Abstract: Structural Styles in Thrust Tectonics

D. A. Nieuwland

This study focuses on thin-skinned thrust tectonics, based on a parametric experiments using single and multilayer sandbox models. Modern analytical techniques were employed such as CT-scanning, 3D-visualisation and workstation interpretation. A new technique was developed to measure in-situ stresses during experiments.

The key parameters selected for this study were: basal friction, type of detachment material, rotational compression, obstacles in the basement and syntectonic sedimentation. High basal friction results in short thrust sheets, curved ramps and few backthrusts, low basal friction leads to long thrust sheets, straight relatively steep ramps and more backthrusts. In the detachment phase ductile viscous and non-viscous material both act as low friction decollement. During the overthrust phase a viscous substratum flows into the frontal thrust plane and enables tilting of the thrust sheets, obviating the need for internal structural accommodation. A non-viscous substratum is limited to squeeze flow, allowing only little rotation and requires accommodation within the thrust sheet by means o backthrusting. Rotational compression leads to a tapered thrust belt and the occasional formation of en-echelon out-of-sequence thrusts within the main thrust sheets. A basement high in front of a developing thrust belt acts as a nucleation site for thrusting, increasing or decreasing the normal the length of a thrust sheet. Syn-tectonic sedimentation results in out-of-sequence thrusting, combined with high basal friction the thrust front curves upwards to a steep thrust tip. In general, every change in the dynamic equilibrium controlling the development of a normal piggy-back sequence, will result in out-of-sequence thrusting.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994