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

基性岩墙是曾经将玄武岩熔岩输送到地球表面的充满岩浆的裂隙的遗迹，通常保存着岩浆凝固和冷却时形成的残余或“化石”磁性，由此可以计算出岩墙在冷却时的磁极位置和纬度。通过对原始含铀矿物进行精确的放射性(U-Pb)测年，可以获得岩墙的年龄和磁化程度。元古代岩墙的年龄在6亿到3000万年之间，交错的前寒武纪屏蔽丰富。盾构主要由古老的花岗岩组成，周围环绕着较年轻的山带或造山带。花岗岩凭借其韧性，帮助加固了堤坝，使其免受造山带的影响。因此，尽管这些岩墙年代很长，但它们异常原始，特别是在地盾的内部，并保存了它们原始的矿物学和古地磁特征。因此，它们代表了前寒武纪古地磁漂移大陆的视极游路径的基石。古地磁学是在前寒武纪组装大陆碎片的唯一确定方法。因此，如果一个大陆上的已知矿产省可以延伸到相邻的大陆上，则可以通过建立与目前分散的大陆碎片的联系来解决地质时代的超大陆旋回性问题，这些大陆碎片可能具有经济应用价值。超级大陆现在处于地球科学研究的前沿，联合国教科文组织关于元古代超级大陆存在的国际地球科学项目(编号417和509)。此外，即将召开的努纳会议将突出镁铁质岩浆作用，特别是岩墙的作用，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拼接在一起(Bleeker，2004)。拟议的关于前寒武纪岩墙群的古地磁研究将有助于确定加拿大、格陵兰、印度和中国的准确可靠的古地磁极点位置，从而将在这一更广泛的全球背景下提供帮助，并为与地幔对其边缘造山事件的响应程度有关的更多局部问题提供解决方案。

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.