Regional timing and spatial distribution of Miocene extension in the northern Basin and Range Province

The northern Basin and Range Province has experienced multiple periods of extension in the Tertiary, but the location, timing and magnitude of the various events remain controversial. In this thesis, regional apatite fission-track (180), U-Th/He (90) data and 40Ar/39Ar ages (30) of tilted volcanic units are presented that help constrain the timing and spatial distribution of extensional faulting across the northern Basin and Range Province. Thermochronological data were collected in the Beaver Dam Mountains, the Canyon Range, House Range, Egan Range, Grant Range, White Pine Ranges, Toiyabe Range, Wassuk Range, Singatse Range, Carson Range, and White Mountains. The data point to the Early and Middle Miocene (18-12 Ma) as a period of major extensional faulting and basin-range formation. Although relatively short-lived at the scale of the province, this event produced large-magnitude extension. The region affected includes a large portion of the northern Basin and Range Province, from the Canyon Range to the east to the Singatse Range to the west and from the Ruby Mountains to the north to the Colorado River region to the south. Many of the faults that developed during this time continued to slip at younger times, but in general the amount of post-Miocene slip has not been sufficient to exhume rocks with younger totally or partially reset ages. The thermochronological data suggest that the present-day spatial distribution of deformation in the Basin and Range is not just a modern phenomenon, but has remained virtually unchanged since the Late Miocene with lesser extensional faulting in the central Basin and Range occurring thereafter.; Systematically younger fission track and (U-Th)He ages from 12 Ma to 4 Ma in the transition zone between the northern Basin and Range Province and Sierra Nevada document a widening of the province and a progressive encroachment of faulting into the Sierra Nevada. Structural and (U-Th)/He age data, in particular from the White Mountains, also demonstrate that transtensional faulting in the western Basin and Range Province associated with the Walker Lane Belt probably commenced in the late Miocene and Pliocene, overprinting earlier Miocene extensional structures. Transtensional slip along existing normal faults and locally developed pull-apart structures was sufficient to exhume partially annealed apatite fission track ages and totally reset (U-Tb)/He ages. Late Miocene - Pliocene transcurrent shear in the western Basin and Range Province appears to affect a large region of the western Cordillera inboard of the San Andreas fault, thus distributing plate boundary related deformation associated with North America - Pacific relative motion.