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

在过去的二十年里，陆壳可以被加热到极端、超高？这一点已经变得很清楚。在变质作用和造山活动期间，大面积地区的气温(UHT)超过900°C(约1650°F)。地壳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悬而未决的问题，它对岩石强度、岩浆(可能从深处上升产生矿床和火山喷发)的产生、热传递和地球？S总体上的热平衡具有重要意义。该项目将专注于在康涅狄格州东北部新发现的超高温岩石，这是美国发现的第一个地区性超高温岩石。在泥盆纪阿巴拉契亚山脉建造期间，这些岩石在地表以下至少35公里(约22英里)的深度经历了大约1000摄氏度(超过1800华氏度)的极端温度条件。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条件提供了新的线索。此外，这些岩石包含了大量证据，证明以前在超高温下存在富含二氧化碳的流体，因此可能对地壳中的碳循环和长期碳循环具有重要意义。超高温变质作用的基本假设将被检验，包括：从地幔快速折返；辐射成因地壳的俯冲；软流圈上涌；机械应变加热；来自地幔岩浆的热输入；以及流体的热传递。基本数据收集将包括地质关系的实地测绘；矿物的电子微探针分析；岩石的大量化学分析；离子微探针对锆石的U-Pb测年；以及矿物和流体包裹体类型的微拉曼分析。这些数据将被用来确定岩石的压力-温度-时间历史；地壳流体成分；铀、钍和钾的衰变产生的放射性热；以及其他对假设检验至关重要的地质变量。该项目将支持和培训耶鲁大学博士和本科生，并将研究成果整合到耶鲁大学皮博迪自然历史博物馆的公共科学推广项目中。

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.