Collaborative Research: Water Concentration and Distribution in the Oceanic Lithosphere

化学化合物H2O在液体状态下被称为水，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、流变性和塑性行为，以及材料的热学和电学性质。在H2O被海洋地壳深处的矿物结合的情况下，这可能导致岩浆的增强生成，从而导致火山喷发，并改变岩石圈的可塑性和变形。在岩浆上升到地表的地区，这种H2O被释放出来，形成了全球H2O循环的重要组成部分。由于地球上的大部分H2O被锁定在地壳和地幔的矿物中，因此，通过对大洋玄武岩中未脱气的玻璃和熔融包裹体的H2O含量与不相容的稀土元素(如Ce)的比较，主要通过分析大洋玄武岩中的未脱气玻璃和熔体包裹体来推断H2O在各种地幔和岩石圈储集层中的浓度和分布。这只是对地球H2O含量的粗略估计。这项研究建立在试点研究结果的基础上，并使用一种新的方法来确定海洋地幔和岩石圈矿物中储存了多少水，从地幔岩性中的其他地球化学示踪剂中分离出水的机制，以及水的去向及其如何影响大洋岩石圈的电导率和流变性。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)、支持一名性别在科学界代表性不足的研究人员，以及将在NASA德克萨斯州休斯敦约翰逊航天中心接受尖端分析仪器培训的学生培训。这项研究还包括与比利时和日本科学家进行国际合作，并将数据公之于众。这项研究要解决的问题包括：查看水是否独立于岩石圈中的亲岩石元素变化，以及如果观察到脱钩，是否由扩散负责；查看辉石是否通常是高水、低固相线储层；研究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的结构结合水的含量设置上限；水的浓度是否反映在岩石圈样品的水系统学中；以及岩石圈中的水分布与熔融程度、深度、岩性和交代剂之间是否存在系统的相关性。为了解决这些问题，将使用傅里叶变换红外光谱(FTIR)来确定一系列地点和构造环境中特征良好的新鲜(即未改变的)橄榄岩和辉石岩中的H2O浓度，这些地点和构造环境包括大西洋的加那利群岛、南印度洋的克尔盖伦高原、太平洋的夏威夷和萨摩亚群岛及安通爪哇高原、以及北冰洋的莱纳海槽。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锶、氢、钕和铅的放射性同位素，将有助于确定过程、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.