Archean continental weathering: Revisiting the Sr isotope seawater curve

授予威斯康星大学麦迪逊分校的这一奖项将帮助我们了解早期地球和地球早期海洋的化学特征。它是跨学科的，可以颠覆陈旧且不受约束的范式。该提案将解决早于 2-1/2 亿年前的太古宙的一些非常重要的问题：板块构造何时开始，大陆地壳形成的速度有多快，是否分阶段发生，这如何影响生命的进化，以及新兴大陆及其船上的生命如何影响海洋化学以及带状铁地层的出现和设置？由专家开发的一套 K-12 教育材料将通过 NSF 资助的公众门户网站传播，研究成果将用于设计和开发“太古代世界”插图，这些插图将纳入麦迪逊地质博物馆的游览中。这项工作将为板块构造的开始日期和横向构造过程的作用提供基本约束。对太古代碳酸盐的加深了解将直接影响带状铁矿层（铁矿石的主要来源）的开发。这项工作将限制太古宙的地形和测高（地平/水世界场景）。支持者将通过研究七套特征极其明确的海洋碳酸盐来完善现有的过于简单化的 87Sr/86Sr 太古代海水曲线。这是一次认真的尝试，旨在了解锶在太古宙海水中的停留时间，以及它如何因地幔和大陆来源的变化而发生变化。太古宙任何新的海水 87Sr/86Sr 曲线都将对我们对太古代地球化学的理解产生真正的变革性影响，有助于解决太古宙中的铁层和碳酸盐是否沉积在受限盆地与开放海洋中的争议，以及限制太古宙硅质大陆物质的分区风化通量。该项目还将使用 REE Y 系统学来处理热液输入与大陆风化的起源和程度以及太古宙海水的氧化态，并在 NASA 的资助下对相同的样品进行 C、O、Mg、Fe 和 Mo 同位素研究。这项工作是 NSF-NASA 在早期地球方面的机构间合作。

This award to the University of Wisconsin Madison will help us understand the early Earth and the chemical characteristics of Earth's early oceans. It is interdisciplinary, and could turn over old and ill-constrained paradigms. This proposal will address some very important questions from the Archaean, earlier than 2-1/2 billion years ago: when did plate tectonics begin, how quickly was continental crust built up, did it occur in episodes, how did this affect evolution of life, and how did the emerging continents and their on-board life affect ocean chemistry and the appearance and setting of banded iron formations? Sets of K-12 educational material developed by specialists will be disseminated through the NSF-funded Portal to the Public, and the research results will be used to design and develop illustrations of 'Archean Worlds,' which will be incorporated into tours of the Madison Geology Museum.The work will provide fundamental constraints on the starting date for plate tectonics and the role of lateral tectonic processes. The enhanced understanding of Archean carbonates will bear directly upon the development of banded iron formations, the chief source of iron ore. This work will constrain Archaean topography and hypsometry (the Flat Earth/Water World scenarios). The proponents will refine the existing overly simplistic 87Sr/86Sr Archean seawater curve by looking at seven suites of extremely well characterized marine carbonates. This is a serious attempt at understanding the residence time of Sr in Archaean seawater, and how this may have changed due to changes in the mantle and continental sources. Any new seawater 87Sr/86Sr curve for the Archaean would have a truly transformative effect on our understanding of Archean geochemistry by helping to settle the controversy on whether iron formations and carbonates in the Archean were deposited in restricted basins vs. open ocean, as well as constraining Archaean subareal weathering fluxes of silicic continental material. The project will also use REE+Y systematics to deal with the origin and extent of hydrothermal input vs. continental weathering as well as the oxidation state of Archaean seawater, and perform work on the same samples with C, O, Mg, Fe, and Mo isotopes with funding from NASA.This work is a NSF-NASA inter-agency collaboration on Early Earth.