Geochemical characterization and geochronology of Earth's primitive crust

地球原始地壳的地球化学特征和年代学

• 批准号: 435589-2013
• 负责人: ONeil, Jonathan
• 金额: $ 2.33万
• 依托单位: University of Ottawa
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2018
• 资助国家: 加拿大
• 起止时间: 2018-01-01 至 2019-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=661211
• 关键词: Geochemical; characterization; geochronology; Earth; primitive

Our knowledge of the Earth's early evolution is very limited due to the scarcity of preserved rock samples from this era of Earth history. Most information on the primitive Earth comes from the study of detrital zircons dated at ~4.4 billion years old found in much younger sediments in Western Australia. The oldest surviving rock samples available at the surface of the Earth are between 4.0 and 3.7 billion years old, leaving the first 500 million years of our planet's history unrepresented in the rock record. Therefore the nature of the Earth's early crust and the processes responsible for its formation remain largely speculation. Recent work using 142-Neodymium, an isotopic tool particularly sensitive to rock formation prior to 4 billion years old, suggests that rocks from the Nuvvuagittuq terrane in Northern Quebec are as old as 4.4 billion years. These rocks would therefore represent the oldest rock on Earth. This terrane is however only a very small portion of crust and the study of other old crustal terranes is critical in order to understand how and when the first continents formed. This proposal seeks funding to support research focused on ancient terrains. Their study will help to constrain the evolution of the early Earth and the geological processes responsible for the formation of the primitive crust. This research will focus on three ancient Canadian terranes: 1) The Saglek Gneiss Complex (Labrador) which is a terrane comprising rocks as old as 3.8 billion years. This area is still relatively uncharacterized and its precise evolution through time is largely unknown. 2) The Central Slave Basement Complex (Northwest Territories) comprises rocks dated at ~4 billion years called the Acasta gneisses. The Acasta gneiss formed from granitic rocks derived by the melting of older basaltic rocks. Further investigation of basaltic rocks in this area could allow the identification of an older precursor to the Acasta gneisses. 3) The Nuvvuagittuq Greenstone Belt (Ungava peninsula, Quebec) is interpreted to represent the oldest preserved crust on Earth. Research in this area will help to better constrain the geological processes responsible for early crust formation and could also lead to the identification of more preserved fragments of early crust in this region.

由于这个地球历史时代的保存岩石样本稀缺，我们对地球早期进化的了解非常有限。关于原始地球的大多数信息来自对西澳大利亚州年轻的沉积物中约44亿年龄的碎屑锆石的研究。 地球表面上可用的最古老的幸存岩石样品在40至37亿年之间，使我们地球历史的前5亿年没有代表摇滚记录。因此，地球早期地壳的性质和导致其形成的过程仍然在很大程度上是猜测。最近使用142-Neodymium的工作是一种在40亿年前对岩石形成特别敏感的同位素工具，这表明来自魁北克北部Nuvvuagittuq Terrane的岩石年龄高达44亿年。因此，这些岩石将代表地球上最古老的岩石。但是，这个地层只是地壳的一小部分，对其他旧地壳地层的研究对于了解第一洲的形成方式和何时形成至关重要。该提案寻求资金支持关注古代地形的研究。他们的研究将有助于限制地球早期的演变以及导致原始地壳形成的地质过程。这项研究将重点关注三个古代加拿大地形：1）萨格尔克片麻岩综合体（拉布拉多），它是一个岩石，占地38亿年。该区域仍然相对未表征，其精确的演变在很大程度上是未知的。 2）中央奴隶地下综合体（西北地区）包括约40亿年的岩石，称为Acasta Gneisses。阿卡斯塔片麻岩是由较老的玄武岩融化得出的花岗岩岩石形成的。进一步研究该地区的玄武岩可以识别出较旧的前体，以鉴定出Acasta片麻岩。 3）Nuvvuagittuq绿石带（魁北克省UNGAVA半岛）被解释为代表地球上最古老的保存壳。在这一领域的研究将有助于更好地限制负责早期地壳形成的地质过程，也可能导致鉴定该地区早期地壳的更加保存的碎片。