Hu Yan, Teng Fang-Zhen, Plank Terry, Chauvel Catherine
Isotope Laboratory, Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA.
Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964-8000, USA.
Sci Adv. 2020 Dec 2;6(49). doi: 10.1126/sciadv.abb2472. Print 2020 Dec.
Oceanic crust and sediments are the primary K sinks for seawater, and they deliver considerable amounts of K to the mantle via subduction. Historically, these crustal components were not studied for K isotopes because of the lack of analytical precision to differentiate terrestrial variations. Here, we report a high-precision dataset that reveals substantial variability in oceanic plates and provides further insights into the oceanic K cycle. Sixty-nine sediments worldwide yield a broad δK range from -1.3 to -0.02‰. The unusually low values are indicative of release of heavy K during continental weathering and uptake of light K during submarine diagenetic alteration. Twenty samples of altered western Pacific crust from ODP Site 801 display δK from -0.60 to -0.05‰, averaging at -0.32‰. Our results indicate that submarine alteration of oceanic plates is essential for generating the high-δK signature of seawater. These regionally varying subducting components are heterogeneous K inputs to the mantle.
大洋地壳和沉积物是海水中钾的主要汇，它们通过俯冲作用将大量的钾输送到地幔。从历史上看，由于缺乏区分陆地变化的分析精度，这些地壳成分未被用于研究钾同位素。在此，我们报告了一个高精度数据集，该数据集揭示了大洋板块中存在显著的变异性，并为大洋钾循环提供了进一步的见解。全球69个沉积物的δK范围很广，从-1.3‰到-0.02‰。异常低的值表明在大陆风化过程中重钾的释放以及在海底成岩蚀变过程中轻钾的吸收。来自ODP 801航次的20个西太平洋变质地壳样本的δK值在-0.60‰到-0.05‰之间，平均为-0.32‰。我们的结果表明，大洋板块的海底蚀变对于产生海水的高δK特征至关重要。这些区域变化的俯冲成分是地幔中异质的钾输入。
