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Tungsten Isotope Composition of Archean Crustal Reservoirs and Implications for Terrestrial μ182W Evolution
Geochemistry, Geophysics, Geosystems ( IF 2.9 ) Pub Date : 2020-06-23 , DOI: 10.1029/2020gc009155
Jesse R. Reimink 1, 2 , Andrea Mundl‐Petermeier 3, 4 , Richard W. Carlson 2 , Steven B. Shirey 2 , Richard J. Walker 3 , D. Graham Pearson 5
Affiliation  

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.

中文翻译:

太古代地壳储层的钨同位素组成及其对陆地μ182W演化的启示

地球上主要的地球化学储层在约4.5×10 9 年内的演化仍需深入研究。短寿命放射性核素同位素比(142 Nd / 144 Nd和182 W / 184 W)形式的地球化学工具扩展了我们对现代地球和古代地球中地球化学变异性的理解。在这里,我们给出了从 太古宙的一个1.1×10 9年的时间跨度形成的奴隶克拉通的一组岩石中的142 Nd / 144 Nd和182 W / 184 W数据。岩石始终高182 W / 184 W,但是142Nd / 144 Nd低于大块地幔并随时间增加。142 Nd / 144 Nd随时间下降的变异性可能反映了硅酸盐地球中组成异质性的均质性,该均质性最初是由4.2 Ga之前发生的分化事件造成的。Slave样品中记录的182 W / 184 W升高有助于精炼硅酸盐地球更广泛的W同位素演化模型。在全球范围内,形成陆壳的太古宙地幔以182 W / 184 W占主导地位,与现代上地幔相比,升高了10-15 ppm。奴隶克拉通缺乏大量的科马提石,但已经升高182 W / 184 ▼直到2.9嘎。该观察结果,与具有低其它科马提套件的存在组合的182 W / 184 W,表明深层次源贡献低182 W / 184在地球太古W上。182 W / 184 W的区域变异性可以通过在充分混合的硅酸盐地球和岩心或下地幔的一部分受到其与同位素相互作用影响的下地幔部分之间进行化学和/或同位素交换来解释。
更新日期:2020-07-18
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