Behavior of Monazite and Zircon During Amphibolite-Facies Fluid-Rock Interaction: Implications for U-Th-Pb Geochronological Interpretations

建造一座山脉需要多长时间？地质学家现在可以解决这个基本问题，因为现代同位素技术可以以前所未有的精度确定岩石中单个矿物颗粒的年龄。随着年龄测定方法的改进，很明显，矿物可以保存数百万年甚至数十亿年时间间隔的多个地质事件的复杂记录。流体，包括富水溶液和硅酸盐熔体，在造山过程中流经地壳，携带着热量和化学物质，如温室气体（如二氧化碳）和有价值的矿石金属。在这方面，一个目前争论激烈的基本问题是：这些迁移流体是否影响了通常研究的矿物（如独居石和锆石）的U-Th-Pb同位素系统，从而提供了在造山过程中流体流过地球的实际速率和时间记录？为了解决这个问题，我们的建议寻求建立新的岩石学和地球化学标准，以确定流体渗透对独居石和锆石的形态、化学和同位素系统的影响。本文主要对南极东部纳皮尔杂岩太古宙片麻岩的早古生代变质流体—岩石相互作用带进行了电子探针、岩石化学和离子探针研究。最终，我们的发现有望确定流体渗透的完整压力-温度-时间历史，并对冈瓦纳超大陆组合的构造和年代学模型产生影响。

EAR-0001084Ague, CarsonHow long does it take to build a mountain range? Geologists can now address this basic question because modern isotopic techniques allow the ages of individual mineral grains in rocks to be determined with unprecedented accuracy. As age determination methods improve, it has become apparent that minerals may preserve a complex record of multiple geologic events separated in time by millions or even billions of years. Fluids, including water-rich solutions and silicate melts, flow through Earth's crust during mountain building, carrying with them heat and chemical species such as greenhouse gases (e.g., CO2) and valuable ore metals. In this regard, a fundamental question actively debated today is: do these migrating fluids impact the U-Th-Pb isotopic systematics of commonly studied minerals like monazite and zircon, providing a record of the actual rates and timing of fluid flow through the Earth during mountain building? To address this question, our proposal seeks to develop new petrological and geochemical criteria to identify the effects of fluid infiltration on the morphology, chemistry, and isotopic systematics of monazite and zircon. The research centers on electron microprobe, rock chemical, and ion-microprobe study of well characterized, Early Paleozoic metamorphic fluid--rock interaction zones cutting the Archaean gneisses of the Napier Complex, East Antarctica. Ultimately, our findings are expected to determine the complete pressure-temperature-time history of the fluid infiltration, and have implications for tectonic and chronological models of the assembly of the Gondwana supercontinent.