Collaborative Research: Thermal Evolution of North American Lower Crust: U-Pb Thermochronological Constraints on the Seismic Properties of the Lithosphere

合作研究：北美下地壳热演化：U-Pb热年代学对岩石圈地震特性的约束

• 批准号: 0746246
• 负责人: Kevin Mahan
• 金额: $ 10.86万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-04-01 至 2012-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0746246&HistoricalAwards=false
• 关键词: Collaborative; Research; Thermal; Evolution; North

Thermal Evolution of North American Lower Crust: U-Pb Thermochronological Constraints on the Physical Properties of Continental LithosphereCrucial to the EarthScope initiative are the age, thermal evolution, and physical properties of North American lithosphere. The age and origin of the present-day lithospheric velocity structure deduced from seismic studies are constrained mostly by knowledge of the age, thermal history, and physical properties of the exposed continental crust. However, lower crustal rocks (from 30-45 km depth) contain a rich history that may be connected more directly to the formation and stabilization of the sub-adjacent lithospheric mantle and the North American craton. Unlike mantle rocks, a time-temperature history of the lower crust can be constrained through dating of accessory minerals with radioactive clocks that begin recording time at different temperatures (closure temperature) from 1000 degrees C to ~400 degrees C. This allows continent-scale mapping of the timescales from assembly to stabilization to tectonic reactivation and heating at a depth of greater than 30 km. Relatively slow cooling rates (0.5 degrees C/million years) at lower crustal conditions controls the closure temperature for minerals such as rutile, apatite, and titanite, allowing a time-temperature history of lower crustal to be determined over the range from 1000 degrees C to 400 degrees C. Since the temperature at the base of the crust in stable continental lithosphere is very near the closure temperatures for rutile and apatite, these minerals become remarkably sensitive monitors of perturbations to the thermal structure, including basaltic magmatism (underplating), lithospheric thinning and/or asthenospheric upwelling, as well as recording fluid flow events related to far field orogenic events. While there are limited exposures of relatively deep ancient crust in North America, xenoliths provide the only physical samples of lower crust with which to establish direct links between geophysical observation of deep crust and mantle and surface geology. Present efforts are focused on constraining the thermal history, petrologic evolution, and physical properties of the lower crust beneath North America using crustal xenoliths along a N-S trending transect from the northern Archean core of the continent southwards into the Proterozoic accretionary terranes. Additional sample suites in both Kansas and Michigan allow comparisons to samples not overprinted by younger tectonic and thermal events associated with the Cordilleran margin. Examining the thermal evolution of lithosphere from the Archean core of the continent to younger accretionary belts are giving earth scientists a new understanding of the rates associated with continental assembly, and stabilization, as well as providing new insights into the age of thermal and tectonic events that have affected the lithosphere and its thermal structure. Integration of these data with new high-resolution seismic data has the potential to revolutionize our understanding of formation of the North American continent.

北美下层地壳的热进化：U-PB对大陆岩石裂核对地球史倡议的物理特性的热量限制是北美岩石圈的年龄，热进化和物理特性。从地震研究中得出的当今岩石圈速度结构的年龄和起源主要受到暴露大陆壳的年龄，热历史和物理特性的了解。 但是，下层岩石（从30-45 km的深度）包含丰富的历史，可以更直接地与亚腹部岩石圈地幔和北美克拉通的形成和稳定相关。与地幔岩不同，下层地壳的时间温度历史可以通过与放射性时钟的辅助矿物进行约会来限制，这些矿物是在不同温度（封闭温度）开始记录时间（封闭温度）从1000 c到〜400度的时间。这允许从组装到稳定性的稳定量化和诱导量的时间表范围内的大陆大规模映射到更大的量化和诱导量，并供应量高于稳定量。 在较低的地壳条件下，相对缓慢的冷却速率（0.5度C/百万年）控制矿物质（如金红石，磷灰石和钛矿）的闭合温度，允许在1000度至400度的范围内确定较低地壳的时间温度的历史。这些矿物质成为对热结构的扰动的非常敏感的监测器，包括玄武岩岩浆（低估），岩石圈稀薄和/或软磷酶上升，以及记录与远处造影剂事件有关的流体流动事件。尽管在北美的相对古老的地壳的暴露量有限，但异种石提供了唯一的较低地壳的物理样本，以建立对地壳，地壳和地幔和表面地质的地球物理观察之间的直接联系。目前的努力集中在沿着N-S趋势层面从非洲大陆北部核心向南进入protererogiac增值底的N-S趋势样带，沿着N-S趋势层面沿着N-S趋势层面来限制北美下皮下的热史，岩石学演化和物理性质。堪萨斯州和密歇根州的其他样品套件都可以比较与与山脉边缘相关的年轻构造和热事件所没有覆盖的样品。 检查岩石圈从大陆的大国核心到年轻的增生带的热演化，使地球科学家对与大陆装配和稳定相关的速率有了新的了解，并提供了对影响岩石圈及其热结构的热和构造事件时代的新见解。 这些数据与新的高分辨率地震数据的整合有可能彻底改变我们对北美大陆形成的理解。