排序方式： 共有49条查询结果，搜索用时 15 毫秒
41.
We compute the transfer of oceanic lithosphere material from the surface of the model to the inner convective mantle at successive
stages of the supercontinental cycle, in the time interval from the beginning of convergence of the continents to their complete
dispersal. The sequence of stages of a supercontinental cycle (Wilson cycle) is calculated with a two-dimensional numerical
model of assembling and dispersing continents driven by mantle flows; in turn, the flows themselves are forming under thermal
and mechanical influence of continents. We obtain that during the time of the order of 300 Myr the complete stirring of oceanic
lithosphere through whole mantle does not occur. This agrees with current ideas on the circulation of oceanic crust material.
Former oceanic crust material appears again at the Earth’s surface in the areas of mantle upstreams.
The numerical simulation demonstrates that the supercontinental cycle is a factor which intensifies stirring of the material,
especially in the region beneath the supercontinent. The reasons are a recurring formation of plumes in that region as well
as a global restructuring of mantle flow pattern due to the process of joining and separation of continents.
The computations of viscous shear stresses are also carried out in the mantle as a function of spatial coordinates and time.
With a simplified model of uniform mantle viscosity, the numerical experiment shows that the typical maximal shear stresses
in the major portion of the mantle measure about 5 MPa (50 bar). The typical maximal shear stresses located in the uppermost
part of mantle downgoing streams (in a zone that measures roughly 200 × 200 km) are approximately 8 times greater and equal
to 40 MPa (400 bar). 相似文献
42.
Izvestiya, Atmospheric and Oceanic Physics - The structure of thermal convection is determined by the spatial distribution of temperature in the mantle. However, in the literature, when modeling... 相似文献
43.
44.
45.
The values of maximum tangential stresses, as well as their spatial orientations, are calculated at each point of the mantle. These calculations are performed for successive stages of the supercontinental cycle in terms of a numerical 2-D model of assembling and diverging continents driven by mantle flows; in turn, the flows themselves are formed under the thermal and mechanical action of continents. Zones of maximum tangential stresses, within which their values are equal to or exceed 30 MPa (300 bar), are shown to be located in places where ascending or descending mantle flows approach the horizontal mantle boundaries. These zones have the shape of a bowl with the broad side toward the boundary, and their maximum tangential stresses are oriented at an angle of about 45° to the horizontal. The dimensions of these zones amount approximately to 300 km laterally and 300 km in depth. Their subhorizontal and subvertical tangential stresses are close to zero. It is also shown that the stress values vary significantly during the evolution of the suboceanic mantle under a new opening ocean (after the breakup of a supercontinent). Thus, the maximum tangential stresses in this vast mantle region at the stage of fast ocean opening are, on average, more than two times higher than at the subsequent slow stage. Note that, at all stages, the axes of the maximum tangential stresses are oriented nearly horizontally or vertically almost throughout the aforementioned area. 相似文献
46.
We present the case for liquid models of Jupiter and Saturn. We then discuss the information which can be obtained about their interior structure from a knowledge of their gravitational moments, and we discuss the nature of presently available data and data which will be necessary to fully exploit future results. 相似文献
47.
V. P. Trubitsyn A. N. Evseev A. A. Baranov A. P. Trubitsyn 《Izvestiya Physics of the Solid Earth》2008,44(8):603-614
A temperature and pressure increase in the mantle causes phase transitions and related density changes in its material. The transition boundary in the pressure-temperature phase diagram is determined by the curve of phase equilibrium with the slope γ = dp/dT. If the slope is nonzero, a phase transition in hot ascending and cold descending mantle flows occurs at different depths and, therefore, either enhances (γ > 0) or slows down convection (γ < 0). The mantle material has a multicomponent composition. Therefore, phase transitions in the mantle are distributed over an interval of pressures and depths. In this interval, the concentration of one phase smoothly decreases and the concentration of the other increases. The widths of phase transition zones in the Earth’s mantle vary from 3 km for the endothermic transition in olivine at a depth of 660 km to 500 km for the exothermic transition in perovskite, and the high-to-low spin change in the atomic state of iron takes place at a depth of about 1500 km. This work presents results of calculations demonstrating the convection effect of phase transitions as a function of the transition zone width. Transitions of both types with different slopes of the phase curve and different intensities of mantle convection are examined. For the first time, the convection enhancement and an increase in the mass transfer across the phase boundary are quantitatively investigated in the presence of an exothermic phase transition as a function of the slope of the phase curve. The mixing of material under conditions of partially layered convection is examined with the help of markers. 相似文献
48.
49.
The results of numerical modeling for the increase and decrease in the thickness of a highly viscous continental lithosphere under whole-mantle convection on a time interval of 3.5 Ga were considered. It was found that the initial period of lithosphere growth took about 1.1 Ga, followed by a period of its slow thinning because of gradual heating of the mantle by several hundred degrees from the thermal insulation effect of the lithosphere.
相似文献