Structure of the lithosphere and upper mantle in the ocean-continent transition region of the northwestern Pacific Ocean

In this paper, the evolution of the upper mantle and the formation of regions of partial melting of the asthenosphere are simulated numerically within the framework of a single-velocity multilayer hydrodynamic model that takes into account the main phase transitions. The modeling results can be used to formulate problems on the introduction of magmatic melts into the lithosphere and crust in the ocean-continent transition region. The region from the marginal sea and the ocean-continent transition zone of the northern Pacific Ocean to the rift zone was numerically studied. To formulate the numerical problem, the data on the analysis of the structure of the earth's crust and upper mantle in the ocean-continent transition region of the northwestern Pacific Ocean were used, carried out by seismic tomography methods using the GIS-ENDDB geoinformation and computing system (Mikheeva, 2016). Tomographic data made it possible to determine the regional structure of magmatic systems in the lithosphere and upper mantle of the northern Pacific Ocean. Analysis of these data, together with data on gravity and magnetic anomalies in the earth's crust, allowed us to estimate the levels and areas of transformation of the earth's crust and lithospheric mantle by past magmatic processes. The fields of shear wave velocities with vertical polarization for the areas of manifestation of PTTS for different depths of the mantle lithosphere and mantle of the northern part of the Pacific Ocean are shown in Figure 1 according to data (Schaeffer, Lebedev, 2013) in the format of the shadow model GIS-ENDDB in relative units.

Figure 1. Tomographic maps of vertically polarized shear wave anomalies for areas of PTTS manifestation at depths of 50, 100, 200, 300, 400, 500 km (according to [Schaeffer, Lebedev, 2013])

The results of the simulation of the ocean-continent transition zone and the northern part of the Pacific Ocean to the North American rift zone, calculated using a multilayer model taking into account seismic tomography data (Perepechko, Sharapov, 2014), are shown in Figure 2. The red zones indicate the melting regions that form the asthenosphere. The development of an active convective flow in the initially heterogeneous upper mantle leads to the appearance of ascending flows on the right boundary of the computational domain, corresponding to the north of the West Pacific rift belt.

Figure 2. Temperature distribution (blue) and degree of partial melting of mantle rocks (red) along the section of the northern part of the Pacific Ocean (at 47° N). The time corresponds to 72 and 149 million years after the emergence of active convective flow in the upper mantle.

Grant No. 24-27-00411.