Active dextral strike-slip faulting records termination of the Walker Lane belt at the southern Cascade arc in the Klamath graben, Oregon, USA

Abstract

Whether or not northward growth of the Walker Lane belt relates to northward motion of the Mendocino triple junction remains an open question in the study of western North American plate deformation. Uncertainty about the potential linkage arises from an incomplete understanding of how and where dextral transtension in the Walker Lane belt terminates on its northern end. To address this issue, we used bare-earth airborne light detection and ranging (LiDAR) topographic data to reveal the geomorphic record of active dextral transtensional deformation in the Klamath graben in the backarc of the southern Cascade arc, south-central Oregon, USA. Fault scarps in late Pleistocene glacial deposits indicate that at least 0.3 mm/yr of NW-SE dextral shear characterizes slip on the NW-striking Howard Bay fault system within the Klamath graben. Dextral slip on the Howard Bay fault is transferred northwestward into extension on N-striking normal faults within the Cascade arc. Thus, active faults in the Klamath graben mark the northern terminus of a dextral transtensional fault system spanning the southern Cascadia backarc from Crater Lake southward to the northern Sierra Nevada. A review of published geologic slip rates throughout the region of the southern Cascade arc suggests that dextral slip from the Walker Lane belt is transferred both into contractional structures in the northern Sacramento Valley and transtensional structures in the southern ~200 km section of the Cascadia backarc. Termination of transtensional deformation into the southern Cascade arc suggests that the Walker Lane belt propagates independently of the Mendocino triple junction and that, instead, expansion of the Basin and Range Province plays a central role in development of the Walker Lane belt.

Characterizing strain between rigid crustal blocks in the southern Cascadia forearc: Quaternary faults and folds of the northern Sacramento Valley, California

“…Northwest translation of the SNGV block drives large-scale northwest-directed transtensional dextral shear deformation east of the Sierra Nevada (e.g., Unruh et al, 2003) and in the Cascadia backarc (e.g., Langenheim et al, 2015;Waldien et al, 2019), a portion of which extends westward between and south of the volcanic centers of the southern Cascade arc ( Fig. 4; Blakely et al, 1997).…”

Effects of structure and volcanic stratigraphy on groundwater and surface water flow: Hat Creek basin, California, USA

“…In the upper Deschutes River drainage basin, Tertiary to Quaternary volcanic rocks interact with the Brothers, Sisters, and Green Ridge section of the Metolius fault zones (Gannett et al 2001); whereas, the upper Klamath River basin hosts volcanic rocks that are faulted and as old as the pre-Tertiary and can locally be compartmentalized by faults (Gannett et al 2007). Both drainage basins lie in regions where faulting and arc volcanism intersect (Blakely et al 1997;Gannett et al 2007;Waldien et al 2019). Moreover, both basins contain rocks that are markedly older and have lower permeability, indicating possible permeability reduction with increased alteration to clay (Jefferson et al 2010;Burns et al 2015Burns et al , 2017a, which would enable a more comprehensive study of the relationship between compartmentalization, faulting and age/alteration.…”

A Late Cenozoic Kinematic Model for Fault Motion Within Greater Cascadia

“…Strike slip has been documented as far north as 42.4°N, near Klamath Falls, where Waldien et al. (2019) infer a minimum dextral slip rate of 0.3 mm/yr on a single fault since late Pleistocene. We implement the northward decrease in strike slip as a transition to block rotation as central Oregon is approached.…”

“…As this zone meets the Cascade arc in southernmost Oregon, there is a transition from right-oblique transtension to extension with little evidence of strike slip (e.g., Blakely et al, 1997;Wells et al, 1998). Strike slip has been documented as far north as 42.4°N, near Klamath Falls, where Waldien et al (2019) infer a minimum dextral slip rate of 0.3 mm/yr on a single fault since late Pleistocene. We implement the northward decrease in strike slip as a transition to block rotation as central Oregon is approached.…”