Detailed heat flo
w surveys on the oceanic trench slope offshore Nicaragua and Central Chile indicate heat flo
w values lo
wer than the expected conductive lithospheric heat loss and lo
wer than the global mean for crust of that age. Both areas are characterised by pervasive normal faults exposing basement in a setting affected by bending-related faulting due to plate subduction. The lo
w heat flo
w is interpreted to indicate increased hydrothermal circulation by the reactivation and ne
w creation of faults prior to subduction. A previous global approach
[1] [Stein C.A., Heat flo
w and flexure at subduction zones, Geophys. Res. Lett. 30 (2003) doi:10.1029/2003GL018478] failed to detect similar features in the global but sparse data set. Detailed inspection of the global data set suggests that the thickness of the sedimentary blanket on the incoming plate is an important factor controlling the local hydrogeological regime. Areas
with a relatively thick sedimentary cover do not sho
w any heat flo
w anomaly
while areas
where normal faulting exposes basement suffer from increased hydrothermal activity. Both geochemical data from arc volcanoes and seismological evidence from intra slab events suggest that the flux of
water into the deep subduction zone is larger in areas characterised by reactivated hydrothermal circulation. It is reasonable to assume that the larger
water flux is caused by serpentinization of the upper mantle, facilitated by bending-related faults cutting into the upper mantle.