Vertical-displacement history of an active Basin and Range fault based on integration of geomorphologic, stratigraphic, and structural data

Abstract

Knowledge of the last reactivation age of faults in the western Basin and Range province (western North America) is key to understanding the recent evolution of the province in the context of the Pacific-North America plate boundary region. The Dixie Valley fault system (DVFS;Nevada, USA) is an important active normal fault in this region, but its slip history is not well known. Our goal is to determine the age of faulting initiation and the history of vertical displacement at the million-year time scale. We used well data from the Dixie Valley geothermal field and geologic maps to calculate offsets of geologic units. Tectonic events and their ages were determined from knickpoint analysis in the Stillwater Range. We then matched basin unconformities and knickpoints to obtain a vertical displacement history. The age of inception of the modern DVFS is likely between 13 and 7 Ma. The total vertical displacement of the geologic units is between 3 and 3.5 km, and most of it occurred in the last 2-3 Ma. Assuming an erosion rate between 0.03 and 0.07 m/ka, the maximum vertical displacement rate (similar to 1-2 mm/a) occurred between 3 and 0.5 Ma, and resulted in similar to 2 km of vertical displacement. Finally, the age-versus-distance profile of the Stillwater Range crest is tapered at both ends, as expected for a propagating range-bounding normal fault, but it also has two maxima matching the deepest parts of the Dixie Valley basin. This indicates that the present-day DVFS may have started out as two separate strands that connected within 2-3 Ma of inception. Our work shows that the combination of stratigraphic and structural data from the basin with geomorphological data from the adjacent mountain range is suitable for placing constraints on the displacement history at the million-year time scale of an active range-bounding normal fault. The resulting displacement-time paths for normal faults may not be as uniform as commonly assumed.