QUANTIFYING THE KINEMATICS OF DETACHMENT FOLDS USING 3-DIMENSIONAL GEOMETRY - APPLICATION TO THE MEDIANO ANTICLINE (PYRENEES, SPAIN)

The kinematics of detachment folds have been described by three differ ent models: (1) hinge migration is responsible for fold amplification, (2) fold amplification is due to Limb rotation, and (3) both hinge mi gration and limb rotation cause fold amplification, ri numerical metho d is proposed to determine which of these mechanisms is responsible fo r the formation of natural detachment folds, This procedure consists o f measuring and plotting geometric data collected from cross sections constructed across the termination of a fold where shortening dies out laterally, or in an area with a lateral shortening gradient, Assuming that observed spatial variations in fold geometry reflect temporal ge ometric evolution, the procedure allows determination of equations tha t govern the kinematics of the particular detachment fold analyzed, To validate the results obtained from the application of this technique to natural examples, they must be contrasted with other indicators of fold-amplification mechanisms such as micro- structures, mesostructure s, and syntectonic sediment patterns, This analysis is applied to an a symmetric growth fold, the Mediano anti-cline in the Southern Pyrenees of Spain, and shows that it grew due to limb rotation and minor hinge migration, These data, coupled with analysis of the growth stratal pa tterns using reverse and forward modeling techniques, are used to deri ve deformation rates and to display the kinematics of this fold.