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，它们在地球历史的大部分时间里聚集在一起，今天的样子与第一个地质时期（太古代）结束时的样子大不相同。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，它保留了几个非常古老的地壳块（克拉通），年龄超过25亿年（局部超过40亿年），每一个都是由成群的岩浆（辉绿岩脉）横切而成的，这些岩浆侵入了更大的克拉通区域，因为这些块开始断裂和漂移。到18亿年前，由此产生的克拉通块体和它们的岩脉重新组合在一起，形成了一个新的超大陆（劳伦西亚）。对岩脉的精确测年是有用的，因为岩脉的年龄还记录了地球磁场“冻结”的时间，由此可以推断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，主要在2.5-1.8 Ga之间，涉及选定的加拿大太古宙克拉通地块（Superior， Slave和Nain省）：(1)获得不同克拉通地块上岩脉群的精确年龄，并尽可能匹配共轭集；(2)确定这些地块上岩脉群事件的范围和几何形状；(3)建立和比较不同克拉通地块上精确年代事件的原始古磁极（即使用“关键极”法）。一旦对这三个相对暴露较好的地块有了更完整的记录，就可以与世界范围内其他可能在太古宙晚期属于同类古地体的克拉通进行更有意义的比较。对这些古元古代岩脉群进行克拉通尺度的铪和钕同位素研究，将评估这些大火成岩省岩浆的假设地幔柱来源的性质。

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.