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Wu, Jonathan E., and Ken R. McClay,
Two-dimensional Analog Modeling of Fold and Thrust Belts: Dynamic Interactions with Syncontractional Sedimentation and Erosion
Jonathan E. Wu,1 Ken R. McClay2
1Fault Dynamics Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, United Kingdom
2Fault Dynamics Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, United Kingdom
Saifal Janai, Matt Woollard, Lela Isa, and Rachel Evans are gratefully acknowledged for conducting several of the analog model experiments as part of the M.Sc. tectonics course at Royal Holloway, University of London, United Kingdom. Frank Despinois of the Fault Dynamics Research Group, Royal Holloway, is thanked for his expertise and assistance in preparing animations that enabled the analysis of the models. Funding for Jonathan Wu's Ph.D. research at Royal Holloway is from Shell International EP. We are grateful to Cesar Witt and Jose De Vera for many helpful comments and suggestions. Ben Clements and Rob Barnes are thanked for improving the final manuscript. Juergen Adam is thanked for advice and discussions on ring shear testing of analog model materials.
The effects of syncontractional sedimentation and erosion on simple, critically tapered Coulomb wedges were evaluated by conducting twelve two-dimensional analog model sandbox experiments. All 12 models produced critically tapered Coulomb wedges with topographic slopes of 6–10 above horizontal basal detachments. The model without syncontractional sedimentation or erosion exhibited a general forward-breaking sequence with synchronous thrust activity. Syncontractional sedimentation produced longer wedges composed of fewer major forward-vergent thrusts and lowered thrust activities in the foreland. Syncontractional erosion inhibited forward propagation of the deformation front, decreased the number of major thrusts, and increased thrust activities in the hinterland. Where combined, the effects of syncontractional sedimentation and erosion were complementary.
At the scale of individual folds, syncontractional sedimentation altered fold evolution by producing limb rotation and a front-limb trishear zone formed by tip-line thrust splays. At this scale, syncontractional erosion did not cause significant changes to the fold geometries as they developed.
Comparisons of the model thrust wedges with natural fold and thrust wedges indicate that the Nankai accretionary prism, with its well-ordered array of closely spaced thrusts, would be typical of fold and thrust belts with low rates of surface processes. In contrast, the fold and thrust belts of offshore Niger Delta, the central Apennines, and the sub-Andes are characterized by buried, widely spaced, low-activity thrusts in the foreland that would be typical of high syncontractional sedimentation. High syncontractional erosion would produce very active hinterland thrusts resembling the present-day Taiwan fold and thrust belt. Changes in thrust-wedge dynamics caused by increased syncontractional erosion in the model wedges imply that subaerial fold and thrust belts, with higher erosion, would evolve differently from their submarine counterparts.
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