Geologic Cross Section of the North American Plate near 36° Latitude, Part I: Western U.S. from the Pacific Oceanic Crust to the Mid-Continent

Abstract

A geologic cross section across the southern United States near latitude 36° provides an up-to-date working model for the structure of the North American plate and its interactions with the upper mantle asthenosphere. The American Geological Institute, in dedication to Marcus E. Milling, will produce an annotated 1:1 M-scale technical cross section across the continent useful to researchers, and a 1:2 M-scale geological cross section useful for K-12, the general public, and introductory college geology classes. The visual product will consist of an oblique DEM, to add a 3D component, along with the cross section at 4:1 vertical exaggeration that will portray the geology to depths of 250 km. The cross section extends from the eastern to the western margin of the North American plate. The western half consists of a tectonically active domain in which plate boundary deformation is inducing and interacting with a complex intraplate deformational field in a 1000-km-wide uplifted orogenic plateau that extends as far east as the Great Plains. This wide deforming plate margin domain provides a field laboratory for understanding the structure and evolution of continental plates. The western segment of the GeCSNAP cross section extends from the coastal Franciscan accretionary complex, across the Salinia forearc microplate, the San Andreas fault, the Cretaceous forearc basin, the Sierra Nevada Mesozoic magmatic arc, the eastern California shear zone of the Basin and Range province, the Colorado Plateau, the Rio Grand rift, the Rocky Mountains, and the western Great Plains. A theme of the cross section is dynamic mantle flow under the western U.S. where lithosphere is sinking beneath the Sierra Nevada and asthenosphere is upwelling in the Basin and Range, near the western edge of the Colorado Plateau, and in the Rio Grande rift.