FRONTAL ACCRETION: AN INTERNAL CLOCK FOR BIVERGENT WEDGE DEFORMATION AND SURFACE UPLIFT

Abstract

We propose a conceptual model of frontal accretion within bivergent wedges, which is based on two-dimensional sandbox simulations and the analysis of particle displacement fields. Each frontal accretion cycle consists of a thrust initiation, an underthrusting phase, and a reactivation phase. The location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable. Therefore the frontal accretion cycle can be considered as an internal clock for wedge-scaled deformation and surface uplift. We further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle. Surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle. We estimate cycle duration to range between 104 and 105 years, which is thus similar to the time frame of climatic cycles. The proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic, paleoseismologic, and geologic estimates of fault slip.