Effects of Basement Structure, Sedimentation and Erosion on Thrust Wedge Geometry: An Example from the Quebec Appalachians and Analogue Models

Abstract

The Taconian fold and thrust belt of the Quebec Appalachians displays typical structures such as inverted normal faults, ramp and flat structures, sub-horizontal detachments, triangle zones and backthrusts. The development of these structures is not, however, consistent along the belt and seems to be spatially related to variations in palaeotopography and stratigraphic architecture of the Middle-Late Ordovician foreland basin, which developed in front of the Taconian tectonic wedge. A triangle zone is bounded by backthrusts in the southeastern limb of the Chambly-Fortierville syncline and by imbricate faults of the thrust wedge parautochthonous units. The triangle zone dies out to the northeast as the basement shallows. Reinterpretation of reflection seismic lines shows that there is a link between the structural geometry of the thrust belt and depth to basement and the presence of pre-existing basement structures. The deflection of frontal thrusts relative to the general SW-NE strike of the orogen occurs over an oblique, deep-seated basement escarpment.In order to better understand factors controlling the formation of structures in the study area, analogue sandbox modelling was used to study thrust systems developed above irregular basement structures and affected by syntectonic sedimentation and erosion. Sand layers were constructed with a décollement level; step-like escarpments were introduced in the model's basement, oriented either parallel or oblique to the shortening direction. Basement depth variations in models controlled the geometry of thrust wedges. Deflection and rotation of frontal detachments was influenced by the presence of an oblique, steep basement escarpment in front of the growing wedge, by gradual changes of sand layer thickness across the ramp and by differential slip along the basal detachment. Deflection developed due to differential forward motion of the hanging wall along the strike of the fault and counter-clockwise rotation about a vertical axis. Syntectonic sedimentation induced forward propagation of flat detachments, resulting in the formation of a piggyback basin. Syntectonic erosion and sedimentation affected the thrust wedge kinematics; a series of backthrusts and/or triangle zones developed at the rear of the wedge. These structures developed above the deeper-seated basement and died out towards basement highs. Our modelling results and geological data support the hypothesis that pre-existing basement structure, syntectonic sedimentation, and erosion could be responsible for the development of triangle zones and frontal thrust deflection in the Quebec Appalachians. RÉSUMÉLa ceinture de plissement et de chevauchement taconique des Appalaches du Québec illustrent des structures typiques, telles que failles normales renversées, rampes, structures plates, décollements subhorizontaux, zones triangulaires et rétrochevauchements. Cependant, l'évolution de ces structures est plutôt inégale le long de la ceinture et, sur le plan spatial, elle semble relative aux variations paléotopogra...

Structural geometries and magnitude of shortening in the eastern Kura fold‐thrust belt, Azerbaijan: Implications for the development of the Greater Caucasus Mountains

“…An alternative interpretation is that these structural geometries and propagation histories result from efficient erosion acting upon the Kura fold‐thrust belt during its formation to shift deformation toward the hinterland. Numerous analogue and numerical models have linked the presence of efficient surface processes during the development of a fold‐thrust belt to both out‐of‐sequence thrust development [e.g., Koyi et al ., ; Mugnier et al ., ; Simpson , ; Storti and McClay , ] and localization of deformation in a hinterland antiformal stack [e.g., Bonnet et al ., ; Konstantinovskaya and Malavieille , ; Konstantinovskaya et al ., ; Malavieille , ]. Although focused erosion is one possible unifying mechanism to explain the characteristics of both the Akharbakhar‐Qäbälä and Garamäryäm‐Längäbiz regions, this idea is problematic given the structural and stratigraphic indicators of relatively high rates of syn‐tectonic sedimentation in the map area and thus, we do not favor this interpretation.…”

Sandbox modeling of evolving thrust wedges with different preexisting topographic relief: Implications for the Longmen Shan thrust belt, eastern Tibet

“…Previous workers have suggested that the development of transverse zones in a setting of pure shortening is controlled by lateral contrasts; e.g., differences in the shortening rate [ Reiter et al , ], the thickness of incoming sediment [ Marshak and Wilkerson , ; Soto et al , ], the rheology of the décollement [e.g., Cotton and Koyi , ; Schreurs et al , ; Vidal‐Royo et al , ; Ruh et al , , ], the basement geometry [ Wilkerson et al , ; Calassou et al , ; Corrado et al , ; Konstantinovskaya et al , , ], or the indenter offset [ Ruh et al , ]. Moreover, transverse structures, such as lateral ramps, tear faults, or the turning points of curved thrusts, usually form continuous zones that have their roots at the boundaries marking the imposed lateral differences [ Calassou et al , ; Marshak , ].…”

“…(3) The initial front of the proto wedges was designed to be linear. (4) Surface processes such as syntectonic sedimentation and erosion were not modeled during the shortening, even though they are known to have significant impacts on thrust behavior [e.g., Hardy et al , ; Persson and Sokoutis , ; Konstantinovskaya and Malavieille , ; Polonia et al , ; Konstantinovskaya et al , ]. Nevertheless, in the Longmen Shan thrust system, syntectonic sedimentation was rare in the late Cenozoic [e.g., Jia et al , ], and erosion should also have been limited after the highly resistant Pengguan and Baoxing massifs were exposed.…”

Effects of cohesion on the structural and mechanical evolution of fold and thrust belts and contractional wedges: Discrete element simulations

“…However, mechanical constraints are difficult to obtain in the field and are less than reliable in ancient fold and thrust belts [Gray et al, 2014]. For these reasons, forward modeling approaches, both analog and numerical, are used to investigate the internal structure and evolution of fold and thrust belts and other contractional wedges around the world [e.g., Mulugeta, 1988;Willet, 1999;Stockmal et al, 2007;Konstantinovskaya et al, 2009;Bigi et al, 2010;Simpson, 2011]. Such studies, however, often emphasize the large-scale geometric evolution of such systems, providing little insight into controlling mechanical processes.…”