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.