Fig. 5.

The ε⁵³Cr and ε⁵⁴Cr values for terrestrial rocks (Table 5) and chondrites. The black circles and squares are terrestrial crustal and mantle rocks respectively, while the black triangles are artificial standards (i.e., NIST SRM 3112a and SCP-Cr). The ε⁵³Cr and ε⁵⁴Cr values for terrestrial rocks are correlated with a slope of 1.37 ± 0.65 (N = 15, MSWD = 0.1), regressed by Model 1, Isoplot R (Vermeesch, 2018). This correlation indicates the residual mass-dependent Cr isotope fractionation. The gray and colorful bars indicate the average ε⁵³Cr values (with 2SE uncertainty) for bulk silicate Earth (BSE; N = 15) and chondrites (N = 88), respectively. The two artificial standards are not considered to represent the Cr isotope composition of Earth. There is a ε⁵³Cr deficit of 0.12 ± 0.02 between BE and chondrites, which potentially indicate an early volatile fractionation of proto-Earth. The ⁵⁵Mn/⁵²Cr for BE of 0.22-0.54, was estimated by Sun (1982), Wang et al. (2018), Wänke and Dreibus (1988) and (Palme and O’Neill, 2014), while the ⁵⁵Mn/⁵²Cr for chondrites are from those ofthe ECs (0.71; having the same isotope compositions with Earth for multiple elements) and CIs (0.82; are regarded to represent the chemical composition of the Solar System). In this figure, ⁵⁵Mn/⁵²Cr ratios of0.71-0.82 are only from ECs and CI chondrites, but note that some other groups of chondrites (e.g., CV, CO and CK in Fig. 4) may have an Earth-like ⁵⁵Mn/⁵²Cr ratios. No systematic differences were observed in data measured by MC-ICP-MS in this study and by TIMS in the literature.isotope-corrected D’Orbigny angrite. However, this ⁵³Mn-⁵³Cr correlation line likely represent a mixing line that does not have any chronological significance.