Collaborative Research: The Record of Early Cretaceous Growth of the Nevadaplano From Syn-orogenic Deposits of the Sevier Hinterland

长期以来，研究人员一直对山脉及其形成过程感兴趣。美国西部的科迪勒拉山脉长期以来被解释为一个山脉带，是由于大洋地壳俯冲到大陆地壳之下而形成的。尽管是一个“类型”的山区带，但是，问题仍然存在的时间和规模的地表隆起在大部分的长期俯冲关闭的北美西海岸在中生代。对南美洲安第斯山脉的深入研究使一些人认为，地表隆起滞后于俯冲作用引起的缩短;这与地表隆起和缩短应该同时发生的传统观点背道而驰。本研究的目的是提供一个估计的表面海拔相对较早的科迪勒拉山脉建设事件，在此期间发生了大量的缩短。这一估计，结合现有的地表高程估计从结束的科迪勒拉事件和地壳增厚的最大水平，应使我们能够确定是否发生地表隆起后，或在中生代期间与缩短同步。这些结果有可能教会我们很多关于岩石圈对不同类型的山带俯冲的反应，这对地震活动和灾害具有广泛的影响。此外，由于我们使用古代气候数据来估计古代海拔，因此该项目将为地球历史上相对温暖时期的古代气候条件提供有价值的见解，以及动物和植物如何随着时间的推移对气候和海拔变化做出反应。在拉斯维加斯自然历史博物馆和塞拉学院（罗克林，加利福尼亚州）的博物馆展览，将告知游客有关山区发展的新发现，以及中生代植物和动物曾经居住在该地区。其他重要的社会成果包括为三名早期职业研究人员提供支持;扩大对重要STEM（科学，技术，工程和数学）学科的参与;以及发展研究基础设施。研究结果将在同行评审的科学文献和专业科学会议上介绍;分析数据将通过可访问的社区数据库提供。为了确定早白垩世期间内华达州中部的地表高度，项目小组将使用常规和“成块”稳定同位素地球化学来估计古代温度和水的稳定同位素组成。然后将这些数据与来自犹他州时间等效的雪松山组的类似数据集进行比较（一项正在进行的研究），以估计腹地古海拔。这些数据将与沉积学、古生物学、孢粉学、地质测绘和凝灰岩地质年代学相结合，以提供有关该地区古代环境的关键背景，从而加强对地球化学记录的解释，并改进由此产生的古海拔估计。当放置在现有的框架内的时间和规模的地壳缩短发生在塞维尔orthopolitan，古海拔估计将被用来区分三个表面海拔的情况下，每一个不同的地球动力学的影响。假设地壳在缩短的整个过程中伴随着地壳增厚的均衡补偿作用，直接从缩短的历史中预测出1-2公里的地表高程。海拔低于此将意味着地壳增厚与致密的低层岩石圈的产生相一致，海拔高于此将表明，在造山作用早期，致密的岩石圈的去除。这项研究的结果将提供有价值的洞察范围内的岩石圈过程，在俯冲相关的造山作用，以及提供有价值的古代气候数据，为美国西部。此外，这项研究将推动古测高比现有的数据集更早的时间，所以我们对古测高中使用的典型方法进行修改，以确定这些非常古老的古海拔将是有价值的，推动古测高估计在其他造山系统进一步回到过去的时间。

Researchers have long been interested in mountain belts and the processes that create them. The Cordillera of the western United States has long been interpreted as a mountain belt that developed in response to subduction of oceanic crust beneath continental crust. Despite being a "type" mountain belt, however, questions remain about the timing and magnitude of surface uplift during much of the prolonged duration of subduction off of the west coast of North America during the Mesozoic. Intensive study of the South American Andes has led some to suggest that surface uplift lags behind the shortening that occurs in response to subduction; this runs counter to the conventional wisdom that surface uplift and shortening should occur in tandem with each other. This study aims to provide an estimate of surface elevation relatively early in the Cordilleran mountain building event, during which a large amount of shortening took place. This estimate, combined with existing surface elevation estimates from the end of the Cordilleran event and at greatest levels of crustal thickening, should enable us to determine whether surface uplift occurred after or in tandem with shortening during the Mesozoic. These results have the potential to teach us a great deal about the response of the lithosphere to subduction in different types of mountain belts, which has broad implications for seismic activity and hazards. In addition, because we use ancient climate data to estimate ancient elevations, this project will provide valuable insight into ancient climate conditions during a relatively warm period in Earth's history, and also how animals and plants respond to both climate and elevation change through time. Museum displays at the Las Vegas Natural History Museum and Sierra College (Rocklin, CA), will inform visitors about the new findings related to mountain development, as well as Mesozoic plants and animals which once inhabited the area. Other important societal outcomes include providing support for three early career researchers; broadening of participation in an important STEM (science, technology, engineering, and mathematics) discipline; and development of research infrastructure. Results of the research will be presented in the peer-reviewed scientific literature and at professional science meetings; analytical data will be made available via publically accessible community data repositories. To determine surface elevation in central Nevada during the Early Cretaceous, the project team will use conventional and "clumped" stable isotope geochemistry to estimate ancient temperature and stable isotope composition of water. These data will then be compared to similar datasets from the time-equivalent Cedar Mountain Formation in Utah (a study in progress) in order to estimate hinterland paleoelevation. These data will be integrated with sedimentology, paleontology, palynology, geologic mapping and tuff geochronology to provide critical context about the ancient environment of the region that will bolster the interpretations of the geochemical records and improve the resulting paleoelevation estimates. When placed in the existing framework of the timing and magnitude of crustal shortening that occurred during the Sevier orogeny, the paleoelevation estimates will be used to distinguish between three surface elevation scenarios, each with distinct geodynamic implications. Surface elevations of 1-2 kilometers are predicted directly from the shortening history, assuming that isostatic compensation accompanied crustal thickening throughout the duration of shortening. Elevations lower than this would imply that crustal thickening coincided with generation of dense lower lithosphere, and elevations higher than this would suggest that removal of dense lithosphere operated early during orogenesis. The results of this study will provide valuable insight into the range of lithospheric processes that operate during subduction-related orogenesis as well as provide valuable ancient climate data for the western United States. In addition, this study will push paleoaltimetry farther back in time than existing datasets, so modifications we make to typical approaches used in paleoaltimetry to determine these very ancient paleoelevations will be valuable for pushing paleoaltimetry estimates in other orogenic systems further back in time.