Publication Date:
2023-11-13
Description:
Ocean island basalts (OIB) show variable 〈sup〉182〈/sup〉W deficits that have been attributed to either early differentiation of the mantle or core‐mantle interaction. However, 〈sup〉182〈/sup〉W variations may also reflect nucleosynthetic isotope heterogeneity inherited from Earth's building material, which would be evident from correlated 〈sup〉182〈/sup〉W and 〈sup〉183〈/sup〉W anomalies. Some datasets for OIB indeed show hints for such correlated variations, meaning that a nucleosynthetic origin of W isotope anomalies in OIB cannot be excluded. We report high‐precision W isotope data for OIB from Samoa and Hawaii, which confirm previously reported 〈sup〉182〈/sup〉W deficits for these samples, but also demonstrate that none of these samples have resolvable 〈sup〉183〈/sup〉W anomalies. These data therefore rule out a nucleosynthetic origin of the 〈sup〉182〈/sup〉W deficits in OIB, which most likely reflect the entrainment of either core material or an overabundance of late‐accreted materials within OIB mantle sources. If these processes occurred over Earth's history, they may have also been responsible for shifting the 〈sup〉182〈/sup〉W composition of the bulk mantle to its modern‐day value. We also report Mo isotope data for some Hawaiian OIB, which reveal no resolved nucleosynthetic Mo isotopic anomalies. This is consistent with inheritance of 〈sup〉182〈/sup〉W deficits in OIB from the addition of either core or late‐accreted material, but only if these materials have a non‐carbonaceous (NC) meteorite‐like heritage. As such, these data rule out significant contributions of carbonaceous chondrite (CC)‐like materials to either Earth's core or late accretion.
Description:
Plain Language Summary:
Some ocean island basalts (OIB) may contain a record of processes and characteristics of the deepest parts of Earth's mantle, including at the boundary between the iron‐rich core and mantle. Like some prior studies, we measured tungsten isotopes within OIB from Hawaii and Samoa, and report that tungsten isotopes in these OIB differ in their characteristics compared to what is observed in modern rocks that are most representative of the upper part of Earth's mantle. One explanation for these tungsten isotope anomalies is that they are a signature of chemical interaction between the core and lower mantle, suggesting that the core 'leaks' into the lower mantle. Another possibility proposed here is that these tungsten isotope anomalies reflect ancient crust that contained dense, meteorite‐like materials, which sank to the bottom of the mantle during Earth's early history. Using isotopes of another element, molybdenum, we show that the source(s) of these tungsten isotope anomalies do not contain a significant number of materials that originated from the outer Solar System before being added to Earth during its formation.
Description:
Key Points:
〈sup〉182〈/sup〉W deficits in ocean island basalts are confirmed, but correlated 〈sup〉182〈/sup〉W–〈sup〉183〈/sup〉W anomalies present in prior datasets are not confirmed.
〈sup〉182〈/sup〉W deficits may reflect core‐mantle interaction or an overabundance of late‐accreted materials, but not nucleosynthetic effects.
Mo isotope data similar to BSE estimate; W‐Mo data rule out significant contribution of CC‐like material to Earth's core or late accretion.
Description:
Deutsche Forschungsgemeinschaft
http://dx.doi.org/10.13039/501100001659
Description:
https://doi.org/10.35003/YCUKOX
Keywords:
ddc:551.9
;
core‐mantle interaction
;
late accretion
;
tungsten isotopes
;
molybdenum isotopes
;
ocean island basalts
;
nucleosynthetic effects
Language:
English
Type:
doc-type:article
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