Chondritic ingredients: I. Usual suspects and some oddballs in the Leoville CV3 meteorite


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Abstract– Reduced CV3 chondrites are relatively pristine rocks and prime candidates for studies exploring processes that predated planet formation. We closely examined the petrographic features and trace elemental composition of different CV3 constituents in the accretionary breccia Leoville. The petrographic results are presented here. Our sample (2.2 cm2) is not brecciated. The main ingredient—about 65 area%—is fine- to coarse-grained ferromagnesian type I chondrules. Minor constituents (in order of 2-D abundance) include refractory inclusions, Al-rich chondrules, and very fine-crystalline clasts of moderately volatile composition. Type II chondrules and metal nuggets occur sporadically. The chondrule–matrix ratio is approximately 3:1. Medium- and coarse-grained chondrules exhibit porphyritic textures, probably caused by incomplete melting, and frequent, partial or continuous, recrystallized dust rims. The fine-grained population most likely represents randomly sectioned dust rims. The rim material and some of the medium-grained objects are relatively troilite-rich. Iron-nickel metal is rare. In addition, almost all constituents show strikingly ragged or convoluted outlines. Only a few, rim-less components exhibit smooth contours. Evidence for incomplete melting and the formation of recrystallized or igneous rims in carbonaceous chondrites is well established, suggesting that both processes were widespread events. The observed features in Leoville support this conclusion. In addition, our findings indicate that surface abrasion in a turbulent dust-filled regime may have taken place after the consolidation of dust rims. Alternatively, the irregular, convoluted nature of at least the rimmed chondrules may have been inherent to the dust accretion event and was not erased by subsequent heating.