Back to Exploration – 2008 CSPG CSEG CWLS Convention 441 Effects of Basement Structure, Sedimentation and Erosion on Thrust Wedge Geometry: An Example from the Quebec Appalachians and Analogue Models Elena Konstantinovskaya* INRS-ETE, Quebec, QC EKonst@ete.inrs.ca D. Rodriguez Laval University, Quebec QC, Canada D. Kirkwood GSC-Quebec, Quebec QC, Canada L.B. Harris INRS-ETE, Quebec, QC, Canada and R. Theriault MRNF, Quebec, QC, Canada Summary The Taconian fold and thrust belt of the Quebec Appalachians displays typical structures such as inverted normal faults, ramp and flat structures, sub-horizontal detachments, triangle zones and backthrusts. The development of these structures is not, however, consistent along the belt and seems to be spatially related to variations in palaeotopography and stratigraphic architecture of the Middle-Late Ordovician foreland basin, which developed in front of the Taconian tectonic wedge. A triangle zone is bounded by backthrusts at the southeastern limb of the Chambly-Fortieville syncline and by imbricate faults of the thrust wedge parautochthonous units. The triangle zone pinches out to the northeast as the basement shallows. Re-interpretation of reflection seismic lines shows that there is a link between structural geometry of the thrust belt and depth to basement and the presence of pre-existing basement structures. A 40º-50º deflection of frontal thrusts relative to the general SW-NE strike of the orogen occurs against an oblique, deep-seated basement escarpment. Thrust systems developed above irregular basement structures and affected by syn-tectonic sedimentation and erosion were studied by analogue sandbox modelling. Sand layers were constructed with a décollement level; step-like escarpments were introduced in model basement oriented either parallel or oblique to the general transport direction. Basement depth variations in models influenced the geometry of thrust wedges. Deflection of frontal thrusts and lateral thrust