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.

由于地球历史这个时代保存下来的岩石样本稀缺，我们对地球早期演化的了解非常有限。关于原始地球的大多数信息都来自对在西澳大利亚更年轻的沉积物中发现的距今约 44 亿年前的碎屑锆石的研究。 地球表面现存最古老的岩石样本年龄在 4.0 至 37 亿年前之间，这使得我们星球历史的前 5 亿年在岩石记录中没有得到体现。因此，地球早期地壳的性质及其形成过程在很大程度上仍然是猜测。最近使用 142-Nd（一种对 40 亿年前岩石形成特别敏感的同位素工具）进行的研究表明，来自魁北克北部 Nuvvuagittuq 地体的岩石已有 44 亿年的历史。因此，这些岩石代表了地球上最古老的岩石。然而，这个地体只是地壳的一小部分，对其他古老地壳地体的研究对于了解第一批大陆是如何以及何时形成的至关重要。该提案寻求资金来支持针对古代地形的研究。他们的研究将有助于限制早期地球的演化以及原始地壳形成的地质过程。这项研究将重点关注三个古老的加拿大地体：1) 萨格莱克片麻岩杂岩（拉布拉多），这是一个由岩石组成的地体，其历史长达 38 亿年。该区域的特征相对较少，其随时间的精确演变在很大程度上是未知的。 2) 中央奴隶地下室综合体（西北地区）由大约 40 亿年前的岩石组成，称为阿卡斯塔片麻岩。阿卡斯塔片麻岩是由较古老的玄武岩融化而形成的花岗岩形成的。对这一地区玄武岩的进一步研究可以识别出阿卡斯塔片麻岩的更古老的前体。 3) Nuvvuagittuq 绿岩带（魁北克省安加瓦半岛）被解释为代表地球上保存最古老的地壳。该领域的研究将有助于更好地限制早期地壳形成的地质过程，也可能导致识别该地区保存更完好的早期地壳碎片。