古地磁设施与研究

古地磁学是一门研究岩石记录下的地球古代磁场的学科. 了解地球磁场过去的构造可以让地质学家准确地确定岩石序列的年代, 重建大陆古地理, 并量化大岩体的绝对旋转和倾斜.

The Paleomagnetic laboratory at 推荐全球十大博彩公司排行榜 was founded in 2004 with the help of a National Science Foundation Equipment grant awarded to Dr. 奥尔罗威尔, 由布林莫尔地质系和推荐全球十大博彩公司排行榜教务处资助. 布林茅尔实验室的主要功能是研究过去大陆的构造, 特别是大型超级大陆的合并和分散, 帮助理解褶皱冲断带形成的力学和运动学, 为了更好地了解碳酸盐和红层岩石的再磁化过程, 以及地壳剪切带磁化率的各向异性. 这个实验室可供其他感兴趣的学者使用.

研究

超级大陆的生命周期

Precambrian continental reconstructions have recently become the subject of renewed interest following the proposal that all major continental blocks were part of a long-lived late Proterozoic supercontinent: Rodinia. While the existence of a major long-lived (~2500-500 Ma) Proterozoic supercontinent had earlier been advocated on the basis of paleomagnetic data, the more recent reconstructions of a short-lived Rodinia have largely been based on geological evidence linking truncated Meso-Proterozoic mobile belts. 在后一种情况下，罗迪尼亚的组合以格伦维尔年龄变形(约1)为标志.1 Ga)在Laurentia边缘, 冈瓦那大陆东部, 亚马逊和波罗的海, 在所谓的SWEAT或AUSWUS连接中，劳伦西亚西部边缘面向东南极洲. 罗丁尼亚大陆元素的分裂和再分配似乎开始于c. 750年前，东冈瓦纳与劳伦西亚西部边缘分离. 这次裂谷事件和随后的裂谷元素的漂移最终导致了~550 Ma更大冈瓦纳的合并.

Dr. Weil's research is focused on the life cycle of the proposed Rodinia supercontinent - its amalgamation 和 breakup - 和 on the supercontinent's paleogeography. 在没有保存完好的海洋岩石圈和海洋磁异常记录的情况下，侏罗纪之前的任何时间, 古地磁资料是推断古大陆古地理的唯一定量手段. 对于Laurentia, 位于罗丁尼亚岛中心的克拉通, 缺乏高质量的晚元古代古地磁资料, 我们迫切需要更多的数据来确定这一时期的古地理和构造历史.

目前的研究主要集中在美国西南部的几个元古代沉积岩和火成岩层序上.S. 包括:1)亚利桑那州的大峡谷超级群;2)犹他州的乌塔山群.

泛大陆合并

现代海洋的海底, 最多可以追溯到侏罗纪早期, 携带着磁反转记录，为盘古大陆分裂前的构造提供了有力的证据, i.e.盘古大陆A型. This configuration is in agreement with paleomagnetic data from all of Pangea's major blocks for the latest Triassic through Early Jurassic. 然而, the Permian 和 Triassic paleomagnetic data from Gondwana 和 Laurussia show an appreciable mismatch (overlap) in a Pangea A fit. 因此, 如果古地磁资料代表了冈瓦纳和劳鲁西亚在二叠纪和三叠纪的位置, 它们需要在泛大陆a段形成大约2000公里的大陆重叠, 这是不可能的. 来解决这个难题, paleomagnetists have suggested: 1) unrecognized magnetic overprints; 2) a tighter fit between the northern 和 southern continents (Pangea A2); 3) the existence of a significant non-dipole component of the geomagnetic field; or 4) a more north-easterly, 冈瓦纳的非重叠位置(泛大陆B). Although the more easterly position of Gondwana in Pangea B remedies the overlap observed in Late Paleozoic 和 Mesozoic paleomagnetic data for the Pangea A-type fit, it also requires a 3500 km megashear to accommodate the dextral translation needed to arrive at a Pangea A-type fit by the Latest Triassic. 这种从盘古大陆B向盘古大陆A的右移被认为发生在二叠纪, 可能延伸到三叠纪.

The enormous length 和 the irregular plate-boundary geometry required by Gondwana 和 Laurussia's configuration in Pangea B would result in a recognizable fault system with regions of transpression 和 transtension. 然而, 几乎没有地质证据表明在泛大陆合并时期存在广泛的右旋断裂系统. 正相反, most geologists envision a more or less north-south (in present-day coordinates) collision in which the northern margins of 非洲 和 南美 collided along the southern margin of 欧洲 和 eastern margin of 北美, 分别. 这个模型导致盘古大陆a型配置, 否定了有争议的泛大陆B到A巨型听证会的必要性.

一些博士. Weil's research reports regional paleostress directions derived for the Late Carboniferous 和 Permian from analysis of the Cantabria-Asturias Arc's deformation history. CAA沿北美洲和北美洲之间古板块边界的位置, 欧洲和北亚)和冈瓦纳(非洲), 南极洲, 澳大利亚, 南美, 和印度)是研究盘古大陆形成期间板块相互作用的理想场所. The structural 和 paleomagnetic results from the CAA indicate two main tectonic phases: 1) collision 和 subduction (east-directed polarity) in the hinterl和 of the Cantabria-Asturias regions in Westphalian 和 Stephanian times, 2)冈瓦纳向北迁移并与伊比利亚碰撞, 华力西欧洲, 最后是二叠纪时期的劳伦西亚. This tectonic model requires that final Variscan deformation experienced by northern Iberia has a remote paleostress field oriented north-south in present-day coordinates 和 NNE-SSW in paleogeographic coordinates parallel to the 最初的线性 belt. This tectonic scenario contradicts the transpressive WNW-ESE paleostress field in present-day coordinates 和 NW-SE paleostress field in paleogeographic coordinates for Iberia that is required in the hypothetical Pangea B to Pangea A dextral megashear model. 因此, this megashear is not supported by results from the CAA due to the obliquity of the observed paleostress field with the inferred paleostress field for dextral megashear, Pangea B构造被拒绝.

弯曲褶皱-逆冲带的运动学与力学

Nearly a century ago geologic observers had already recognized the importance 和 sought the meanings of oroclines - or curved mountain belts. 1955年，S。.W. 凯里首先创造了“orocline”(希腊语中的“山”和“弯”)一词来表示, 在计划上弯曲成马蹄形或肘形的造山系统.在这个最初的定义中，“造斜”一词是带的代表, 最初的线性, 后来经历了一个曲率. 近年来，这个术语已经发展到包括所有具有原生或次生诱导曲率的造山带.

凯里认为，造斜是地球上最有趣的构造特征之一, 他们可以, 如果理解, 为大陆进化提供了一把钥匙, 并将地球的所有其他结构特征整合成一个连贯的模式. 尽管凯里在评价奥罗克林斯的重要性时显得有些热心, 我同意他的观点，即造斜是地球上最迷人的构造特征之一. 从它的地图视图来看，几乎每个造山带都有一定程度的曲率. 因此, 了解这些独特特征的起源和发展是最重要的.

Dr. 奥尔罗威尔的研究重点是了解形成高弯曲山带的运动学和力学. 他使用了经典的构造地质学野外技术以及详细的古地磁和岩石地磁分析. 目前博士. 韦尔的研究主要集中在欧洲西南部的伊比利亚-阿莫里亚弧, 落基山脉州的塞维尔冲断带, 以及北美东部阿巴拉契亚造山带的部分地区.

造山相关碳酸盐岩再磁化

The final amalgamation of Pangea during the late Paleozoic Variscan-Alleghanian orogeny is widely recognized as having caused global-scale remagnetizations. 虽然主要在石灰石中报道, 这一事件影响了盘古大陆所有主要板块的多种沉积岩, 包括, 但不限于, 北美, 欧洲, 亚洲, 非洲, 和澳大利亚. The ubiquity of these remagnetizations has led to considerable rock magnetic research focused on the possible cause(s) 和 carrier(s) of this pervasive event. Two main mechanisms have been proposed for the remagnetization of Paleozoic limestones: 1) the acquisition of a thermoviscous remanent magnetization (TVRM) caused by burial 和 prolonged exposure to elevated temperatures, 和 2) the acquisition of a secondary chemical remanent magnetization (CRM) through magnetic mineral growth activated by basinal brines 和 other orogenic fluids. 目前普遍认为次生有机质是古生代碳酸盐岩再磁化的主要原因, 和 that TVRMs are unlikely given the relatively low burial temperatures determined for carbonates studied (< 250o C). 尽管这一过程的普遍性已被广泛接受, 再磁化的机理, 及其与造山运动和造山流体运移的关系, 还是没有完全理解. 为了进一步了解，必须确定CRM载体的矿物学和成因细节. 最终, a better underst和ing of the origin 和 distribution of NRM carriers will allow comparison between affected Paleozoic carbonates from varying localities, 以确定它们是否在晚古生代瓦里斯坎-阿勒哈尼亚造山运动中获得了相似的CRMs, 和, 结果是, 重新磁化的碳酸盐是否具有共同的岩石磁性特征, 再磁化历史，从而得出类似的岩石-流体相互作用.

为了更好地了解晚古生代再磁化事件的起源和全球优势, 以及它提出的碳酸盐“指纹”, 对几种古生代再磁化碳酸盐的详细研究正在进行中. 表征晶体形态和粒度分布, 并确定磁性残留物存在于哪些矿物中, 将整块岩屑与磁性萃取物和“非磁性”残渣的岩石磁性进行了比较. 这些岩石的磁性包括磁滞参数, 三维等温剩余磁化(IRM)退磁, IRM的收购, 饱和IRM (SIRM), 和非滞后剩磁(ARM), 和低温消磁. 描述磁性颗粒的形态和化学成分, 扫描电子显微镜(SEM)用于磁提取和薄切片.

集体, the rock magnetic 和 SEM results should provide identification of the mineralogy 和 grain size of remanence carriers in remagnetized carbonates, 并确定在这些碳酸盐中发现的岩石磁性“指纹”的来源. 最终, these results will be used to elaborate on the mechanism of carbonate remagnetization 和 on the relationship between remagnetization events, 区域变形, 造山流体与全球构造事件.