A 400 Myr subduction memory in the mid-ocean ridge source

Jacqueline Eaby Dixon , R. Dietmar Müller , Adriana Dutkiewicz, Ben Mather

The upper mantle sampled by mid-ocean ridges carries the volatile imprint of past subduction, but the global distribution of hydration through time and how long that imprint survives mixing and melt extraction are poorly known. We investigate the history of mantle hydration by calculating where and when hydration occurred using a plate reconstruction model of subducted water over the past 410 Myr. We compare model results to present-day mantle hydration based on H₂O/Ce in ~1,340 mid-ocean ridge basalt (MORB) glasses from ~1,050 sites. Estimated hydration ages vary by region: ~120 Ma for the Arctic, ~320 Ma for the northern Mid-Atlantic Ridge (NMAR), ~220 Ma for the mid-latitude Mid-Atlantic, and ~380 Ma for the southern Mid-Atlantic (SMAR). Most Pacific ridges show no evidence of hydration. Globally, MORB derived from mantle with a modeled hydration age has a higher median H₂O/Ce than MORB from mantle with no modeled water delivery (249 versus 200). Neither hydration age nor duration affects H2O/Ce in present-day MORB. Agreement between model and data is particularly strong in the North Atlantic and Arctic. Here, hydrated mantle remained largely undisturbed until the post-130 Ma westward migration of North America. Subduction signatures may remain detectable as long as 400 Myr after hydration, well beyond the lifetime of the plate configuration that produced them.