Integrating precise U-Pb geochronology and paleomagnetism: breackup, drift and reassembly of Canada's cratonic elements

整合精确的 U-Pb 地质年代学和古地磁学：加拿大克拉通元素的分裂、漂移和重组

• 批准号: 312446-2006
• 负责人: Hamilton, Michael
• 金额: $ 1.45万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2007
• 资助国家: 加拿大
• 起止时间: 2007-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=361546
• 关键词: Integrating; precise; Pb; geochronology; paleomagnetism

Canada is a collage of crustal blocks and terranes that have come together over most of Earth's history, appearing quite different today than it did by the end of the first great interval of geological time (the Archean).  My research involves the use of high-precision uranium-lead (U-Pb) geochronology to understand the detailed growth and demise of the Earth's crust and how its component parts were gradually assembled. Canada is unique in that it preserves several very old blocks of crust (cratons), older than 2.5 (and locally >4.0) billion years old - each of which are crosscut by swarms of mafic magmas (diabase dykes) that intruded larger cratonic areas as the blocks began to rift and drift apart.  By 1.8 Ga (billion years ago), the resulting reassembled organization of cratonic blocks and their dykes were swept together into a new supercontinent (Laurentia). Precise dating of mafic dykes is useful because the age also records the time when the direction of the Earth's magnetic field was 'frozen in' and from this, the paleolatitude and orientation of the dyke and its host craton can be deduced. I propose to determine Paleoproterozoic continental reconstructions, mostly between 2.5-1.8 Ga,  involving selected Canadian Archean cratonic blocks (Superior, Slave and Nain provinces) by: (1) obtaining precise ages for mafic dyke swarms on the different cratonic blocks, and matching conjugate sets, where possible, (2) identifying the extent and geometry of these events on the blocks, and (3) establishing and comparing primary paleomagnetic poles for precisely-dated events on the different cratons (i.e. using the "key pole" method).  Once a more complete record is better understood for these three relatively well exposed blocks, more meaningful comparisons can be made with other cratons worldwide that may have been kindred ancient terranes during the late Archean. A program of craton-scale hafnium and neodymium isotopic studies of these Paleoproterozoic dyke swarms will assess the nature of hypothesized mantle plume sources for these Large Igneous Province magmas.

加拿大是一个拼贴的地壳块体和块体，在地球的大部分历史中聚集在一起，今天看起来与第一个地质时间间隔（太古代）结束时完全不同。我的研究涉及使用高精度铀铅（U-Pb）地质年代学来了解地壳的详细生长和消亡以及其组成部分如何逐渐组装。加拿大的独特之处在于，它保存了几个非常古老的地壳块（地壳），年龄超过2.5岁。（局部> 40）亿年-每一个都被成群的镁铁质岩浆横切当这些块体开始断裂和漂移分开时，侵入更大的板块构造区域的（闪长岩脉）。（10亿年前），由此产生的重组组织的古陆块和他们的堤坝被席卷到一起，成为一个新的超大陆（劳伦）。基性岩脉的精确定年是有用的，因为年龄也记录了地球磁场方向被“冻结”的时间，从中可以推断出岩脉及其宿主克拉通的古纬度和方向。我建议确定古元古代大陆重建，主要是在2.5-1.8 Ga之间，包括选定的加拿大太古代古陆块（上级省、奴隶省和奈因省）：（1）获得不同板块上基性岩墙群的精确年龄，并在可能的情况下匹配共轭集，（2）确定这些板块上事件的范围和几何形状，（3）建立和比较不同古地磁体上精确定年事件的原始古地磁极（即使用“关键极”方法）。一旦对这三个相对较好出露的地块有了更完整的记录，就可以与世界上其他古地磁体进行更有意义的比较，这些古地磁体可能是太古代晚期古地磁体的亲属。这些古元古代岩墙群的铪和钕同位素研究计划将评估这些大火成岩省岩浆的假设地幔柱来源的性质。