EXTENSIONAL TRANSVERSE AND TRANSFER FAULTS, TIMPAHUTE AND MT. IRISH RANGES, SOUTHERN NEVADA

Transverse and transfer faults allow differences in ages, amounts, locations, or directions of extension in large regions. Two N-striking transfer faults and two E-striking transverse fault systems in the Timpahute and Mt. Irish Ranges, southern Nevada, exemplify such differences in loci and directions of extension. The Timpahute Range and Mt. Irish form an E-trending block with little internal extension. The block is defined by the E-W Penyoer Spring fault system (PSFS) on the north, the N-S Mt. Irish fault on the east, the E-W Crescent Spring fault system (CSFS) on the south, and the N-S Schofield Pass fault on the west.

PSFS faults strike E-W and dip steeply. Piercing points across the PSFS are offset ~1 km by dip slip and ~1 km by left slip on the east. In contrast, on the west piercing points are offset ~1.5 km by dip slip and ~6 km by left slip. Between these areas and on the N, ~N-S striking normal faults end at the PSFS. On the south, no significant normal faults crop out. The normal faults accommodate 5 km of E-W extension. This value equals the difference in left slip between the E (~1 km) and W ends (~6 km) of the PSFS. Thus, the normal faults transfer their slip onto the PSFS as strike slip.

The Mt. Irish fault, on the east, strikes N-S and dips steeply. Much of this fault is a reactivated Mesozoic thrust. On the north, some PSFS faults terminate at the Mt. Irish fault and transfer slip onto it. On the south, the strike-slip fault cuts away from the thrust and is cut by the CSFS.

CSFS faults strike E-W and dip 45-60 degrees S. The faults are dip slip as shown by slickenlines, slickenfibers, and grooves and mullions. They down drop the area south of the E-W structural block. Also, Cenozoic normal faults south of the CSFS generally strike E-W or NW-SE suggesting N-S to NE-SW extension.

On the west, the CSFS ends at the N-striking Schofield Pass fault, which dips steeply. No faults are exposed for several km west of the Schofield Pass fault. Thus, the CSFS transfers slip onto the Schofield Pass fault. On the north, the Schofield Pass fault is cut by the PSFS.

This network of N- and E-striking fault systems (1) accommodates the change from E-W on the north to N-S and NW-SE on the south; (2) allows transfer of slip around the Timpahute - Mt. Irish block, little extension occurred within the block; and (3) allows a change in the loci and directions of extension in the region.