Strain variation in Fold-and-Thrust belts implications for construction of retrodeformable models

Deformation in fold-and-thrust belts such as the Himalayas can be represented by the displacement vector field. The strain component of the displacement vector field across the fold-andthrust belt varies from near zero in externall thrust sheets to a significant part of the field in internal thrust sheets . In addition, strain exhibits three-dimensional patterns in parts of internal sheets, near fault zones, and in the overturned limbs of fault-related folds due to superposition of penetrativestrain13; producing deformation events. This paper examines superposition of these strain producing deformation events in some detail and points out situations in fold-and-thrust belts wherein the finite strain becomes three-dimensional. This suggests that the plane-strain assumption used in the construction of retrodeformable models of fold-and-thrust belt evolution break down in these situations and the models lose their validity . Therefore, current techniques used for construction of retrodeformable models in fold-and-thrust belts need to be modified and three-dimensional models which include three-dimensional finite and incremental strain data need to be constructed for an accurate study of the evolution of geometry and kinematics in fold-and-thrust belts