Collaborative Research: Testing Hypotheses for the Laramide Orogeny

落基山脉南部的拉拉米德造山作用被认为是由于美国西部大部分地区之下的海洋板块以极低的角度俯冲而成，并在此基础上发展了相当多的文献。但目前设想的低角度俯冲在几何、物理和时间上都存在困难。该项目测试了目前的框架，并与另一种框架进行了对比，该框架提出，拉拉米德造山运动是怀俄明州较浅的板块与厚厚的岩石圈相互作用的结果。研究集中在三个方面：南落基山脉抬升前沉积厚积的时间和原因，火成岩活动的时间和来源，以及板块几何结构变化与美国西部构造作用的可能联系。通过地层学和沉积学研究，将提高怀俄明州中东部和科罗拉多州晚白垩世盆地时间发展的分辨率。将通过简单的板块弯曲计算确定作用在岩石圈上的力。将获得该地区关键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，并检查这些岩石的地球化学，以确定水化作用(弧型岩浆作用)与减压熔融作用(弧后岩浆作用)的相对作用。数值实验将能够量化不同类型板块几何形状对岩石圈的作用力，并探索次生对流系统对大陆变形和岩浆作用的可能关系。在大约7500万年前到4500万年前的期间，从新墨西哥州到蒙大拿州的一个地区，以前的内陆海变成了落基山脉。在这次造山事件(拉拉米德造山运动)的影响中，包括科罗拉多州大部分主要矿藏的形成，科罗拉多州西部、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，导致科罗拉多州中部的地震灾害和美国西部大部分地区的地热资源。它是远离构造板块边界的山脉建设的最好和最神秘的例子之一。因此，对落基山脉地区的地质理解取决于对这一造山事件的性质和起源的更好了解。这项研究集中在事件中最无法解释的方面，以最好地约束其过去的历史和现在的行为。这项工作的圆满完成将大大提高对世界各地类似事件的了解，其中一些事件可能还产生了由于此类事件的不同寻常的性质而仍未被发现的资源。

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.