Testing Pangea Reconstructions with New Late Permian - Early Triassic Paleomagnetic Studies

用新的晚二叠世-早三叠世古地磁研究测试盘古大陆重建

• 批准号: 0634807
• 负责人: Rob Van der Voo
• 金额: --
• 依托单位: Regents of the University of Michigan - Ann Arbor
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-04-01 至 2011-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0634807&HistoricalAwards=false
• 关键词: Testing; Pangea; Reconstructions; New; Late

Pangea, as it existed in late Paleozoic and early Mesozoic time, consisted of a northern group of continents (Laurasia, comprised of North America, Greenland, Europe and Asia) and the southern Gondwana assembly, which includes South America, Africa, Australia, Madagascar, India, and Antarctica. It is generally assumed that in Pangea, Gondwana's Northwest-African margin was adjacent to North America's Appalachian margin; this reconstruction is called Pangea-A. However, for times before the Late Triassic the available data from paleomagnetism derived from Gondwana and Laurasia do not agree well with the Pangea-A fit, which have led scientists to either question the validity of these data or to propose a different fit, called Pangea-B. The main problem with the Pangea-B reconstruction is that everyone agrees that by Late Triassic time, the fit was that of Pangea-A, which implies that Pangea-B transformed into Pangea-A in Permian or Triassic time. The relative movements to accomplish this change consist of a surprisingly large 3500-km or greater dextral mega-shear between Gondwana and Laurasia. For such a mega-shear, little geological evidence exists, and geologists have therefore ignored the Pangea-B proposal. Relevant Late Permian and Early Triassic paleomagnetic data have thus far remained of demonstrably inferior quality, and we intend, therefore, to collect new paleomagnetic data for this time interval to test Pangea fits, and to determine whether a change from Pangea-B to Pangea-A occurred before or after the Late Permian, if it did occur at all. The majority of the new collections will be from Argentina, where stratified volcanic rocks exist that will likely yield reliable results. The supercontinent Pangea is a very fundamental and prominent aspect of the ancient geography of the Earth, and the accuracy of its configuration is of interest to anyone studying Earth Science. The aim of this study is to determine whether there is any evidence for a Pangea reconstruction in Late Permian-Early Triassic paleomagnetic data, in which northwestern South America was located adjacent to the Appalachian margin of North America. Such a Pangea-B reconstruction is rather different from the classically and widely accepted Pangea-A fit in which northwestern South America is, instead, adjacent to the Texas margin of North America. The available paleomagnetic records for Permian and Early Triassic time surprisingly seem to favor Pangea-B, which has puzzled geologists for decades. If Pangea B existed, then it must have undergone a large wrenching movement during either the Permian or the Triassic. This study intends to establish whether the previous, rather preliminary results that favor Pangea-B are supported by carefully determined new paleomagnetic data. If Pangea-B is found to have existed, the study will by inference have obtained evidence for enormous lateral fault movements, of the order of 3500 km in length or more, the likes of which are not documented for any time in the post-Pangea history of the Earth, that is, in the last 200 million years.

盘古大陆存在于古生代晚期和中生代早期，由北部的大陆群（劳亚大陆，由北美洲、格陵兰岛、欧洲和亚洲组成）和南部的冈瓦纳大陆群组成，包括南美洲、非洲、澳大利亚、马达加斯加、印度和南极洲。一般认为，在盘古大陆，冈瓦纳的非洲西北部边缘与北美的阿巴拉契亚边缘相邻；这种重建被称为泛古陆a。然而，在晚三叠世之前，从冈瓦纳和劳拉亚获得的古地磁数据与盘古- a的拟合不太一致，这导致科学家们要么质疑这些数据的有效性，要么提出另一种拟合，称为盘古- b。重建泛古陆- b的主要问题是，大家都认为晚三叠世是泛古陆- a的拟合期，这意味着泛古陆- b在二叠纪或三叠纪转变为泛古陆- a。完成这一变化的相对运动包括冈瓦纳和劳亚之间一个惊人的3500公里或更大的右侧巨型切变。对于这样一个巨型切变，几乎没有地质证据存在，因此地质学家忽略了泛古大陆- b假说。到目前为止，相关的晚二叠世和早三叠世古地磁数据的质量仍然明显较差，因此，我们打算收集这一时间段的新古地磁数据来测试盘古大陆的拟合性，并确定从盘古大陆b到盘古大陆a的变化是否发生在晚二叠世之前或之后，如果确实发生过的话。新收集的大部分将来自阿根廷，那里存在分层火山岩，可能会产生可靠的结果。超大陆盘古大陆是地球古代地理的一个非常基本和突出的方面，其构造的准确性是任何研究地球科学的人都感兴趣的。本研究的目的是确定在晚二叠世-早三叠世古地磁资料中是否有证据表明南美洲西北部与北美的阿巴拉契亚边缘相邻。这样的泛古陆- b重建与经典的、被广泛接受的泛古陆- a拟合有很大的不同，后者认为南美洲西北部与北美的德克萨斯边缘相邻。令人惊讶的是，现有的二叠纪和早三叠纪的古地磁记录似乎更倾向于盘古大陆b，这让地质学家困惑了几十年。如果泛大陆B存在，那么它一定在二叠纪或三叠纪经历了一次巨大的扭曲运动。这项研究的目的是确定先前的有利于泛古陆- b的初步结果是否得到了精心确定的新的古地磁数据的支持。如果发现盘古大陆- b确实存在，那么根据推断，这项研究将获得巨大的横向断层运动的证据，其长度约为3500公里或更长，这样的运动在后盘古大陆的地球历史中，即过去2亿年里，没有任何时间记录过。