Bottom simulating reflectors (BSRs)
were detected in multichannel seismic reflection data acquired in the vicinity of Isla Mocha across the southern Chile margin and near 33°S. Geothermal gradients
were determined from the depth of the BSR that is interpreted to mark the thermally controlled base of a gas hydrate layer. Ground truth for the assessment and additional thermal constraints
were provided by do
wnhole measurements obtained during Ocean Drilling Program (ODP) Leg 202 in Site 1233 at 41°S and Sites 1234 and 1235 near 36°S. Both BSR-derived data and do
wnhole temperatures
were used to calculate heat flo
w anomalies and provide ne
w constraints on the thermal regime of the continental slope and do
wngoing slab in Chile bet
ween 32°S and 41°S. Do
wnhole chemical logs of Th, U, and K from Site 859 of ODP Leg 141 have been used to assess the radiogenic heat production in the margin
wedge. Heat production is lo
w (
![](/images/glyphs/BQ1.GIF)
0.8 μW/m
3). Ho
wever, kno
wledge of this reduces the errors of estimating the contribution from frictional heating along the subduction thrust fault. With respect to the Eocene age of the incoming oceanic lithosphere, heat flo
w appears to decrease land
ward of the deformation front as expected due to the advective transport of heat into the subduction zone by the do
wngoing slab. Calculations of conductive fore-arc heat flo
w sho
w that the modelled seafloor heat flo
w agrees
with the measured heat flo
w only if there is negligible frictional heating. At 33°S, temperatures in the fault zone reach 100°C approximately 60 km land
ward of the deformation front and are coincident
with the onset of earthquake activity and hence mark the up-dip limit of the seismogenic zone. The up-dip limit shifts sea
ward going to the south, reflecting the progressive south
ward decrease of lithospheric age of the subducting plate.