The Continental Crust beneath the Western Amerasia Basin: Mechanisms of Subsidence

Abstract

Abstract —The western part of the large Amerasia Basin in the Arctic Ocean comprises the smaller basins of Podvodnikov and Makarov. Judging by the sedimentary structure and the crustal subsidence history, both basins were developed on the continental crust despite their 3–4 km water depths. By the early Miocene, prior to the rapid formation of the basins, the crustal surface had been close to the sea level for a long time. Lithospheric stretching had a minor input to the subsidence, which was rather driven mainly by the prograde metamorphism of gabbro in the lower crust and its transformation into denser eclogite. The mechanism of subsidence associated with the metamorphic transformation from gabbro to eclogite implies that high-velocity eclogite belongs to the lower continental crust metamorphosed under the effect of mantle fluids. This idea undermines the seismic and gravity basin models that commonly attribute mafic eclogite to the sub-Moho lithospheric mantle on the basis of P-wave velocities similar to those in peridotite and interprets the crust beneath the Podvodnikov and Makarov basins as thin continental and oceanic crustal types, respectively.