STRUCTURAL EVOLUTION OF THE MAYNARD LAKE FAULT (MLF) WITHIN THE LEFT-LATERAL PAHRANAGAT SHEAR ZONE (PSZ), NEVADA, USA

The Basin and Range province of western North America can be subdivided into three Cenozoic geological and geophysical sub-provinces/rift segments: Northern, Central, and Southern. The boundary between the northern and central sub-provinces, is marked by caldera complexes and ENE-striking left-lateral strike-slip fault zones such as the Pahranagat shear zone (PSZ). More detailed documentation of the geometry, timing, and kinematics of the PSZ is critical to understanding the development of the sub-province/rift segment boundary. One of the three major strike-slip faults within the PSZ is the Maynard Lake fault (MLF). Our new 1:12000 scale mapping of the Maynard Lake Fault (MLF) along with cross sections and stereographic interpretation clarifies the geometry, kinematics and relative timing of faults associated with the MLF.

Within the northern Sheep Range-southern East Pahranagat Range area, a strike-slip duplex is exposed along the PSZ. The duplex is bound by two left-lateral strike-slip faults. The northern bounding fault has a component of reverse slip. Four folds occur within and adjacent to the duplex area. The duplex folds trend SW and N whereas folds adjacent to the duplex trend, NE, and ENE. The southern bounding fault has a component of normal slip and it appears to be the main strand of the MLF. The duplex includes four normal faults and three reverse faults, therefore the duplex accommodates both extension and shortening along with the strike slip.

Three fault sets (ENE, N-S, and NW) are distinguished according to the fault strike orientation including the duplex faults. All fault sets cut Miocene rocks, and so, are Miocene or younger in age. The ENE-striking fault set is the MLF and the N-S strike fault set appears to be synchronous, based on cross-cutting relationships. The NW-striking fault set is older as it is cut by the ENE and N-S fault sets. The N- and ENE-striking faults observed within Quaternary units indicate that the MLF is most probably still active, which is consistent with modern seismicity data in the region.

In conclusion, our dataset including the map data, cross-cutting relationships, constructed cross-sections, and stereographs propose at least two stages of deformation within the MLF: 1. Oligocene-Miocene NW-striking fault set and 2. Late Miocene-Quaternary N-S and ENE striking fault sets.