Comparative orogenesis of accretionary orogens

积累的野外证据表明，太古宙至今构造样式发生了长期变化。随着时间的推移，造山作用的方式如何以及为什么会发生变化，这些问题的一些答案可能来自于对构造过程的理解，比如弧-弧和/或弧-大陆碰撞，为什么会沿着一些山带的走向和走向改变性质。增生造山带为研究这一主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的。我在阿巴拉契亚-卡利多尼德山带和南北美洲科迪勒拉进行的构造研究表明，形成这些增生造山带的一部分的弧-大陆碰撞，在局部从硬（穿透性缩短和上部板块的变质作用延伸到弧-沟间隙之外）和热转变为软（上部板块的缩短局限于弧-沟间隙，但不超过）和沿和/或沿走向的冷（例如Taconic， Famatina和Klondike造山带）。而另一些则表现出很少或没有变化，保持柔软和寒冷（如佩诺布斯科特、盐碱、鹿角和潘潘亚造山）。控制这些构造样式变化的构造参数和过程尚不清楚。基于对这些造山带重要方面的多学科研究的比较研究表明，在具有相对良好的暴露和地质年代学限制的关键地区，构造样式发生了重大变化，旨在确定这些山带的特征结构和/或其他共同的构造元素。研究结果将促进能够解释构造风格差异的假设的发展，这些假设将通过对中亚造山带（CAOB）的北山造山带等其他显示沿走向和/或跨走向构造风格差异较大的山带的研究以及与现有数值模拟结果和三维实验室实验的比较进一步验证。本文提出的学生研究重点是研究北山造山带柳源蛇绿岩杂岩的脊-俯冲模式及其对该山带观测到的构造样式（硬/软）变化的潜在影响（ph . 1），以及纽芬兰-阿巴拉契亚山脉Baie Verte地区榴辉岩的同步碰撞发掘（ph . 2），这一过程在阿巴拉契亚北部其他地区极为罕见或缺失。榴辉岩产于俯冲前的Laurentian边缘段，而相邻的上板块弧前盆地和增生棱柱则基本不存在，这可能是由于弧前逆冲的构造移动所致。这些和/或其他因素可能影响了Taconic造山运动构造样式的沿走向变化。

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.