Geodynamic Peaks in Alpinotype Orogenies and Changes in Ocean-Floor Spreading During Late Jurassic-Late Tertiary Time

Abstract

Modern data indicate that peaks of tectonic displacement alternate with relative tectonic quiescence and that dates of changes in plate motion coincide with times of orogeny. These relations seem to be substantiated by contemporaneity of major discontinuities in seafloor spreading and widespread angular unconformities related to mountain building. Examples are the spreading discontinuities 112, 77, 40, and 10 m.y. ago which are coeval with intense orogenic phases. They are turning points in geotectonic development of the earth--major orogenies occur contemporaneously with first-order readjustments in the plate-tectonic pattern and are reflected in sea-level changes. Thus a close kinematic relation of the processes is suggested. Evidently, orogenic paroxysms are geneticall associated with episodic reorganizations in direction and rate of plate motion. Alpinotype mountain building occurred along mobile continental margins of plates as soon as these were affected by intense compressive orogenic stress caused by a change to convergent interplate motions. Thus, phases of geodynamic activity become apparent in the history of lithospheric plate motions. The specific timing of these phases is an essential geologic parameter and base for further reproduction of plate-tectonic evolution in time and space.