Collaborative Research: Using Well-dated Paleomagnetic Poles from the Kalahari and Congo Cratons to Constrain Rodinia Configurations and the Assembly of Central Gondwana

一个由美国和非洲科学家组成的合作小组正在从非洲大陆的两个主要组成部分——非洲中部和南部的刚果和喀拉哈里克拉通（纳米比亚和坦桑尼亚）——获取约束良好的古地磁极。这两个研究区都含有各种各样的火成岩，这些火成岩位于8.5 -7亿年前，这是地球历史上一个关键的时间框架。在此期间，古罗迪尼亚超大陆开始分裂，为随后大陆块的重新排列奠定了基础，形成了更年轻的冈瓦纳超大陆。该小组正在对卡拉哈里和刚果克拉通中选定的岩石单元的大量样品进行古地磁研究，以限制两个克拉通在罗迪尼亚分裂期间和冈瓦纳合并之前的原始相对位置。这项工作与一个详细的同位素测年程序相结合，旨在对岩石的磁化年龄产生严格的限制，并确定初级磁化是否受到后续热事件的干扰。刚果和喀拉哈里克拉通形成了冈瓦纳中部的基石，大约5.5亿年前，随着当今南部大陆不同部分的碰撞，冈瓦纳中部形成。从两个克拉通获得年代久远的极点，将允许测试冈瓦纳组合的相互竞争的模型：在冈瓦纳形成之前，刚果和卡拉哈里克拉通是被一个广阔的海洋盆地分开的，还是这两个克拉通已经大致处于它们现在的相对位置。后一种情况意味着冈瓦纳大陆的中心部分是从早期的罗迪尼亚超大陆继承而来的，而人们对后者知之甚少。该项目本质上是合作性的，涉及美国德克萨斯基督教大学、麻省理工学院、德克萨斯大学奥斯汀分校、南非开普敦大学、纳米比亚地质调查局和坦桑尼亚达累斯萨拉姆大学的工作人员。来自美国和非洲的学生都参与了现场和实验室工作。

A collaborative team of U.S. and African scientists are acquiring well-constrained paleomagnetic poles from two of the major building blocks of the African continent, the Congo and Kalahari cratons in central and southern Africa (Namibia and Tanzania). Both study areas contain a variety of igneous rocks emplaced 850-700 million years ago, which is a critical time frame in Earth history. During this interval, the ancient supercontinent of Rodinia was beginning to break apart, setting the stage for subsequent rearrangement of continental land masses to form the younger Gondwana supercontinent. The team is carrying out paleomagnetic studies on an extensive suite of samples from selected rock units in the Kalahari and Congo cratons in order to constrain the original relative positions of the two cratons during breakup of Rodinia and prior to assembly of Gondwana. This work is coupled with a detailed program of isotopic dating, designed to produce rigorous constraints on the age of magnetization in the rocks and to determine whether the primary magnetization has been disturbed by subsequent thermal events. The Congo and Kalahari cratons formed the keystone of central Gondwana, which was assembled about 550 million years ago as different parts of the present-day southern continents collided. Acquisition of well-dated poles from both cratons will allow testing of competing models for Gondwana assembly: were the Congo and Kalahari cratons separated by a wide ocean basin before formation of Gondwana or were the two cratons already in roughly their present-day relative positions. The latter scenario would imply that the central part of Gondwana was inherited from the earlier Rodinia supercontinent, about which little is known. The project is collaborative in nature and involves workers at Texas Christian University, Massachusetts Institute of Technology, and the University of Texas at Austin in the US, and at the University of Cape Town in South Africa, the Geological Survey of Namibia, and the University of Dar es Salaam in Tanzania. Students from both the US and Africa are involved in the field and laboratory work.