相变对金星地幔对流影响的数值模拟

发布时间：2018-06-08 01:48

本文选题：金星 + 灾难性表面更新　；参考：《中国科学:地球科学》2015年05期

【摘要】：利用三维球壳模型通过数值模拟研究了相变对金星地幔对流的影响.模型假定地幔物质流变特性与温度和压力强相关,并包含橄榄石到尖晶石的放热相变和尖晶石到钙钛矿的吸热相变.通过对不同瑞利数、不同相变Clapeyron斜率和不同相变深度的模型的计算分析,发现:(1)吸热相变对相变面上下物质交换具有阻碍作用,增加相变Clapeyron斜率的绝对值,会减小相变面处的径向质量流和归一化径向质量流、并减少地幔热柱个数,即上下物质交换减弱、相变的阻碍作用加强、对流波长增加;(2)增大瑞利数Ra,也使对流波长增加或热柱个数减少,但对相变面上下物质交换的影响主要反映在对流强度与Ra的关系上,即Ra增加,对流强度增加,相变面处的径向质量流增大,上下物质交换量增大.而Ra增加,归一化径向质量流变化不大,即Ra对相变的阻碍作用的影响不大.这不同于二维模型中瑞利数的增加将很大程度上增加相变的阻碍作用的结论;(3)吸热相变面深度的少许增加会略微减少热柱个数,但对相变面上下物质交换的影响很小.虽然与已有研究一致,吸热相变能阻碍相变面上下物质交换,但这种阻碍作用在三维模型中并不会导致物质在界面上下大量堆积.上下物质交换量随时间变化不大,地幔对流结构相对稳定.这与二维模型中存在周期性的大量物质交换明显不同.这说明相变的作用将难以导致金星表面的大量岩浆作用,或者说相变难以导致金星灾难性的表面更新.
[Abstract]:A three-dimensional spherical shell model is used to study the effect of phase transition on the convection of the Venus mantle by numerical simulation. The model assumes that the rheological properties of the mantle material are strongly dependent on the temperature and pressure, including the exothermic phase transition of olivine to spinel and the endothermic phase transition of spinel to perovskite. The slope and difference of different phase transition Clapeyron of different Rayleigh numbers and different phase changes are made. The calculation and analysis of the model of the phase change depth show that: (1) the endothermic phase transition has a hindrance to the material exchange on the surface of the phase change surface. Increasing the absolute value of the slope of phase change Clapeyron will reduce the radial mass flow and the normalized radial mass flow at the phase transition surface, and reduce the number of the mantle plumes, that is, the exchange of the upper and lower materials is weakened, and the blocking effect of the phase transition is strengthened. The convection wavelengths increase; (2) increasing the number of Rayleigh numbers Ra increases the convection wavelength or the number of hot columns, but the effect on the material exchange on the phase change surface is mainly reflected in the relation between the convection intensity and the Ra, that is, the increase of Ra, the increase of the convection intensity, the increase of the radial mass flow at the phase transition surface, the increase of the mass exchange in the upper and lower surfaces, and the increase of the Ra and the normalized radial mass. There is little change in the volume flow, that is, Ra has little effect on the blocking effect of phase transition. This is different from the increase of the Rayleigh number in the two-dimensional model. (3) a little increase in the depth of the heat absorption phase change surface will slightly reduce the number of hot column, but it has little effect on the material exchange on the phase change surface. It is consistent that the endothermic phase transition can impede the exchange of material on the surface of the phase change surface, but this hindrance does not lead to a large accumulation of material in the interface. The amount of material exchange varies little with time, and the convection structure of the mantle is relatively stable. This is obviously different from the periodic mass exchange in the two-dimensional model. The effect of Ming phase transformation will hardly lead to massive magmatism on the surface of Venus, or that transformation will hardly lead to catastrophic surface renewal of Venus.
【作者单位】：蒙城地球物理国家野外科学观测研究站;中国科学技术大学地球和空间科学学院地震与地球内部物理实验室;
【基金】：国家自然科学基金项目(批准号:41474082,91014005) 中国科学院知识创新工程重要方向项目(编号:KZCX2-YW-QN507)资助
【分类号】：P185.2

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