Effect of overburden thickness on thrust belt geometry and development

摘要

Laboratory sand models simulating development of thrust belts indicate that (1) distance between the backstop and the first‐formed thrust is a linear function of initial sand layer thickness; (2) spacing between the first two thrusts is most likely a nonlinear function of initial sand layer thickness; (3) initial dip of successive ramps decreases progressively toward the foreland because of variations in principal stress directions with depth and/or changes of mechanical properties of sand with increasing overburden; (4) faults to the hinterland steepen and become less active as hinterland thrust sheets undergo penetrative shear during sand wedge growth; and (5) new ramp initiation occurs to the hinterland of the basal detachment tip line. These observations can be interpreted both in context of area‐balance considerations and soil mechanics theory. If initial sand layer thicknesses in our models represent syntectonic overburden in natural thrust belts (i.e., distance between the ground surface and the detachment), then our results suggest that locations of some thrust belt salients are controlled by along‐strike variations in stratigraphic thicknesses and that initial thrust spacing decreases progressively to the foreland if the thrust belt involves a foreland‐tapering basin. Furthermore, our sand model observations suggest that the concept of a fixed, rigid backstop in the hinterland of thrust belts may be misleading. As a consequence of thickening, the hinterland portion of the thrust belt becomes stabilized and effectively becomes the backstop