Collaborative Research: Water Concentration and Distribution in the Oceanic Lithosphere

合作研究：海洋岩石圈中的水浓度和分布

• 批准号: 1624310
• 负责人: Anne Peslier
• 金额: $ 18.33万
• 依托单位: Jacobs Technology Inc.
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-08-15 至 2019-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624310&HistoricalAwards=false
• 关键词: Collaborative; Research; Water; Concentration; Distribution

The chemical compound H2O, which in its liquid state is called water, when it occurs bound in minerals and other solids, influences melting, rheology and plastic behavior of the mineral or material, and the material's thermal and electrical properties. In the case where H2O is bound in minerals deep in the ocean crust, this can result in enhanced generation of magmas, hence volcanic eruptions, and changes in the plasticity, deformation of the lithosphere. In areas where magmas rise to the surface, this H2O is released and forms an important part of the global cycle of H2O. Because most of the H2O on Earth is locked up in minerals in the crust and mantle, the concentration and distribution of H2O in various mantle and lithospheric reservoirs have been inferred primarily from analyses of undegassed glasses and melt inclusions in oceanic basalts through a comparison of their H2O content with incompatible rare earth elements like Cerium. This only provides a rough estimate of the H2O content of the Earth. This research builds off the results of a pilot study and uses a novel new approach to determine how much H2O is stored in minerals in the oceanic mantle and lithosphere, the mechanisms that fractionate H2O from other geochemical tracers in mantle lithologies, and the fate of the H2O and how it impacts the electrical conductivity and rheology of the oceanic lithosphere. Broader impacts of the work include support of a faculty member at an institution in South Carolina, an EPSCoR state (i.e., a state that does not receive significant federal funding), support of a researcher whose gender is under-represented in the sciences, and student training who will get trained on cutting-edge analytical instrumentation at NASA at the Johnson Space Center in Houston, TX. Impacts also include international collaboration with Belgian and Japanese scientists and making the data accessible to the public.Questions to be addressed by this research include seeing if H2O varies independently from lithophile elements in the lithosphere and if diffusion is responsible if decoupling is observed; looking to see if pyroxenes are typically a high-H2O, low-solidus reservoir; examine if H2O solubility in minerals under lithospheric pressures and temperatures put an upper limit on how much structurally bound H2O is held in the unaltered lithosphere; whether H2O concentrations are reflected in the H2O systematics of lithospheric samples; and whether there are systematic correlations between H2O distribution in the lithosphere and the degree of melting, depth, and lithology and metasomatic agents. To address these issues, Fourier Transform Infrared Spectroscopy (FTIR) will be used to determine the H2O concentrations in well-characterized, fresh (i.e., unaltered) peridotites and pyroxenites from a suite of locations and tectonic settings that include the Canary Islands in the Atlantic Ocean; the Kerguelen Plateau in the South Indian Ocean; the Hawaiian and Samoan Islands and the Ontong Java Plateau in the Pacific Ocean; and the Lena Trough in the Arctic Ocean. Additional geochemical indicators, such as trace element compositions of minerals and radiogenic isotopes of Sr, Hf, Nd, and Pb in minerals and rocks will be used to help determine if there is a link between process, mineralogy, and H2O content/behavior.

化合物 H2O 在液态时称为水，当它与矿物和其他固体结合时，会影响矿物或材料的熔化、流变和塑性行为，以及材料的热性能和电性能。 如果 H2O 与海洋地壳深处的矿物质结合，这会导致岩浆生成增加，从而导致火山喷发，以及岩石圈可塑性和变形的变化。在岩浆上升到地表的地区，这种 H2O 被释放出来，并形成全球 H2O 循环的重要组成部分。由于地球上的大部分 H2O 被锁存在地壳和地幔的矿物中，因此，各种地幔和岩石圈储层中 H2O 的浓度和分布主要是通过对大洋玄武岩中未脱气玻璃和熔融包裹体的分析，通过比较它们的H2O 含量与不相容的稀土元素（如铈）。 这仅提供了地球 H2O 含量的粗略估计。这项研究以试点研究的结果为基础，并使用一种新颖的方法来确定大洋地幔和岩石圈的矿物中储存了多少 H2O、从地幔岩性中的其他地球化学示踪剂中分馏 H2O 的机制，以及这些物质的命运。 H2O 及其如何影响海洋岩石圈的电导率和流变性。 这项工作的更广泛影响包括南卡罗来纳州（EPSCoR 州，即没有获得大量联邦资助的州）的一个机构的一名教职人员的支持，一名性别在科学领域代表性不足的研究人员的支持，以及学生培训将在德克萨斯州休斯顿约翰逊航天中心的美国宇航局接受尖端分析仪器的培训。影响还包括与比利时和日本科学家的国际合作，以及向公众提供数据。这项研究要解决的问题包括观察 H2O 的变化是否独立于岩石圈中的亲石元素，以及如果观察到解耦，扩散是否是造成这种现象的原因；寻找辉石是否是典型的高 H2O、低固相线储层；检查岩石圈压力和温度下矿物中 H2O 的溶解度是否对未改变的岩石圈中结构结合的 H2O 的含量设置了上限； H2O 浓度是否反映在岩石圈样品的 H2O 系统学中；岩石圈中H2O的分布与熔融程度、深度、岩性和交代剂之间是否存在系统相关性。为了解决这些问题，傅里叶变换红外光谱 (FTIR) 将用于确定一系列位置和构造环境（包括大西洋加那利群岛）中特征明确的新鲜（即未改变的）橄榄岩和辉石岩中的 H2O 浓度海洋;南印度洋的凯尔盖朗高原；夏威夷群岛、萨摩亚群岛以及太平洋的翁通爪哇高原；和北冰洋的勒拿海槽。其他地球化学指标，例如矿物的微量元素成分以及矿物和岩石中 Sr、Hf、Nd 和 Pb 的放射性同位素，将用于帮助确定过程、矿物学和 H2O 含量/行为之间是否存在联系。