Evaluating Seawater Contamination and Assimilation in Mid-Ocean Ridge Magmatic Systems

随着海洋地壳的老化和由于板块构造而从洋中脊扩展中心移动到地球表面，然后俯冲回地幔，海洋地壳的地球化学变化有助于确定地壳和上覆海洋的地球化学质量平衡。这项研究具有潜在的变革性，因为它将致力于确定海底玄武岩熔体包裹体中的硼同位素作为地球化学指标，可以表明热液改变的海洋地壳与海底喷发的新上升熔岩相互作用的程度和深度。 伍兹霍尔海洋研究所的离子微探针将检查取自东太平洋东太平洋隆起附近海底的火山岩熔体包裹体，并分析其中硼和氧的同位素。这些数据将与熔体包裹体及其相关火山玻璃中的主要元素和微量元素以及挥发性物质的其他地球化学分析相结合。项目目标将包括确定浅层地壳岩浆房中海水改变的海洋地壳的同化是否是洋中脊火山过程中的常见过程，以及更进化的硅质火山岩是否具有更高的硼同位素比率，这可以明确地与不断增加的同化过程联系在一起。另一个目标是确定热液循环在快速扩张中心渗透到洋壳的深度。这项工作的更广泛影响包括为两名早期职业研究人员提供支持，其中一名研究人员的性别在科学领域代表性不足，而这些研究人员之前没有获得国家科学基金会的支持，以及本科生培训。

The geochemical alteration of ocean crust, as it ages and moves from mid-ocean ridge spreading centers across the surface of the earth due to plate tectonics, and then subducts down back into the mantle, helps determine the geochemical mass balance of the crust and overlying ocean. This research is potentially transformative in that it will work to establish boron isotopes in melt inclusions in seafloor basalts as a geochemical proxy that can indicate the extent and depth at which hydrothermally altered ocean crust interacts with new rising lavas erupting on the seafloor. Melt inclusions from volcanic rocks taken from the seafloor near the East Pacific Rise in the eastern Pacific Ocean will be examined and the isotopes of boron and oxygen in them will be analyzed by the ion microprobe at the Woods Hole Institution of Oceanography. These data will be combined other geochemical analyses of the major and trace elements and volatile species in the melt inclusions and their associated volcanic glasses. Project goals will include determination of whether assimilation of seawater-altered ocean crust in shallow crustal magma chambers is a common process in mid-ocean ridge volcanic processes and whether more evolved, silicic, volcanic rocks have higher boron isotope ratios that can be unequivocally tied to increasing assimilation processes. An additional goal is to determine to what depth hydrothermal circulation penetrates down into ocean crust at fast spreading centers. Broader impacts of the work include support of two early career researchers with no prior NSF support, one who is of a gender under-represented in the sciences, and undergraduate student training.