Mundl-Petermeier A, Viehmann S, Tusch J, Bau M, Kurzweil F, Münker C
Department of Lithospheric Research, University of Vienna, Vienna, Austria.
Institute of Geology and Mineralogy, University of Cologne, Cologne, Germany.
Nat Commun. 2022 May 16;13(1):2701. doi: 10.1038/s41467-022-30423-3.
Radiogenic isotope systems are important geochemical tools to unravel geodynamic processes on Earth. Applied to ancient marine chemical sediments such as banded iron formations, the short-lived Hf-W isotope system can serve as key instrument to decipher Earth's geodynamic evolution. Here we show high-precision W isotope data of the 2.7 Ga old banded iron formation from the Temagami Greenstone Belt, NE Canada, that reveal distinct W differences in alternating Si-rich (7.9 ppm enrichment) and Fe-rich (5.3 ppm enrichment) bands reflecting variable flux of W from continental and hydrothermal mantle sources into ambient seawater, respectively. Greater W excesses in Si-rich layers relative to associated shales (5.9 ppm enrichment), representing regional upper continental crust composition, suggest that the Si-rich bands record the global rather than the local seawater W signature. The distinct intra-band differences highlight the potential of W isotope signatures in banded iron formations to simultaneously track the evolution of crust and upper mantle through deep time.
放射性同位素体系是揭示地球地球动力学过程的重要地球化学工具。应用于古老的海洋化学沉积物，如条带状铁建造，短寿命的铪-钨同位素体系可作为解读地球地球动力学演化的关键手段。在此，我们展示了来自加拿大东北部蒂马加米绿岩带的27亿年古老条带状铁建造的高精度钨同位素数据，这些数据揭示了在富硅（富集7.9 ppm）和富铁（富集5.3 ppm）交替条带中明显的钨差异，分别反映了来自大陆和热液地幔源的钨进入周围海水的通量变化。相对于代表区域上地壳组成的相关页岩，富硅层中更大的钨过剩（富集5.9 ppm）表明，富硅条带记录的是全球而非局部海水的钨特征。条带内明显的差异突出了条带状铁建造中钨同位素特征在整个地质历史时期同时追踪地壳和上地幔演化的潜力。
