High Heat Flow Anomaly Within the St Paul Fracture Zone: Heat Advection and/or Inherent Thermal Structure?

Heat flow across oceanic transform faults (TFs) and fracture zones (FZs) has rarely been studied in detail, despite these features representing distinct thermal boundaries within the oceanic lithosphere. Here, we present heat flow measurements across the St Paul fracture zone (SPFZ) in the equatorial Atlantic Ocean, from 48 Ma crust in the south to 71 Ma in the north. To the north of the FZ we find a basal heat flow of 63 mWm(-2), and to the south a basal heat flow of 79 mWm(-2), both in agreement with plate cooling models. However, within the SPFZ we find a heat flow of 83 mWm(-2), greater than the values of the adjacent crust and 10-15 mWm(-2) higher than predicted from conductive cooling models, suggesting that the thermal structure of the FZ has been modified. Evidence from seismic and sub-bottom profiler data indicate recent active deformation within the SPFZ, potentially driven by lithospheric flexure across the FZ or temporal changes in TF configuration. We propose that this deformation may enable fluid circulation and heat advection within the basement, creating the seafloor heat flow anomaly within the FZ. These findings suggest that FZs may remain important zones predisposed to host deformation and fluid flow in the oceanic lithosphere, despite not being active plate boundaries.