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

由于板块构造的作用，洋壳随着年龄的增长而从大洋中脊扩张中心穿过地球表面，然后向下俯冲回到地幔，这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性，因为它将致力于建立海底玄武岩熔体包裹体中的硼同位素，作为一种地球化学指标，可以指示受热液改变的洋壳与海底新喷发的熔岩相互作用的范围和深度。将检查从东太平洋东太平洋隆起附近的海底采集的火山岩熔体包裹体，并将使用伍兹霍尔海洋研究所的离子探针分析其中的硼和氧的同位素。这些数据将与熔融包裹体及其相关火山玻璃中的主要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在地壳浅层岩浆室中海水蚀变的海洋结壳同化是否是大洋中脊火山过程中的常见过程，以及演化程度较高的硅质火山岩是否具有较高的硼同位素比率，这可能明确地与不断增加的同化过程有关。另一个目标是确定热液环流在快速扩散中心向下渗透到洋壳的深度。这项工作的更广泛影响包括支持两名先前没有NSF支持的早期职业研究人员，一名在科学界代表性不足的性别研究人员，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.