Thermo-hydraulics of the Peruvian accretionary complex at 12°S

Coupled heat and fluid transport at the Peruvian convergent margin at 12°S wasstudied with finite element modelling. Structural information was available from two seismicreflection lines. Heat production in the oceanic plate, the metamorphic basement, and sedimentswas estimated from literature. Porosity, permeability, and thermal conductivity for the modelswere partly available from Ocean Drilling Program (ODP) Leg 112; otherwise we used empiricalrelations. Our models accounted for a possible permeability anisotropy. The decollement was bestmodelled as a highly permeable zone (10⁻¹³ m²). Permeabilities of thePeruvian accretionary wedge adopted from the model calculations fall within the range of 2 to7×10⁻¹⁶ m² at the ocean bottom to a few 10⁻¹⁸ m² at the base and need to be anisotropic. Fluid expulsion at the sea floor decreases graduallywith distance from the deformation front and is structure controlled. Small scale variations of heatflux reflected by fluctuations of BSR depths across major faults could be modelled assuming highpermeability in the faults which allow for efficient advective transport along those faults.

The models were constrained by the thermal gradient obtained from the depth of bottomsimulating reflectors (BSRs) at the lower slope and some conventional measurements. We foundthat significant frictional heating is required to explain the observed strong landward increase ofheat flux. This is consistent with results from sandbox modelling which predict strong basalfriction at this margin. A significantly higher heat source is needed to match the observed thermalgradient in the southern line.