Collaborative Research: Integrating tectonics, climate, and mammal diversity

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The researchers seek to understand how movement of tectonic plates, which produced major mountain barriers and influenced regional climate, controlled the evolution and geographic distribution of mammals in western North America. The EarthScope Transportable Array, a network of seismic stations, has produced data that allow an unprecedented view of the Earth's structure in the western United States, providing a unique starting point from which to consider how it came to have the 3-D structure that is imaged by seismic methods. This, combined with a rich published record of structures that record changes in plate tectonics and deformation history over the past 36 Ma, allows us to estimate crustal thickness and topography throughout the western US over this important interval in mammal evolution. The researchers propose to use 3D models to understand the collapse of topography in the western US, which led to marked changes in mammal diversification that coincide with changes in the strain rates recorded in the fault movement record. The research will be accomplished through collaboration of teams that will 1) Improve dating of the sedimentary record that contains the mammalian record, as well as focused sampling of fossils from under-represented areas and time intervals, 2) produce 3D models for lithosphere modification that account for changes in heat flux and boundary conditions, 3) model regional climate that builds on topographic constraints, 4) analyze mammal speciation and diversification and its links over time with topography and climatic gradients, and 5) synthesize all of the results into a 4D model for change through the past 36 Ma. The ultimate goal is to produce a more fundamental understanding of the factors responsible for crustal and topographic changes and how these influence mammal speciation and diversification. The quantitative analysis of crust and mantle dynamics provides an important framework for advancing knowledge in fields linked to the economic geology (mineral belts) of the southwestern US. The research will provide valuable technical training to high school, undergraduate, graduate and post-doctoral researchers. The collaborative team will develop several outreach products, including an informational video for the general public, materials for museum presentations and exhibits at the University of Michigan Museum of Natural History, the departmental Museum Display at Stony Brook, and materials for talks and presentations to the public.The integrated topography model shows a Nevadaplano of ~4.36 +/- 0.4 km (1-sigma) average elevation in central, eastern, and southern Nevada, western Utah, parts of easternmost California, and central portions of westernmost Arizona at 36 Ma. Our model shows that highlands of the Nevadaplano connected to a continuous mountain chain through southeastern Arizona and into northern Mexico. This topography results from the long history of crustal shortening from Sevier - Laramide orogenies. The topography of this massive range collapsed from 36 Ma to the present, leading to as much as 200% extension, the present-day Basin and Range, and exhumation of metamorphic core complexes along the belt of thickened crust. Distributions of lithospheric body forces continue to drive this collapse today. Differences in gravitational potential energy are known to drive extensional deformation, particularly in regions of extreme topography. Yet the reasons for the timing of the collapse, along with the magnitudes and distributions of deviatoric stresses responsible for the collapse, remain enigmatic. The changing topography associated with extensional collapse dramatically altered the climate and mammal diversity dynamics of the western Cordillera. Our research targets three topics within the Integrated Earth System: (1) The topography, distribution, and 3-D deviatoric stresses responsible for the collapse history, (2) The climatic response to the collapse and generation of climate gradients, and (3) The response of mammal lineages and faunas to changing topographic and climate gradients and removal of topographic barriers. No previous study of climate gradients and their impact on mammal diversity has ever been integrated with quantitative kinematic and dynamic reconstructions of continental deformation. The intellectual merit of this study involves the power of combining these fields, while incorporating formal uncertainties in models at all stages of analysis.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.