Collaborative Research: The Effects of Melt Depletion on Mantle Density and Velocity

为了理解上地幔的流动，必须对驱动这种流动的密度变化进行量化。造成密度变化的过程是温度、融化量和地幔成分的变化。成分变化的一个主要原因是熔融耗尽，当地幔岩石（橄榄岩）部分熔化时发生。在这种情况下，一些元素，如铁，优先分配到熔体中，留下未熔化的岩石（残余）在这些元素中耗尽。熔体耗竭在构造圈形成、洋中脊熔体聚焦、羽板相互作用和熔体驱动对流中具有重要意义。熔体枯竭也可能改变地震速度，使枯竭的地幔成像。此外，地球物理研究越来越多地利用熔体枯竭的密度效应来推断地幔的组成。该项目的目的是量化熔体损耗的组成、密度和速度效应，并解决理论模型和捕虏体研究之间的差异。为此，研究人员将测量在1-5 GPa压力下熔体去除对橄榄岩的成分影响，并将这些成分变化转化为密度和非调和速度变化。这项研究将通过为新科学家提供研究经验来加强发现和理解；通过鼓励怀俄明大学和加州大学戴维斯分校之间的合作；并通过促进地幔岩石学、矿物物理学和地震学的跨学科研究。为了鼓励这项工作的广泛传播，结果将发布在怀俄明大学主办的一个网站上，其中将包括地球动力学建模者的密度和速度的参数化（最初的结果已经被纳入加州大学洛杉矶分校的对流模型），以及用于计算地幔密度和速度作为成分、温度和压力的函数的免费Matlab脚本。研究也将在科学会议和部门研讨会上进行介绍。

To understand flow in the upper mantle, the density variations that drive this flow must be quantified. Processes that create density variations are changes in temperature, the amount of melting, and the composition of the mantle. A primary cause of compositional variations is melt depletion, which occurs when mantle rock (peridotite) is partially melted. In this case, some elements, such as Fe, preferentially partition into the melt, leaving the unmelted rock (the residuum) depleted in these elements. Melt depletion is of fundamental importance in tectosphere formation, melt focusing at mid-ocean ridges, plume-plate interaction, and melt-driven convection. Melt depletion may also modify seismic velocities, allowing depleted mantle to be imaged. Furthermore, the density effects of melt depletion are increasingly being used in geophysical studies to infer the composition of the mantle. The aim of this project is to quantify the compositional, density, and velocity effects of melt depletion, and resolve the differences between theoretical models and xenolith studies. To do so, the investigators will measure the compositional effects of melt removal on peridotite at pressures between 1-5 GPa, and convert these compositional variations to density and anharmonic velocity variations. This study will enhance discovery and understanding by providing research experience to a new scientist; by encouraging cooperation between the University of Wyoming and the University of California, Davis; and by promoting interdisciplinary research in mantle petrology, mineral physics, and seismology. To encourage broad dissemination of this work, results will be posted on a web site hosted by the University of Wyoming, which will include parameterizations of density and velocity for geodynamical modelers (initial results already are being incorporated into convection models at UCLA), and freely available Matlab scripts for calculating mantle density and velocities as function of composition, temperature, and pressure. Research will also be presented at scientific meetings and departmental seminars.