ИСТИНА

The regional problem’s formulation [1-3] raises many questions. i) Fundamental importance have the boundary conditions at the lower boundary of region. Hard impermeable boundary condition is postulated in [1] at a depth of 350km, and in [2] at a depth 1000km. In [3] used more reasonable, soft mix condition ∂vᶻ/∂z=−vᶻ/H, which let lower boundary be permeable. Accordance our global modeling results [4] we postulate, that impermeable boundary coincides with the endothermic phase transition at 670km. In this case we have known also the temperature of phase transition at this boundary. ii) To weaken the influence of lateral boundaries we move them away from the main region. iii) If modern mantle state is simulated, then maybe use the data of seismic tomography to determine the density, but is objectionable use this data else for calculation the distribution of temperature and viscosity [1, 2]. In our case when a historical simulation is needed, there are not tomographic data and the initial state is fully unknown. All these uncertainties lead to the multiplicity of regional solutions, another words we have deals with an ill-posed problem. Therefore follow Tikhonov [5], to select the right solution should add the conditions regularization. For regularization numerical modeling of the Arctic region we used geological information about position of subduction zones or plums. According to geological data [6, 7], Fig. 1, there was an ancient (Neoproterozoic) continent – Arctida. During tithonian-aptian time (150 -110 Ma ago) existed two active zones of subduction (shown thick line in Fig. 1 left) – PaleoAnyui and Pacific. During this time the “Chukotka - Alaska” microplate was break off from the Canadian Arctic Archipelago and collision with Eurasia, it means that was open the Canadian Basin and closed the South Anyui paleocean. After that PaleoAnyui subduction was stopped and actively worked only Pacific zone (see Fig. 1 center). Hence southward motion of fragments an ancient continent was redirected to the eastward, so in the Cenozoic was formed the Eurasian Basin Fig.1. Fig. 1. Paleo and modern geological data for Arctic region Have been done numerical simulations [6, 7] the geodynamic evolution of the Arctic region. At first, we simulated the upper mantle convection (Fig. 2 left). As regularization condition of our solution we must get the position of subduction zones, shown in Fig. 1. To get desired result we had supported downwelling flows in these zones. For calculation we used the model of thermal convection in viscous medium in the Boussinesq approximation taking into account the temperature dependence of viscosity (by I.Karato). From the results of this calculation we had taken tension on the base of the lithosphere (Fig. 2, 3 centers). After that, we recalculated displacements (Fig. 2, 3 right), strains and stresses arising into lithospheric plate, using a nonlinear elastic-plastic rheology for heterogeneous medium (Fig. 3 left). From this calculation were determined the area of destruction associated with the excess of the limits of the tensile and shear. Fig. 2. Upmantle convection and Formation of Amerasia Basin at 150-110 Ma ago. Fig. 3. Lithosphere Plate Deformation and Beginning at 110 Ma ago of Eurasian Basin Formation. Fig. 4. Agreement upper mantle convective simulation with tomography image. The simulation results [6, 7] are in agreement with different independent empirical data, including a regional P-wave tomography image after [8], Fig. 4. References 1. N.P. Fay, R.A. Bennett, J.C. Spinler, E.D. Humphreys Small-scale upper mantle convection and crustal dynamics in southern California // Geochemistry Geophysics Geosystems Volume 9, Number 8, 12 August 2008. Q08006, doi:10.1029/2008GC001988 2. A. Ismail-Zadeh, A. Aoudia, G.F. Panza Three-dimensional numerical modeling of contemporary mantle flow and tectonic stress beneath the Central Mediterranean // Tectonophysics 482 (2010) 226–236. 3. W. Gorczyk, A.P. Willner, T.V. Gerya, J.A.D. Connolly, J.P. Burg Physical controls of magmatic productivity at Pacific-type convergent margins: Numerical modelling // Physics of the Earth and Planetary Interiors 163 (2007) 209–232. 4. V.D. Kotelkin, L.I. Lobkovskii Thermochemical Theory of Geodynamical Evolution // Doklady Earth Sciences, 2011, Vol. 438, Part 1, pp. 622–626. 5. A.N. Tikhonov, V.Ya. Arsenin Solutions of Ill-Posed Problems. John Wiley, New York, 1977. 6. L.I. Lobkovsky, I.A. Garagash, M.V. Kononov, V.E. Verzhbitsky, V.D. Kotelkin Tectonics of Deforming Lithosphere Plates and Mz-Kz geodynamics of Arctic Region. In “Geology and Geoecology of Eurasian Continental Margins”. Moscow: GEOS, 2010. Vol. 2, pp. 8-40 (in Russian). 7. L.I. Lobkovsky, M.V. Kononov, I.A. Garagash, V.E. Verzhbitsky, V.D. Kotelkin 3D Geodynamics of Arctic Region and Model of Amerasian Basin Formation. International Conference on Arctic Margins, 2011, Sessions entitled: ICAM VI http://www2.gi.alaska.edu/ICAMVI/Presentations.html 8. D. Zhao, F. Piraino, L. Liu Mantle structure and dynamics under Eastern Russia and adjoining regions // Geologiya i geofizika, 2010. Vol. 51, N 9, pp. 1188 -1203 (in Russian).