Thrust sheet evolution in the Kinlochewe region of the Moine Thrust Zone, N.W. Scotland and the Pelvoux-Brianconnais, French Alps

Balanced and restored cross sections demonstrate a minimum 16 km shortening below the Moine Thrust and minimum restored wi1ths of 17 km between the La Meije and Combeynot Thrusts (external Alps), and 54 km between the frontal Subbrianconnais Thrust and the western Brianconnais Zone (internal Alps). Imbricate thrusts within the Moine Thrust Zone branch off a floor thrust which cuts up stratigraphic section from basement (Lewisian gneiss) to Cambrian shelf sediments parallel to the ESE-WNW movement direction. Cut-off relationships and fold geometries within the Pelvoux-Brianconnais suggest a change in move-ment direction of thrust sheets during the evolution of the French Alps from ENE-WSW for the Brianconnais and Sub-brianconnais Zones to ESE-WNW for the External Zones. Higher thrust sheets are frequently flexured as a result of slip on lower thrust surfaces (in-sequence thrusting). Important examples occur of Imver thrust assemblages which are truncated by higher thrust surfaces (out-of-sequence thrusting). Strains within thrust sheets from the Kinlochewe region suggest 0%-20% layer parallel shortening may develop in the footwall to an abandoned thrust as a tip strain to a newly developing thrust. Variations in strain may reflect variable propagation rates; differential displacement has resulted in differential movement within thrust sheets. Fault-bend folds (structurally necessary folds) have developed following slip of thrust sheets across irregular thrust surfaces and buckle folds have grown during shortening within the sheet. Extensional fault sheets (surge zones) can be mapped out in the Briancon region which both truncate and are flexured by thrust structures; important extensional structures have developed during evolution of the thrust belt