Hadean silicate differentiation preserved by anomalous 142Nd/144Nd ratios in the Réunion hotspot source

Abstract

Active volcanic hotspots can tap into domains in Earth's deep interior that were formed more than two billion years ago. High-precision data on variability in tungsten isotopes have shown that some of these domains resulted from differentiation events that occurred within the first fifty million years of Earth history. However, it has not proved easy to resolve analogous variability in neodymium isotope compositions that would track regions of Earth's interior whose composition was established by events occurring within roughly the first five hundred million years of Earth history. Here we report Nd/Nd ratios for Réunion Island igneous rocks, some of which are resolvably either higher or lower than the ratios in modern upper-mantle domains. We also find that Réunion Nd/Nd ratios correlate with helium-isotope ratios (He/He), suggesting parallel behaviour of these isotopic systems during very early silicate differentiation, perhaps as early as 4.39 billion years ago. The range of Nd/Nd ratios in Réunion basalts is inconsistent with a single-stage differentiation process, and instead requires mixing of a conjugate melt and residue formed in at least one melting event during the Hadean eon, 4.56 billion to 4 billion years ago. Efficient post-Hadean mixing nearly erased the ancient, anomalous Nd/Nd signatures, and produced the relatively homogeneous Nd/Nd composition that is characteristic of Réunion basalts. Our results show that Réunion magmas tap into a particularly ancient, primitive source compared with other volcanic hotspots, offering insight into the formation and preservation of ancient heterogeneities in Earth's interior.

Hot and Heterogenous High‐3He/4He Components: New Constraints From Proto‐Iceland Plume Lavas From Baffin Island

“…However, no resolvable 142 Nd/ 144 Nd anomalies are observed in either Baffin Island (de Leeuw et al, ) or Iceland (Andreasen et al, ; Debaille et al, ). The implications of the lack of observable 142 Nd/ 144 Nd anomalies in Iceland hotspot lavas (which contrasts with resolvable 142 Nd/ 144 Nd variability at other hotspots; Horan et al, ; Peters et al, ) are not yet clear, but may still leave open the possibility of Baffin Island lavas sampling the depleted residue of Hadean terrestrial differentiation (see section S3.2. ), which in turn would be consistent with the primitive Pb isotopic compositions of the least crustally contaminated Baffin Island lavas (Jackson et al, ; this study).…”

Geochemistry and petrogenesis of Archean mafic rocks from the Amsaga area, West African craton, Mauritania

“…2016; Schneider et al, 2018), but so far this limited data shows either no anomalies or very minor anomalies only one or two µ units from terrestrial. With the advent of similar sized anomalies found in modern day OIB basalts (Peters et al, 2018), their significance in determining the type of mantle dynamics in the Archean seems minimal.…”

Enigmatic origin of diamond-bearing rocks revealed

“…The idea that part of the deep mantle has remained isolated from its surroundings is supported by the discovery of traces of primitive material in volcanic rocks called ocean island basalts, which might originate from regions known as seismically anomalous zones that are found at the core-mantle boundary 5,6 . A primitive source has also been attributed to many other types of rock, such as granitoids 7 .…”

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