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.

地球目前正在通过全球板块构造 (GPT) 进行对流，这是迄今为止在所有已知行星体中独一无二的机制，在 GPT 中，地球的刚性外壳（岩石圈）被分解成沉入地球内部的板块。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，并且对金属矿床的聚集发挥了控制作用，但我们不知道如何以及何时进行。 GPT 是否开始演化？如果是的话，如何演化？为了回答这些基本问题，俯冲带（GPT 的主要表现形式）是主要目标。然而，地球目前所有活跃的俯冲带都位于海平面以下。此外，即使是最古老的活跃俯冲带也相对年轻，仅在我们认为 GPT 活跃的时期的最后 10% 才开始。的记录古老的、灭绝的俯冲系统作为蛇绿岩保存在洲际缝合带中，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地质调查，这些档案也涵盖了地球历史的很大一部分。因此，该研究计划的具体目标是限制导致俯冲带启动的过程，并调查这些过程是否从那时起就开始演化。为了做到这一点，我的研究小组将研究三个年龄对比的化石俯冲系统：努纳维克昂加瓦半岛 20 亿年前的蛇绿岩、纽芬兰阿巴拉契亚山脉 4.85 亿年前的蛇绿岩和魁北克，以及青藏高原 170 至 1.3 亿年前的蛇绿岩，我的研究小组将利用我们最近的研究成果。科学突破并限制了最初的下板块埋藏时间，以揭示俯冲起始的时间和模式。 事实上，一些蛇绿岩下面是非常重要的岩石，称为变质底，代表了地幔中沉没的第一个物质的残余物。我们表明，我们可以通过测定这些变质底部石榴石的生长来限制俯冲起始的时间，并推断俯冲起始的机制。通过与上覆蛇绿岩的年龄进行比较，记录全球所有年龄的化石俯冲系统中编码的俯冲起始的地球动力学环境和机制，将有助于确定 GPT 构造在地球上开始的时间和原因（如果它已经进化）。需要回答这些问题，以便我们了解我们的行星是如何运作的、是什么让它如此独特、GPT 与生命的联系有多紧密，以及是什么控制着矿物质的分布。资源。