Geochronology of Bedrock-hosted Secondary Iron Oxides and Shallow Crustal Fluid-flow and Brittle Deformation Histories

基岩中次生铁氧化物的地质年代学和浅地壳流体流动和脆性变形历史

• 批准号: 1219653
• 负责人: Peter Reiners
• 金额: $ 35.05万
• 依托单位: University of Arizona
• 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: 2012-10-01 至 2016-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1219653&HistoricalAwards=false
• 关键词: Geochronology; Bedrock; hosted; Secondary; Iron

Bedrock-hosted secondary Fe-oxide minerals are practically ubiquitous in faults, fractures, and localized high porosity zones in shallow crustal rocks. Unlike primary minerals, their formation is usually the result of reactions associated with fluid migration long after formation of the host rock. Radioisotopic dates and compositional information preserved in secondary Fe-oxides have the potential to reveal much about the timing and dynamics of regional fluid flow histories, as well as processes that create high permeability zones, like brittle deformation, in bedrock. Despite their potential, bedrock-hosted secondary oxides have proven difficult to date by radioisotopic means. However, new results show that, in many cases, (U-Th)/He dating provides apparently reliable and geologically consistent dates suggesting significant potential for this approach. This project will develop methods for radioisotopic dating and geochemical characterization of bedrock-hosted secondary iron-oxide minerals and focuses primarily on (U-Th)/He geo- and thermochronology of hematite and associated iron-oxide minerals in these environments, combined with characterization of trace element and oxygen isotopic compositions of the minerals. The goal is to use dates and compositions of these secondary phases to constrain the timing and conditions of brittle deformation that created the voids in which the minerals formed, and understand the timing and conditions of fluid flow that resulted in their precipitation. This project develops these approaches in a range of geologic settings, primarily in the western U.S., where results can be compared with other geologic and geochronologic constraints.Dates and compositions of secondary iron-oxides have the potential to improve the understanding of the timing and conditions of a wide range of important processes ranging from brittle fault movement, to groundwater migration, to atmospheric conditions, to ancient episodes of bedrock exposure. This project will also provide support for continued community use of the Arizona Radiogenic Helium Dating Lab, and support for a summer student workshop on low-temperature thermochronology, allowing visiting students to perform analyses and learn how to use and interpret thermochronology in geologic research.

基岩托管的继发性氧化矿物实际上在浅层地壳岩石中的断层，断裂和局部高孔隙区域无处不在。与原代矿物不同，它们的形成通常是与液体迁移相关的反应很长时间后很长时间形成宿主岩石的结果。在次级二氧化物中保存的放射性分析日期和组成信息有可能揭示大量有关区域流体流史的时机和动态，以及在基岩中产生高渗透率区域（如脆性变形）的过程。尽管有潜力，但基岩托管的次生氧化物被证明很难通过放射性分析手段约会。但是，新的结果表明，在许多情况下，（u-th）/HE约会提供了明显可靠且在地质上一致的日期，这表明了这种方法的巨大潜力。该项目将开发用于放射性分析的方法和基岩托管的次级铁氧化矿物质的地球化学表征，并主要集中于（u-th）/血液中的（u-th）和在这些环境中相关的铁矿和相关铁氧化物矿物质的地球和热量，并结合痕量元素和氧同位素的表征。目的是使用这些次级阶段的日期和组成来限制脆性变形的时机和条件，从而造成矿物形成的空隙，并了解导致其沉淀的流体流动的时机和条件。该项目在一系列地质环境中开发了这些方法，主要在美国西部，在那里可以将结果与其他地质和地质学约束进行比较。次级铁氧化物的日子和组成有可能提高人们对从脆性断层运动到地面迁移的广泛重要过程的时间和条件的理解。该项目还将为持续社区使用亚利桑那州放射氦约会实验室提供支持，并支持对低温热量学的夏季学生讲习班，从而使来访的学生能够进行分析并学习如何在地质研究中使用和解释热量学。