Introduction

Oceanic plateaus and large aseismic ridges are difficult to subduct (Vogt et al. 1976; Nur and Ben-Avraham 1982; Burke et al. 1978; Burke 1988); therefore, they may be accreted to continents (Abbott and Mooney 1995; Saunders et al. 1996; Kerr et al. 1997a). Some investigators have suggested they represent a major component of continental growth (Abbott 1996; Condie 1997c). Buoyancy models by Cloos (1993) indicate that oceanic plateaus up to about 17-km thick are easily subductable, although they may be partially obducted during collision.

When oceanic plateaus and aseismic ridges (hereafter collectively referred to as oceanic plateaus) reach about 30 km in thickness, they become too buoyant to subduct (Cloos 1993; Abbott 1996). Those formed during the last 200 Myr comprise a significant volume of crust in oceanic basins (3.7 × 106 km3) (Schubert and Sandwell 1989), and if these were all accreted to the continents, the total volume of continental crust would increase by about 5%. Although several remnants of oceanic plateaus accreted to continental crust have been described, there is a curious sparsity of large accreted oceanic plateaus. This is especially puzzling because many relatively large ocean plateaus exist in the oceans today, and these should collide and at least partially accrete to the continents in the future. Of the several reasons for a paucity of oceanic plateaus in the geologic record, Saunders et al. (1996) favor recycling of oceanic plateaus into the mantle at subduction zones.