Abstract
The interest of this paper is to investigate the initiation of triangle zones at the front of fold-and-thrust belts by analyzing the virtual velocity fields in triangle wedges. It allows achieving five collapse mechanisms by delamination, shear, and compaction of competing for the formation of triangle zones as follows. The first mechanism is the classical Coulomb shear thrust. The second is delamination at the frontal part of the décollement with straight back thrust, while the third is delamination with curvy back thrust. The fourth is the combination of ramp with Coulomb shear and shear-enhanced compact fault, while the fifth is the combination of the exchanging motion on the ramp and thrust. The dominating mechanism in the formation of triangle zones relies on the competition of the least upper bound of each mechanism when subjected to tectonic force. The controlling factors of the competition are discovered as follows: (1) the frictional characters and cohesion of horizontal décollements and thrust, (2) the slope of the topography of accretion wedge, and (3) the thickness and rock density of the front toe of accretion wedge.
Highlights
The style of deformation at the front of fold-and-thrust belts is often characterized by triangle zones with forwarddipping ramps (e.g., Southeastern Canadian Cordillera [1] and the foothill of the Longmen Shan [2,3,4,5] which is the eastern margin of the Tibetan Plateau)
The results indicate the change of the decollement by a ramp from the lower flat decollement to the upper decollement happens
Five collapse mechanisms by delamination, shear, and compaction are introduced to the competition in the formation of triangle zone front of fold-and-thrust belts as follows
Summary
The style of deformation at the front of fold-and-thrust belts is often characterized by triangle zones with forwarddipping ramps (back thrust) (e.g., Southeastern Canadian Cordillera [1] and the foothill of the Longmen Shan [2,3,4,5] which is the eastern margin of the Tibetan Plateau). This prototype is a triangle wedge with an accretion layer at its front. The third feature is the curvature of the fault emanating from the upper decollement These deformation mechanisms required either shear, opening, or compaction of velocities discontinuities which are highlighted in the same figure. The proposition for this prototype comes from the following review of the literatures on triangle zones
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