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

加拿大是地壳块体和地体的拼贴画，它们在地球历史的大部分时间里聚集在一起，今天看起来与第一个地质时代(太古宙)结束时的样子截然不同。我的研究涉及使用高精度的铀铅(U-Pb)年代学来了解地壳的详细生长和消亡，以及它的组成部分是如何逐渐组装的。加拿大的独特之处在于，它保存了几块非常古老的地壳(克拉通)，年龄超过25亿年(当地为40亿年)--每一块都被大量的镁铁质岩浆(辉绿岩墙)横切，随着这些块开始裂解和漂移，侵入更大的克拉通地区。到1.8Ga(10亿年前)，克拉通块和它们的岩墙重新组合在一起，一起被扫入一个新的超级大陆(劳伦斯)。镁铁质岩墙的精确测年是有用的，因为该年龄还记录了地球磁场的方向被冻结的时间，由此可以推断出岩墙及其宿主克拉通的古纬度和方位。我建议确定古元古代大陆重建，主要是在2.5-1.8Ga之间，涉及选定的加拿大太古代克拉通地块(高级、从属和内恩省)，方法是：(1)获得不同克拉通地块上镁铁质岩墙群的准确年龄，并在可能的情况下匹配共轭集合，(2)确定这些地块上这些事件的范围和几何形状，以及(3)建立和比较不同克拉通上精确测年事件的原始古地磁极(即使用“关键极”方法)。一旦对这三个相对暴露得较好的地块有了更完整的记录，可以与世界各地的其他克拉通进行更有意义的比较，这些克拉通可能是太古宙晚期的古老地体的同类。对这些古元古代岩墙群进行克拉通规模的Hf和Nd3+同位素研究，将评估这些大型火成岩省岩浆假设的地幔热柱来源的性质。

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.