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是什么？地球内部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发展起来的地质温度计。其中最受欢迎的是主要的基于元素的辉石温度计，它在确定地球的热结构方面发挥了重要作用。S上地幔。斜辉石和正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。S上地幔。研究表明，地幔岩石中斜辉石与正辉石的稀土元素丰度比值对温度敏感。提出的研究的主要目标是开发一种辉石温度计，该温度计建立在两种辉石之间的温度依赖REE分布的基础上。这种新型温度计最重要的优点之一是它具有较高的闭合温度。这意味着人们可以潜在地读取现在暴露在地表的岩石的高温历史。在这个项目中，布朗大学的研究人员将通过结合实验室晶体生长和微量元素分配实验以及来自地球的平衡良好的含双辉石的超镁铁和基铁样品的化学分析，校准稀土-双辉石温度计。S上地幔和下地壳。结合已发表的高质量辉石岩-熔体微量元素分配数据，他们将利用非线性最小二乘法建立斜辉石岩-熔体、正辉石岩-熔体和正辉石岩-斜辉石岩体系中稀土元素分配的内部一致晶格应变模型。利用实验室校准的温度和成分依赖的正辉石-斜辉石REE分配模型，他们将能够通过测量两种共存辉石中的REE丰度来计算超镁铁质或基性样品的平衡温度。概述了新温度计在一系列地质背景下的超镁铁性和基性岩石中的潜在应用。该项目的广泛影响将源于地球温度计和辉石岩-熔体REE分配模型对岩石学、地球化学和地球动力学应用的重要性。这项研究的结果将为不同的岩石学家、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。内部一致的辉石岩-熔体REE分配模型将为地球化学家推断地球和行星内部的熔融过程提供关键参数。双辉石质ree - 2温度计的高闭合温度可以为岩石学家、地球动力学家和行星科学家提供新的工具来估计岩石圈的冷却速率和热结构，从而更好地了解月球、火星和其他行星体的基性和超基性岩石的热化学历史。这项研究的结果也将通过公开讲座以及本科和研究生课程传播给更广泛的受众。最后，建议的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，并为研究生提供实验，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.