TRANSVERSE FAULTS IN RIFTING: TIMPAHUTE LINEAMENT, EAST-CENTRAL NEVADA

E-W-trending transverse zones within the Basin and Range province (BRP) of western North America are well recognized, yet their role(s) in the evolution of this rift remains vague. The Timpahute lineament is a major transverse zone in the BRP that extends from western Utah into central Nevada. This lineament coincides with the northern edge of the boundary zone between the Northern (NBR) and Central (CBR) Basin and Range sub-provinces. We consider how this zone contributes to development of the broader rift system. Is this lineament a transfer zone accommodating heterogeneous extension or not? Does it reflect the development of the sub-province boundary? Here we assess the western part of this lineament and the dynamic conditions under which it formed. New detailed geologic mapping (1:24000) along the western Timpahute lineament along with regional and other detailed data, suggest that this section is an E-W-striking fault zone with dominantly down-to-the-south normal displacement. Faulting occurred post-18.5 Ma as determined by the cross-cutting relationship with the Hiko Tuff. N-S extension in the BRP is uncommon, especially at a regional scale. Gravity data show a regional E-W trending anomaly in spatial proximity to this lineament. Other transverse zones in the BRP do not display this relationship, suggesting that the Timpahute lineament is distinctive. Notably, this lineament coincides with the area where interplay between Farallon slab rollback and a slab window is thought to occur. We suggest that the Timpahute lineament reflects the reactivation of a deep-seated E-W-trending basement structure during dynamic uplift and thermal upwelling related to the interplay of the Farallon slab (rollback) and slab window (opening) during Oligo-Miocene time. The location and orientation of the Timpahute lineament appears to be controlled by the deep-seated structure, which we interpret to be an essential part of the boundary between the CBR and NBR. Our results suggest that not all lineaments/transverse zones are strike-slip transfer structures that accommodate heterogeneous extension. The down-to-the-south Timpahute lineament appears to reflect the interaction between slab rollback and a slab window superimposed on a pre-existing crustal architecture that influences the development of the NBR-CBR boundary.