Fossil Subduction Systems and the Evolution of Plate Tectonics

化石俯冲系统和板块构造的演化

• 批准号: RGPIN-2020-06400
• 负责人: Guilmette, Carl
• 金额: $ 3.13万
• 依托单位: Université Laval
• 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=755011
• 关键词: Fossil; Subduction; Systems; Evolution; Plate

The Earth is currently convecting through Global Plate Tectonics (GPT), a regime that is so far unique amongst all known planetary bodies. In GPT, the Earth's rigid outer shell, the lithosphere, is broken into plates that sink in the planet's interior, a process called subduction. We know that GPT played an important role in the emergence and sustainability of life, and exerts a control on the foci of metals as ore deposits. Yet we don't know how and when GPT began, whether it evolved since its onset, and if so how? To answer such fundamental questions, subduction zones, the main manifestation of GPT, are prime targets. However, all of the Earth's currently active subduction zones are under sea level, making the direct study of their rock record difficult. Moreover, even the oldest active subduction zones is relatively young, having initiated only in the last 10% of the period we think GPT was active. As an alternative, my research program aims at deciphering the geological record of ancient, extinct subduction systems preserved onland as ophiolites in intercontinental suture zones. These fossil subduction systems are exposed in mountain ranges, and are thus fully accessible for direct geological investigation of their rock record. These archives also cover a large portion of the Earth's history, potentially reaching as far back as the onset of GPT. The specific objectives of this research program are thus to constrain the processes leading to the initiation of subduction zones and to investigate whether these processes evolved since the onset of GPT. In order to do so, my research group will study three fossil subduction systems of contrasting age: the 2.0 billion years old ophiolite of the Ungava Peninsula, Nunavik, the 485 million years old ophiolites of the Appalachian mountains in Newfoundland and Québec, and the 170 to 130 million years old ophiolites of the Tibetan Plateau. My research group will take advantage of our recent scientific breakthrough and constrain the timing of initial lower plate burial in order to reveal the timing and mode of subduction initiation. Indeed, some ophiolites are underlain by very important rocks termed metamorphic soles, representing remnants of the very first material that sank in the mantle when the subduction zone nucleated. We showed that we can constrain the timing of subduction initiation by dating the growth of garnet in these metamorphic soles, and infer a mechanism for subduction initiation by comparing with the age of the overlying ophiolite. Documenting the geodynamic settings and mechanisms leading to subduction initiation encoded in fossil subduction systems of all ages across the globe will contribute to constraining when and why GPT tectonics began on Earth, if it has evolved, and how. Such questions need to be answered in order for us to understand how our planets work, what makes it so unique, how strongly are GPT and life linked, and what controlled the distribution of mineral resources.

地球目前正通过全球板块构造（GPT）对流，这是迄今为止所有已知行星体中唯一的一种机制。在GPT中，地球坚硬的外壳，岩石圈，被打破成板块，沉入行星的内部，这个过程称为俯冲。我们知道，GPT在生命的出现和可持续性方面发挥了重要作用，并对金属矿床的焦点施加控制。然而，我们不知道GPT是如何以及何时开始的，它是否从一开始就进化了，如果是的话，又是如何进化的？要回答这些基本问题，俯冲带，GPT的主要表现，是主要目标。然而，地球目前所有活跃的俯冲带都在海平面以下，这使得直接研究它们的岩石记录变得困难。此外，即使是最古老的活动俯冲带也相对年轻，仅在我们认为GPT活动的最后10%期间才开始。作为一种替代方案，我的研究计划旨在破译古老的地质记录，灭绝俯冲系统保存在陆地上作为蛇绿岩在洲际缝合带。这些化石俯冲系统暴露在山脉中，因此完全可以对其岩石记录进行直接的地质调查。这些档案还涵盖了地球历史的很大一部分，可能可以追溯到GPT的开始。因此，本研究计划的具体目标是限制导致俯冲带开始的过程，并调查这些过程是否自GPT开始演变。为了做到这一点，我的研究小组将研究三个年龄相差悬殊的化石俯冲系统：努那维克昂加瓦半岛的20亿年前的蛇绿岩，纽芬兰和魁北克阿巴拉契亚山脉4.85亿年前的蛇绿岩，以及青藏高原1.7亿至1.3亿年前的蛇绿岩。我的研究小组将利用我们最近的科学突破，限制初始下板块埋藏的时间，以揭示俯冲开始的时间和模式。事实上，一些蛇绿岩的下面是非常重要的岩石，称为变质底，代表着俯冲带成核时沉入地幔的第一批物质的残余。我们发现，我们可以限制俯冲开始的时间，通过测年的石榴石在这些变质鞋底的生长，并推断俯冲开始的机制，通过与上覆蛇绿岩的年龄比较。记录地球动力学背景和机制，导致俯冲开始编码在所有年龄的化石俯冲系统在地球仪将有助于限制何时和为什么GPT构造开始在地球上，如果它已经演变，以及如何。这些问题需要得到回答，以便我们了解我们的行星是如何工作的，是什么使它如此独特，GPT和生命的联系有多紧密，以及是什么控制了矿产资源的分布。