Superposed normal faults in the Ely Springs Range, Nevada: Estimates of extension

Paleozoic rocks of the Ely Springs Range were cut by down-to-the-east domino-style normal faults, which resulted in W-dipping strata and gently E-dipping faults. Oligocene volcanic rocks were deposited across these structures, before the entire assemblage was rotated to the east on a down-to-the-west listric normal fault. This rotation returned the domino-style faults to steeper dips and the Paleozoic rocks to gentle dips. Step-wise palinspastic restoration to the pre-fault geometry indicates 70-210% horizontal extension. If the sub-Tertiary unconformity were not recognized, a non-rotational reconstruction of the currently steep normal faults in the Paleozoic strata would yield an erroneously small estimate of extension. Geologists working in extended terrains should consider the possibility that unrecognized extensional rotations occurred. If that possibility is high, estimates of horizontal extension should be considered as minima.