Preliminary Geologic Map of the Lower Pahranagat Lake NW Quadrangle, Lincoln County, Nevada
by Thomas Price, Michael Evans, Mahmud M. Muhammad, Max Hinson, Alexis McIntyre, Alexander Peck, Philip Hahn, and Wanda J. Taylor
Series: Open-File Report 2017-03
Format: plate: 34.5 x 27.5 inches, color
View/Download/Purchase: http://pubs.nbmg.unr.edu/Prelim-Lower-Pahranagat-Lake-NW-p/of2017-03.htmThe Lower Pahranagat Lake NW quadrangle, Lincoln County, Nevada, includes Paleozoic strata, a Cretaceous-Tertiary sedimentary interval, Cenozoic units, and structures of at least two different deformations.
The exposed Paleozoic formations range from Ordovician Pogonip Group to Devonian Simonson Dolomite. These rocks are mostly carbonate, but some siltstone and sandstone, including the Eureka Quartzite, are interlayered. The Cenozoic units are subdivided into an Oligocene to Miocene section and a Pliocene to Quaternary section. The Oligocene-Miocene section contains mostly ash-flow tuffs that range from the 27.57 Ma Monotony Tuff to the ~15 Ma Kane Springs Wash tuff with minor siliciclastic intervals. The Pliocene-Quaternary section consists of clast-supported conglomerate to clayey sand that was deposited in two different ages, older and younger, of alluvial to fluvial environments.
The older of the two deformations is associated with the Sevier orogeny or associated central Nevada thrust belt and Nevadaplano. The Jurassic or Cretaceous Gass Peak thrust lies to the southeast of the quadrangle and the correlative Pahranagat and Mt. Irish thrusts are exposed to the north. In the quadrangle, this deformation is represented by one small reverse fault exposed in the north and tilting of the Paleozoic rocks. The angle across the Paleogene unconformity is about 35° in the northern and central parts of the quadrangle. A paleo-hill of Paleozoic rocks against which the Tertiary-Cretaceous sedimentary unit through the 22.56 Ma Harmony Hills Tuff are in buttress unconformity occurs in the northern part of the quadrangle. The presence of this paleo-hill suggests notable erosion. The second interval of deformation occurred in the Miocene-Quaternary as shown by normal-, oblique-, and strike-slip faults. The majority of these faults cut all of the exposed tuffs indicating that they are younger than the ~15 Ma Kane Wash Tuff. Based on crosscutting relationships, at least three ages of deformation occurred within the quadrangle: (1) 22.2 and 18.6 Ma, (2) 18.6 to 15.3 Ma, and (3) post 15 Ma. The major post-15 Ma structures are part of the NE-striking, left-lateral Pahranagat shear zone (a.k.a. Pahranagat fault system). Parts of each of three major left-lateral faults of that system are exposed: the Arrowhead Mine fault in the north, the Buckhorn fault in the center, and the Maynard Lake fault in the south. The km-scale Buckhorn syncline lies just north of the Buckhorn fault and folds rocks as young as the ~15 Ma Kane Wash Tuff. This syncline plunges gently NE and is an open fold. The Buckhorn syncline is interpreted as a fault propagation fold related to left-lateral slip along the Buckhorn fault based on subparallel orientations and timing. Small strike-slip duplexes occur along the Arrowhead Mine and Maynard Lake faults. Each duplex occurs near a bend in a strike-slip fault, which suggests that the duplexes accommodate changes in fault strike.
Partial support provided by the U.S. Geological Survey, National Cooperative Mapping Program award number G15AC00157, 2015.
A note from the authors (Department of Geoscience; University of Nevada, Las Vegas): We thank James Faulds and Angela Jayko for their support of this project. We also thank our valuable field assistants Jeremy Miera and Jeffrey Kinney.