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GMEG - Geology, Minerals, Energy, & Geophysics Science Center

Geologic framework of the Northern Great Basin

 

 

 

Northern Basin and Range Geologic Mapping

The northern Basin and Range has a long and complex tectonic history, including Paleozoic and Mesozoic shortening, major mid-Tertiary volcanism, and the pervasive Cenozoic normal faulting that formed its modern topography. The problem is that the timing and even approximate magnitude of Cenozoic strain are presently unknown across large parts of the Basin and Range, especially the area of central Nevada north of the well-studied Las Vegas / Colorado River extensional province, east of the Walker Lane - Eastern California shear zone (subject of recent and ongoing academic research), and south of the concentration of Eocene mineral deposits in the Elko - Carlin area. We have identified 3 primary areas for detailed study (geologic mapping at scales ranging from 1:24,000 to 1:100,000), including:

  1. The central Grant Range, where Mesozoic and Cenozoic structures in the Grant Range and adjacent basins played a key role in the formation of mineral and petroleum resources, but the kinematics and timing of deformation are not presently known. The Grant Range hosts several historic Au- and W-lode mining districts, and adjacent Railroad Valley contains productive oil fields sourced from both Paleozoic and Eocene rocks and produced from both fractured Paleozoic rocks and porous Oligocene ash-flow tuffs. The main problem is to evaluate the amount of extension across this region by constructing and restoring geologic cross sections based on modern mapping of the volcanic section.
  2. The north-central Toiyabe Range, which lies close to several very large Carlin-type gold deposits and is presently being explored for both gold resources as a potential geothermal energy site. The location and viability of these resources depends greatly on their relationship to Tertiary extensional structures, but three previous studies have drawn three different conclusions about the timing and kinematics of extensional faulting. The problem is to reconcile these interpretations into a coherent tectonic model for formation of the north-central Toiyabe Range and adjacent valleys.
  3. The Stillwater Range, which is bounded against neighboring Dixie Valley by an east-dipping normal fault that produced an M 7.1 earthquake in 1954. Since 1988, Dixie Valley has been home to the largest (66 MW) single geothermal power plant in Nevada, which produces energy from fluids circulating in the Dixie Valley fault system. Geologic hazards and geothermal resources in this region are thus both fundamentally controlled by extensional fault systems, but the timing and kinematics (fault geometry) of extensional faulting in the Stillwater Range remain unclear.

Objectives: The objective of this task is to refine our large-scale understanding of the timing and structural style of Cenozoic deformation, volcanism and sedimentary basin formation in the northern Basin and Range. Specific research objectives will vary between the three primary study areas described above, but for each area we intend to produce new geologic maps at 1:24,000 to 1:50,000 scale (based on both new mapping and compilation of existing mapping), construct retrodeformable cross sections from these maps, and test and refine these cross-sections by collecting new geophysical, paleontologic, geochronologic, and thermochronologic data. We will integrate data from these studies with results from better-known areas to the north, west, and south.

   

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