JUST WHERE IS THE NORTHERN TERMINATION OF THE WALKER LANE? POSSIBLE ASSOCIATIONS TO DEXTRAL OBLIQUE-STRIKE SLIP FAULTING IN NORTHERN CALIFORNIA AND SOUTHEASTERN OREGON

The numerous NW-SE trending faults of southeastern Oregon could be the result of the same tectonic driver as that producing the Walker Lane. The faults in southeastern Oregon have NW-SE orientations and display dextral oblique to strike-slip relative motions, similar to structures in the Walker Lane (Pezzopane and Weldon, 1993; Crider, 2001; Jordan et al., 2004; Trench et al., 2012). The question then becomes how are they related to Walker Lane structures? By definition, Walker Lane structures have been created from the northwest translation of the Sierra Nevada crustal block relative to North America and therefore accommodate 15%-20% relative motion between these two plates (Faulds et al., 2005). So, if this block is translating northwestwards, then could there be deformation not only adjacent to this crustal block (i.e., Walker Lane per se) but also in front of it (i.e., northern California and southeastern Oregon)? Conversely (or perhaps not), there has been much evidence for the clockwise rotation of the Cascadia forearc (e.g., Wells and Simpson, 2001) and resultant clockwise rotation in the back-arc region of Oregon (Trench et al., 2012). Blakely et al. (1997) postulate that strain is being transferred from dominantly strike-slip domains of the Walker Lane northwards to E-W directed extension in the High Cascades via N-S and NW-SE trending normal and strike-slip faults, respectively, associated with Quaternary volcanic centers of the southern High Cascades, also alluded to by Oldow (2001), Figure 1. How much of this rotation is due to oblique convergence between the Juan de Fuca and North American plates versus the northward translation of the Sierra Nevada crustal block? The origin of the faulting in southeast Oregon is thus problematic in that it could be related to Basin and Range tectonics, the rotation of the Cascade forearc, and/or the forces that are generating the Walker Lane.