|Schreurs, G., Hänni, R. and Vock, P. 2002. Analogue modelling of transfer zones in fold and thrust belts: a 4-D analysis. Schellart, W. P. and Passchier, C. 2002. Analogue modelling of large-scale tectonic processes. Journal of the Virtual Explorer, 7, 43-49.|
Analogue modelling of transfer zones in fold and thrust belts: a 4-D analysis
We show the results of two experiments with identical boundary conditions, except for the shape of the basal layer of viscous PDMS (Fig. 1). In experiment 73 the model had two lateral PDMS-sand boundaries parallel to, and one frontal boundary perpendicular to, the shortening direction (Fig. 1a). In experiment 75, one side of the PDMS layer was oblique to the shortening direction (at an angle of 35°), while the other side was parallel to it (Fig. 1b). Purely for descriptive purposes we refer to the sand-corundum-sand layers as the brittle domain, and to the sand-corundum-sand layers with a basal viscous PDMS layer as the brittle-viscous domain. In both experiments the structural evolution in the brittle domain differed markedly from the one in the brittle-viscous domain. X-ray CT volumetric data were acquired from the area indicated in Fig. 1.
73 Evolution of structures in cross-sections through the brittle
and brittle-viscous domain
In the brittle domain, progressive deformation caused the basal detachment to be activated in front of the pop-up structure and a new thrust imbricate formed. Activity along the older forward thrust ceased and fault movement began to occur along the newly developed forward thrust in its footwall. With increasing deformation, another in-sequence imbricate thrust formed.
In the brittle-viscous domain, however, progressive deformation resulted in the development of a new frontal thrust far away from the mobile wall at the forward boundary between basal PDMS and sand. Displacement along the forward thrust of the pop-up structure near the mobile wall ceased. Because of continuing movement of the mobile wall, the forward thrust of the pop-up became progressively steeper and the triangular block bounded by forward thrust, backthrust and mobile wall underwent a rotation about a horizontal axis. This boundary effect caused bulging and extension in the upper part of the fault-bend fold and small normal faults formed in its outer arc. As progressive shortening increased, backthrusts formed at the lower bend of the active frontal ramp in the brittle-viscous domain. In this domain, an out-of-sequence thrust appeared in the region between the existing forward thrusts. Movement along the out-of-sequence thrust took place at the same time as displacement along the foremost forward thrust. Displacement along this out-of-sequence thrust was also coeval with movement along backthrusts of the frontal pop-up structure and resulted in a complex interference pattern.
73 in surface view and the development of a transfer zone