Precambrian dyke swarms and their geodynamic significance

前寒武纪堤群及其地球动力学意义

• 批准号: 7824-2010
• 负责人: Halls, Henry
• 金额: $ 1.24万
• 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: 2011
• 资助国家: 加拿大
• 起止时间: 2011-01-01 至 2012-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=474287
• 关键词: Precambrian; dyke; swarms; their; geodynamic

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.

地球科学家之间正在形成一种共识，即超级大陆的重复形成及其随后的分散可能是过去30亿年来地球表面行为的基本模式。地幔对流的动力学模拟表明，两个对跖超级羽，交替增长和下降可能是负责大陆的聚合和分散。为了确定大陆在任何一个时间的位置，需要高精度的U-Pb定年和古地磁。我的研究贡献涉及后者，我描述了五个项目，正在进行的和新的。所有这些都涉及基性岩脉，裂缝沿着玄武岩岩浆一旦上升通过地壳之前凝固。岩脉大量存在，代表着大陆分裂的时期。它们在最初冷却时是地磁场方向的绝佳替代者，因此是限制大陆何时以及如何分散的重要地质单元。由于它们的方向和大小，它们也提供了洲际相关的关键单位，有助于恢复分散之前的大陆配置。所有正在研究的岩墙群都是前寒武纪的，因此它们的古地磁数据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同一广阔的位置，它们将充当某种地质网球运动员，其中大陆代表许多来回击球的球，其轨迹的复杂性通过彼此的近距离接触而体验！ 已知至少有两个例子表明，羽流中心的年龄相差数百万年，但它们在同一位置重新出现，并给出了相似的古地磁极位置。 第三个例子目前正在测试中，可能会加强大陆以“手风琴”式的方式重新占据超级羽流地点的情况。