Open AccessTungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ 182 W Evolution
Author(s) -
Reimink Jesse R.,
MundlPetermeier Andrea,
Carlson Richard W.,
Shirey Steven B.,
Walker Richard J.,
Pearson D. Graham
Publication year - 2020
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2020gc009155
Subject(s) - archean , geology , craton , geochemistry , mantle (geology) , continental crust , crust , radiogenic nuclide , early earth , isotope , hadean , silicate , paleontology , tectonics , chemistry , physics , organic chemistry , quantum mechanics
The evolution of Earth's major geochemical reservoirs over ~4.5 × 10 9 years remains a matter of intense study. Geochemical tools in the form of short‐lived radionuclide isotope ratios ( 142 Nd/ 144 Nd and 182 W/ 184 W) have expanded our understanding of the geochemical variability in both the modern and ancient Earth. Here, we present 142 Nd/ 144 Nd and 182 W/ 184 W data from a suite of rocks from the Slave craton that formed over a 1.1 × 10 9 year time span in the Archean. The rocks have consistently high 182 W/ 184 W, yet 142 Nd/ 144 Nd that is lower than bulk mantle and increased over time. The declining variability in 142 Nd/ 144 Nd 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 182 W/ 184 W 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 182 W/ 184 W 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 182 W/ 184 W until 2.9 Ga. This observation, combined with the presence of other komatiite suites that have low 182 W/ 184 W, suggests that deep‐seated sources contributed low 182 W/ 184 W in the Archean Earth. The regional variability in 182 W/ 184 W 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.