The roles of complex mechanical stratigraphy and syn-kinematic sedimentation in fold development: insights from discrete-element modelling and application to the Pico del Águila anticline (External Sierras, Southern Pyrenees)
Oskar Vidal-Royo, Stuart Hardy, Josep Anton Muñoz, 2011. "The roles of complex mechanical stratigraphy and syn-kinematic sedimentation in fold development: insights from discrete-element modelling and application to the Pico del Águila anticline (External Sierras, Southern Pyrenees)", Kinematic Evolution and Structural Styles of Fold-and-Thrust Belts, J. Poblet, R. J. Lisle
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A 2D discrete-element modelling technique is used to explore the effects of complex mechanical stratigraphy and syn-kinematic sedimentation in the development of the Pico del Águila anticline (External Sierras, Southern Pyrenees). The stratigraphy (Middle Triassic–Oligocene in age) involved in this structure is characterized by a gross interlayering of competent and incompetent units, which leads to a striking variation in outcrop-scale deformation of the units observed in the field. The numerical model attempts to reproduce the stratigraphic variation seen in the field by using a mechanical stratigraphy that contains a complex interlayering of competent/incompetent units. Two experiments are presented. Model 1 tests the response of this complex mechanical stratigraphy to shortening under conditions that lead to the formation of a detachment fold. This experiment shows that folding mechanisms vary abruptly depending on the mechanical properties of the materials involved: the incompetent units are strongly internally deformed, accommodating much layer-parallel shearing; the competent units deform by rigid-body translation/rotation, localized faulting and minor internal shearing. Model 2 tests the effect of syn-kinematic sedimentation under identical boundary conditions: these sediments stabilize the fold against gravitational instabilities and cause a concentration of deformation in the core of the structure, leading to a tighter, narrower fold.
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Fold-and-thrust belts occur worldwide, have formed in all eras of geological time, and are widely recognized as the most common mode in which the crust accommodates shortening. Much current research on the structure of fold-and-thrust belts is focused on structural studies of regions or individual structures and on the geometry and evolution of these regions employing kinematic, mechanical and experimental modelling. In keeping with the main trends of current research, this title is devoted to the kinematic evolution and structural styles of a number of fold-and-thrust belts formed from Palaeozoic to Recent times. The papers included in this book cover a broad range of different topics, from modelling approaches to predict internal deformation of single structures, 3D reconstructions to decipher the structural evolution of groups of structures, palaeomagnetic studies of portions of fold-and-thrust belts, geometrical and kinematical aspects of Coulomb thrust wedges and structural analyses of fold-and-thrust belts to unravel their sequence of deformations.