Collisional Response of the Middle to Upper-lower Crust: A Himalayan Analogue in West Greenland

两个大陆板块的碰撞导致了一系列壮观的地质现象，包括造山、地震和岩浆活动。对大陆-大陆碰撞构造的理解大多源于正在进行的喜马拉雅-西藏造山系统，这是这一基本过程最著名的例子。山脉和高原的4-D动力学和结构是上地壳和中/下地壳之间复杂相互作用的结果，它们分别主要通过脆性和韧性机制变形。然而，喜马拉雅-青藏系脆-韧性转换带之下地壳的作用必然主要依赖于脆性区上部的观测。尽管有这些局限性，模型调用大规模的韧性流动在一个有限的通道中的熔融弱化材料在中地壳和它的控制造山运动，在很大程度上是基于这一地区。 一个完整的，暴露良好的，深侵蚀的古老山脉带，暴露中/深地壳将允许直接观察岩石经历的过程推测从研究更高层次的造山带和数值模型。一个由得克萨斯大学和丹麦岩石圈中心的地质学家组成的国际研究小组认为，这样一个地区存在于西格陵兰岛，我们正在测试一个假设，即两个前寒武纪（约100万年）。1.8在西格陵兰（Rinkian带和Nagssugtoqidian造山带）发现的一个单一的，+1100 km宽的，不对称的碰撞造山带。由于碰撞后折返的适当水平，该地区（100%暴露在高山环境中）将作为一个独特的网站，直接观察大陆-大陆碰撞的中地壳和浅层-下地壳的反应。因此，这个可进入的区域将作为喜马拉雅-西藏造山系统的深部模拟。这些以过程为导向的目标要求在这个+1100 km的造山带中描述变形和变质作用的类型、时间、持续时间和穿时性。在过去的三个夏天，我们的研究小组（由嘉士伯和NERC资助）在西格陵兰的实地工作建立在以前的绘图和研究计划的基础上，以表征该地区的结构演变。美国国家科学基金会的这项资助支持了一项广泛的U-Pb地质年代学计划，该计划将对该带的演化施加关键的绝对时间限制。正如喜马拉雅山是我们今天大陆-大陆碰撞的最佳例子一样，西格陵兰岛被设想为研究碰撞构造背景下发生的深度过程的世界级基准点。更好地了解这些地壳层次的变形样式和反馈，将有助于我们更好地了解这种构造背景下的地形、地震、地面运动和变形。此外，西格陵兰古元古代综合构造模型的制定将提供最后一块拼图，以更好地了解古元古代东北劳伦的增长和稳定。这将代表十多年国际研究的高潮，其中包括美国，加拿大和欧洲的团体。

The collision of two continental plates causes a wide range of spectacular geological phenomena including mountain building, earthquakes and magmatism. Much of the understanding of continent-continent collisional tectonics stems from the on-going Himalayan-Tibetan orogenic system, the best known example of this fundamental process. The 4-D dynamics and architecture of mountains and high plateaus are the consequence of a complex interplay between the upper and middle/lower crust, which deform primarily by brittle and ductile mechanisms, respectively. However, the role of crust below the brittle-ductile transition in the Himalayan-Tibetan system necessarily relies mainly on observations collected in the upper part of the brittle realm. Despite these limitations, models invoking large-scale ductile flow in a restricted channel of melt-weakened material in the mid-crust and its control on mountain building, are based heavily on this region. A complete, well-exposed, deeply-eroded ancient mountain belt that exposes middle/deep crust would permit direct observation of rocks that experienced the processes speculated about from studies of higher level orogens and numerical models. An international research team composed of geologists from the University of Texas and the Danish Lithosphere Centre, believe that such an area exists in West Greenland and we are testing a hypothesis that that two Precambrian (ca. 1.8 billion years) orogens identified in West Greenland (Rinkian Belt and Nagssugtoqidian Orogen) represent a single, +1100 km wide, asymmetric collisional orogen. Due to the appropriate levels of post-collisional exhumation, this region (with 100% exposure in an alpine setting) will serve as a unique site to directly observe the response of the middle and shallow-lower crust to continent-continent collision. As such, this accessible region will serve as a deep analogue to the Himalayan-Tibean orogenic system. These process-oriented objectives require that the style(s), timing, duration and diachroneity of deformation and metamorphism be characterized across this +1100 km orogen. Over the past three summers, field work in West Greenland by our research group (funded by Carlsberg and NERC) builds upon previous mapping and research programs to characterize the structural evolution of the region. This NSF grant supports an extensive U-Pb geochronology program that will place critical absolute time constrains on the evolution of this belt. Just as the Himalayas serves as our best example of continent-continent collision today, the West Greenland is envisioned as being a world-class, benchmark site for studying processes occurring at depth in collisional tectonic settings. A better understanding of deformation style(s) and feed back of these crustal levels will improve our understanding of topography, earthquakes, ground motion and deformation in this tectonic setting. Additionally, formulation of an integrated tectonic model for the Paleoproterozoic of West Greenland will provide the last major piece of the puzzle to better understand the growth and stabilization of Paleoproterozoic NE Laurentia. This will represent the culmination of over a decade of international research that has included groups in the USA, Canada and Europe.