Bibliographic Details
| Title: |
Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ182W Evolution. |
| Authors: |
Reimink, Jesse R., Mundl‐Petermeier, Andrea, Carlson, Richard W., Shirey, Steven B., Walker, Richard J., Pearson, D. Graham |
| Source: |
Geochemistry, Geophysics, Geosystems: G3; Jul2020, Vol. 21 Issue 7, p1-16, 16p |
| Subject Terms: |
TUNGSTEN isotopes, ARCHAEAN, ANALYTICAL geochemistry, RADIOISOTOPES, GEOCHEMICAL modeling |
| Abstract: |
The evolution of Earth's major geochemical reservoirs over ~4.5 × 109 years remains a matter of intense study. Geochemical tools in the form of short‐lived radionuclide isotope ratios (142Nd/144Nd and 182W/184W) have expanded our understanding of the geochemical variability in both the modern and ancient Earth. Here, we present 142Nd/144Nd and 182W/184W data from a suite of rocks from the Slave craton that formed over a 1.1 × 109 year time span in the Archean. The rocks have consistently high 182W/184W, yet 142Nd/144Nd that is lower than bulk mantle and increased over time. The declining variability in 142Nd/144Nd with time likely reflects the homogenization of compositional heterogeneities in the silicate Earth that were initially created by differentiation events that occurred prior to 4.2 Ga. The elevated 182W/184W recorded in the Slave samples help refine models for the broader W‐isotope evolution of the silicate Earth. Globally, the Archean mantle that formed continental crust was dominated by 182W/184W elevated by some 10–15 ppm compared to the value for the modern upper mantle. The Slave craton lacks significant volumes of komatiite yet has elevated 182W/184W until 2.9 Ga. This observation, combined with the presence of other komatiite suites that have low 182W/184W, suggests that deep‐seated sources contributed low 182W/184W in the Archean Earth. The regional variability in 182W/184W may be explained by invoking chemical and/or isotopic exchange between a well‐mixed silicate Earth and the core or a portion of the lower mantle whose W‐isotope composition has been influenced by interaction with the core. Key Points: Felsic rocks from the Slave craton down to 2.95 Ga in age were sourced from an Archean depleted mantle that formed between 4.1 and 3.5 GaThey have higher W‐isotope compositions than the modern mantle, a signature that is difficult to explain by lack of late‐accreted materialThe Slave craton also lacks komatiites, so we propose that Archean komatiites are ancient analogs to modern ocean island basalts, suggesting that addition of komatiites throughout Earth history lowered the silicate Earth's µ182W [ABSTRACT FROM AUTHOR] |
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| Database: |
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