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Nature, Extent, and Timing of Ultrahigh-temperature Metamorphism, Acadian Orogen, Connecticut

康涅狄格州阿卡迪亚造山带超高温变质作用的性质、范围和时间

基本信息

批准号：
1250269
负责人：
Jay Ague
金额：
$ 31.83万
依托单位：
Yale University
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：
2013-01-01 至 2016-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1250269&HistoricalAwards=false
关键词：
Nature Extent Timing Ultrahigh temperature

项目摘要

Over the past two decades it has become clear that the continental crust can be heated to extreme, ?ultrahigh? temperatures (UHT) in excess of 900 °C (about 1650 °F) over large regions during metamorphism and mountain building events. How metamorphic rocks of the crust reach such extreme temperatures remains a fundamental unresolved problem in the geosciences, with major implications for rock strength, generation of magmas (which may ascend from depth to produce ore deposits and volcanic eruptions), heat transfer, and Earth?s overall heat budget. This project will focus on newly-discovered UHT rocks in northeastern Connecticut, the first regional UHT locality found in the United States. The rocks underwent extreme temperature conditions of roughly 1000 °C (more than 1800 °F) at depths of at least 35 km (about 22 miles) below the surface during Appalachian mountain building in the Devonian Period. This discovery will force a rethinking of how the deep rocks of the Appalachian mountains were formed, and shed new light on how UHT conditions can be reached. Moreover, the rocks contain abundant evidence for the former presence of CO2-rich fluids at ultrahigh temperatures, and thus could have important implications for carbon cycling in the crust and the long-term carbon cycle. Fundamental hypotheses for UHT metamorphism will be tested including: rapid exhumation from the mantle; underthrusting of radiogenic crust; asthenospheric upwelling; mechanical strain heating; heat input from mantle-derived magmas; and heat transfer by fluids. Basic data collection will involve field mapping of geologic relations; electron microprobe analyses of minerals; bulk chemical analyses of rocks; U-Pb dating of zircons by ion microprobe; and micro-Raman analyses of mineral and fluid inclusion types. These data will be used to determine pressure-temperature-time histories for the rocks; crustal fluid compositions; radiogenic heat production due to the decay of uranium, thorium, and potassium; and other geologic variables critical for hypothesis testing. The project will support and train Yale Ph.D. and undergraduate students, and integrate research results into public science outreach programs at the Yale Peabody Museum of Natural History.

在过去的二十年里，人们已经清楚地认识到，大陆地壳可以被加热到极端，？你说呢？在变质作用和造山运动期间，大面积地区的超高温（UHT）温度超过900 °C（约1650 °F）。地壳的变质岩如何达到如此极端的温度仍然是地球科学中一个基本的未解决的问题，对岩石强度，岩浆的产生（可能从深处上升产生矿床和火山爆发），热传递和地球有重大影响？的总热量预算。该项目将重点关注康涅狄格州东北部新发现的UHT岩石，这是美国发现的第一个区域性UHT地点。这些岩石在泥盆纪阿巴拉契亚山脉建造期间经历了大约1000 °C（超过1800 °F）的极端温度条件，深度至少在地表以下35公里（约22英里）。这一发现将迫使人们重新思考阿巴拉契亚山脉深处的岩石是如何形成的，并为如何达到超高温处理条件提供了新的思路。此外，岩石包含丰富的证据，以前存在的富CO2流体在100 ℃，因此可能有重要的意义，在地壳中的碳循环和长期的碳循环。超高温变质作用的基本假设将进行测试，包括：从地幔的快速折返;下冲的放射性地壳;软流圈上涌;机械应变加热;热输入来自地幔岩浆;和流体的热传递。基本数据的收集将涉及地质关系的实地测绘;矿物的电子显微探针分析;岩石的整体化学分析;用离子显微探针测定锆石的U-Pb年代;矿物和流体包裹体类型的显微拉曼分析。这些数据将用于确定岩石的压力-温度-时间历史;地壳流体成分;由于铀、钍和钾的衰变而产生的放射性热;以及对假设检验至关重要的其他地质变量。该项目将支持和培养耶鲁大学博士。和本科生，并将研究成果纳入耶鲁皮博迪自然历史博物馆的公共科学推广计划。