Precambrian dyke swarms and their geodynamic significance

地球科学家正在形成一种共识，即超级大陆的反复形成及其随后的扩散可能是过去30亿年地球表面行为的基本模式。地幔对流动力学模拟表明，两个对跖超级羽流交替增长和下降，可能是大陆聚集和分散的原因。为了确定大陆在任何时候的位置，高精度的U-Pb年龄定年和古地磁都是必要的。我的研究贡献与后者有关，我描述了五个正在进行和新的项目。所有这些都与基性岩脉有关，这些裂缝是玄武岩岩浆在凝固前从地壳中升起的裂缝。大量的堤坝代表着大陆分裂的时期。它们很好地保存了它们最初冷却时的地磁场方向，因此是限制大陆何时以及如何分散的重要地质单位。由于它们的方向和大小，它们也提供了大陆间对比的关键单元，有助于恢复大陆在分散之前的形态。所研究的岩脉群年龄均为前寒武纪，因此它们的古地磁资料与盘古大陆之前存在的超大陆有关。如果对跖羽流再次出现在相同的广泛位置，它们将扮演某种地质网球运动员的角色，其中大陆代表许多来回击打的球，它们的轨迹因彼此近距离接触而变得复杂！至少有两个已知的例子表明，羽流中心的年龄相差几亿年，但它们在同一位置重新出现，并给出了相似的古磁极位置。第三个例子目前正在测试中，可能会加强大陆以“手风琴”式的方式重新占领超级羽流地点的情况。

A consensus is emerging among geoscientists that the repeated formation of supercontinents and their subsequent dispersal may be a fundamental pattern in the behavior of the Earth's surface for the last 3000 million years. Dynamic modeling of mantle convection suggests that two antipodal super-plumes, which alternately grow and decline may be responsible for continental aggregation and dispersal. In order to place limits on the location of continents at any one time, both high precision U-Pb age dating together with paleomagnetism is required. My research contribution concerns the latter and I describe five projects, both ongoing and new. All of them involve mafic dykes, fissures along which basaltic magma once rose through Earth's crust before solidifying. Dykes are found in enormous swarms and represent times of continental break-up. They are excellent preservers of the geomagnetic field direction at the time of their original cooling and therefore are important geological units to constrain when and how continents have dispersed. Because of their orientation and size,they also provide key units for inter-continental correlation that help restore continental configurations prior to dispersal. All the dyke swarms being studied are Precambrian in age so that their paleomagnetic data are relevant to supercontinents that existed before Pangea. If antipodal plumes re-occur in the same broad location, they would act as sort of geological tennis players in which the continents represent many balls that are being hit back and forth, with complexities in their trajectories being experienced by close encounters with each other! At least two examples are known of plume centres differing in age by 100's of millions of years, that have reappeared in the same location and which give similar paleomagnetic pole positions. A third example is presently being tested and may strengthen the case for continents re-occupying superplume sites in a "concertina"-like fashion.