Hybrid Accretion of Carbonaceous Chondrites by Radial Transport across the Jupiter Barrier

Abstract

Abstract Understanding the origin of chondritic components and their accretion pathways is critical to unraveling the magnitude of mass transport in the protoplanetary disk, as well as the accretionary history of the terrestrial planet region and, by extension, its prebiotic inventory. Here we trace the heritage of pristine components from the relatively unaltered CV chondrite Leoville through their mass-independent Cr and mass-dependent Zn isotope compositions. Investigating these chondritic fractions in such detail reveals an onion-shell structure of chondrules, which is characterized by 54Cr- and 66Zn-poor cores surrounded by increasingly 54Cr- and 66Zn-rich igneous rims and an outer coating of fine-grained dust. This is interpreted as a progressive addition of 54Cr- and 66Zn-rich, CI-like material to the accretion region of these carbonaceous chondrites. Our findings show that the observed Cr isotopic range in chondrules from more altered CV chondrites is the result of chemical equilibration between the chondrules and matrix during secondary alteration. The 54Cr-poor nature of the cores of Leoville chondrules implies formation in the inner solar system and subsequent massive outward chondrule transport past the Jupiter barrier. At the same time, CI-like dust is transferred inward. We propose that the accreting Earth acquired CI-like dust through this mechanism within the lifetime of the disk. This radial mixing of the chondrules and matrix shows the limited capacity of Jupiter to act as an efficient barrier and maintain the proposed noncarbonaceous and carbonaceous chondrite dichotomy over time. Finally, also considering current astrophysical models, we explore both inner and outer solar system origins for the CV chondrite parent body.