Bending a geological icon: Oroclines, Pangea, and the supercontinent cycle

弯曲的地质标志：Oroclines、Pangea 和超大陆旋回

• 批准号: RGPIN-2014-06533
• 负责人: Johnston, Stephen
• 金额: $ 2.19万
• 依托单位: University of Alberta
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=633765
• 关键词: Bending; geological; icon; Oroclines; Pangea

Pangea, the most recognizable of Earth Science icons, is the focus of my research. Wegener depicted Pangea as having formed in response to the Carboniferous continental collision of Gondwana in the south with Laurussia in the north giving rise to the Appalachian (in America) – Variscan (in Europe) Orogen. How one interprets the Appalachian - Variscan Orogen is dependent upon the nature of significant map-view bends that characterize both mountain belts. Are these map-view bends 'primary' paleogeographic features (promontories and recesses), or are they secondary 'oroclines' - formerly linear orogens that have been subsequently buckled about vertical axes of rotation? Most models assume the bends are primary structures, and imply that the final collision was preceded by an accretionary period during which 'peri-Gondwanan' continental ribbons (Avalonia; Meguma; South Portuguese Zone) that rifted from the north margin of Gondwana, opening the Rheic Ocean, collided with and accreted to the southern margin of Laurussia. Furthermore, Primary models imply that: 1 - peri-Gondwanan terranes are restricted to a belt bound by the Rheic suture to the south and the Laurussian autochthon to the north; 2 - multiple sutures characterize the southern margin of Laurussia, where they separate the peri-Gondwanan terranes, whereas a single Rheic suture bounds the north margin of the intact Gondwana passive margin; 3 - crustal thickening and orogenesis resulted from entry of the Gondwana passive margin into a subduction zone dipping beneath Laurussia; and 4 - post-collisional deformation of Pangea is explicable in terms of a within-plate, intra-continental tectonic setting. Support for an alternative model comes from our recent research of the Variscan Orogen in Iberia. Paleomagnetic, structural and stratigraphic studies demonstrate that the orogen is characterized by two coupled secondary oroclines that formed between 305 and 295 Ma, and which define a continental scale S-fold. Palinspastic restoration of the oroclines yields a 2300 km long previously linear NNE-striking orogen, and indicate that 1100 km of shortening at translation rates in excess of 10 cm/a was required to produce the oroclines. In our new model of the orogen, in which oroclinal buckling explains the map-view geometry of the orogen: 1 - peri-Gondwanan terranes (South Portuguese zone) lie east of the Rheic suture; 2 - Instead of being bound by a single Rheic suture, the Gondwana passive margin sequence forms a continental ribbon bound to the east by the Rheic suture, and to the west by a separate suture represented by ophiolite in NW Iberia; 3 – Variscan orogenesis is a product of subduction of the Gondwanan ribbon continent to the west beneath an oceanic arc, and not beneath Laurussia; and 4 - so-called post-collisional intra-Pangean orocline formation, which involved 1100 km of translation at rates of >10 cm/a, requires the involvement of subduction and hence the presence of oceanic lithosphere within the heart of Pangea well into the Permian. A program of geological, paleomagnetic, geochronological and geochemical studies focused along select transects across the Variscan orogen will test these contrasting models of Pangea construction. Expected outcomes include an improved understanding of Earth's paleogeography; better constraints on the relationship between Earth System evolution, including extinction events, and the supercontinent cycle; and an augmentation of outreach opportunities including public and school presentations.

盘古大陆，地球科学中最知名的图标，是我研究的重点。韦格纳认为盘古大陆的形成是石炭纪大陆碰撞的结果，南起冈瓦纳，北至劳鲁西亚，形成阿巴拉契亚（美洲）-华力西（欧洲）造山带。人们如何解释阿巴拉契亚-华力西造山带取决于两个山脉带的显著地图视图弯曲的性质。这些地图上的弯曲是“主要的”古地理特征（海岬和凹陷），还是次要的“造山带”--以前的线性造山带，后来围绕垂直的旋转轴弯曲？大多数模型假设弯曲的主要结构，并暗示最后的碰撞之前的增生期，在此期间，“周冈瓦纳”大陆带（阿瓦隆尼亚; Meguma;南葡萄牙区），从冈瓦纳的北部边缘断裂，打开Rheic海洋，碰撞和增生到南部边缘的Laurussia。此外，Primary模型还表明：1 -冈瓦纳周边陆缘局限于南接Rheic缝合线、北接Laurussian原地体的地带，2 -多条缝合线分隔了冈瓦纳周边陆缘，而单一的Rheic缝合线则限定了完整的冈瓦纳被动陆缘的北缘; 3 -地壳增厚和造山作用导致的冈瓦纳被动边缘进入俯冲带下倾斜劳鲁西亚和4 -后碰撞变形的盘古大陆是可以解释的板块内，大陆内的构造环境。我们最近对伊比利亚的华力西造山带的研究支持了另一种模式。古地磁、构造和地层研究表明，造山带的特征是两个耦合的次级造山带，形成于305和295 Ma之间，并确定了大陆尺度的S-褶皱。造山带的Palestinastic恢复产生一个2300公里长的线性NNE-罢工造山带，并表明，1100公里的缩短在平移速率超过10厘米/年，需要产生的造山带。在我们的新的造山带模型中，其中造山带屈曲解释了造山带的地图视图几何形状：（南葡萄牙区）位于莱茵缝合线以东; 2 -冈瓦纳被动边缘序列不是被单一的Rheic缝合线束缚，而是形成了一个大陆带，由Rheic缝合线束缚在东部，3 -华力西造山作用是冈瓦纳带状大陆向西俯冲到洋弧之下而不是劳鲁西亚之下的产物; 4 -所谓的碰撞后泛大陆内造山带的形成，它涉及以>10 cm/a的速率平移1100 km，需要俯冲的参与，因此在泛大陆的中心存在大洋岩石圈，直到二叠纪。一个地质学、古地磁学、年代学和地球化学研究项目将集中在华力西造山带的沿着选定的断面上，以检验这些盘古大陆构造的对比模型。预期成果包括：增进对地球古地理学的了解;更好地限制地球系统演化（包括灭绝事件）与超大陆周期之间的关系;增加外联机会，包括公共和学校介绍。