Regional Heat Flow in the Vicinity of the Chile Triple Junction Constrained by the Depth of the Bottom-Simulating Reflection

Abstract

The depth of the bottom-simulating reflection (BSR) observed from seismic-reflection data throughout the Chile Triple Junction region is used to estimate the temperature at the base of the gas hydrate stability field and to calculate the regional pattern of heat flow. Brown et al. (this volume) calibrate temperature-depth conditions at the BSR, which we use to estimate temperatures from BSR depths. Seismic velocity information needed to estimate BSR depths from seismic arrival times, and thermal conductivity data are provided by Leg 141 drilling. The heat-flow pattern varies greatly across the Darwin Fracture Zone. North of the Darwin F.Z., along seismic Line 743, heat flow shows a seaward decreasing trend across the accretionary wedge from 80 mW/m2 30 km from the wedge toe, to 40 mW/m2 10 km from the wedge toe. The decrease in heat flow is opposite to what is expected from the age variation of the underlying oceanic crust and is interpreted to be low because of recent tectonic thickening of the accretionary complex. South of the fracture zone, heat flow reflects the young age of the underlying oceanic crust as it shows a seaward increasing trend from -80 mW/m2 in the mid slope area to as high as 200 mW/m2 at the toe of the trench slope, increasing with decreasing age of the crust. Heat flow contours south of the Darwin F.Z. parallel the Chile Ridge, except near the deformation front; where heat flow contours are oriented along the deformation front. We attribute the heat flow pattern near the deformation front to advective heat transport from pore fluids escaping near the wedge toe. Tectonic thickening does not have as noticeable an effect on the heat flow south of the Darwin F.Z. as north of it, and tectonic thickening may be less active near the triple junction.