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

海洋地壳的地球化学变化，随着它的年龄增长，从洋中脊扩散中心穿过地球表面，然后俯冲回地幔，有助于确定地壳和上覆海洋的地球化学物质平衡。这项研究具有潜在的变革意义，因为它将致力于在海底玄武岩的熔体包裹体中建立硼同位素，作为地球化学代理，可以指示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。研究人员将对东太平洋东太平洋隆起附近海底火山岩的熔体包裹体进行研究，并利用伍兹霍尔海洋研究所的离子探针分析其中的硼和氧同位素。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海水蚀变海洋地壳在浅层地壳岩浆房中的同化是否是洋中脊火山作用的共同过程，以及是否更演化的硅质火山岩具有更高的硼同位素比率，这可以明确地与同化作用的增加联系起来。另一个目标是确定在快速扩张的中心，热液循环向下渗透到海洋地壳的深度。这项工作的更广泛影响包括支持两名没有获得NSF支持的早期职业研究人员，一名在科学领域性别代表性不足的研究人员，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.