From seismic interpretation we can argue that basal and frontal accretions are the main processes that model this part of the Chilean margin. Frontal accretion areas are characterized by a smoothed oceanic crust top, anticline reliefs, high offset thrusts and positive flowers structures; while, basal accretion areas, are characterized by an irregular oceanic crust top, uplifted slope, low offset thrusts, normal faults affecting the upper prism sediments, negative flower structures and re-activated thrusts. In particular the BSR is strong and continuous, within prism sediments, where the frontal accretion processes are acting, while it is weak and discontinuous where the active process is the basal accretion. We can suppose that the uplifting by basal accretion generates extensional tectonic movements. This can favour fluid escape and, consequently, a change of temperature. A consequence of this change is that the BSR disappears or becomes weaker. It is possible to extrapolate that strong and continuous BSRs can be developed in presence of frontal accretion processes, because it is most probable that high-fluid flux can occur in compressive conditions, while weak and discontinuous BSR can be associated to basal accretion, because off-crapped sediments can uplift the entire accretionary prism favouring fluid escapes.


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