Piggyback basin development above a thin-skinned thrust belt with two detachment levels as a function of interactions between tectonic and superficial mass transfer: The case of the Subandean Zone (Bolivia)

The Subandean fold and thrust belt of Bolivia is characterised by two major detachment levels and large piggyback basins. 'Sand-box' and numerical models have been used to study sedimentation and erosion control on thrust belt evolution and to study the retroactive effects of tectonics on piggyback development in thin-skinned thrust belts with two detachment levels. Analogue models show that surface processes play a dominant role in controlling wedge evolutions: erosion promotes fault reactivation and tectonic delamination (passive roof duplex) while sedimentation promotes forward shifting of the frontal thrust and consequently piggyback basin development. Numerical models were used to understand the development of the Subandean fold and thrust belt of Bolivia. Numerical experiments show that the simultaneity of basement tilting and high sedimentation rates promotes the formation of a stable tectonic wedge. Outer and inner faults are alternately active during the beginning of deformation, a kinematic evolution that favours the development of piggyback basins between. The step-by-step history of the thrust belt predicts that each change in tectonic location is recorded with large unconformities in basins, but these unconformities are not well preserved from progressive erosion in the final geometry. (C) 2000 Elsevier Science B.V. All rights reserved.