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.
Highlights
Chondrites are fragments of primitive planetesimals and represent sedimentary agglomerates comprising the Solar System’s oldest and least altered planetary building blocks
Our findings show that the observed Cr isotopic range in chondrules from more altered CV chondrites is the result of chemical equilibration between chondrules and matrix during secondary alteration
All chondrules are surrounded by fine-grained dust rims (FGRs) and the space between the FGRs is occupied by intra-chondrule matrix (ICM), which includes chondrule fragments and larger sulfide and metal grains
Summary
Chondrites are fragments of primitive planetesimals and represent sedimentary agglomerates comprising the Solar System’s oldest and least altered planetary building blocks They primarily consist of three components, namely chondrules, matrix and less abundant refractory inclusions, which represent the first formed solids in the protoplanetary disk (Connelly et al 2012). Chondrites and their components provide a unique time window into the early evolution of the gaseous protoplanetary disk when the planets accreted their main masses These objects are typically divided into non-carbonaceous (NC) and carbonaceous (CC) chondrites, and it has been suggested that the former accreted in the terrestrial planet region (i.e., sunward of Jupiter), whereas the latter accreted in the accretion region of gas giant planets. This divergent heritage of chondrites is based on the relatively volatile-rich nature of CC, the distribution of chondritic components in the chondrite groups and their distinct isotope systematics relative to NC (Budde et al 2016; Warren 2011)
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