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

长期以来，研究人员一直对山地及其形成过程感兴趣。长期以来，美国西部的科迪勒拉一直被解释为响应洋壳俯冲到大陆地壳之下而发展起来的山带。尽管是一个“类型”的山带，但在中生代北美西海岸的大部分时间里，地面抬升的时间和强度仍然存在疑问。对南美洲安第斯山脉的深入研究导致一些人认为，地表抬升滞后于因俯冲而发生的缩短；这与地表抬升和缩短应同时发生的传统观点背道而驰。这项研究旨在提供科迪勒山造山事件中相对较早的地表高度估计，在此期间发生了大量的缩短。这一估计结合科迪勒事件结束和地壳增厚程度最高时的现有地表高度估计，应使我们能够确定地表抬升是在中生代期间发生缩短之后还是同时发生的。这些结果有可能告诉我们许多关于岩石圈对不同类型山脉带俯冲的响应，这对地震活动和灾害具有广泛的意义。此外，由于我们使用古代气候数据来估计古代海拔，该项目将提供有价值的洞察地球历史上相对温暖时期的古代气候条件，以及动植物如何随着时间的推移对气候和海拔变化做出反应。拉斯维加斯自然历史博物馆和塞拉学院(加利福尼亚州罗克林)的博物馆展览将向参观者介绍与山脉发展有关的新发现，以及曾经居住在该地区的中生代动植物。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；扩大对一个重要的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议的科学文献和专业科学会议上公布；分析数据将通过公众可访问的社区数据储存库提供。为了确定早白垩世时内华达州中部的地表高度，该项目团队将使用常规的和“成团的”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。然后将这些数据与犹他州时间相当的雪松山地层(一项正在进行的研究)中的类似数据集进行比较，以估计腹地古海拔。这些数据将与沉积学、古生物学、孢粉学、地质制图和凝灰岩地质年代学相结合，以提供关于该地区古代环境的关键背景，从而支持对地球化学记录的解释，并改进由此产生的古海拔估计。当被置于塞维尔造山期间地壳缩短的时间和规模的现有框架中时，将使用古高程估计来区分三种地表高程情景，每一种情景都具有不同的地球动力学影响。根据缩短历史直接预测地表高度为1-2千米，假设均衡补偿伴随着地壳在整个缩短过程中的增厚。低于这一高度意味着地壳增厚与致密低岩石圈的形成相一致，高于这一高度将意味着在造山作用期间致密岩石圈的早期去除。这项研究的结果将对与俯冲有关的造山作用过程中的岩石圈过程提供有价值的洞察，并为美国西部提供有价值的古代气候数据。此外，这项研究将把古高度学推向比现有数据集更早的时间，因此我们对古高度学中用于确定这些非常古老的古海拔的典型方法所做的修改，对于进一步推算其他造山带系统的古高度学估计将是有价值的。

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.