THE ROLE OF TRANSVERSE FAULTS IN GREAT BASIN EXTENSION: TRANSFER FAULTS OR N-S EXTENSION?

Normal faults may terminate at or be linked by transverse faults, faults that strike normal to the regional structural grain. These structurally integral components of extension may accommodate changes in the magnitude, direction, timing, or location of extension. A complete understanding of extensional deformation requires 3-D assessment of the linkages and terminations of normal fault systems. Thus, to evaluate the role of transverse faults in Great Basin extension, we examined the Crescent Spring fault zone (CSFZ), a transverse fault zone in the Mount Irish and Timpahute ranges, central Nevada.

The CSFZ and other regional transverse faults are part of the broadly defined Timpahute lineament (TL), an E-trending structural zone at this latitude. We use new geologic map data (1:24,000 scale), geometric analyses and kinematic analyses to document the structural style of the CSFZ and assess how it interacts with other Cenozoic faults. Based on cross-cutting relations, four Cenozoic extensional episodes are evident: pre-volcanic (pre-27 Ma), syn-volcanic (~27-18 Ma), Miocene (?) post-volcanic, and Miocene (?)- Pliocene or Quaternary post-volcanic extension. Pre-volcanic extension is defined by E-striking and N-striking faults that are overlapped by the ~27 Ma Monotony Tuff with moderate relief below the sub-Tertiary unconformity. Syn-volcanic faults are late Oligocene to Miocene, E-striking faults that accommodated minor N-S-directed extension. Syn-volcanic extension is also indicated by Tertiary lacustrine limestone & conglomerate that accumulated in extensional basins prior to the emplacement of the overlying ~26 Ma Shingle Pass Tuff. Post-volcanic, N-S-directed extension along E-striking, normal- and oblique-slip faults is documented by kinematic indicators.

In summary, pre-volcanic, pre-~27 Ma E-W-directed extension was followed by N-S-directed syn-volcanic and post-volcanic Miocene extension that in turn was followed by a return to E-W-directed extension along N-striking faults. This extensional pattern is consistent with fault studies in the Timpahute and Hiko ranges and implies that the CSFZ and other faults along the TL may have accommodated regional changes in the stress field over time.