PLUTONIC STRUCTURE OF THE DEEP-SEA BASINS IN THE SEA OF OKHOTSK REGION

Abstract

The original continental crust of the deep-sea basins in the Sea of Okhotsk region was considerably reworked by tectonic and magmatic processes, whereby it has become substantially denser while less thick. The subcrustal lithospheric mantle of the South Okhotsk basin is characterized by the high velocities of longitudinal seismic waves (8.4 km/s) and higher density values, accordingly. A poly-astenospheric model is proposed for the South Okhotsk deep-water basin: it comprises three asthenospheric layers separated by hardened layers. The roof of the upper mantle asthenosphere in the basins is observed at shallow depths (70–75 km), showing low electrical resistivity (r=3–10 Om×m). The asthenospheric layers contain the substantial amounts of magmatic melts (11–16 %), which significantly reduce their viscosity. Emplacement of basic-ultrabasic melts in the Earth's crust and subcrustal lithospheric mantle (i.e. dense mass redistribution, and consolidation of the crust and mantle), as well as the lower viscosity asthenospheric layers facilitate the isostatic subsidence during the formation of deep-sea basins. The deep structure of the continental Pannonian basin, characterized by a high heat flow, is compared to the deep structure of the neotectonic deep-water depression in the Sea of Okhotsk region.

Keywords

• earth's crust
• asthenosphere
• layer
• viscosity
• sea of okhotsk