New Evidence for Cretaceous Strike-Slip Faulting in the United States Cordillera and Implications for Terrane-Displacement, Deformation Patterns, and Plutonism

Abstract

Early to mid-Cretaceous dextral strike-slip faulting, involving up to 400 km displacement, has been documented in the southern Sierra Nevada of California.In western Idaho, the Salmon River suture juxtaposes unrelated oceanic and continental rocks along a major, near-vertical shear zone that was active in the Early to mid-Cretaceous. These two structural zones have been treated as separate entities; however, new data indicate that they likely connect via a structural discontinuity in northwest Nevada and southeast Oregon, herein called the western Nevada shear zone (WNS).

Current structures within the WNS record dip-slip contractional deformation; however, regional relations (structural and stratigraphic) indicate a mismatch in the early Mesozoic geology of rocks across the WNS that is best explained by dextral strike-slip displacement of several 100 km. These relations argue that an early strike-slip structure along the WNS was reactivated and obscured during later regional shortening deformation, most likely related to the Cretaceous Sevier orogeny. The WNS is along strike and broadly coeval with the Salmon River suture zone and strike-slip boundaries in the Sierra Nevada. We hypothesize that all these features are related elements of a major structural boundary in the western United States Cordillera. This boundary is interpreted to have accommodated significant dextral strike-slip displacement of outboard arc terranes of the Cordillera in the Early Cretaceous, followed by reactivation as a localized contractional zone in the mid-Cretaceous during the Sevier orogeny. Cretaceous batholiths of the United States Cordillera closely parallel the boundary, which we suggest formed a major crustal flaw that localized and facilitated emplacement of arc magmas.