【作者】 李杨；

【导师】 黄金水；

【作者基本信息】 中国科学技术大学 ， 地球物理， 2010， 硕士

【摘要】 地幔对流作为地球动力学的一个基本概念,对地球以及类地行星的动力学演化研究起着重要作用。本文通过介绍对地幔对流的认识的发展,描述地幔对流的控制方程,简化条件以及无量纲化的方法,来初步介绍地幔对流的基础理论。之后综述了当前地球物理学界关于D”层钙钛矿(PV)-过钙钛矿(PPV)相变对地幔对流的影响的一些研究进展。重点介绍了Nagakawa和Paul Tackley在过钙钛矿相变的克拉伯龙曲线斜率变化对地幔对流的影响,以及Marc Monnereau和David A.Yuen在研究相变截断温度对相变面的形态结构和地幔对流的影响。以前面几位地球物理学家对D”层的研究结论为基础,为了探讨地幔底部以及核幔边界出现的异常结构,以及这些异常对我们认识地幔对流和地球动力学演化的帮助,更主要的是通过钙钛矿-过钙钛矿的相变这一强放热反应所能在核幔边界提供的强的温度约束条件来研究这些条件下俯冲岩石圈在下地幔形态结构。论文通过有限元方法在三维直角坐标下尝试了一个简单的数值模型,在加入了钙钛矿-过钙钛矿相变这一条件下进行演化计算。通过数值模拟的结果我们可以得到一下结论:1在地幔对流达到相对稳定的情况下,俯冲岩石圈可以达到下地幔底部,并进行堆积。2尽管发生在核幔边界D”层上方的钙钛矿-过钙钛矿相变是一个强放热反应,但这个反应并不会使得地幔对流变得不稳定和与时间相关。3钙钛矿-过钙钛矿相变为俯冲岩石圈在下地幔形态结构的研究提供了很好的温度约束条件,在温度场中我们可以看到清晰的下界面。由于本研究仅仅考虑到了热-化学对流的一些基本参数以及相变面情况,而俯冲板块的形态结构的差异还可能由于热传导的横向不均匀性,介质的各向异性,以及地幔介质的可压缩性等等引起。所以把这些可能影响到俯冲板块形态结构的参数引入数值模型中对进一步完善实验结果会有很大的帮助。更多还原

【Abstract】 As a fundimantle concept of geodynamics,’mantle convection’has played an important role in both the research in earth geodynamics process and the terrestrial planets geodynamics process.The thesis briefly introduces the basic theories of‘Mantle Convection’by representing the Control function,Boussinesq approximation as well as the nondimensional method. Then introduced the numerical computing method– Finite Element Method(FEM) and the code we employ in our research- CitcomCu.After that ,the thesis summarizes several viewpoints and previous works of the problem’the effect of the PPV phase trasition on the mantle convection’Mainly focus on the work Nagakawa and Paul Tackley have done on the Clayeron Slope’s value,and the research Marc Monnereau and David A. Yuen have taken on detecting the relationship between the Clayperon Slope and the temperature intercept. The PPV phase change provide us a strong constrain in the temperature field in CMB.After the numerical calculation ,we come to the conclusions:1 the subducted lithosphere could reach the CMB and the mantle convection can be still stable.2 The exothermic reaction doesn’t destabilizes the thermal boundary.3 With the PPV phase change in our numerical convection model, we could get a more obvious temperature field in CMB.This study only take into account the effect of the PPV phase change into the thermal-chemical mantle convection.However,there are other different physical properties such as latent heating and elastic constants and thermal generation rate and so on.Therefore ,it would be a better research to take these properties into the numerical model.更多还原