Passive continental margins and abyssal plains

Abstract

Nearly the entire Atlantic Ocean and large portions of the Indian Ocean are surrounded by passive continental margins (Fig. 4.1). In contrast, the Pacific Ocean is mostly bordered by active continental margins. As mentioned in Chapter 1, passive continental margins are not plate boundaries because the continental plate is firmly attached to the adjacent oceanic plate. Nevertheless, some displacement occurs at faults along these margins which, because of the small movement involved, is considered to be intraplate tectonics. Passive continental margins develop when continental rift systems separate the continental block and generate juvenile oceanic crust between the separated parts. The oceanic crust is generated by a new spreading axis as is currently the case in the Red Sea (Fig. 3.16). The initial oceanic crust is welded to the adjacent thinned continental crust and the intraplate margin is formed. Therefore, the oldest parts of oceanic crust in an Atlantic-style ocean are always in the immediate neighborhood of the passive continental margins (Fig. 2.12).