Along Strike Variations in Heat Flow 1.Shallow Thermal Structure of the Middle America Trench, Costa Rica Robert Harris, COAS Oregon State University Ingo Grevemeyer, Leibniz Institute for Marine Sciences, IFM-GEOMAR Thomas Henke, Udo Barckhausen, Christian Mueller, Soenke Neben, Federal Institute for Geosciences and Natural Resources, BGR Cesar R. Ranero, ICREA at Instituto de Ciencias del Mar, CSIC, Barcelona Heiner Villinger, University of Bremen 2. Heat Flow across Nankai along NanTroSeize Transect Robert Harris, COAS, Oregon State University Friederike Schmidt-Scheirhorn, University of Bremen IODP Scientists Expedition 314/315/316

Shallow Thermal Structure of the Middle America Trench, Costa Rica

Correlation between observed and BSR derived estimates of heat flow Heat Flow q=k  T/  z

Heat Flow at Selected Areas Mound Culebra

Heat Flow Map, Costa Rica

Conclusions 1. Good correlation between observed values of heat flow and derived values of heat flow based on BSRs. 2.Variations of heat flow observed along strike, likely due to fluid flow. 3.For shallow subduction zone, conductive reference models are inadequate. Take home points 1.Variations in heat flow along strike important for better understanding thermal regime of subduction. 2.Fluid flow likely modifying temperatures along subduction thrust 3.Need to incorporate fluid flow in thermal models of shallow subduction zone (Nusselt number approximateion, e.g., Spinelli et al.)

Heat flow along Nankai Trough

Cross section of holes and seismic line along NanTroSeize Transect Philippine Sea plate megasplay top of subducting basement accretionary prism forearc basin

Conclusions 1.APCT3 and DVTP provide internally consistent and high quality results. 2. Heat flow values determined from drilling are generally lower than those determined from shallow probe data, especially towards the deformation front. 3.Reconciling these lower values obtained deeper in the section with shallow probe measurements requires a concave thermal gradient. 4. Along strike variations in heat flow are observed and shallow portion of subuction thrust is not adequately modeled using conductive reference models.