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.

Three‐dimensional numerical models with varied material properties and erosion rates: Implications for the mechanics and kinematics of compressive wedges

“…In the second snapshot (150 ka), several thrusts within the foreland are active, including the range front (Figure 3c). The most active foreland thrust shifts with time in a way similar to 2-D discrete element [Naylor and Sinclair, 2007] and analog models [Hoth et al, 2007]. Elevation, rock uplift and surface uplift are all invariant along strike (Figures 3d, 3e, and 3f).…”

“…However, neither model nor real wedges are truly critical and they likely exhibit more complex behavior [e.g., Hoth et al, 2006Hoth et al, , 2007Naylor and Sinclair, 2007]. In the models presented here and in analog [e.g., Hoth et al, 2006Hoth et al, , 2007 and discrete element models [Naylor and Sinclair, 2007] the wedge grows by the accretion of material into frontal thrust.…”

“…Given these examples and results from both numerical [Naylor and Sinclair, 2007; this study] and analog [Hoth et al, 2006[Hoth et al, , 2007 modeling, it appears that transient accommodation of strain may be a rather common process. Thus caution should be used when extrapolating slip rates from different temporal scales, particularly within the outboard region of a two-sided wedge [Hoth et al, 2007].…”

“…[21] Without any variation in topography, material properties or erosion rate along strike, the 3-D two-sided wedge develops exactly as the equivalent 2-D two-sided wedge described often in the literature [e.g., Koons, 1990;Beaumont et al, 1992;Willett et al, 2003;Hoth et al, 2006Hoth et al, , 2007. The resolution of our 3-D models is necessarily coarser than that of most analog and 2-D numerical models and thus we are unable to model the actual thrust spacing (i.e., that observed in the field) in detail.…”

“…Each has their own advantages and disadvantages. Analogue models are inherently three-dimensional and can usually be run to large strains, they are visual and, with the use of CT scanning, can yield approximations of the 3-D strain, strain rate and other parameters [e.g., Marques and Cobbold, 2002;Soto et al, 2006aSoto et al, , 2006bHoth et al, 2006Hoth et al, , 2007. Numerical solutions allow the models to be interrogated at any point in time or space to yield velocities, stresses, strain, strain components, etc.…”