MIOCENE-PLIOCENE(?) FOLDS AND THE LEFT-LATERAL BUCKHORN FAULT WITH REGIONAL IMPLICATIONS, PAHRANAGAT SHEAR ZONE, NEVADA

Folds related to strike-slip faults in extended regions can reveal aspects of the development and evolution of the fault system. For example, do the folds reflect fault propagation or transpression? Fold-fault relations along the boundary zone between the Northern and Central Basin and Range sub-provinces can shed light on the evolution of this zone that extends from the Eastern California Shear Zone and/or Walker Lane Belt, to the Wasatch Fault Zone/Intermountain Seismic Belt. Our purpose is to increase the understanding of the sub-province/rift segment boundary development through investigating the Buckhorn syncline (BS), Buckhorn anticline (BA), and the major left-lateral fault near them, the Buckhorn fault (BF). The kilometers across BS and smaller BA, named here, fold Miocene tuffs within the NE-striking left-lateral Pahranagat shear zone (PSZ), which forms the central part of the boundary zone. The BF is the central of three major strike-slip faults that form the PSZ, which together with the Caliente-Enterprise zone to the NE forms a Miocene-Quaternary transfer zone along the sub-province boundary. The relative timing of deformation and development of the BS, BA and BF were determined through geometric and spatial data collected by mapping in the East Pahranagat Range, southern Nevada, at a 1:12,000 scale. The absolute timing of deformation is constrained to younger than the stratigraphically highest deformed tuff, the Kane Wash Tuff. This tuff yielded a 15.3 Ma age from ⁴⁰Ar/³⁹Ar dating of sanidine. The BF, BS and BA formed after 15.3 Ma, and thus, cross-cutting relationships are used to put these in sequence. The BS is a gentle to open, upright, syncline. It is oriented 27°, 032°, subparallel to the BF, and occurs along the western BF where offset decreases to the SW along strike; the formation of the BS resulted from the westward propagation of the BF. The BA folds a limb of the BS and trends 010°, not parallel to the BS, thus, the two folds formed sequentially. The BA resulted from multiple factors including drag along the BF and local shortening inside a bend in the BF. In summary, after 15.3 Ma the BF propagated SW forming the BS and then the BA deformed a limb of the BS near a bend in the BF suggesting that bend is a later feature; this history suggests prolonged deformation within the development of the sub-province boundary zone.