Application of Siderophile Elements to the Study of the Chemical Structure and Mixing History of the Oceanic Mantle

亲铁元素在大洋地幔化学结构和混合历史研究中的应用

• 批准号: 1423879
• 负责人: Richard Walker
• 金额: $ 28万
• 依托单位: University of Maryland, College Park
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-08-15 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1423879&HistoricalAwards=false
• 关键词: Application; Siderophile; Elements; Study; Chemical

The oceanic mantle may comprise more than 60% of the mass of the Earth. The modern oceanic mantle is known to be chemically and isotopically heterogeneous, primarily documented through studies of mid-ocean ridge basalts (MORB). The processes that resulted in the creation of the heterogeneities were most likely dominated by a combination of partial melting (melt removal), metasomatism (melt/fluid addition) and incorporation of recycled crust (via subduction). The relative impacts of each of these processes, the timing of the processes, and the length scales of the resulting heterogeneities remain topics of considerable debate. Clarifying the causes, timing and spatial extent of chemical and isotopic heterogeneities in the oceanic mantle is, therefore, critical for refining our knowledge of the present bulk composition of this major terrestrial reservoir, for achieving a more complete understanding of how the chemical and isotopic composition of Earth's mantle evolved through time, and for assessing the efficiency by which the oceanic mantle is convectively mixed today. To tackle these issues, sections of the oceanic mantle accessible in four ophiolite complexes (tectonically emplaced slivers of oceanic lithosphere) will be studied. The targeted ophiolites range in age from 1.95 billion years old to 6 million years old. The study will primarily focus on examining the absolute and relative abundances of siderophile (iron-loving) elements in the mantle rocks exposed in these locations. The study will seek to answer fundamental questions about the present and past oceanic mantle including: 1) What is the geometry of long-term, exceptionally melt-depleted portions of the oceanic mantle? 2) Do common oceanic mantle lithologies, such as pyroxenites and dunites, have chemical compositions and sufficient volume to be implicated in the generation of certain volcanic rocks with unusual compositions, for example some Hawaiian lavas? 3) Have key geochemical parameters in the oceanic mantle changed through time? If so, can they be correlated with the rates of processes that may have acted on the mantle through time. In addition to answering these questions about the chemical structure of the oceanic mantle, comparison of data from ophiolites spanning nearly two billion years will begin the process of documenting secular changes in the chemical structure of this mantle.

海洋地幔可能占地球总质量的60%以上。现代海洋地幔在化学上和同位素上是不均匀的，这主要是通过对洋中脊玄武岩（MORB）的研究来证明的。导致非均质性形成的过程很可能是部分熔融（熔体去除）、交代作用（熔体/流体加入）和回收地壳结合（通过俯冲）的综合作用。这些过程的相对影响，过程的时间，以及由此产生的异质性的长度尺度仍然是相当有争议的话题。因此，阐明海洋地幔中化学和同位素非均质性的原因、时间和空间范围，对于完善我们对这一主要陆地储层目前整体组成的认识，对于更全面地了解地球地幔的化学和同位素组成是如何随时间演变的，以及对于评估海洋地幔对流混合的效率至关重要。为了解决这些问题，将研究四个蛇绿岩复合体（海洋岩石圈的构造侵位条）中可达的海洋地幔剖面。目标蛇绿岩的年龄从19.5亿年到600万年不等。这项研究将主要集中在检查这些地点暴露的地幔岩石中亲铁元素的绝对丰度和相对丰度。这项研究将试图回答关于现在和过去的海洋地幔的基本问题，包括：1)长期的、异常融化的海洋地幔部分的几何形状是什么？2)常见的海洋地幔岩性，如辉石岩和泥质岩，是否具有化学成分和足够的体积，从而与某些具有不寻常成分的火山岩（例如夏威夷熔岩）的形成有关？3)海洋地幔的关键地球化学参数是否随时间而变化？如果是这样的话，它们是否可以与随着时间的推移可能作用于地幔的过程的速率相关联呢？除了回答这些关于海洋地幔化学结构的问题之外，对跨越近20亿年的蛇绿岩数据的比较将开始记录这个地幔化学结构的长期变化。

项目成果

Length-scales of chemical and isotopic heterogeneity in the mantle section of the Shetland Ophiolite Complex, Scotland

• DOI: 10.1016/j.epsl.2018.02.020
• 发表时间: 2018-04
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: B. O’Driscoll;R. Walker;P. Clay;J. Day;R. Ash;J. Daly

Oceanic and Continental Lithospheric Mantle in the 1.95-Ga Jormua Ophiolite Complex, Finland: Implications for Mantle and Crustal Evolution

芬兰 1.95 Ga Jormua 蛇绿岩杂岩中的海洋和大陆岩石圈地幔：对地幔和地壳演化的影响

• DOI: 10.1093/petrology/egad080
• 发表时间: 2023
• 期刊: Journal of Petrology
• 影响因子: 3.9
• 作者: Finlayson, Valerie A;Haller, Mitchell;Day, James M;Ginley, Stephen;O'Driscoll, Brian;Kontinen, Asko;Hanski, Eero;Walker, Richard J
• 通讯作者: Walker, Richard J