Cordilleran Section - 108th Annual Meeting (29–31 March 2012)

Paper No. 3
Presentation Time: 15:10

STRATIGRAPHY AND STRUCTURE OF THE NORTHERN HIGHLAND RANGE, COLORADO RIVER EXTENSIONAL CORRIDOR, SOUTHERN NEVADA


MCKEE, Ryan A., Department of Geology, San Jose State University, One Washington Square, San Jose, CA 95192 and MILLER, Jonathan S., Geology, San Jose State University, San Jose, CA 95192-0102, ramckee@gmail.com

The northern Highland Range (Nevada) occupies a critical structural position just to the north of the Black Mountains accommodation zone in the northern Colorado River Extensional Corridor (CREC), that separates west-tilted crustal blocks to the south from east-tilted blocks to the north. New 1:24000 scale mapping was completed to better understand the structural and volcanic/depositional evolution of the northern Highland Range near the accommodation zone.

The basal strata in the northern Highland Range are a thin (240 m) series of aphyric trachyandesites and crystal-rich trachydacite flows and breccia domes that sit nonconformably on Precambrian basement. Above this are 3000 m of monotonous intercalated trachyandesites and trachyandesite breccias, with a lithic tuff sequence (640 m) occurring in the middle part of the sequence. The regionally extensive Tuff of Bridge Spring (15.2 Ma) and Tuff of Mt. Davis (30-40 m) ignimbrites cap the trachyandesite sequence; boulder conglomerates comprise the remaining strata above the ignimbrites. Mainly N to NE-striking intermediate dikes variably cut the basement and overlying strata. Petrographic similarities between dikes and some flows suggest they likely served as feeders.

The strata are predominantly east-tilted 20° to 40°, and cut by a series of NW- to NE-trending, mostly W-dipping (40°-90°) normal faults with variable displacements (10’s to 1000+ m). In the southern part of the map area, which is at the northern boundary of the accommodation zone (a NW-plunging anticline), N-trending faults are cut by NW-trending faults. North of the accommodation zone boundary, faults mostly trend N or NE and a small basement horst is present. Dikes in the south are consistently N-striking but also change to either NE or NW-strikes in the north. Stratal tilts indicate the northern Highland Range is part of the east-tilted Lake Mead structural domain but the changing orientations of faults and dikes suggest a complicated strain field, perhaps a result of the western CREC breakaway fault (McCullough Range Fault) dying out at depth to the north beneath the mapping area.