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

University Of Colorado At Boulder, Boulder CO

Investigators

Abstract

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.