Thermochemical Models of Earth's Mantle Convection: New Insight from Fractionation and Outgassing Processes

玄武岩地球化学记录了有关地幔动力学的信息，表明地幔中至少有5个储集层。然而，这种储集层的动力学意义是不受约束的。为了协调各种类型的观测数据，最近产生了几个新的地球动力学模型，其中包括地幔中不同成分的层。研究人员将通过使用地幔中热化学对流的数值模型来评估这些模型和相关模型，以确定不同动力学模型预测的地球化学特征。模拟将包括代表各种化学物种的示踪剂。海脊的部分熔融过程被考虑在内，在洋壳和岩石圈之间产生分馏，并向大气中放出气体。这些过程没有包括在以前的大尺度、完全动态的对流模式中。这些模拟跟踪了古代洋壳，包括榴辉岩和橄榄岩之间的固有密度变化，以及不均匀的产热率。研究人员将探讨他们不同的模型是否能够再现玄武岩的一些特征，并与地球动力学观测(如热流)相一致。他们还将测试结果对岩石学和地球动力学参数的敏感性。

Basalt geochemistry records information about mantle dynamics, indicating that there are at least five reservoirs in the mantle. However, the dynamical meaning of such reservoirs is ill-constrained. Efforts to reconcile the full range of types of observational data have recently given rise to several new geodynamic models that include layers of different composition in the mantle. The investigators will evaluate these and related models, by using numerical models of thermo-chemical convection in the mantle to determine the geochemical signatures predicted by different dynamical models. Simulations will include tracers to represent various chemical species. Partial melting processes at ridges are taken into account, yielding fractionation between oceanic crust and lithosphere, and outgassing into the atmosphere. These processes have not been included in previous large-scale, fully dynamic, convective models. The simulations keep track of ancient oceanic crust, and include intrinsic density variations between eclogite and peridotite, as well as inhomogeneous heat production rates. The investigators will address the ability of their different models to reproduce some of the features of basalt, and to be in agreement with geodynamical observations such as the heat flow. They will also test the sensitivity of the results to petrologic and geodynamic parameters.