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岩石的拼贴画，在地球历史的大部分时间里，这些块体和岩石聚集在一起，今天看起来与第一个地质时期（太古代）结束时大不相同。 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体，年龄超过25亿年（局部地区超过40亿年）-每个块体都被成群的镁铁质岩浆（difficult dyke）横切，当块体开始断裂和漂移时，侵入更大的地壳区域。 到了18亿年前（10亿年前），这些板块和它们的岩脉重新组合在一起，形成了一个新的超大陆（劳伦大陆）。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）建立和比较不同板块上精确定年事件的原始古地磁极（即使用“关键极”方法）。 一旦对这三个相对暴露较好的区块有了更完整的记录，就可以与世界各地可能在太古代晚期与古代古生物有亲缘关系的其他古生物进行更有意义的比较。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。

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.