Hydrothermal Models Constrained By Fine-Scale Seismic Velocities Confirm Hydrothermal Cooling Of 7-63 Ma South Atlantic Crust

Although 70% of the Earth's heat loss occurs in the oceans, the nature of hydrothermal heat flow in oceanic crust is controversial. Lithospheric cooling models, heat flow measurements, and seismic experiments provide conflicting accounts on the longevity of hydrothermal systems and their efficiency at removing heat from the crust. Here we present five hydrothermal models along a crustal flowline in the western South Atlantic at similar to 31 degrees S to quantify how conductive and advective heat loss change as a function of crustal age and structure. The model sites cover crustal ages of 7-63 Ma and are collocated with planned drill sites of International Ocean Discovery Program Expeditions 390 and 393. We constrained our hydrothermal models with detailed physical property distributions that we estimated from new high-resolution seismic velocity models. The hydrothermal models yield conductive and advective heat fluxes that closely match lithospheric cooling models and conductive heat flow measurements on the seafloor, supporting a hydrothermal sealing age of similar to 65 Ma. Our results also agree with global estimates of fluid volume flux into the oceans and are consistent with a previously published analysis of upper crustal seismic velocities in the study area, indicating ongoing hydrothermal activity at relatively old crustal ages. This study broadly confirms and unifies existing concepts of oceanic heat flow and its modes of transport. Moreover, it provides a regional framework of seismic velocities and modeled hydrothermal fluxes, in which future in-situ measurements can be integrated.