THE CONTINENTAL CRUST BENEATH THE WESTERN AMERASIA BASIN: MECHANISMS OF CRUSTAL SUBSIDENCE
E.V. Artyushkov1, O.E. Smirnov2, P.A. Chekhovich1,3
1Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, Moscow, Russia
2FSBI “VNIIOkeangeologiya”, St. Petersburg, Russia
3Lomonosov Moscow State University, Moscow, Russia
Keywords: Ultradeep basins, gravity anomalies, isostatic equilibrium, CDP seismic reflection survey, crustal stretching, eclogitization, Moho, Amerasian Basin, Podvodnikov Basin
Abstract
The western part of the wide Amerasian Basin in the Arctic Ocean includes two small basins: the Podvodnikov and the Makarov ones. Analysis of the data on the sedimentary-cover structure and the crustal-subsidence history suggests that despite the large depth of water (3-4 km), both basins are underlain by continental crust. Before the rapid formation of deep-water basins in the early Miocene, the crustal surface was close to the sea level for a long time. Lithospheric stretching made only a minor input to the crustal subsidence. The main cause of the subsidence was prograde metamorphism in the lower continental crust with the transformation of gabbroids into denser eclogite-type rocks. The P -wave velocities in eclogites and mantle peridotites are rather similar. Therefore, when interpreting the seismic data, high-velocity eclogites are commonly considered as the uppermost part of the mantle located below the Moho, while the overlying rocks are shown as attenuated continental crust in the Podvodnikov Basin and as oceanic crust in the Makarov Basin. The proposed mechanism makes it possible to modify the model of crustal structure and to interpret high-velocity eclogites as the lower part of the continental crust that has undergone prograde metamorphism under the impact of mantle fluids.
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