Bringing lower crustal rocks closer to the surface: testing exhumation models in the Grenville Province

让下地壳岩石更接近地表：在格伦维尔省测试折返模型

• 批准号: RGPIN-2014-04593
• 负责人: Gervais, Félix
• 金额: $ 1.89万
• 依托单位: École Polytechnique de Montréal
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=707959
• 关键词: Bringing; lower; crustal; rocks; closer

It is fascinating to think that the core-zone of mountain belts generally exposes large areas of rocks formerly located very deep in the crust (i.e.20-50 km). Understanding how these rocks were brought towards the surface, a phenomenon termed "exhumation", is one of the most challenging problem faced by geologists. It has traditionally been ascribed to extension that commonly follows relaxation of compressive stresses at the end of a mountain building phase, but a growing body of evidences indicate that rocks are transported towards the surface during the compressive stages as well. Advanced numerical models even point to complex coupling between the flow of hot and ductile rocks located deep in the core of a growing mountain belt and climate-driven surface erosion. The archetypal of this later model, commonly referred to as "channel flow", is the Himalayas, for which numerous studies have indicated a relatively good match between modeled and observed features. My research program focuses on the much more accessible Laurentians in Québec where the vestige of an ancient Himalayan-scale mountain belt, the Grenville Province, is exposed. Investigating this one billion years old mountain belt is an excellent complement for the Himalayan studies, because it has obviously completed its mountain building and vanishing phases and it exposes a much larger areas of rocks formerly located in the deep crust. The backbone of the program is a diagnostic test of exhumation models adapted to the Grenville Province from the generic test published during my doctoral studies. The scientific approach of my team, led by graduate students shouldered by undergraduate students, Canadian and international collaborators, provincial surveys, is to: 1) conduct detailed geological mapping and structural analysis of key areas; 2) date the main structures; 3) determine pressure-temperature-time paths followed by rocks across studied transects. The current research program is the first conducted in the Grenville Province to integrate geophysics, field mapping, and advanced structural analyses, with cutting-edge laboratory analyses such as phase equilibria modeling, numerical modeling of diffusion in minerals, and high-resolution U-Pb geochronology. The improved understanding of the tectonic evolution of the Grenville Province will allow for testing the validity of numerical models and, in turn, provides information on parameters needed to improve them. Along the way, publications of the advancement methods required to complete the various projects will benefit to all researchers working in high-grade rocks by providing them an efficient methodology to study these complex rocks and by giving insights into deformation and metamorphic processes taking place in the deep crust. Zooming out a bit, it is important to realize that although it has traditionally not been targeted for mineral exploration, the Grenville Province do contains interesting mineral deposits, notably in metals identified as strategic because of the urgency to meet the exponentially increasing World needs. This is most likely because they sit in complexly deformed and metamorphosed rocks, and thus requires a strategic and efficient exploration strategy, which is impossible without the kind of solid scientific foundation that this research program aims at building. Finally, the most significant impact of the proposed research program will be the formation of a future generation of high-quality field geologists, who are becoming a rarity in this world of technological advancements, but without whom such advancements would be impossible, for they provide its essential raw constituents.

令人着迷的是，山脉带的核心区通常暴露出以前位于地壳非常深(即20-50公里)的大片岩石。了解这些岩石是如何被带到地表的，这一现象被称为“掘尸”，是地质学家面临的最具挑战性的问题之一。传统上，它被归因于通常伴随着造山阶段末期压应力松弛而发生的伸展，但越来越多的证据表明，在挤压阶段，岩石也向地表输送。先进的数值模型甚至指出，位于不断增长的山带核心深处的热岩和韧性岩石的流动与气候驱动的地表侵蚀之间存在复杂的耦合。后一种模型的原型，通常被称为“河道流”，是喜马拉雅山脉，许多研究表明，模型特征和观测特征之间存在相对较好的匹配。 我的研究项目重点放在魁北克更容易接近的劳伦蒂斯人身上，那里暴露着古喜马拉雅规模的山脉地带格伦维尔省的遗迹。研究这条10亿年的古老山带是喜马拉雅研究的极好补充，因为它显然已经完成了造山和消亡阶段，它暴露了更大的以前位于地壳深部的岩石区域。该计划的主干是对适合格伦维尔省的挖掘模型进行诊断测试，该测试来自于我在博士学习期间发表的通用测试。我的团队由本科生、加拿大和国际合作者、省级调查的研究生领导，他们的科学方法是：1)对关键地区进行详细的地质填图和构造分析；2)确定主要构造的日期；3)确定所研究横断面上岩石所遵循的压力-温度-时间路径。目前的研究计划是格伦维尔省第一个将地球物理、野外测绘和高级结构分析与尖端实验室分析相结合的研究计划，如相平衡建模、矿物扩散的数值模拟和高分辨率U-Pb地质年代学。对格伦维尔省构造演化的更好了解将有助于检验数值模型的有效性，进而提供关于改进这些模型所需参数的信息。在此过程中，完成各种项目所需的推进方法的出版将为所有从事高品位岩石工作的研究人员提供一种有效的方法来研究这些复杂的岩石，并通过深入了解地壳深部发生的变形和变质过程。 稍微缩小一点，重要的是要认识到，尽管格伦维尔省传统上并不是矿产勘探的目标，但它确实拥有有趣的矿藏，特别是被确定为具有战略意义的金属，因为满足世界指数级增长的需求的紧迫性。这很可能是因为它们位于复杂变形和变质的岩石中，因此需要一个战略和有效的勘探战略，如果没有这个研究计划旨在建立的那种坚实的科学基础，这是不可能的。最后，拟议的研究计划最重要的影响将是形成下一代高素质的野外地质学家，他们在这个技术进步的世界中正变得稀有，但如果没有他们，这种进步将是不可能的，因为他们提供了必要的原始成分。