Research Paper THEMED ISSUE: Origin and Evolution of the Sierra Nevada and Walker Lane GEOSPHERE Implications for the structure of the Hat Creek fault and transfer of right-lateral shear from the Walker Lane north of Lassen Peak, GEOSPHERE; v. 12, no. 3 northern California, from gravity and magnetic data doi:10.1130/GES01253.1 V.E. Langenheim, R.C. Jachens, L.J.P. Muffler, and M.A. Clynne 8 figures; 1 table; 1 supplemental file U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA CORRESPONDENCE: zulanger@ usgs .gov ABSTRACT Valley block, into this region has been attributed to northward migration of CITATION: Langenheim, V.E., Jachens, R.C., Muf- the Mendocino triple junction 200–300 km to the west (Faulds et al., 2005), fler, L.J.P., and Clynne, M.A., 2016, Implications for the structure of the Hat Creek fault and transfer of Interpretation of magnetic and new gravity data provides constraints on along with northwest translation of the Sierra Nevada–Great Valley block right-lateral shear from the Walker Lane north of the geometry of the Hat Creek fault, the amount of right-lateral offset in the (Unruh et al., 2003). Many publications (e.g., Stewart, 1988; Muffler et al., Lassen Peak, northern California, from gravity and area between Mount Shasta and Lassen Peak (northern California, USA), and 2008; Busby, 2013) do not show the Walker Lane extending north of Lassen magnetic data: Geosphere, v. 12, no. 3, p. 790–808, doi:10.1130/GES01253.1. confirmation of the influence of preexisting structure on Quaternary faulting. Peak (Fig. 1). Yet others have argued that right-lateral shear continues north Neogene volcanic rocks coincide with short-wavelength magnetic anomalies of Lassen Peak, perhaps as part of the enigmatic Northern California shear Received 21 August 2015 of both normal and reversed polarity, whereas a markedly smoother magnetic zone (Wesnousky, 2005, fig. 2 therein), which includes the predominantly Revision received 8 January 2016 field occurs over the Klamath Mountains and Paleogene cover there. Although normal Hat Creek and McArthur faults. The amount of right-lateral offset Accepted 18 February 2016 the magnetic field over the Neogene volcanic rocks is complex, the Hat Creek is unknown for the shear zone, although faults in the northern Walker Lane Published online 24 March 2016 fault, which is one of the most prominent normal faults in the region and have as much as 30 km of displacement (Wesnousky, 2005; Faulds et al., forms the eastern margin of the Hat Creek Valley, is marked by the eastern 2005). Right-lateral shear may step to the west, producing uplift and folding edge of a north-trending magnetic and gravity high 20–30 km long. Model- through the Inks Creek fold belt of Harwood and Helley (1987) (ICF in Figs. ing of these anomalies indicates that the fault is a steeply dipping (~75°–85°) 1 and 2) in the northern Great Valley (Unruh et al., 2003) and very specula- structure. The spatial relationship of the fault as modeled by the potential-field tively to the Grizzly Peak anticline in the eastern Klamath Mountains (GPA data, the youngest strand of the fault, and relocated seismicity suggest that in Fig. 2; Sawyer, 2013). Alternatively, the Walker Lane has been depicted as deformation continues to step westward across the valley, consistent with a extending as far north as the Klamath graben (KG in Fig. 1; Oldow and Cash- component of right-lateral slip in an extensional environment. man, 2009), with extensional faults overprinted by possible young strike-slip Filtered aeromagnetic data highlight a concealed magnetic body of Meso- movement (Waldien, 2012; Waldien and Meigs, 2013). Dextral shear in and zoic or older age north of Hat Creek Valley. The body’s northwest margin north of the Hat Creek region might be expected, given oblique subduction strikes northeast and is linear over a distance of ~40 km. Within the resolution of the Gorda plate beneath the North American plate (Fig. 1), and, although of the aeromagnetic data (1–2 km), we discern no right-lateral offset of this geodetic data indicate right-lateral shear north of Lassen Peak, it is clearly body. Furthermore, Quaternary faults change strike or appear to end, as if to accommodated by clockwise crustal rotation north of the California-Ore- avoid this concealed magnetic body and to pass along its southeast edge, gon border (McCaffrey et al., 2007, 2013; Fig. 1 inset) rather than by discrete suggesting that preexisting crustal structure influenced younger faulting, as strike-slip faults. The boundary between the Oregon coast block, which has previously proposed based on gravity data. been rotating since the Miocene, and the Walker Lane is poorly defined, and the amount, if any, of right-lateral shear and how it may be accommodated in this region is not well known. INTRODUCTION The most studied fault north of Lassen Peak is the Hat Creek fault (Muffler et al., 1994; Walker, 2008; Blakeslee and Kattenhorn, 2013; Kattenhorn et al., The Hat Creek fault is located at or near the junction of major tectonic 2016), which is well expressed geomorphically and offsets units as young as provinces in northern California (USA): the Sierra Nevada–Great Valley the Hat Creek Basalt, dated as 24 ± 6 ka (Turrin et al., 2007; refined to 23.8 ± block, southernmost Cascade arc, Basin and Range, Oregon coast block, 1.4 ka by Rood et al., 2015) and ca. 15 ka periglacial deposits (Muffler et al., For permission to copy, contact Copyright and northern end of the Walker Lane (Fig. 1). The encroachment of the 1994). Although the Hat Creek fault is a significant normal fault that may reflect Permissions, GSA, or [email protected]. Walker Lane, a zone of right-lateral shear east of the Sierra Nevada–Great westward encroachment of Basin and Range extension (Muffler et al., 2008), © 2016 Geological Society of America GEOSPHERE | Volume 12 | Number 3 Langenheim et al. | Hat Creek fault and transfer of right-lateral shear Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/790/4092661/790.pdf 790 by guest on 30 September 2021 Research Paper INSET COLUMBIA 50 EMBAYMENT 46 45 X Juan de Fuca OREGON Plate COAST Fig. 8 44 BLOCK 40 C A S C A D E KG A R C KLAM Oregon LEGEND Idaho 42° Gorda MTNS Nevada spreading ridge MS Plate ATH BASIN subduction zone LP ICF AND W 40° transform fault MENDOCINO A GREAT SIERRA NEL TRIPLE K RANGE extension direction from JUNCTION E R Unruh et al. (2003) VALLEY BL L 38° rotation sense of Oregon San A VADA Coast Block Pacific Andreas Fault N E Plate Californi region of dextral shear - OCK a Quaternary Cascades 36° volcanic arc (Hildreth, 2007) gravity lows discussed in Blakely et al. (1997) conductive features 34°N (Bedrosian and Feucht, 2014) Eocene to Miocene tear 0 100 km in subducting slab (Colgan et al., 2011) 126° 124° 122° 120° 118° 116°W Figure 1. Index map showing plate tectonic setting of the western U.S. Study area (white box; Figs. 2–6) is at the junction of the Cascade Arc, Walker Lane, Basin and Range, the Sierra Nevada–Great Valley block, the Klamath Mountains, and the Oregon coast block. ICF—Inks Creek fold belt of Harwood and Helley (1987); KG—Klamath graben; LP—Lassen Peak; MS—Mount Shasta. Inset shows global positioning system velocities of the western U.S. relative to North America (modified from McCaffrey et al., 2013). Blue x marks the rotation pole of Cascadia. GEOSPHERE | Volume 12 | Number 3 Langenheim et al. | Hat Creek fault and transfer of right-lateral shear Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/790/4092661/790.pdf 791 by guest on 30 September 2021 Research Paper 122°15′ 122° 121°45′ 121°30′ 121°15′W Qs 41°30′N Qv Mt. ACB Tv Qv Shasta Ts Ks Js Qs TRs mv oph Redding Pzs McCloud y oph init 89 SUBTERRANES Tr 41°15′ Tv Tv Figure 2. Geologic map of the study area Pzs (modified from Jennings et al., 2010) Qs super posed on shaded-relief topogra- GPA phy. A–A′—location of profile modeled Big Valley in Figure 7. Qs—Quaternary sediments; McAr Qv—Quaternary volcanic rocks; Tv—Neo- TRs Qs gene vol canic rocks; Ts—Paleogene and Js thur F 299 Neogene sedimentary rocks; Ks—Creta- Ts ceous sedimentary rocks; Js—Jurassic mv River sedimentary rocks; TRs—Triassic sedimen- SM ault Big CM FRM P tary rocks; mv—Mesozoic metavolcanic Klamath Bend BS 41° and intrusive rocks; Pzs—undifferentiated Mountains Paleozoic rocks (note Js, TRs, mv, and Pzs Tv Pi t are part of the Redding subterrane); oph— Br Ordo vician ophiolite (Trinity sub terrane). White lines—major highways; black CB lines—Quaternary faults (U.S. Geological Bu Tv Survey and California Geological Survey, Hat Creek F 2006); heavier black lines—Hat Creek mv Hat fault. ACB—Ash Creek Butte; BB—Bogard BM TRs Creek Buttes; BM—Burney Mountain; Br—Brush Mountain; BS— Burney Springs Mountain; Valley CM—Chalk Mountain; CB—Cinder Butte; A ault A’ ′ FP—Freaner Peak; GPA—Grizzly Peak anti- Ts FP 89 40°45 TRs cline; SM—Saddle Mountain; ICF—Inks MV Creek fold belt; MV—Magee volcano; PP— 299 Prospect Peak; WPP—West Prospect Peak. Ks Qv Towns: Bu—Burney; FRM—Fall River Mills; P—Pittville. WPP BB Ks PP 44 122°12122°0022°022°2 000'' 44 404 °303 ' Lassen Peak 40°30′ Qs Tv Qv ICF 015 0152025km GEOSPHERE | Volume 12 | Number 3 Langenheim et al. | Hat Creek fault and transfer of right-lateral shear Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/12/3/790/4092661/790.pdf 792 by guest on 30 September 2021 Research Paper its left-stepping geometry indicates a small right-lateral, strike-slip component that correlate with positive topographic features in Fig.