Combined Lithophile‐Siderophile Isotopic Constraints on Hadean Processes Preserved in Ocean Island Basalt Sources. (19th March 2021)

• Record Type: Journal Article
• Authors: Peters, Bradley J.; Mundl‐Petermeier, Andrea; Carlson, Richard W.; Walker, Richard J.; Day, James M. D.
• Is Part Of: Geochemistry, geophysics, geosystems. Volume 22:Number 3(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-03-19
• Subjects: core‐mantle interaction -- early Earth -- Earth differentiation -- igneous geochemistry -- mantle heterogeneity -- siderophile elements; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 550.5
• DOI: 10.1029/2020GC009479
• Languages: English
• ISSNs: 1525-2027

Abstract

Abstract: Detection of Hadean isotopic signatures within modern ocean island basalts (OIB) has greatly influenced understanding of Earth's earliest history and long‐term dynamics. However, a relationship between two isotopic tools for studying early Earth processes, the short‐lived 146 Sm‐ 142 Nd and 182 Hf‐ 182 W systems, has not been established in this context. The differing chemical behavior of these two isotopic systems means that they are complementary tracers of a range of proposed early Earth events, including core formation, magma ocean processes, and late accretion. There is a negative trend between 142 Nd/ 144 Nd and 182 W/ 184 W ratios among Réunion OIB that is extended by Deccan continental flood basalts. This finding is contrary to expectations if both systems were affected by silicate differentiation during the lifetime of 182 Hf. The observed isotopic compositions are attributed to interaction between magma ocean remnants and Earth's core, coupled with later assimilation of recycled Hadean mafic crust. The effects of this scenario on the long‐lived 143 Nd‐ 176 Hf isotopic systematics mirror classical models invoking mixing of recycled trace‐element enriched (sedimentary) and depleted (igneous) domains in OIB mantle sources. If the core provides a detectible contribution to the tungsten element budget of the silicate Earth, this represents a critical component to planetary‐scale tungsten mass balance. A basic model is explored that reconciles the W abundance and isotopic composition of the bulk silicate Earth resulting from both late accretion and core‐mantle interaction. The veracity of core‐mantle interaction as proposed here would have many implications for long‐term thermochemical cycling. Plain Language Summary: Radioactive elements with relatively short half‐lives can be used as tools to study the geological processes that took place in the earliest part of Earth's history. Two of these short‐lived radioactive tools, the samarium‐neodymium and hafnium‐tungsten systems, are correlated in the Réunion hotspot source and it is suggested that this results from influences from Earth's metallic core and the preservation of four‐billion‐year old crust in the deep Earth. The idea that a geochemical fingerprint of Earth's core may make it to the surface has important consequences for broader understanding of Earth's thermal and chemical evolution and possibly changes previous assumptions about the role of late addition of meteorites in establishing Earth's modern tungsten isotopic composition. Key Points: There is a negative trend between the μ 142 Nd‐μ 182 W compositions of Réunion ocean island basalts (OIB) and primitive Deccan continental flood basalts Réunion hotspot Nd‐W isotopic compositions may reflect early magma ocean crystallization and core‐mantle interaction Stripping of W during subduction can explain the difference in μ 142 Nd‐μ 182 W compositions between Réunion OIB and Samoan or Hawaiian OIB