Comparative orogenesis of accretionary orogens

积累的野外证据表明，从太古宙到现在，构造样式发生了长期的变化。造山作用如何以及为什么随着时间的推移似乎改变了风格，一些答案可能来自于对为什么构造过程，如弧-弧和/或弧-大陆碰撞，在一些山脉带沿走向和跨走向发生性质变化的洞察。增生造山带为研究这一问题提供了最好的机会，因为弧和其他构造元素的增生通常是短暂的，相关的变形通常是局部性的。我在阿巴拉契亚-喀里多内德山脉带以及北美和南美洲科迪勒拉进行的持续构造研究表明，构成这些增生造山带一部分的弧陆碰撞在局部发生了变化，从硬的(上板块的穿透性缩短和变质作用延伸到弧沟间隙之外)和热到软(上板块的缩短局限于弧沟间隙内，但不超过弧沟间隙)和沿走向和/或跨越走向的冷(例如塔科尼克、法马蒂纳和克朗代克造山)，而其他造山运动几乎没有变化，仍然保持软和冷(如Penobcot、Salinic、Antler和Pampean造山)。导致这些构造样式变化的控制构造参数和过程鲜为人知。基于对这些造山带的重要方面进行的多学科研究的比较研究显示，在具有相对较好的曝光率和地质年代学限制的关键地区，构造风格存在重大变化，旨在确定这些造山带共有的特征结构和/或其他构造要素。这些结果将刺激能够解释构造样式差异的发展假说，这一假说将通过对其他山脉带的研究进一步检验，这些研究表明，沿走向和/或跨走向的构造样式存在很大差异。例如中亚造山带的北山造山带(CAOB)，并与现有的数值模拟结果和基于实验室的三维实验进行了比较。这里提出的学生研究集中在研究北山造山带中形成柳园蛇绿岩杂岩的脊-俯冲模式及其对该山脉中观测到的构造样式(硬与软)变化的潜在影响(Phd1)以及纽芬兰阿巴拉契亚山脉Baie Verte地区榴辉岩的同碰撞折返(PHD2)，这一过程在阿巴拉契亚北部其他地方极其罕见或根本没有。榴辉岩赋存于俯冲前过度伸展的劳伦特边缘，而邻近的上板块弧前盆地和增生棱柱大部分缺失，可能是由于弧前逆冲作用的构造搬运所致。这些和/或其他因素可能与塔肯造山的构造样式沿走向的变化有关。

Accumulated field evidence suggest that there was a secular change in tectonic style from the Archean to present. Some of the answers how and why orogenesis seems to have changed in style over time may come from insight into why tectonic processes, such as arc-arc and/or arc-continent collisions change in nature along and across strike in some mountain belts. Accretionary orogens provide the best opportunity to research this topic, because accretions of arcs and other tectonic elements are commonly short-lived and associated deformation is typically localized. My ongoing tectonic research in the Appalachian-Caledonide mountain belt and the North- and South American Cordillera has documented that the arc-continent collisions that form part of these accretionary orogens, locally changed from hard (penetrative shortening and metamorphism of upper plate extends beyond the arc-trench gap) and hot to soft (upper plate shortening localised in arc-trench gap, but not beyond) and cold along and/or across strike (e.g Taconic, Famatina and Klondike orogenies), whereas others show little or no variation and remained soft and cold (e.g. Penobscot, Salinic, Antler and Pampean orogenies). The controlling tectonic parameters and processes responsible for these variations in tectonic style are poorly known. Comparative research based on multidisciplinary studies of important aspects of these orogens showing major variations in tectonic style in critical areas with relatively good exposure and geochronological constraints, are geared to identify the characteristic structures and/or other tectonic elements shared by such mountain belts. The results will stimulate developing hypotheses capable of explaining the differences in tectonic style, which will be further tested by research in other mountain belts showing large variations in tectonic style along and/or across strike, such as the Beishan orogen of the Central Asian Orogenic Belt (CAOB) and comparisons with existing numerical modelling results and 3-D laboratory-based experiments.Student research proposed herein focusses on investigating the ridge-subduction model for forming the Liuyuan ophiolite complex in the Beishan orogen and its potential impact on the observed variations in tectonic style (hard vs soft) in this mountain belt (PhD1) and the syn-collision exhumation of eclogites in the Baie Verte area of the Newfoundland Appalachians (PhD2), a process extremely rare or absent elsewhere in the Northern Appalachians. The eclogites occur in a segment of the Laurentian margin that was hyperextended prior to subduction, whereas the adjacent upper plate forearc basin and accretionary prism are largely absent, probably due to tectonic removal by forearc underthrusting. These and/or other factors may have had a bearing on the along strike variations in tectonic style of the Taconic orogeny.