Paleomagnetism and proterozoic dyke swarms continental configurations and evolution of the earth's core

古地磁和元古代岩脉群大陆构造和地核演化

• 批准号: 7824-2006
• 负责人: Halls, Henry
• 金额: $ 2.4万
• 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: 2007
• 资助国家: 加拿大
• 起止时间: 2007-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=363068
• 关键词: Paleomagnetism; proterozoic; dyke; swarms; continental

Mafic dykes, the remains of magma-filled fissures that once fed basaltic lava to the Earth's surface, frequently preserve a remanent or "fossil" magnetism that formed at the time of magma solidification and cooling, and from which the magnetic pole position and latitude of the dyke at the time of cooling can be calculated.  The age of the dyke, and hence its magnetization, can be obtained by precise radioactive (U-Pb) dating of primary U-bearing minerals. Proterozoic dykes of many ages between 600 and 3000 million years old, criss-cross Precambrian shields in abundance. A shield is largely composed of ancient granitic rocks  surrounded by younger mountain-belts or orogens. By virtue of their toughness the granites have helped to buttress the dykes from the effects of these orogens. The dykes, despite their great age, are therefore unusually pristine, especially in the interiors of the shields, and preserve their original mineralogy, and paleomagnetic signature. Therefore they represent the cornerstone upon which Precambrian paleomagnetic apparent polar wander paths for drifting continents are defined. Paleomagnetism  represents the only definitive way to assemble continental fragments in the Precambrian. The question of super-continent cyclicity through geological time can thus be addressed  and links made to presently dispersed continental fragments that may have economic applications, if known mineral provinces on one continent can be extended into adjoining ones. Super-continents are now  at the forefront of Earth Science enquiry with UNESCO International Geoscience Projects (Nos .417 and 509) on the existence of Proterozoic super-continents. Also an upcoming NUNA conference will highlight the role of mafic magmatism, and dykes in particular, in providing a U-Pb "bar-code" for each Precambrian fragment that may help in fitting them together (Bleeker, 2004). The proposed paleomagnetic research on Precambrian dyke swarms will contribute precisely dated reliable paleomagnetic pole positions from Canada, Greenland, India and China and thus will help in this wider global context, and also provide solutions to more local problems relating to the extent that shields have responded to the orogenic events around their margins.

镁铁质岩脉是充满岩浆的裂缝的遗迹，曾经向地球表面输送玄武岩熔岩，经常保存着岩浆凝固和冷却时形成的残余或“化石”磁性，从这些磁性可以计算出冷却时岩脉的磁极位置和纬度。通过对原生含铀矿物进行精确的放射性（U-Pb）定年，可以确定岩脉的年龄，从而确定其磁化强度。元古代的岩脉年龄在6亿到30亿年之间，纵横交错的前寒武纪护盾丰富。地盾主要由古老的花岗岩组成，周围是年轻的山带或造山带。由于它们的韧性，花岗岩有助于支撑岩脉免受造山带的影响。尽管这些岩脉年代久远，但却异常原始，尤其是在盾的内部，并保留了原始的矿物学和古磁特征。因此，它们代表了确定漂移大陆的前寒武纪古地磁视极漂移路径的基石。古地磁是唯一确定的方法来组合前寒武纪的大陆碎片。因此，地质时期的超大陆旋回问题就可以得到解决，如果一个大陆上已知的矿产省可以扩展到相邻的省，就可以与目前分散的大陆碎片建立联系，这些大陆碎片可能具有经济应用价值。超级大陆现在是联合国教科文组织国际地球科学项目（no . 5）的地球科学研究的前沿。417和509)关于元古代超大陆的存在。此外，即将召开的NUNA会议将强调岩浆活动，特别是岩脉的作用，为每个前寒武纪碎片提供U-Pb“条形码”，这可能有助于将它们组合在一起（Bleeker, 2004）。提出的对前寒武纪岩脉群的古地磁研究将提供来自加拿大、格陵兰岛、印度和中国的精确年代可靠的古地磁极位置，从而有助于在更广泛的全球背景下，并为更多与地盾对其边缘造山活动的反应程度有关的局部问题提供解决方案。