Field and Numerical Analyses of the Thermal, Mechanical, and Fluid Evolution of Extensional Detachment Zones

伸展脱离带的热、机械和流体演化的现场和数值分析

• 批准号: 0838541
• 负责人: Christian Teyssier
• 金额: $ 35万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-01 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838541&HistoricalAwards=false
• 关键词: Field; Numerical; Analyses; Thermal; Mechanical

This project is a combined field-based and numerical modeling study of the circulation of surface fluids in zones of orogenic collapse. The study focuses on extensional detachment zones that define metamorphic core complexes and are located between the brittle upper crust and the hot and commonly partially molten lower crust. Surface fluids penetrate the crust down to the detachment zones and likely play a major role in the heat transfer and deformation localization that characterize detachments. Several detachment sections along the North American Cordillera, from British Columbia to Arizona, are sampled and analyzed for microstructures, oxygen isotopic ratios, and thermochronology. These results are used as input to develop and test permeability models of the upper crust and detachment zones. Models address fluid flow from the crustal scale, where fluid circulation is a heat-transfer agent, to the grain scale where fluids interact with ductile deformation processes. This study evaluates the degree of fluid-rock interaction in detachment zones and the thermal and mechanical role of fluids in orogenic collapse. In addition, knowing the isotopic fluid composition of surface fluids promotes an evaluation of the topographic and environmental changes that took place during the collapse of the North American Cordillera in Cenozoic time.Who would think that rain water can descend 10 miles into the Earth?s crust? There is now ample evidence this is the case in regions that meet two conditions: (1) the crust is being pulled apart by the forces of tectonics, resulting in open cracks and fractures that canalize fluids; and (2) the region has a high geothermal gradient because it is heated from below by the rapid upward transfer of hot rocks and magma. These conditions promote the convective circulation of surface waters that remove heat from the crust as a radiator coolant fluid cools a car?s engine. Convective water flow is active today in regions such as the Great Basin in the southwestern United States where recharge of cool fluids and discharge of hot fluids (hot springs, mineralized areas) define hydrothermal systems. This project explores the deepest regions of fossil hydrothermal systems that formed during Cenozoic time (last 50 million years) in the North American Cordillera and that have been brought to the surface by tectonics and erosion. A combined field and modeling study of these regions helps understand how fluid circulations influence the thermal budget and the deformation of the crust. In addition, retrieving the composition of water that originated at the Earth surface at different times during the Cenozoic gives information on the topographic evolution of the Cordillera that evolved from a majestic Andean-like plateau to a dissected mountain range.

该项目是一项基于现场和数值模拟相结合的研究造山塌陷带中地表流体循环的研究。这项研究的重点是伸展拆离带，它们定义了变质核杂岩，位于脆性的上地壳和热的、通常部分熔融的下地壳之间。地表流体向下穿透地壳直到拆离带，并可能在表征拆离带的热传递和变形局部化方面发挥主要作用。从不列颠哥伦比亚省到亚利桑那州，沿北美科迪勒拉的几个滑脱剖面被取样并分析了显微结构、氧同位素比率和热年代学。这些结果被用作建立和检验上地壳和滑脱带渗透率模型的输入。模型解决了从地壳尺度到颗粒尺度的流体流动，在地壳尺度上，流体循环是一种热传递媒介，在颗粒尺度上，流体与韧性变形过程相互作用。这项研究评估了拆离带中流体-岩石相互作用的程度，以及流体在造山带崩塌中的热作用和力学作用。此外，了解地表流体的同位素流体成分有助于评估新生代北美科迪勒拉崩塌期间发生的地形和环境变化。谁会想到雨水能深入地球10英里？S地壳？现在有充分的证据表明，在满足两个条件的地区是这样的：(1)地壳正被构造力拉开，导致开放的裂缝和裂缝，使流体变成运河；(2)该地区具有很高的地温梯度，因为它被热岩和岩浆的快速向上转移从下面加热。这些条件促进了地表水的对流循环，当散热器冷却液冷却汽车S发动机时，地表水从外壳中带走热量。今天，在美国西南部的大盆地等地区，对流水流动活跃，在那里，冷流体的补充和热流体(温泉、矿化区)的排放定义了热液系统。该项目探索了北美科迪勒拉新生代时期(最后5000万年)形成的化石热液系统最深处的区域，这些系统由于构造和侵蚀而浮出地表。对这些区域的场和模拟相结合的研究有助于理解流体循环如何影响地壳的热收支和变形。此外，通过提取新生代不同时期地表水的组成，可以了解科迪勒拉山脉从雄伟的安第斯高原演变为剥离的山脉的地形演化过程。