Reconstruction modeling of crustal thickness and paleotopography of western North America since 36 Ma

Alireza Bahadori, William E. Holt, & E. Troy Rasbury

Published April 20, 2018, SCEC Contribution #8019

The complex deformation history of the western United States since 36 Ma involves adramatic transition from a subduction-dominated to a transform-dominated margin. This transition involved widespread extension, collapse of topography, and development of the interior Basin and Range region. The topographic collapse resulted in significant exhumation of deep crustal rocks exposed in metamorphic core complexes of the southwestern Cordillera. We use calculated position estimate changes for the western United States from previous work based on a comprehensive compilation of geological and structural information, and incorporation of constraints from Pacific plate motion history to determine lithospheric strain rates through time, and integrate these strain rates to provide quantitative models of crustal thickness and surface elevation, along with formal standard errors, since 36 Ma. Our crustal thickness model at 36 Ma is consistent with a significant crustal welt, with an average thickness of ~56.5 ± 2.5 km, in eastern portions of northern to southern Nevada as well as parts of eastern California and through Arizona. Our final integrated topography model shows a Nevadaplano of ~3.95 ± 0.3 km average elevation in central, eastern, and southern Nevada, western Utah, and parts of easternmost California. A belt of high topography also trends through northwestern, central, and southeastern Arizona at 36 Ma (Mogollon Highlands). Our model shows little to no elevation change for the Colorado Plateau and the northern Sierra Nevada (north of 36°N) since at least 36 Ma, and that between 36 and 5 Ma, the Sierra Nevada was located at the Pacific Ocean margin, with a shoreline on the eastern edge of the present-day Great Valley.

Key Words
Basin and Range, Sierra Nevada, Nevadaplano, Crustal Thickness, Paleo-elevation, Metamorphic Core Complexes.

Bahadori, A., Holt, W. E., & Rasbury, E. (2018). Reconstruction modeling of crustal thickness and paleotopography of western North America since 36 Ma. Geosphere, 14(3), 1207-1231. doi: 10.1130/GES01604.1.