UNFOLDING - AN INVERSE APPROACH TO FOLD KINEMATICS

Preserved fold shapes usually reveal little about their kinematic evol ution. Syntectonic strata preserved in growth synclines in contact wit h a fold, however, can permit ''unfolding'': a sequential reconstructi on of fold growth backward through time from a geometry observed at pr esent to an initial undeformed state. Such reconstructions can define the kinematics of fold growth. Growth strata associated with anticlina l forelimbs in the Ebro basin exhibit depositional tapering of beds on fold flanks and progressive limb rotation. Unfolding a well-dated det achment fold defines its kinematic evolution and coevally varying rate s of shortening, forelimb uplift, and forelimb rotation. Interplay of these rates with sedimentation rates controls onlap and offlap relatio ns.