotope effects during partial condensation and evaporation best explain V isotope anomalies previously attributed to solar particle irradiation. We also report initial excesses of 10Be and argue that CV CAIs possess essentially a homogeneous level of 10Be, inherited during their formation. Based on numerical modeling of 50V–10Be co-production by irradiation, we show that CAI formation during protoplanetary disk build-up likely occurred at greater heliocentric distances than previously considered, up to planet-forming regions (~1AU), where solar particle fluxes were sufficiently low to avoid substantial in-situ irradiation of CAIs.
