OROGENESIS: COLLISION, PLATE CAPTURE, MANTLE WAVES, DYNAMIC TOPOGRAPHY AND TECTONIC DUNKS - CAUSES, CHARACTERISTICS, AND MANIFESTATIONS

Convergence, collision, and plate coupling, followed by capture and abrupt change in plate motion, are manifest by plate drag or plate rotation accommodated by plate-bounding strike-slip faults and recorded by core complexes, magmatic flare-ups, and, in places accumulation of black shale, as well as transpression at restraining bends. The change of plate motion causes coupled slabs and cratonal roots, attached to the base of the captured plate and protruding hundreds of kilometers downward, to move across and through the mantle, thereby disturbing and displacing mantle material. The displaced mantle forms a bulge or bow-like wave as it is pushed away from the moving plate. The wave, which is assumed to form soon after capture, moves away from the moving captured plate, creating dynamic topography as it passes under and uplifts oceanic and continental plates, commonly for about 15 Ma or until decoupling takes place. Under oceans, passage of the wave is postulated to uplift the oceanic crust displacing water onto to land and draining enclosed small ocean basins as well as leading to formation of atolls. At continental plate margins, the wave may induce subduction and uplift during which: 1) a large amount of water-rich sediment is pushed under plate margins causing migmatization, 2) marginal rift basins are inverted and destabilized causing mass-gravity downslope movements, 3) passive margin sections are uplifted causing exhumation of wave-cut terraces, incision by streams, and formation of olistostroms. Where the wave encounters a major intracontinental discontinuity such as a suture or fault, entrained lithosphere may be emplaced to 10’s or 100’s of km depth, where eclogite may form. Concurrently, bivergent, far-traveled nappes develop above regional thrust faults. Within cratonal domains, pre-existing basins may be shortened and inverted, forming domes, and widespread domains are uplifted and erosionally exhumed to form regional unconformities, which may be covered by sheet-like bodies of sandstone following passage of the wave and subsequent subsidence. Resumption of continuing extension causes tectonic exhumation, marked by a “tectonic dunk”, many of which are recorded globally.