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Dissipation of Tungsten-182 Anomalies in the Archean Upper Mantle: Evidence from the Black Hills, South Dakota, USA by Nao Nakanishi; Igor S. Puchtel; Richard J. Walker; Peter I. Nabelek is a Earth and Planetary Sciences article available to read on EtoBox.

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Most Eoarchean rocks are characterized by positive μ182W anomalies averaging ∼ +13 ppm (where μ182W values are the part per million difference in 182W/184W between a sample and a laboratory reference material presumed to be representative of the bulk silicate Earth, BSE). Prior studies have concluded that the positive 182W anomalies in the upper mantle disappeared by the end of the Archean, yet the timing, nature, and causes of the inferred transition remain poorly understood. In this study, we obtained SmNd mantle extraction model ages (TDM) and μ182W values for Neoarchean and Paleoproterozoic granitic and metasedimentary rocks from the Black Hills, South Dakota, USA. The rocks examined have TDM model ages ranging between ∼3.6 Ga and 2.3 Ga, permitting the tracing of the evolution of 182W in the upper mantle precursors to these rocks, during the purported period of isotopic transition. Of these crustal rocks, the 2.55 Ga Little Elk Granite, with an average TDM age of ∼3.2 Ga, is characterized by a well resolved positive anomaly (μ182W = +8.2 ± 3.1, 2SE). This observation is consistent with a modest diminution in the upper mantle μ182W value relative to the Eoarchean average. By co

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Author

Nao Nakanishi; Igor S. Puchtel; Richard J. Walker; Peter I. Nabelek

Publisher

Elsevier BV

Published

2023

Language

EN

Field

Earth and Planetary Sciences (Physical Sciences)