Mass dependent δ74/70Ge variations within chondrites: Insights on inner–outer Solar System dichotomy

The moderately siderophile and volatile elements are strong tracers of early solar nebula processes, including condensation and accretion-collision of meteorite parent bodies. Among them, the germanium (T50% condensation=825K) shows significant isotopic fractionation between metal and silicate phases in undifferentiated chondrites and in differentiated planetesimal reservoirs (i.e. mantle–core) [1,2]. Additionally, germanium isotopic data (δ74/70Ge‰) correlate with oxygen anomalies (Δ17O) in ordinary chondrites [1], demonstrating its capacity to trace oxidizing processes during accretion as well as genetic links between parent bodies. Here we present new high precision δ74/70Ge data obtained on bulk carbonaceous (CC) and ordinary (OC) chondrites, and an enhanced version of the δ74/70Ge–Δ17O correlation to assess NC-CC dichotomy.

Bulk CC have positive δ74/70Ge values, showing exceptional large variations of ≈1‰, from CI (Orgueil) with the heaviest composition (δ74/70Ge=+0.901±0.060‰) toward lighter composition in CV (Allende) (δ74/70Ge=+0.096±0.120‰), whereas bulk ordinary chondrites display negative δ74/70Ge [1]. The δ74/70Ge values and matrix fraction (%) of OCs and CCs are positively correlated and describe a mixing line between CI composition and a [Ge]-depleted–δ74/70Ge-light component. In addition, OC and CC type chondrites present fundamental stable δ74/70Ge dichotomy that follow O, Ti, and Cr isotopic anomalies [3]. Within CC, the mass dependent δ74/70Ge compositions are exceptionally well correlated with D17O, e54Ti, and e54Cr, questioning the origin and processes that lead to isotopic signature dichotomy between the inner and outer the Solar System.

[1] Florin G. et al. (2020) GCA 269:270-291. [2] Luais B. (2007) EPSL 262:21-36. [3] Warren P. (2011) EPSL 311:93-100.