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

开发用于含辉石镁铁质和超镁铁质岩石的稀土元素双辉石温度计

• 批准号: 1220076
• 负责人: Yan Liang
• 金额: $ 20.62万
• 依托单位: Brown University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-07-01 至 2014-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1220076&HistoricalAwards=false
• 关键词: Developing; REE; two; pyroxene; Thermometer

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.

地球和行星内部的温度？S是了解地球和行星体的热和化学演化的关键参数。一种被广泛用于从地球上读取岩石温度的标准工具？S内部是地质温度计，它是基于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。其中最受欢迎的是主要的元素基辉石温度计，它们在确定地球上地幔的热结构方面发挥了重要作用-S上地幔。单斜辉石和斜辉石是控制S上地幔岩石中稀土元素丰度和分布的主要造岩矿物。地幔岩石中单斜辉石和斜方辉石的稀土元素丰度比对温度敏感。提出的研究的一个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稀土元素随温度变化的分布之上。这种新型温度计最重要的优点之一是它的闭合温度更高。这意味着人们可能会读到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实验室晶体生长、微量元素分配实验和化学分析相结合的方法，对来自地球上地幔和下地壳的含超镁铁质和镁铁质的平衡的双辉石样品进行校准。他们将与已发表的高质量辉石熔体微量元素配分数据一起，利用非线性最小二乘回归方法，建立单斜辉石-熔体、斜辉石-熔体和斜辉石-单斜辉石体系中稀土元素内部一致的晶格应变分配模型。通过实验室校准的斜方辉石-单斜辉石稀土分配模型，他们将能够利用测量的两种共存辉石中的稀土丰度来计算超镁铁质或镁铁质样品的平衡温度。概述了这种新型温度计在各种地质环境中对超镁铁质岩石和镁铁质岩石的潜在应用。该项目的更广泛影响将源于地质温度计和辉石熔体稀土分配模型对岩石学、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-熔融稀土分配模型将为地球化学家提供关键参数，以推断地球和行星内部的熔融过程。稀土辉石温度计的高封闭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来估计岩石圈的冷却速度和热结构，以更好地了解来自月球、火星和其他行星体的镁铁质和超镁铁质岩石的热和化学史。这项研究的结果还将通过公开讲座以及本科生和研究生课程向更广泛的受众传播。最后，拟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。