Crustal volumes of the continents and of oceanic and continental submarine plateaus

Abstract

Global topographic data and the assumption of Airy isostasy have been used to estimate the crustal volumes of the continents and the oceanic and continental submarine plateaus. The calculated crustal volumes are 7182 × 10 6 km 3 for the continents, 242 × 10 6 km 3 for continental submarine plateaus, and 369 × 10 6 km 3 for oceanic plateaus. The Falkland Plateau and the Lord Howe Rise are the two largest continental submarine plateaus with volumes of 48 × 10 6 km 3 and 47 × 10 6 km 3, respectively. Total continental crustal volume is 7581 × 10 6 km 3 (including the volume of continental sediments on the ocean floor 160 × 10 6 km 3), in good agreement with previous estimates. Continental submarine plateaus on the seafloor comprise 3.2% of the total continental crustal volume. The largest oceanic plateaus in order of decreasing size are the Ontong-Java Plateau, the Kerguelen Plateau, the Caribbean, the Chagos Laccadive Ridge, the Ninetyeast Ridge, and the Mid-Pacific Mountains. Together they comprise 54% of the total anomalous crustal volume in oceanic plateaus. An upper bound to the continental crust addition rate by the accretion of oceanic plateaus is 3.7 km 3/yr, a value that assumes accretion of all oceanic plateaus, with a total volume of 4.9% of the continental crustal volume, on a 100 Myr time scale. Even if a substantial fraction of the crustal volume in oceanic plateaus is subducted, accretion of oceanic plateaus could make a contribution to continental growth since the upper bound to the addition rate exceeds recent estimates of the island arc addition rate. Subduction of continental submarine plateaus with the oceanic lithosphere on a 100 Myr time scale gives an upper bound to the continental crustal subtraction rate of 2.4 km 3/yr, much larger than recent estimates of crustal subtraction by subduction of seafloor sediments. Effective subduction of all oceanic plateaus implies equally effective subduction of continental submarine plateaus. A potentially important way to recycle continental crust back into the mantle may be the break off of small fragments from the continents, entrapment of the continental fragments in the seafloor, and subduction of the fragments with the oceanic lithosphere. This process may be occurring in the Mediterranean for Corsica and Sardinia.