General discussion

Abstract

J. G. R amsay, F.R.S. (ETH-Zentrum, Zurich, Switzerland). Several of the cross sections and profiles through various parts of the Himalayas that have been presented at the Meeting were based on geometric techniques appropriate to the frontal thrust belt of the Rocky Mountains of Canada and the U.S.A., or to the soft sediment deformation in and around Taiwan. In these reconstructions, faults, especially thrusts, are considered to exert the dominant Control on the forms of structures. Fold forms appear only as fault bend folds developed as a consequence of movement of thrust sheets over irregular step-like thrust plane topography. In these models the effect of rock competence only seems to be considered as a characteristic rock property controlling the ramp-flat geometry of the fault planes, and the rock properties seem to exert little or no influence on the fold style. I would suggest that this current fashion of making constructions to depth is not only mechanically unsound, but it does not accord with the observations of structural geometry.