Integrated Models of Mantle Convection and True Polar Wander, and the Structure of the Earth's Deep Interior

地球内部通过热对流过程在地质时间内冷却下来。缓慢的爬行流使热物质上升，冷物质下沉。这种大规模的环流形成了山脉，并推动了我们在地表观察到的大部分地质过程。地球也在太空中旋转，由于与热对流有关的质量重新分配，自转轴的方向随着时间的推移而缓慢演变。自转轴的变化被称为真极移，在古地磁观测中被发现，并归因于热对流。然而，一般认为旋转对热对流的影响很小。一些新的证据挑战了这一传统观点。板块运动在空间上与旋转轴的方向相关。此外，地球深处的内部有一些独特的特征，这些特征位于赤道上，似乎受到自转的影响。为了更好地理解这两个基本过程，我们建议研究热对流和真极漂移之间的动态相互作用。提出的研究将整合热对流和真正的极地漂移成一个单一的，自一致的行星动力学描述。热对流的数值模型通常基于一组描述质量、热量和线性动量守恒的方程，而真正的极移模型总是基于角动量守恒。通过扩展和推广热对流的通常描述，我们将这两个过程合并成一组方程，允许对流和真极移之间的充分相互作用。我们计划通过向一个名为ASPECT的现有社区软件包添加新功能来解决这些方程，该软件包是在NSF的支持下开发的。在此项目中进行的所有开发将通过地球动力学计算基础设施（www.geodynamics.org）向社区提供。该软件将为其他研究人员提供广泛的潜在应用，包括大陆岩石圈的热化学演化。拟议的研究也将有助于培养研究生和年轻的研究人员在先进的计算方法。

The interior of the Earth cools over geological time through the process of thermal convection. Slow creeping flow allows hot material to rise and cold material to sink. This large-scale circulation is responsible for building mountains and driving most of the geological processes we observe at the surface. The Earth also rotates in space, and the orientation of the spin axis evolves slowly with time due to a redistribution of mass associated with thermal convection. Changes in the spin axis, known as true polar wander, are detected in paleomagnetic observations and are attributed to thermal convection. However, it is generally assumed that rotation has little influence on thermal convection. Several new lines of evidence challenge this conventional view. Plate motions are spatially correlated with the orientation of the rotation axis. In addition, the Earth's deep interior has peculiar features that reside on the equator and appear to be affected by rotation. We propose to investigate the dynamic interaction between thermal convection and true polar wander with the aim of better understanding these two fundamental processes.The proposed research will integrate thermal convection and true polar wander into a single, self-consistent description of planetary dynamics. Numerical models of thermal convection are normally based on a set of equations that describe conservation of mass, heat and linear momentum, whereas models of true polar wander are invariably based on conservation of angular momentum. By expanding and generalizing the usual description of thermal convection, we have combined these two processes into a single set of equations that permit full interaction between convection and true polar wander. We plan to solve these equations numerically by adding new capability to an existing community software package called ASPECT, which was developed with support from NSF. All developments undertaken during this project will be made available to the community through the Computational Infrastructure for Geodynamics (www.geodynamics.org). The software will be useful to other researchers for a wide range of potential applications, including the thermal and chemical evolution of continental lithosphere. The proposed research will also contribute to the training of graduate students and young researchers in advanced computational methods.