Collaborative Research: Water Concentration and Distribution in the Oceanic Lithosphere

化合物H2O在液态时被称为水，当它结合在矿物和其他固体中时，会影响矿物或材料的熔化、流变和塑性行为，以及材料的热学和电学性能。如果水与海洋地壳深处的矿物质结合在一起，这可能会导致岩浆的生成增强，从而导致火山爆发，并改变岩石圈的可塑性和变形。在岩浆上升到地表的地区，这些水被释放出来，形成了全球水循环的重要组成部分。由于地球上的大部分H2O被锁在地壳和地幔的矿物中，所以主要通过分析海洋玄武岩中未脱气玻璃和熔融包裹体的H2O含量与不相容的稀土元素（如铈）的比较，推断出各种地幔和岩石圈储层中H2O的浓度和分布。这只提供了地球水含量的粗略估计。这项研究建立在一项初步研究的基础上，采用了一种新的方法来确定海洋地幔和岩石圈中矿物质中储存了多少水，地幔岩性中其他地球化学示踪剂分离水的机制，以及水的命运以及它如何影响海洋岩石圈的导电性和流变性。这项工作的更广泛影响包括支持南卡罗来纳州一所机构的一名教员，EPSCoR州（即没有获得大量联邦资金的州），支持一名在科学领域性别代表性不足的研究人员，以及将在NASA休斯顿约翰逊航天中心接受尖端分析仪器培训的学生培训。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。这项研究需要解决的问题包括：水是否独立于岩石圈中的亲石元素变化，如果观察到解耦，扩散是否起作用；看看辉石是否是典型的高水、低固相的储层；检查在岩石圈压力和温度下，水在矿物中的溶解度是否对未改变的岩石圈中结构结合的水的保有量设置了上限；H2O浓度是否反映在岩石圈样品的H2O系统中；岩石圈中H2O的分布与熔融程度、深度、岩性和交代介质之间是否存在系统关联。为了解决这些问题，傅立叶变换红外光谱（FTIR）将用于确定来自一系列地点和构造环境（包括大西洋的加那利群岛）的特征良好的新鲜（即未改变的）橄榄岩和辉石岩中的H2O浓度；南印度洋的克格伦高原；夏威夷群岛和萨摩亚群岛以及太平洋的Ontong爪哇高原；以及北冰洋的勒拿海槽。其他地球化学指标，如矿物的微量元素组成和矿物和岩石中的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。

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.