Mass-dependent nickel isotopic variations in achondrites and lunar rocks

Ni isotopes provide a glimpse of Earth’s pre-late-veneer mantle

“…2). This result is, in part, consistent with the previous predication that the early (after core formation) BSE was already displaying a subchondritic Ni isotopic signature before the late veneer ( 10 , 32 ). Nevertheless, it is unclear whether the subchondritic Ni isotopic signature of the present BSE was created solely by a singular large-impact event or gradually formed by continuous multistage accretion.…”

“…The δ 60 Ni of the ~3.8-Ga NUB peridotites are clearly slightly heavier than that (δ 60 Ni = 0.11 ± 0.01‰, 95% CI) of the BSE value estimated from unmetasomatized post-Archean peridotites (Fig. 2) ( 10 – 12 ) but obviously lighter than the average (δ 60 Ni = 0.23 ± 0.02‰, 95% CI) of bulk chondrites ( 10 , 15 , 31 , 32 ) (Fig. 2).…”

“…In contrast to these predictions for minimal high-T/P fractionation of Ni isotopes during core formation in large planetary bodies (e.g., Earth), it was more recently reported that low-pressure and low-temperature core-mantle differentiation within achondrites (e.g., Vesta) from small differentiated bodies can potentially produce relatively large Ni isotopic fractionation ( 32 ), leaving their planetary mantle isotopically light. In a further extension of these results, it was proposed that an aubrite-like differentiated planetary body (Theia) whose mantle was enriched in light Ni isotopes, collided with, and merged into the proto-Earth during the Moon-forming giant impact ( 10 , 32 ), leading to a lowering of Earth’s mantle from an approximately chondritic composition (δ 60 Ni = 0.23 ± 0.02‰) to the modern estimate (δ 60 Ni = 0.11 ± 0.01‰) for the BSE. Some researchers ( 31 ) have cast doubt on whether the proto-Earth was chondritic in Ni isotopes, introducing other possible scenarios such as chondrule-rich accretion ( 15 ) and nebular fractionation ( 52 ), but these models are difficult to reconcile with isotopic evidence from lithophile to siderophile systems that support a chondritic character to Earth’s building blocks ( 1 , 3 , 4 ).…”

“…Blue, purple, and gray shaded fields represent the 95% CIs for the NUB sample group (δ 60 Ni = 0.16 ± 0.01‰; altered rocks are excluded from the mean), BSE estimate [δ 60 Ni = 0.11 ± 0.01‰; recalculated from 40 unmetasomatized post-Archean mantle peridotites; data from ( 10 – 12 )] and different groups of chondrites (δ 60 Ni = 0.23 ± 0.02‰), respectively. The δ 60 Ni values of ordinary (OC), carbonaceous (CC), and enstatite (EC) chondrites; ureilites; iron meteorites; and lunar meteorites ( 10 , 15 , 31 , 32 ) are also shown for comparison.…”

Nickel Isotope Fractionation During Magmatic Differentiation

“…Repeated analysis of two in‐house pure Ni solutions (WSJ‐1 and WSJ‐2) yield δ 60/58 Ni values of −0.53‰ ± 0.04‰ (2SD, n = 19), and +0.32‰ ± 0.06‰ (2SD, n = 17), consistent with our 2‐year monitor of the two Ni solutions (−0.53‰ ± 0.04‰ and +0.32‰ ± 0.05‰; S.‐J. Wang et al., 2023). Each sample solution was measured at least three times in a sequence, and the average value was reported.…”