Carbonate Clumped Isotope Thermometry of the Notch Peak Contact Metamorphic Aureole

缺口峰接触变质光环的碳酸盐簇同位素测温

• 批准号: 1322058
• 负责人: John Eiler
• 金额: $ 27万
• 依托单位: California Institute of Technology
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-15 至 2017-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1322058&HistoricalAwards=false
• 关键词: Carbonate; Clumped; Isotope; Thermometry; Notch

The circulation of water deep in the earth?s crust underlies a variety of highly significant geological processes, including formation of ore bodies, heat flow in geothermal fields, and the thermal, mineralogical and chemical evolution of crustal rocks and magmas. Most crustal water circulation occurs at depths of less than 10 kilometers because this is the range over which pores and fractures remain open against the pressure of overlying rocks. One of the great challenges to our understanding of this phenomenon is that our tools for measuring the temperatures experienced by rocks in this upper portion of the crust generally provide only semi-quantitative or relative constraints. And, this ambiguity in temperature confounds efforts to define the chemistry of waters that have reacted with rocks. For this reason, our firmest grip on crustal water-rock reaction is confined to narrow (~1 km) haloes of hot rock immediately surrounding intruding magmas, where elevated temperatures drive mineralogical reactions that can be used as rigorous temperature constraints. This project will re-examine this problem using a recently invented method of thermometry that allows for the precise quantitative measurement of temperatures of water-rock reaction over a wide range of temperatures common to the upper 10 km of the crust. This method, 'carbonate clumped isotope thermometry', is based on the grouping together of rare isotopes of carbon and oxygen into the same molecular groups in minerals such as calcite and dolomite. Analysis of these rare isotopic molecules is technically challenging but enabled by recent innovations in mass spectrometry, and has led to advances in the study of past climates, topography of the earth's surface, temperatures of faults, geologic histories of petroleum deposits, body temperatures of dinosaurs and other problems. The method should also define the isotopic compositions of waters that co-existed with carbonate minerals, letting one 'map' the circulation of fluid at depth. This project will be the first time this tool has been applied to a significant problem in the thermal and chemical evolution of the deep crust. The study area, Notch Peak, Utah, is exceptionally well exposed and well studied, meaning the results of this project's measurements can be compared to detailed models of the distribution of heat and fluids. An expected outcome of this project is that quantitative, predictive models of temperatures and fluid migration pathways in this environment will be extended out of the narrow belt of hot rocks that surrounds the Notch Peak magmatic intrusion and into the broad surrounding region of more typical crustal rocks. This result could lead to advances in understanding of ore bodies, oil and gas fields, and hydrothermal energy resources.

地球深处的水循环？中国的地壳是各种重要地质作用的基础，包括矿体的形成、地热田中的热流以及地壳岩石和岩浆的热演化、矿物学演化和化学演化。大多数地壳水循环都发生在10公里以下的深度，因为在这个深度范围内，孔隙和裂缝会在上覆岩石的压力下保持开放。对我们理解这一现象的最大挑战之一是，我们测量地壳上部岩石温度的工具通常只能提供半定量或相对的限制。而且，这种温度上的模糊性使人们难以确定与岩石发生反应的沃茨的化学性质。出于这个原因，我们对地壳水岩反应的最坚定的把握仅限于侵入岩浆周围的热岩的狭窄（约1公里）晕，其中升高的温度驱动矿物学反应，可用作严格的温度约束。该项目将利用最近发明的测温方法重新研究这一问题，这种方法可以精确定量测量地壳上部10公里常见的各种温度范围内的水岩反应温度。这种方法，“碳酸盐聚集同位素测温法”，是基于在方解石和白云石等矿物中将稀有的碳和氧同位素分组到相同的分子组中。分析这些稀有的同位素分子在技术上具有挑战性，但最近质谱技术的创新使其成为可能，并导致了对过去气候，地球表面地形，断层温度，石油矿床地质历史，恐龙体温和其他问题的研究取得了进展。该方法还应该确定与碳酸盐矿物共存的沃茨的同位素组成，让人们“绘制”深层流体的循环。该项目将是这一工具首次应用于地壳深部热演化和化学演化的重大问题。研究区域位于犹他州的Notch Peak，暴露情况非常好，研究也非常充分，这意味着该项目的测量结果可以与热量和流体分布的详细模型进行比较。该项目的一个预期成果是，在这种环境中的温度和流体迁移路径的定量预测模型将扩展到Notch Peak岩浆侵入体周围的狭窄热岩带之外，并扩展到更典型的地壳岩石的广泛周围区域。这一结果可能会导致对矿体、油气田和热液能源的认识的进步。