Hypsometric History of the North American Continental Interior and Implications for Mantle Dynamics

该项目是一项跨学科研究，旨在了解大陆内部显生宙地层记录的长期侵蚀剖面的厚度、空间范围和演化，以了解地球表面古海拔的神秘变化以及地幔性质的变化如何影响其历史。人们早就认识到，在地质学家的过去，大陆内部发生了隐秘性的海拔变化，但这种变化很难用传统的板块构造模型来调和，因为在传统的板块构造模型中，变形主要与板块边缘或板块边缘附近的过程有关。主要研究人员认为，地壳垂直运动的变化（称为动态地形）与地球岩石圈与地幔深处对流的相互作用有关。该项目将结合热年代学、地质年龄限制和3D建模，以测试与地幔动力学如何影响地表过程有关的假设。该项目为进一步了解地壳的变形如何与行星内部深处的过程联系在一起做出了根本性的贡献。除了科学目标的研究外，该项目还有助于研究基础设施；正在支持一名教员的研究工作，该教员是地球科学中一个代表性不足的群体的成员；正在为STEM（科学、技术、工程和数学）学科的博士生培养做出贡献；支持一名来自科罗拉多大学学生固体地球科学研究经验项目（RESESS）的本科生实习生的参与，这是一个促进地球科学多样性的项目；并为美国和澳大利亚科学家之间的国际合作提供机会。大陆内部隐秘性的表生高程变化不容易用板块边缘构造论来解释，这表明地球动力学和大陆演化的基本方面尚未被理解。然而，这一问题在地质调查中受到的关注相对较少。动力地形是由地幔对流产生的正常牵引作用下地球表面的垂直运动产生的，它为北美内部表面历史的一些方面提供了一个有吸引力的解释，否则这些方面很难用构造过程来解释。然而，尽管动态建模工作的复杂性和多样性不断增加，但要确定地测试这些模型仍然具有挑战性。现在对地质约束的需求巨大，以便更好地校准动态模型并区分不同的预测。本研究采用的多步骤方法的特点是：1)在适当的尺度上获取热年代学数据以推断区域趋势；2)通过热年代学和地质约束耦合重建区域埋藏、拆顶和高程变化历史；3)将该地表历史与热化学对流三维动力学模型的垂直运动预测进行比较。4)对动态模型进行合理修正，评价拟合对不同参数的敏感性。本研究围绕两个关键假设展开，这些假设涉及地幔动力学对北美内部地表演化的控制，这些假设来自于以前的工作。提议将这些过去的努力在空间上扩展到大陆更广泛的区域，并在时间上扩展到白垩纪。假设1：与超大陆演化相关的地幔流动对北美内陆古生代-中生代早期的构造演化具有重要的控制作用。假设2：整个美国中部的白垩纪埋藏比之前认识到的更为丰富，这是准确校准法拉龙板块演化动态模型的关键。

The project represents an interdisciplinary study aimed at understanding the thickness, spatial extent, and evolution of long-eroded sections of the Phanerozoic stratigraphic record across the continental interior in order to understand cryptic variations in paleoelevation of the Earth's surface and how variations in the properties of the mantle have influenced its history. It has long been recognized that cryptic elevation changes in the continental interior have occurred through the geologist past, but such changes are difficult to reconcile by conventional plate tectonic models in which deformation is largely related to processes at or near plate margins. The principal investigators posit that variations in vertical motion of the Earth's crust, termed dynamic topography, are related to the interaction of the Earth's lithosphere with convection deep within the mantle. The project will involve a combination of thermochronology, geologic age constraints, and 3D modeling to test hypotheses related to how mantle dynamics of the Earth's mantle affects surface processes. The project represents a fundamental contribution to furthering understanding of how deformation of the Earth's crust may be linked with processes deep within the planets interior. In addition scientific goals of the research, the project is contributing to research infrastructure; is supporting the research efforts of a faculty member who is a member of an underrepresented group in the geosciences; is contributing to the training of a Ph.D. student in a STEM (Science, Technology, Engineering, and Mathemathics) discipline; is supporting the involvement of an undergraduate student intern from the University of Colorado's Research Experiences in Solid Earth Science for Students (RESESS), which is a program that promotes diversity within the Earth Sciences; and is providing for international collaboration between U.S. and Australian scientists. Cryptic epeirogenic elevation change in continental interiors is not easily accounted for by plate margin tectonism, suggesting that fundamental aspects of geodynamics and continental evolution are not yet understood. Nevertheless, this problem has received comparatively little attention in geologic investigations. Dynamic topography, produced by vertical motion of the Earth's surface in response to normal traction generated by mantle convection, provides an attractive explanation for aspects of the North American interior surface history that otherwise are not easily explained by tectonic processes. However, despite the increasing sophistication and diversity of dynamic modeling efforts, it remains challenging to definitively test these models. There is now enormous demand for geologic constraints to better calibrate dynamic models and discriminate between their different predictions. The multistep approach to be employed in this study is characterized by 1) thermochronology data acquisition at a scale appropriate to deduce regional trends, 2) reconstruction of the regional burial, unroofing and elevation change history by coupling of thermochronologic and geologic constraints, 3) comparison of this surface history with the vertical motion predictions of a 3D dynamic model of thermochemical convection, and 4) experimentation with reasonable modifications to the dynamic model to evaluate the sensitivity of the fit to different parameters. This study is framed around two key hypotheses concerning mantle dynamic controls on the surface evolution of the North American interior that emerged from previous work. The proposed will expand these past efforts spatially across a broader region of the continent as well as temporally into the Cretaceous. Hypothesis 1: Mantle flow associated with supercontinent evolution was an important control on the Paleozoic-early Mesozoic hypsometric history of the North American interior. Hypothesis 2: Cretaceous burial was more substantial across the entire central U.S. than recognized previously, which is key for accurately calibrating dynamic models of Farallon slab evolution.