Geometry of Cenozoic extensional faulting: Dixie Valley, Nevada

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Journal Article: Geometry of Cenozoic extensional faulting: Dixie Valley, Nevada

Precise definition of geometric relationships between individual basins and ranges may help to reveal the mechanical processes of Basin and Range Cenozoic extensional faulting at depth. Previous studies have attempted to identify simple horsts and grabens, tilted crustal blocks with planar faulting, or tilted crustal blocks with listric faulting in the shallow crust. Normal faults defining these crustal blocks may root (1) individually in the ductile lower crust, (2) in regional or local low-angle detachment faults, or (3) in igneous intrusions or decoupling surfaces produced by the intrusions. The present study, in Dixie Valley, west-central Nevada, makes use of a seismic reflection survey, gravity models, seismograms from earthquakes occurring on December 16, 1954, and geometrical block models. These data show a structurally asymmetric basin bounded by a single zone of faulting on the northwest and by a downbowed and step-faulted floor to the southeast. The northwest bounding fault is moderately dipping (50°) and planar to a depth of 3 km. The southeast boundary is step-faulted, and altogether the faults indicate an extension of 20% across the valley at the rate of 0.38 mm/y for the last 8 my. Synthetic earthquake seismograms confirm a focal depth of 15 km and fault dip of 62° for the Fairview Peak earthquake and suggest that the focal depth of the Dixie Valley earthquake was also 15 km instead of the previously reported 40 km. Local microearthquakes cluster around 10-15 km. The geometrical block models indicate that crustal horst-graben faulting and planar, high-angle normal faults rooted in a low-angle detachment surface do not readily account for development of the subsidiary (step) faults found in Dixie Valley. Extension of the crust by intrusion may develop high-angle faults and, with further intrusion, may develop the subsidiary faults and produce a complex, sagged, asymmetric graben like Dixie Valley.

David A. Okaya and George A. Thompson

Published Journal 
Tectonics, 1985

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David A. Okaya,George A. Thompson. 1985. Geometry of Cenozoic extensional faulting: Dixie Valley, Nevada. Tectonics. .

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