Analogue models of transpressive systems

This paper presents three series of analogue models of transpressional defo rmation in a brittle/ductile system: (1) simple transpression, (2) transpre ssion combined with erosion of uplifted areas of the hanging wall above the deformation front, and (3) transpression combined with erosion of the hang ing wall and sedimentation at the foot of uplifted zones. In each series of experiments, different convergence angles cu, from 0 degrees (pure wrenchi ng) to 900 (pure thrusting) were applied to the models. Results show a shar p contrast between structures formed at alpha less than or equal to 15 degr ees (wrench-dominated transpression) and alpha greater than or equal to 30 degrees (thrust-dominated transpression). For a low convergence/strike-slip ratio (0 degrees less than or equal to alpha less than or equal to 15 degr ees), the deformation is localized and structures are typical of a strike-s lip regime (R and Y faults). For higher convergence angles (30 degrees less than or equal to alpha less than or equal to 90 degrees), the deformation is similar for all models, with an elongate asymmetric uplift showing fault -propagation-fold geometries and flanked by thrust-wrench faults. Fault dip s also show a significant change from move than 70 degrees for alpha less t han or equal to 15 degrees to less than 40 degrees for alpha > 30 degrees. For alpha greater than or equal to 30 degrees, the geometry of the main fau lts at the borders of the uplift zone is modified by P faults. In experimen ts with erosion and sedimentation, and thrust-dominated transpression, new faults with increasing dips form during progressive deformation, branching on the main fault at the base of the model. (C) 2001 Elsevier Science Ltd. All rights reserved.