Collaborative Research: Testing Hypotheses for the Laramide Orogeny

落基山脉南部的拉腊米造山带被归因于美国西部大部分地区下方的海洋板块异常低角度的俯冲，在这个假设的基础上，已经发展出了相当多的文献。但是，目前设想的低角度俯冲在几何学、物理学和时间上都存在困难。该项目测试了目前的框架，对替代方案，提出拉腊米造山带是一个浅板厚岩石圈的相互作用的结果，在怀俄明州。研究主要集中在问题的三个方面：南落基山脉隆起之前沉积物厚堆积的时间和原因，火成岩活动的时间和起源，以及板片几何形状变化与美国西部构造运动的可能联系。通过地层学和地质学方法，将提高怀俄明州和科罗拉多中东部晚白垩世盆地的时间发展分辨率。沉积学研究将通过简单的板块挠曲计算确定作用在岩石圈上的力。将获得该地区临界火成岩的新的高分辨率年龄，以便更好地确定侵入活动相对于板块边缘变化的时间，并对这些岩石的地球化学进行检查，以确定水合作用（弧式岩浆作用）与减压熔融作用（弧后式岩浆作用）的相对作用。数值实验将允许量化的力量作用在岩石圈上的不同类型的板片的几何形状，并探讨可能的关系，二次对流系统对大陆变形和岩浆活动。在这段时期，从约75至45万年前，一个前内海被改造成落基山脉的地区，从新墨西哥州延伸到蒙大拿州。在这次造山运动的影响中（拉拉米造山运动）是科罗拉多大部分主要矿床的形成，科罗拉多西部、犹他州东北部和怀俄明州西南部大型油页岩矿床的形成，该地区目前正在开采的许多天然气田的开发，以及继续使该地区变形的条件的形成，导致了科罗拉多中部的地震危险和美国西部大部分地区的地热资源。这是远离构造板块边界的造山运动的最好和最神秘的例子之一。 因此，对落基山脉地区的地质了解取决于对这一造山事件的性质和起源的进一步了解。这项研究的重点是最无法解释的方面的事件，以最好地限制其过去的历史和现在的行为。这项工作的成功完成应能大大增进对世界各地类似事件的了解，其中一些事件可能还产生了资源，但由于这些事件的不寻常性质，这些资源尚未被发现。

The Laramide orogeny in the Southern Rocky Mountains has been ascribed to exceptionally low-angle subduction of oceanic plates beneath most of the western U.S., and a considerable literature has been developed upon that assumption. But there are difficulties with the geometry, physics, and timing of low angle subduction as currently envisioned. This project tests this current framework against an alternative that proposes that the Laramide orogeny was the result of interaction of a shallowing slab with thick lithosphere under Wyoming. The research focuses on three aspects of the problem: the timing and cause of the thick accumulation of sediments prior to uplift of the Southern Rockies, the timing and origin of igneous activity, and the possible connections of changes in slab geometry to tectonism in the western U.S. The resolution of the temporal development of the Late Cretaceous basin of central and eastern Wyoming and Colorado will be improved through stratigraphic and sedimentological studies. Forces acting on the lithosphere through simple plate flexure calculations will be determined. New, high resolution ages of critical igneous rocks in the region will be acquired in order to better determine the timing of intrusive activity relative to changes at the plate margin and examination of the geochemistry of these rocks to will determine the relative role of hydration (arc-style magmatism) vs. decompression melting (back-arc style magmatism). Numerical experiments will allow quantification of the forces acting on the lithosphere for different kinds of slab geometries and also explore the possible relationship of secondary convection systems on continental deformation and magmatism.During the period from about 75 to 45 million year ago a former inland sea was transformed into the Rocky Mountains over an area extending from New Mexico to Montana. Among the effects of this mountain building event (the Laramide Orogeny) are the creation of most of the major mineral deposits in Colorado, creation of the large oil-shale deposits in western Colorado, northeastern Utah, and southwestern Wyoming, development of many of the natural gas fields now being exploited in the region, and creation of conditions that continue to deform the region, leading to earthquake hazards in central Colorado and geothermal resources in much of the western U.S. It is one of the finest and most cryptic examples of mountain building far from a tectonic plate boundary. Geologic understanding of the Rocky Mountain region thus depends upon improved knowledge of the nature and origin of this mountain building event. This study focuses on the most unexplained aspects of the event to best constrain its past history and present behavior. Successful conclusion of this work should greatly improve the understanding of similar events worldwide, some of which might have also produced resources that remain undiscovered owing to the unusual nature of such events.