Mechanical analysis of the geometry of forced-folds

A mechanical model of forced-folding, comprised of an anisotropic cover overlying displaced, rigid basement blocks, is used to investigate the influence of various parameters on theoretical fold form: shape and dip of basement fault, strength of basement-cover contact, and degree of anisotropy of the cover. We show that the degree of anisotropy in the cover largely influences the geometry of the forelimb of the forced-fold. Folds produced in isotropic cover display forelimbs that taper from large dip angles near the basement-cover contact to low dip angles at the ground surface. In contrast, dips in the forelimbs of folds in anisotropic cover are nearly uniform with depth. We show that the basement-cover contact and the shape of the basement fault largely influence the geometry of the backlimb. Backlimb rotation occurs in cover welded to the basement and in cover underlying curved basement faults. In addition, the kinematic features of the theoretical folds are compared with the fold geometry generated by parallel kink and trishear models. Folds in isotropic cover overlying straight basement faults closely resemble the fold forms produced by the trishear kinematic model while fold forms in anisotropic cover more closely resemble folds produced by parallel kink geometric constructions.