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: 2012
• 资助国家: 加拿大
• 起止时间: 2012-01-01 至 2013-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=507554
• 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.

地球科学家正在形成一种共识，即超级大陆的反复形成和随后的扩散可能是过去3000万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，两个交替增长和下降的对极超级热柱可能是大陆聚集和扩散的原因。为了在任何一个时间限制大陆的位置，既需要高精度的U-Pb年龄测定，也需要结合古地磁。我的研究贡献与后者有关，我描述了五个项目，包括正在进行的项目和新的项目。所有这些都涉及镁铁质岩墙，即玄武岩岩浆在凝固之前曾沿着其上升穿过地壳的裂隙。大量的岩墙被发现，它们代表着大陆解体的时代。它们在原始冷却时极好地保持了地磁场的方向，因此是限制大陆何时以及如何分散的重要地质单位。由于它们的方位和大小，它们还为洲际对比提供了关键单位，有助于在扩散之前恢复大陆配置。所有被研究的岩墙群在年龄上都是前寒武纪的，因此他们的古地磁数据与泛古大陆之前存在的超大陆有关。如果反足羽状物再次出现在同一广阔的位置，他们将扮演某种地质网球运动员的角色，在那里，大陆代表着许多被来回击打的球，它们轨迹的复杂性通过彼此的近距离接触来体验！至少有两个已知的例子表明，羽流中心的年龄相差100亿年的S，它们在同一地点重现，给出了相似的古地磁磁极位置。第三个例子目前正在测试中，可能会强化大陆以一种类似于“协奏曲”的方式重新占据超强羽状物位置的理由。