Developing a REE-in-two-pyroxene Thermometer for Pyroxene-bearing Mafic and Ultramafic Rocks

地球的温度？s和行星内部是理解地球和行星体的热演化和化学演化的关键参数。 一种被广泛用于读取地球岩石温度的标准工具？岩石内部是地质温度计，它是根据形成岩石的矿物中主要化学元素的温度和压力分布而开发的。 其中最流行的是主要的元素为基础的辉石温度计，发挥了重要作用，在确定地球的热结构？的上地幔。 单斜辉石和斜方辉石是控制地球岩石中稀土元素丰度和分布的主要造岩矿物。的上地幔。 地幔岩石中单斜辉石与斜方辉石的稀土元素丰度比值对温度敏感。 提出的研究的一个主要目标是开发一个辉石温度计，这是建立在温度依赖的稀土元素之间的两个辉石分布。 这种新型温度计最重要的优点之一是它具有更高的闭合温度。 在这个项目中，布朗大学的研究人员将通过实验室晶体生长和微量元素分配实验，以及对地球上平衡良好的含有两个辉石的超镁铁质和镁铁质样品的化学分析，来校准一个稀土-二辉石温度计。的上地幔和下地壳。 连同已发表的高质量的辉石熔体微量元素分区数据，他们将开发内部一致的晶格应变模型的稀土元素分配系统单斜辉石熔体，斜方辉石熔体，斜方辉石单斜辉石使用非线性最小二乘回归方法。 通过实验室校准的温度和成分依赖的斜方辉石-单斜辉石REE分配模型，他们将能够使用两种共存辉石中测得的REE丰度计算超镁铁质或镁铁质样品的平衡温度。新的温度计的潜在应用，超镁铁岩和镁铁岩从一系列的地质背景进行了概述。 该项目的更广泛的影响将来自地质温度计和辉石熔体稀土元素分配模型的重要性，岩石学，地球化学和地球动力学的应用。 这项研究的结果将为岩石学家，地球化学家，地球动力学家和行星科学家提供有价值的信息，促进地球和行星科学的跨学科整合。 内部一致的辉石熔体稀土元素分配模型将提供关键参数，地球化学家推断在地球和行星内部的熔融过程。 REE-in-Two-Pyroxene温度计的高闭合温度可能为岩石学家、地球动力学家和行星科学家提供一种新的工具，以估计岩石圈的冷却速率和热结构，更好地了解月球、火星和其他行星体的镁铁质和超镁铁质岩石的热历史和化学历史。 这项研究的结果还将通过公开讲座和本科生及研究生课程向更广泛的受众传播。 最后，该项目将为本科生提供实践经验，为高级论文工作提供研究机会，为研究生提供实验，计算和教育经验。

Temperature of the Earth?s and planetary interior is a key parameter in understanding the thermal and chemical evolution of the Earth and planetary bodies. One standard tool that has been widely used to read temperatures of rocks from the Earth?s interior is geo-thermometer that has been developed on the basis of temperature and pressure dependent distribution of major chemical elements in minerals that form the rocks. Among the most popular are the major element-based pyroxene thermometers that have played an important role in determining thermal structure of the Earth?s upper mantle. Clinopyroxene and orthopyroxene are major rock-forming minerals controlling the abundance and distribution of rare earth elements (REE) in rocks from the Earth?s upper mantle. It has been well documented that ratios of REE abundances between clinopyroxene and orthopyroxene in mantle rocks are sensitive to temperature. A principal goal of the studies proposed is to develop a pyroxene thermometer that is built on the temperature-dependent REE distribution between the two pyroxenes. One of the most important advantages of this new thermometer is that it has a higher closure temperature. This means that one can potentially read high temperature history of rocks now exposed on the surface.In this project, researchers at Brown University will calibrate a REE-in-two-pyroxene thermometer through a combination of laboratory crystal growth and trace element partitioning experiments and chemical analysis of well-equilibrated two-pyroxene bearing ultramafic and mafic samples from the Earth?s upper mantle and lower crust. Together with published high quality pyroxene-melt trace element partitioning data, they will develop internally consistent lattice strain models for REE partitioning in the system clinopyroxene-melt, orthopyroxene-melt, and orthopyroxene-clinopyroxene using nonlinear least squares regression methods. With a laboratory calibrated temperature- and composition-dependent orthopyroxene-clinopyroxene REE partitioning model, they will be able to calculate equilibrium temperatures for ultramafic or mafic samples using measured REE abundances in the two coexisting pyroxenes. Potential applications of the new thermometer to ultramafic and mafic rocks from a range of geological settings are outlined. The broader impacts of this project will derive from the importance of geo-thermometer and pyroxene-melt REE partitioning models to petrologic, geochemical, and geodynamic applications. Results from this study will provide valuable information for a diverse group of petrologists, geochemists, geodynamicists, and planetary scientists, promoting cross-discipline integration in Earth and Planetary Sciences. The internally consistent pyroxene-melt REE partitioning models will provide key parameters to geochemists to infer melting processes in the Earth and planetary interior. The high closure temperature of REE-in-two-pyroxene thermometer may provide a new tool to petrologists, geodynamicists, and planetary scientists to estimate cooling rate and thermal structure of the lithosphere, to better understand the thermal and chemical history of mafic and ultramafic rocks from the Moon, Mars, and other planetary bodies. Results from this study will also be disseminated to a broader audience through public lectures and undergraduate and graduate courses. And finally, the proposed project will provide hands-on experience for undergraduates, research opportunities for senior thesis work, and experimental, computational, and educational experience for graduate students.