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

摘要本项目旨在研究晚新生代伸展构造运动时期美国西部中部盆地和山脉部分地区的地形演化。各种古高度计、地质研究和地球物理模型交替预测，美国西部要么经历了明显的晚新生代隆起，要么经历了明显的晚新生代下降，这是由于（或至少与之同步）大规模的大陆内构造作用。在某种程度上，这些不同的结果可能是由于美国西部地质的复杂性，以及许多研究地区在晚新生代可能经历了不同的构造历史。位于拉斯维加斯和内华达山脉之间的中部盆地和山脉省是研究美国西部古地形演化的理想地点，因为1)已经完成了广泛而详细的地质测绘，导致了第三纪伸展期相当完整的古地貌重建；2)最近在该地区进行的描绘地壳结构的被动和主动地震和其他地球物理实验；3)利用捕虏体和火山岩地球化学研究同一时期亚盆地和山脉岩石圈演化的研究。由于研究区玄武岩覆盖范围广，流动年龄范围广，且沙漠环境使其保持相对新鲜，因此新开发的基于玄武岩流泡的古高度计非常适合解决这一问题。PI计划在从内华达山脉到斯普林斯山脉的300公里横断面上对大约40个地点进行古海拔测量，并确定这些地点从中新世晚期到上新世或最近的古海拔。这项研究具有广泛的影响有几个原因；首先，它有力地支持了一个假说，即晚新生代的表生作用影响了美国和全球的气候。这项工作还将多年来通过在变形中添加第三维度来开发盆地和山脉扩展的地图视图古形体重建的工作联系在一起，最后，这项研究将是使用新开发的高度计进行的第一次广泛的构造研究。与高度计的开发人员和处理样品的分析设施的合作应该会导致未来使用该高度计的简化过程，以及测试和演示其在构造研究中的使用。

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.