Contrasting styles of orogenesis and the amalgamation of Pangea

造山运动和盘古大陆合并的对比风格

• 批准号: RGPIN-2014-05924
• 负责人: Murphy, JamesBrendan
• 金额: $ 2.7万
• 依托单位: St. Francis Xavier University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2014
• 资助国家: 加拿大
• 起止时间: 2014-01-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=567475
• 关键词: Contrasting; styles; orogenesis; amalgamation; Pangea

Repeated cycles of supercontinent amalgamation and dispersal over the past 2.5 billion years have had a profound effect on Earth’s evolution. The latest of these supercontinents, Pangea, formed in the Late Paleozoic, about 300 million years ago (300 Ma). Although the existence of Pangea is a cornerstone of plate tectonics, the mechanisms responsible for its amalgamation are poorly understood. If current theoretical geodynamic models are applied to an Early Paleozoic paleogeography, they fail to reconstruct Pangea in its conventionally accepted configuration. As a corollary, we have no viable model for the coupling between the Earth’s surface processes and its interior, or for understanding the natural pace of long-term global change, which is profoundly influenced by tectonic processes. This proposal examines the evolution of two major Paleozoic oceans: (i) the “interior” Rheic Ocean whose closure in the Late Paleozoic produced mountain belts (or orogens) formed by continental collisions in the interior of Pangea (e.g. the Appalachian-Variscan orogen) and (ii) the “exterior” Paleopacific Ocean, which produced mountain belts by subduction and accretion along the exterior margins of Pangea (e.g. the Terra Australis Orogen, TAO). I, my students and colleagues will investigate two critical time intervals in Pangea’s development: (i) the 480-400 Ma interval when subduction zones initiated within the Rheic Ocean that eventually gave rise to Pangea, and (ii) the 360-290 Ma Pangea amalgamation where we will investigate the evolution of the mantle during continental collision and the generation of the Variscan orogen. We also will investigate the potential geodynamic linkage between the two fundamentally distinct types of orogenic activities that occurred during these two time intervals. By resolving the uncertainties in the mechanisms and timing of these major tectonic events, we will be able to evaluate potential geodynamic linkages between orogenic events that took place within the interior and those along the periphery of Pangea during its assembly. I plan to investigate two key regions where critical relationships of Rheic Ocean geology are excellently exposed: (i) Iberia where evidence of its initial rifting and final closure (suturing) are well preserved, and (ii) Cornwall, U.K., whose geology lies adjacent to a major suture zone and is key to understanding tectonic evolution of the Variscan orogen. Along the periphery of Pangea, I will focus on Paleozoic and Early Mesozoic complexes in southern Mexico and the Tasmanide fold belt of the TAO in eastern Australia. The geology of southern Mexico provides a rare example of the subduction of Paleopacific lithosphere that was superimposed on a collisional suture zone and the opportunity to investigate the changing mantle and crustal source rocks from the time Pangea formed to the initiation of Pangea breakup. The Tasmanide fold belt has excellently exposed rocks in the 480-400 Ma interval that will allow us to assess potential geodynamic connections between events in the Rheic and Paleopacific oceans. I and my students will study the field relationships and the structural, geochemical, isotopic and petrologic evolution of these key regions in order to deduce the timing and mechanisms of tectonic events that led to the assembly and amalgamation of Pangea. This research also will provide (i) a greater understanding of the geodynamic linkages between the evolution of major Paleozoic oceans, and (ii) a gateway to examine processes responsible for the repeated assembly and dispersal of older supercontinents, which have profoundly influenced the evolution of the Earth’s crust, atmosphere, climate, and life as well as the natural pace of global climate change for the last 2.5 Ga.

过去 25 亿年来，超级大陆合并和分散的反复循环对地球的演化产生了深远的影响。这些超级大陆中最新的一个是盘古大陆，形成于古生代晚期，距今约 3 亿年前（300 Ma）。尽管盘古大陆的存在是板块构造的基石，但对其合并的机制却知之甚少。如果将当前的地球动力学理论模型应用于早古生代的古地理，它们将无法以传统接受的配置重建盘古大陆。由此推论，我们没有可行的模型来解释地球表面过程与其内部之间的耦合，也没有可行的模型来理解长期全球变化的自然速度，而这种变化深受构造过程的影响。该提案研究了两个主要古生代海洋的演化：（i）“内部”瑞克洋，其在古生代晚期闭合，产生了由盘古大陆内部大陆碰撞（例如阿巴拉契亚-瓦里西亚造山带）形成的山带（或造山带）；（ii）“外部”古太平洋，通过沿外部的俯​​冲和增生产生了山带（或造山带）。 盘古大陆边缘（例如，Terra Australis Orogen，TAO）。我、我的学生和同事将研究盘古大陆发展中的两个关键时间间隔：(i) 480-400 Ma 间隔，当时俯冲带在赖克洋内开始，最终形成盘古大陆；(ii) 360-290 Ma 盘古大陆合并，我们将研究大陆碰撞期间地幔的演化和瓦里斯坎造山带的形成。我们还将研究这两个时间间隔内发生的两种根本不同类型的造山活动之间潜在的地球动力学联系。通过解决这些主要构造事件的机制和时间的不确定性，我们将能够评估盘古大陆组装期间发生在内部的造山事件和沿盘古大陆外围发生的造山事件之间潜在的地球动力学联系。我计划调查两个关键区域，其中瑞克洋地质学的关键关系得到了很好的揭示：（i）伊比利亚，其最初裂谷和最终闭合（缝合）的证据保存完好，以及（ii）英国康沃尔郡，其地质毗邻主要缝合带，是了解瓦里西亚造山带构造演化的关键。沿着盘古大陆的外围，我将重点关注墨西哥南部的古生代和早中生代杂岩以及澳大利亚东部 TAO 的塔斯马尼德褶皱带。墨西哥南部的地质提供了古太平洋岩石圈俯冲叠加在碰撞缝合带上的罕见例子，并提供了研究从盘古大陆形成到盘古大陆裂解开始期间地幔和地壳烃源岩变化的机会。塔斯马尼德褶皱带在 480-400 Ma 区间具有极好的暴露岩石，这将使我们能够评估瑞克洋和古太平洋事件之间潜在的地球动力学联系。我和我的学生将研究这些关键区域的场关系以及结构、地球化学、同位素和岩石学演化，以推断导致盘古大陆聚集和合并的构造事件的时间和机制。这项研究还将提供（i）对主要古生代海洋演化之间的地球动力学联系有更深入的了解，以及（ii）研究旧超级大陆反复聚集和分散的过程，这些过程深刻影响了地壳、大气、气候和生命的演化以及过去2.5 Ga的全球气候变化的自然速度。