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

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.