Early evolution of the middle crust in continental collisions

大陆碰撞中地壳的早期演化

• 批准号: RGPIN-2020-05916
• 负责人: SoucyLaRoche, Renaud
• 金额: $ 1.82万
• 依托单位: Institut national de la recherche scientifique
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2022
• 资助国家: 加拿大
• 起止时间: 2022-01-01 至 2023-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=751373
• 关键词: Early; evolution; middle; crust; continental

Large-hot orogens form following continent-continent collision as a result of significant thickening of the lithosphere and melt weakening of the middle crust (15-40 km depth). Melt weakening facilitates lateral spreading at depth, controls the topographic relief and climate at surface, affects magma and fluid migration in the crust, and influence orogenic architecture. The transition from thin, small and cold orogenic wedges dominated by mechanical deformation processes to thick, large and hot orogenic plateaus dominated by thermomechanical deformation processes is poorly documented and forms a major knowledge gap in tectonic research. The development of the melt-weakened middle crust during the early stages of orogenesis can be targeted in specific structural settings and is the primary objective of this proposal. Mid-crustal rocks that are exhumed to the surface during or after continent-continent collisions preserve crucial constraints on the state of the middle crust during orogenesis. Numerical models based on rocks exposed in the present-day hinterland (main mountain belt) of orogens provide much of our understanding of mid-crustal thermal and mechanical properties. However, these rocks rarely preserve any information on the initial stages of continental collision because they are generally overprinted by subsequent metamorphic events. In this proposal, I hypothesize that far-travelled, high metamorphic grade external nappes transported closer to the foreland (front) are exhumed early during the collision evolution, and that such rocks are more likely to record the early stages of continental collision. Two iconic large-hot orogens are targeted by this proposal: the well-characterized active Himalaya of Nepal and India, where early exhumation of mid-crustal units in the foreland is known, and the old Grenville (i.e. the current Laurentides in Québec), where, in comparison, scarce modern petrochronologic and metamorphic studies have been conducted. The Grenville (> 1 billion years old) offers the opportunity to compare Himalayan geodynamic models to a continental collision that evolved to completion. HQP-led projects, including fieldwork and newly available, multifaceted cutting-edge laboratory investigations, will reconstruct the pressure-temperature-time-deformation path and characterize the nature of early-stage metamorphic rocks involved in these two orogens. This research program will provide robust constraints on mid-crustal properties (temperature, pressure, structure) following initial collision. This is fundamental to understand how convergence is accommodated at continent-continent tectonic plate boundaries, how material is transported within the crust, and how the middle crust contributes to shape the earth surface. These refinements to plate tectonic theory provide the necessary foundation for a critical examination of numerical models of continental collision and feedback effects between geological and surface processes.

由于岩石圈的显着增厚和融化的中层外壳（15-40 km深度），大陆大陆碰撞后发生了大热的牛根。融化减弱会促进深度侧面扩散，控制地表的地形浮雕和气候，影响地壳中的岩浆和流体迁移，并影响造山学结构。从机械变形过程主导的薄，小和冷造型的楔形到以热机械变形过程为主的厚，大且热的造山下的平台的过渡很差，并在构造研究中构成了主要的知识差距。在造成造成的早期阶段，融化的中壳的发展可以针对特定的结构环境，是该提案的主要目标。在大陆大陆碰撞期间或之后被挖出到表面的中壳岩石在造山机发生过程中对中壳状态保持着关键的约束。基于在当今腹地（主要山带）斑块中暴露的岩石的数值模型提供了我们对中壳中心热和机械性能的大部分理解。但是，这些岩石很少保留有关连续碰撞初始阶段的任何信息，因为它们通常被随后的变质事件所覆盖。在该提议中，我假设在碰撞演化期间早期挖掘出了远距离传输的高变质级外部纳普（前），并且这种岩石更有可能记录持续碰撞的早期阶段。该提议的目标是两个标志性的大型牛根：尼泊尔和印度的主动主动性喜马拉雅山脉，在那里已知陆地中的中壳单元的早期挖掘出来，以及古老的格伦维尔（即Québec目前的劳伦德斯），相比之下，现代的烟素学研究和梅特罗尔奇研究一直是较低的。格伦维尔（> 10亿年历史）提供了将喜马拉雅地球动物模型与不断发展为完成的连续碰撞进行比较的机会。 HQP领导的项目，包括现场工作和新的多方面的尖端实验室调查，将重建压力 - 温度的时间通知路径，并表征这两个植物涉及的早期变质岩石的性质。该研究计划将在初始碰撞后对中壳特性（温度，压力，结构）提供强大的限制。这是了解如何在大陆被构造板板边界，如何在外壳内运输的材料以及中层外壳如何促进地球表面形状的融合，这是至关重要的。这些对板块构造理论的改进为对地质和表面过程之间连续碰撞和反馈效应的数值模型的批判性研究提供了必要的基础。