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

该项目旨在观察美国西部部分中央盆地和山脉在晚新生代伸展构造作用期间的地形演化。各种古高度计、地质研究和地球物理模型交替预测，美国西部经历了重大的晚新生代隆起或显著的晚新生代大幅下降，这是由于或至少与大规模陆内构造作用同步。这些不同的结果在一定程度上可能是由于美国西部的地质复杂性，以及许多研究地区在晚新生代时期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填图，从而对第三纪伸展进行了相当完整的复古重建；2)最近在该地区进行了被动和活动的地震和其他地球物理实验，描绘了地壳结构；3)利用捕捉体和火山岩的地球化学研究了次盆地和山脉岩石圈在同一时期的演化。基于玄武岩流泡的新开发的古高度计非常适合于研究这一问题，因为该研究区玄武岩覆盖范围广，流的年龄范围广，沙漠环境使它们保持相对新鲜。PI建议在内华达山脉到内华达州斯普林山300公里的样带上对大约40个地点进行古高程测量，并确定这些地点从晚中新世到上新世或最近的古海拔。这项研究具有广泛的影响，原因有几个；首先，它强烈支持晚新生代表生作用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，通过在形变中添加第三个维度来开发盆地和山脉延伸的图视古迹重建，最后，这项研究将是第一次使用新开发的高度计进行广泛的构造研究。与高度计的开发者和处理样品的分析设施的合作应该会简化该高度计的未来使用过程，并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.