Oceanic plateaus

Abstract

Oceanic plateaus are large areas of over-thickened oceanic crust that are generally regarded to have formed by decompression melting of hot mantle plumes. Oceanic plateaus are found throughout the geological record. The thick crustal sections of oceanic plateaus are difficult to subduct. As a result the upper crustal portions of oceanic plateaus are frequently accreted to continental margins and so have been an important contributor to crustal growth throughout Earth’s history. Much of our knowledge of the composition, origin, and structure of oceanic plateaus has come from our study of Cretaceous oceanic plateaus such as the Ontong Java, Caribbean, and Kerguelen plateaus. The homogeneous basalts of the Ontong Java Plateau either indicate a homogeneous mantle source region or, more likely, homogenization of heterogeneous magmas during mantle melting. In contrast, the mantle source region of the Caribbean Plateau is markedly heterogeneous, and high-MgO lavas are abundant. Initial magmatism on the Kerguelen Plateau is associated with the breakup of Gondwana in the Early Cretaceous, and as a result the early plateau, lavas are contaminated with continental crust. Throughout much of Earth’s history, oceanic plateau formation correlates with periods of environmental catastrophic events characterized by oceanic anoxia, leading to black shale formation and mass extinction.