Contrasting styles of orogenesis and the amalgamation of Pangea

在过去的25亿年里，超大陆合并和分散的反复循环对地球的进化产生了深远的影响。这些超级大陆中最新的Pangea形成于晚古生代，大约3亿年前（300 Ma）。尽管盘古大陆的存在是板块构造学的基石，但人们对其合并的机制知之甚少。如果将目前的理论地球动力学模型应用于早古生代古地理，它们无法重建盘古大陆的传统形态。作为一个必然结果，我们没有可行的模型来解释地球表面过程和内部过程之间的耦合，也没有可行的模型来理解长期全球变化的自然速度，这受到构造过程的深刻影响。本研究考察了两个主要古生代海洋的演化：(i)“内部”Rheic洋，其在晚古生代闭合产生了由盘古大陆内部大陆碰撞形成的山带（或造山带）（如阿巴拉契亚-瓦里斯坎造山带）；（ii）“外部”古太平洋，其通过沿盘古大陆外缘的俯冲和增生产生了山带（如Terra Australis造山带，TAO）。我，我的学生和同事将研究盘古大陆发展的两个关键时间间隔：(I) 480-400 Ma的间隔，当俯冲带在里海内开始，最终形成了盘古大陆；（ii） 360-290 Ma的盘古大陆合并，我们将研究大陆碰撞期间地幔的演化和Variscan造山带的产生。我们还将研究在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发生的机制和时间上的不确定性，我们将能够评估盘古大陆内部和外围构造事件之间潜在的地球动力学联系。我计划调查两个关键地区，在这些地区，莱西大洋地质的关键关系得到了很好的揭示：(I)伊比利亚，它的初始裂谷和最终闭合（缝合）的证据保存得很好；（ii）英国的康沃尔，它的地质毗邻一个主要的缝合带，是理解瓦里斯坎造山带构造演化的关键。沿着盘古大陆的外围，我将重点研究墨西哥南部的古生代和早中生代杂岩，以及澳大利亚东部的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，并为研究从泛大陆形成到泛大陆分裂开始的地幔和地壳烃源岩的变化提供了机会。塔斯马尼德褶皱带在480-400 Ma区间有很好的暴露岩石，这将使我们能够评估Rheic和古太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间关系和构造、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融合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的更深入的了解，以及（ii）为检查负责重复组装和分散的古老超级大陆的过程提供了一个门户，这些过程深刻地影响了过去2.5 Ga的地壳，大气，气候和生命的演化以及全球气候变化的自然速度。

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.