CSEDI: Reconciling Geophysical and Geochemical Observations of Mantle Structure

白色和Turcotte 0079975这项研究将严格评估模型的地幔结构的地球化学观测。任何成功的地幔结构和动力学模型都必须同时解释地球化学和地球物理观测。凯洛格等人[Science，283：1881-1884，1999]提出的地幔结构模型在这方面似乎很有前途。本研究的一个主要目标是确定该模型是否与地球化学观测实际上是一致的。具体而言，研究人员将进行以下研究：（1）质量平衡和热流。对于Sr、Ce、Sm、Nd、Lu、Hf、U、Th等难熔亲石元素，则应将地壳加地幔的相对丰度相加，以给出亲石元素的相对丰度。地幔热流在很大程度上是由于U，Th和K的衰变，因此提供了这些元素的丰度的进一步限制。由于地壳和亏损地幔的热流、不相容元素和同位素组成都在一定范围内已知，因此可以限制其他地幔储层的组成和规模。调查人员将利用对地壳和贫化地幔成分的精确估计并结合热流的限制来评价壳幔质量平衡。(2)同位素演化模型。这项工作将研究放射性同位素的演变，特别是U-Th-Pb-He系统，在多水库系统中的元素的停留时间很短。将考虑储层的替代配置，其中包括储层之间物质的稳态和间歇性再循环。目标是限制地幔储层的大小和地幔储层之间的通量。(3)对流混合模型。研究人员将根据现有的数值模拟，使用混合时间与温度和粘度的参数化来模拟储层内的混合和均质化。分析将分为两个部分。首先，将考虑主要陆地水库之间的可变交换率，包括强烈的时间依赖性交换，以确定是否可以获得满足地球化学约束的自洽模型。第二部分将考虑储层内的同位素演化。

White and Turcotte 0079975 This study will critically evaluate models of mantle structure in light of geochemical observations. Any successful model of mantle structure and dynamics must simultaneously explain both geochemical and geophysical observations. The model of mantle structure proposed by Kellogg et al. [Science, 283: 1881-1884, 1999] appears promising in this respect. A major objective of this study will be to determine whether this model is actually consistent with geochemical observation. Specifically, the investigators will carry out the following studies: (1) Mass Balance and Heat Flow. For refractory lithophile elements, such as Sr, Ce, Sm, Nd, Lu, Hf, U, and Th, the crust plus mantle should sum to give chondritic relative abundances. Mantle heat flow is largely due to decay of U, Th, and K and hence provides a further constraint on the abundances of these elements. Since both the heat flow and incompatible element and isotopic composition of the crust and depleted mantle are known within limits, the composition and size of other mantle reservoirs can be constrained. The investigators will evaluate crust-mantle mass balance using refined estimates of crustal and depleted mantle composition and incorporating the constraint of heat flow. (2) Isotope evolution models. This work will examine the evolution of radiogenic isotopes, particularly the U-Th-Pb-He system, in a multi-reservoir system where residence times of elements are short. Alternative configurations of reservoirs will be considered with both steady-state and episodic recycling of material between reservoirs. The objective will be to constrain the sizes of and fluxes between mantle reservoirs. (3) Models of convective mixing. The investigators will model mixing and homogenization within reservoirs using parameterizations of mixing times versus temperature and viscosity based on available numerical simulations. The analyses will be divided into two parts. First, variable rates of interchange, including strongly time-dependent interchange, between major terrestrial reservoirs will be considered to determine whether a self-consistent model can be obtained that satisfies the geochemical constraints. The second part will consider isotopic evolution within a reservoir.