Uniform parameterized theory of convection in medium sized icy satellites of Saturn

We develop a parameterized theory of convection driven by radiogenic and tidal heating. The tidal heating depends on eccentricity e of a satellite’s orbit. Using parameterized theory we determine the intensity of convection as a function of e and satellite’s properties. The theory is used for 6 medium sized satellites of Saturn. We find that endogenic activity on Tethys and Dione is possible if e exceeds some critical values e _cr . For Enceladus, e was probably close to the present value for billions of years. We cannot find constrains for e of Mimas and Iapetus. The theory successfully predicts the possibility of present endogenic activity in Dione and rules out such activity in Tethys. Both these facts were recently confirmed by Cassini mission.     

Parameterized thermal model of a mixed mantle convection

IntroductionTectonicevolutionisinfluencedbythermalhistoryoftheEarth.TheEarthhasabout4.6Gahistory.ThermalenergyfromtheinterioroftheEachprovidesthemainpowerfortectonicevolution.ItnotonlycontrolstheformationofthelayeredstructuresinsidetheEarth,butalsopromotesthetectonicmovementsofthesurfaceplatesduringthegeologicalera.ThestudyofthethermalhistoryoftheEarthhaspassedseveralstages.Inearlystudies,onlyconductivemechanism(Lubimova,1958)isdiscussedinthethermalevolution.However,theimpotalceofthermalco…     

月表温度对于月幔对流影响的数值模拟研究

行星内部对流计算中, 一般都将其表面温度作为常温处理.但在月球、水星等无大气的天体表面, 温度与纬度明显相关, 月球两极和赤道的平均温度相差可以达到100 K以上.纬度相关的温度边界条件, 是否会影响天体早期对流特征与内部热状态, 过去没有得到重视和研究.本文使用有限元方法进行了二维球壳对流模型的热演化模拟, 以评估无大气行星上, 与纬度高度相关的表面温度对其内部对流和演化的影响.模拟计算结果表明, 表面温度会对月球对流形态产生较大影响, 两极因为相对更冷而易于形成下降流, 上升流更倾向于从赤道位置开始, 在早期演化中表现得尤为明显.受边界条件影响, 月球两极与赤道的岩石圈厚度差异可以达到400 km以上.今后在研究太阳系内月球、水星一类没有大气的天体演化、特别是早期演化时, 对于表面温度纬度相关分布的影响应该予以考虑.

     

Possible effects of lateral viscosity variations induced by plate-tectonic mechanism on geoid inferred from numerical models of mantle convection

In a traditional analytical method, the convective features of Earth’s mantle have been inferred from surface signatures obtained by the geodynamic model only with depth-dependent viscosity structure. The moving and subducting plates, however, bring lateral viscosity variations in the mantle. To clarify the effects of lateral viscosity variations caused by the plate-tectonic mechanism, I have first studied systematically instantaneous dynamic flow calculations using new density-viscosity models only with vertical viscosity variations in a three-dimensional spherical shell. I find that the geoid high arises over subduction zones only when the vertical viscosity contrast between the upper mantle and the lower mantle is O(10³) to O(10⁴), which seems to be much larger than the viscosity contrast suggested by other studies. I next show that this discrepancy may be removed when I consider the lateral viscosity variation caused by the plate-tectonic mechanism using two-dimensional numerical models of mantle convection with self-consistently moving and subducting plates, and suggest that the observed geoid anomaly on the Earth’s surface is significantly affected by plate-tectonic mechanism as a first-order effect.     

地幔对流拖曳力对中国大陆岩石层变形的影响

采用较为符合实际岩石层变形的非线性幂指数本构关系,基于ANSYS有限元平台, 模拟了近20万年来中国大陆地区地表运动及演化过程,探讨了印度板块挤压作用和地幔对流拖曳力各自对于中国大陆地区地表形变运动格局的影响.模拟结果与观测数据的比较表明：在印度板块的挤压和地幔拖曳力联合作用下,中国及东亚大陆岩石层运动形变模式能够和现代GPS观测有较好的吻合; 印度大陆和欧亚大陆的碰撞以及印度大陆的持续向北推进、挤压所产生的应力环境,一直主导了以青藏高原为核心的我国西部地域岩石圈构造、运动和演化,但其影响随着远离青藏高原地区而逐渐变小;地幔对流产生的作用于岩石层底部的拖曳力是中国大陆（特别是远离碰撞带）岩石层运动构造变形的重要驱动力.然而在构造复杂和东部靠近太平洋板块的区域,模型预测结果和GPS观测还存在一定的差距,这说明在未来的中国大陆岩石层变形运动的数值模拟中,应当采用更为复杂的构造模型和驱动力因素.