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

研究大型山脉演化的地质学家面临的一个基本困难是无法直接观察在活动山脉下方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已经被倒置或侵蚀的古老山脉，目前暴露出山脉表面最深的结构层次。东格陵兰岛的利物浦地（LL）的岩石暴露了加里东山脉的根源，这是一条横跨格陵兰岛的山脉，在大约4.4亿至3.6亿年前的时间跨度内，斯堪的纳维亚半岛与北美大陆碰撞形成。在挪威地质学家的协助下，皇后学院和加州理工圣路易斯奥比斯波学院的教师，研究生和本科生之间的合作努力将确定加里东纪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。这个项目的结果将特别感兴趣的研究人员在积极变形山区地带，如喜马拉雅山变形。现场和实验室分析的高压和超高压（UHP）片麻岩从利物浦土地将被用来测试模型的俯冲和折返的超高压（UHP）片麻岩在碰撞造山带的覆盖板。 利物浦地与劳伦大陆相关，这意味着在加里东造山运动期间，当波罗的海俯冲到下面时，它位于上板块。这些研究人员以前在LL的工作已经确定了榴辉岩和幔源石榴石橄榄岩可能与波罗的海，除了一个年轻的超高压岩石和一个老的中地壳片麻岩岩石之间的构造地层缝合线。这些发现挑战了普遍接受的超高压岩石圈形成模型，其中大陆岩石圈被负浮力海洋岩石圈拉到地幔深处，以及岩石圈尺度正断层下盘的折返模型。我们提出了一个结构，地球化学和地热年代学研究的LL片麻岩杂岩1）定义的构造背景和交代历史的地幔楔纳入LL片麻岩，2）确定劳伦特与波罗的海源区的LL片麻岩杂岩，和3）表征的运动学和时间的构造地层缝合线负责折返在LL。拟议的工作有望阐明地球动力学过程，包括海洋盆地关闭期间多个超高压事件的可能性，地壳地幔相互作用和交换过程中的造山运动，以及下地壳至中地壳熔融。

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.