13 Structural Geology and Tectonics

Thursday, 19 May 2011
8:00 AM - 12:00 PM
Elm

TECTONIC DEVELOPMENT IN THE WHITE PINE RANGE AND EAST-CENTRAL NEVADA

Paper number: 13-8
Program: Technical Sessions
Time: 10:00 AM – 10:20 AM

Authors

Abstract

The Phanerozoic tectonic evolution of western North America consists of multiple contractional and extensional events that are recorded in Nevada. Rocks in the White Pine Range (WPR), of east-central Nevada, record the deformational events that occurred in the late Paleozoic, Mesozoic and Cenozoic. Deformation in the late Paleozoic, between the Antler and Sonoma orogenies, is documented in several locations throughout central Nevada as an angular unconformity. The Mesozoic contractile structures in the WPR are known as the Illipah fold and thrust belt, which is a part of the central Nevada thrust belt (CNTB). The youngest structures are extensional faults that overprint the contractional structures and were active in the Cenozoic. Documenting the structural style of these deformations contributes to understanding the tectonic evolution of western North America. The questions to be addressed include: (1) do the late Paleozoic, Pennsylvanian-Permian, rocks record a previously unrecognized deformation; (2) does the Illipah fold and thrust belt record east to west shortening; and (3) is the Cenozoic extension dominated by low-angle normal faulting?

Detailed geologic mapping at a scale of 1:12,000 in the central WPR and various structural analyses were performed to address these questions. Stereographic projections were used to determine structural orientations and kinematics. The key structure is a broad fold train that strikes N-S, which is refolded into a NW-SE trend. Extensional faults trend N-NE and dip 25°, these are cut by NW trending faults that dip 15-20°. Retrodeformable and deformed state cross-sections were constructed to interpret structural geometries, calculate amounts of contraction and extension, and to construct a temporal stepwise structural development. Biostratigraphic dating of fusilinids will be used to define the age of unconformities in the field area.

The initial results (1) further constrain the tectonic style of the CNTB to be mainly large folds, (2) define a better stratigraphy for Pennsylvanian and Cenozoic volcanic rocks by subdivision of existing units, and (3) provide a geologic map and insight for future exploration of hydrocarbons in Railroad Valley.