Paleotopography of an Evolving Extensional Orogen, the Central Basin and Range, Western United States

本项目旨在研究美国西部中央盆地和山脉的一部分在晚新生代伸展构造作用期间的地形演变。各种各样的古高度计、地质研究和地球物理模型交替预测，美国西部经历了显著的晚新生代隆起或大量的晚新生代下降，这是由于大规模的陆内构造作用，或至少与之同步。在某种程度上，这些不同的结果可能是由于美国西部的地质复杂性，以及许多研究地区可能在新生代晚期经历了不同的构造历史。位于拉斯维加斯和内华达州之间的中央盆岭地区是研究美国西部古地形演化的理想地点，因为：（1）广泛而详细的地质填图已经完成，对第三纪伸展作用进行了较为完整的古地理重建; 2）最近在该地区进行的被动和主动地震和其他地球物理实验，这些实验描绘了地壳结构; 3）研究了亚地壳的演化，利用捕虏体和火山岩的地球化学研究了同一时期的盆地和山脉岩石圈。一种新开发的基于玄武岩流囊的古高度计非常适合于解决这个问题，因为在本研究区域玄武岩的广泛覆盖，广泛的流动年龄范围，以及沙漠环境，使它们保持相对新鲜。PI建议在从内华达州山脉到内华达州斯普林山脉的300 km横断面上对大约40个地点进行古高程测量，并确定这些地点从中新世晚期到上新世或近代的古高程。这项研究具有广泛的影响，原因有几个：首先，它强烈地依赖于晚新生代地表运动影响了美国和全球气候的假设。这项工作还结合了多年的工作，通过增加第三维的变形，在开发地图视图盆地和山脉扩展的pallastically重建，最后，这项研究将是第一个广泛的构造研究，使用新开发的高度计。与高度计的开发者和处理样品的分析设施的合作，应能为今后使用这种高度计以及测试和演示其在构造研究中的用途提供一个简化的程序。

AbstractThis project is designed to look at the topographic evolution of a portion of the central Basin and Range in the western United States during a period of late Cenozoic extensional tectonism. A variety of paleoaltimeters, geologic studies, and geophysical models have alternately predicted that the western United States has experienced either significant late Cenozoic uplift or substantial late Cenozoic lowering due to, or at least synchronous with, large magnitude intracontinental tectonism. In part these disparate results may be due to the geologic complexity of the western United States, and the fact that many of the study areas may have undergone differing tectonic histories in late Cenozoic time. The central Basin and Range province, between Las Vegas and the Sierra Nevada is an ideal locality to study the paleotopographic evolution of the western United States because of 1) the wide spread and detailed geologic mapping that has been completed, resulting in a fairly complete palinspastic reconstruction of Tertiary extension; 2) recent passive and active seismic and other geophysical experiments in the region which delineate the crustal structure and 3) studies that have examined the evolution of the sub-Basin and Range lithosphere through this same time period using xenoliths and the geochemistry of volcanic rocks. A newly developed paleoaltimeter based on basalt flow vesicles is well suited for approaching this problem due to the extensive coverage of basalts in this study area, the broad age range of the flows, and the desert environment which keeps them relatively fresh. The PI proposes to sample approximately 40 sites for paleoaltimetry across a 300 km transect from the Sierra Nevada to the Spring Mountains, Nevada and determine the paleoelevations of these sites from late Miocene to Pliocene or Recent time.This study has broad impacts for several reasons; first it bears strongly on the hypothesis that late Cenozoic epierogeny has affected climate, both in the United States and globally. The work also ties together years of work in developing map view palinspastic reconstructions of Basin and Range extension by adding a third dimension to the deformation, and finally, this study will be the first broad tectonic study using the newly developed altimeter. Collaborations with both the developers of the altimeter and the analytical facilities which process the samples should result in a streamlined process for future use of this altimeter, as well as testing and demonstrating its use in tectonic studies.