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: 2019
• 资助国家: 加拿大
• 起止时间: 2019-01-01 至 2020-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=681388
• 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，山脉的核心地带通常暴露出以前位于地壳深处（即20 -50公里）的大面积岩石。了解这些岩石是如何被带到地表的，这种现象被称为“折返”，是地质学家面临的最具挑战性的问题之一。它传统上被归因于通常在造山阶段结束时压缩应力松弛之后的伸展，但越来越多的证据表明，岩石在压缩阶段也被搬运到地表。先进的数值模型甚至指出，位于不断增长的山脉带核心深处的高温和韧性岩石流动与气候驱动的表面侵蚀之间存在复杂的耦合关系。后来的模型，通常被称为“通道流”的原型，是喜马拉雅山，许多研究表明，一个相对较好的匹配模型和观察到的功能。** 我的研究项目集中在魁北克省更容易到达的劳伦特人，那里有一个古老的喜马拉雅山脉带的遗迹，格伦维尔省，暴露出来。对这条有10亿年历史的山脉带的调查是对喜马拉雅山脉研究的一个很好的补充，因为它显然已经完成了它的造山和消失阶段，并且暴露了以前位于地壳深处的更大面积的岩石。该计划的骨干是一个诊断测试挖掘模型适应格伦维尔省从通用测试发表在我的博士研究。我的团队的科学方法，由本科生，加拿大和国际合作者，省级调查的研究生领导，是：1）进行详细的地质测绘和关键区域的结构分析; 2）确定主要结构的日期; 3）确定压力-温度-时间路径，然后通过研究横断面的岩石。目前的研究计划是在格伦维尔省进行的第一个整合地球物理学，现场测绘和先进的结构分析，与尖端的实验室分析，如相平衡建模，矿物扩散的数值模拟，和高分辨率的U-Pb地质年代学。对格伦维尔省构造演化的进一步了解将有助于检验数值模型的有效性，并进而提供改进模型所需参数的信息。沿着这条道路，完成各种项目所需的先进方法的出版物将有利于所有研究高级岩石的研究人员，为他们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。** 缩小一点，重要的是要认识到，虽然格伦维尔省传统上不是矿产勘探的目标，但它确实含有有趣的矿藏，特别是被确定为战略性的金属，因为迫切需要满足呈指数增长的世界需求。这很可能是因为它们位于复杂的变形和变质岩石中，因此需要一个战略性和有效的勘探策略，如果没有本研究计划旨在建立的坚实的科学基础，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未来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越来越罕见，但没有他们，这种进步是不可能的，因为他们提供了必要的原始成分。