Is the Wasatch fault footwall (Utah, United States) segmented over million-year time scales?

Abstract

The Wasatch fault zone, Utah, is a 370-km-long segmented normal-fault system with topographic salients, depths of footwall exposure, geomorphic properties, and geophysical anomalies that suggest differential long-term footwall uplift and exhumation on segments that are partitioned by long-lived structural segment boundaries. Apatite (U-Th)/He ages from footwall samples along the range front from the five central footwall segments average 5.3 ± 1.0 Ma. Coupled two-dimensional thermokinematic and helium-diffusion models suggest average long-term (∼5 m.y.) exhumation rates of 0.2–0.4 mm/yr for most of the Wasatch front. The exception is the southern end of the Salt Lake City segment, where exhumation rates are two times as great as elsewhere along the Wasatch front. The relatively invariant He ages and exhumation rates imply that most of the Wasatch did not behave kinematically as independent footwall-segment blocks with differential exhumation amounts over the past 5 m.y. The structural boundaries, such as salients and intrabasin highs that partially delineate segments, may have persisted since the Pliocene and controlled the locations of the surface-rupture segments.