Collaborative Research: Testing Burial/Exhumation Models for the Evolution of a (U)HP Terrane in an Orogenic Upper Plate, Liverpool Land, East Greenland

地质学家在研究大型山脉的演化时面临的一个根本困难是无法直接观察到在活山下面的地壳深处发现的岩石类型和变形模式。克服这一困难的一种方法是研究那些被倒转或侵蚀的古代山脉，并在地表暴露出山脉最深的结构水平。东格陵兰利物浦地（LL）的岩石暴露了喀里多尼德山脉的根，喀里多尼德山脉横跨格陵兰岛的长度，是在大约4.4亿到3.6亿年前斯堪的纳维亚半岛与北美碰撞时形成的。在挪威地质学家的协助下，皇后学院和加州理工学院圣路易斯奥比斯波分校的教师、研究生和本科生将共同努力，确定喀里多尼德火山底部岩石的起源和随后的变形历史，以更好地了解大陆碰撞期间的造山过程。这个项目的结果将对研究像喜马拉雅这样的活跃变形山带的变形的研究人员特别感兴趣。来自利物浦地的高压和超高压（UHP）片麻岩的现场和实验室分析将用于测试碰撞造山带覆盖板块中超高压地形的俯冲和挖掘模型。利物浦地与劳伦西亚的对比表明，在加里东造山运动期间，当波罗的海俯冲到下面时，利物浦地位于板块上部。这些研究人员先前在LL的工作已经确定了榴辉岩和幔源榴石橄榄岩可能与波罗的海有关，此外还发现了一个较年轻的UHP地体和一个较老的中地壳片麻质地体之间的构造地层缝合线。这些发现挑战了普遍接受的特高压地体的形成模式，即大陆岩石圈被负浮力的海洋岩石圈拉到地幔深处，以及在岩石圈尺度的正断层下盘发掘出的特高压地体的模式。我们建议对LL片麻岩杂岩进行构造、地球化学和地热年代学研究，以1)确定LL片麻岩杂岩的构造背景和地幔楔入LL地体的交代历史，2)确定LL片麻岩杂岩的Laurentian和Baltic的物源，以及3)确定LL片麻岩杂岩的构造地层缝合线的运动学和时间特征。提出的工作有望阐明地球动力学过程，包括在海洋盆地关闭期间多重超高压事件的可能性，造山运动期间地壳-地幔相互作用和交换，以及地壳下部至中部融化。

A fundamental difficulty faced by geologists studying the evolution of large mountain ranges is the inability to directly observe the types of rock and deformation patterns that are found at deep crustal levels beneath active mountains. One way to overcome this difficulty is to study ancient mountain ranges that have since been inverted or eroded, and currently expose the deepest structural levels of a mountain range at the surface. The rocks of Liverpool Land (LL), East Greenland, expose the roots to the Caledonides, a mountain range that spanned the length of Greenland, and formed as Scandinavia collided with North America in the time span from about 440 to 360 million years ago. This collaborative effort between faculty and graduate and undergraduate students at Queens College and Cal Poly San Luis Obispo, with assistance from Norwegian geologists, will determine the origin and subsequent deformation history of rocks from the roots of the Caledonides, to better understand the processes of mountain building during continental collision. The results of this project will be of particular interest to researchers studying deformation in actively deforming mountain belts like the Himalaya.Field and laboratory analysis of high pressure and ultra-high-pressure (UHP) gneisses from Liverpool Land will be used to test models for the subduction and exhumation of UHP terranes in the overriding plates of collisional orogens. Liverpool Land has been correlated with Laurentia, implying it was situated in the upper plate during the Caledonian Orogeny as Baltica subducted beneath. Previous work by these investigators in LL has identified eclogites and mantle-derived garnet peridotites possibly correlated with Baltica in addition to a tectonostratigraphic suture between a younger UHP terrane and an older mid-crustal gneiss terrane. These discoveries challenge generally accepted models for the formation of UHP terranes where continental lithosphere is pulled to mantle depths by negatively buoyant oceanic lithosphere, as well as models for their exhumation in the footwalls of lithospheric-scale normal faults. We propose a structural, geochemical, and geo-thermo-chronologic study of the LL gneiss complexes to 1) define the tectonic setting and metasomatic history of the mantle wedge incorporated into the LL terrane, 2) determine Laurentian versus Baltic provenance of the LL gneiss complexes, and 3) characterize the kinematics and timing of tectonostratigraphic sutures responsible for exhumation in LL. The proposed work promises to shed light on geodynamic processes including the possibility of multiple UHP events during the closure of ocean basins, crust-mantle interaction and exchange during orogeny, and lower to midcrustal melting.