SEDIMENT ACCRETION AGAINST A BUTTRESS BENEATH THE PERUVIAN CONTINENTAL-MARGIN AT 120-DEGREES-S AS SIMULATED WITH SANDBOX MODELING

Reflection seismic data from the Peruvian continental margin at 12 deg rees S clearly reveal an accretionary wedge and buttress. Sandbox expe riments applying the physical concept of the Coulomb theory allow the systematic investigation of the growth and deformation of such an accr etionary structure. The style of deformation of the buttress and the i nternal structure of the wedge is observed in the sandbox models. The possibility of underplating material beneath the buttress and the amou nt of tectonic erosion depend on the physical properties of the materi als, mainly internal friction, cohesion and basal friction. Boundary c onditions such as the height of the subduction gate and the thickness of incoming sand also constrain the style of growth of the model accre tionary structure. The configurations of two experiments were closely scaled to reflection seismic depth sections across the Peruvian margin . A deformable buttress constructed of compacted rock powder is introd uced to replicate the basement rock which allows deformation similar t o that in the seismic data. With the sandbox models it is possible to verify a proposed accretionary history derived from seismic and boreho le data. The models also help in understanding the mechanisms which co ntrol the amount of accretion, subduction and underplating as a functi on of physical properties, boundary conditions and the duration of con vergence.