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

为了理解上地幔的流动，必须量化驱动这种流动的密度变化。 造成密度变化的过程是温度的变化、熔化的量和地幔的组成。 成分变化的主要原因是熔体消耗，这发生在地幔岩（橄榄岩）部分熔融时。 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（残留物）耗尽这些元素。 熔体消耗在构造圈形成、洋中脊熔体聚焦、地幔柱-板块相互作用和熔体驱动的对流中具有根本的重要性。 熔体耗尽也可能改变地震速度，使耗尽地幔成像。 此外，熔体贫化的密度效应越来越多地被用于地球物理研究，以推断地幔的组成。该项目的目的是量化熔体消耗的成分，密度和速度的影响，并解决理论模型和捕虏体研究之间的差异。 为此，研究人员将在1-5 GPa的压力下测量熔体去除对橄榄岩的成分影响，并将这些成分变化转换为密度和非谐速度变化。 这项研究将通过为新的科学家提供研究经验，鼓励怀俄明州大学和加州大学戴维斯分校之间的合作，以及促进地幔岩石学、矿物物理学和地震学的跨学科研究，加强发现和理解。 为了鼓励广泛传播这项工作，研究结果将张贴在怀俄明州大学主办的网站上，其中将包括为地球动力学建模人员提供的密度和速度参数（初步结果已经纳入加州大学洛杉矶分校的对流模型），以及免费提供的计算地幔密度和速度作为成分、温度和压力函数的Matlab脚本。 还将在科学会议和部门研讨会上介绍研究成果。

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.