Tectonics, Volcanism, and Stratigraphy within the Evolving Transform Margin North of San Francisco Bay, California themed issue Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California Robert J. McLaughlin1, Andrei M. Sarna-Wojcicki1, David L. Wagner2, Robert J. Fleck1, Victoria E. Langenheim1, Robert C. Jachens1, Kevin Clahan3*, and James R. Allen4 1U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA 2California Geological Survey, 801 K Street, Sacramento, California 95814, USA 3California Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA 4California State University East Bay, Hayward, California 94542, USA ABSTRACT Rodgers Creek fault zone dextral slip rate ated with releasing bends and strike-slip basins. increased from ~2–4 mm/yr 7–3 Ma, to 5–8 The Rodgers Creek–Maacama fault system is The Rodgers Creek–Maacama fault sys- mm/yr after 3 Ma. one such domain of extensional right-lateral tem in the northern California Coast Ranges The Maacama fault zone is shown from faults and releasing bend basins, though the (United States) takes up substantial right- several data sets to have initiated ca. 3.2 Ma long-term history of faulting in the area appears lateral motion within the wide transform and has slipped right-laterally at ~5–8 mm/yr to have included signifi cant compression. Else- boundary between the Pacifi c and North since its initiation. The initial Maacama fault where, the transform boundary zone clearly American plates, over a slab window that zone splayed northeastward from the south includes mixed compressional and extensional has opened northward beneath the Coast end of the Rodgers Creek fault zone, accom- right-lateral faulting. The Bartlett Springs fault Ranges. The fault system evolved in several panied by the opening of several strike-slip zone west of the Sacramento Valley, for exam- right steps and splays preceded and accom- basins, some of which were later uplifted ple (McLaughlin et al., 1990), is predominantly panied by extension, volcanism, and strike- and compressed during late-stage fault zone a steeply east dipping transpressional fault zone slip basin development. Fault and basin re organi zation. The Santa Rosa pull-apart that includes right-stepped strike-slip basins geometries have changed with time, in places basin formed ca. 1 Ma, during the reorgani- (such as the Covelo and Lake Pillsbury basins) with younger basins and faults overprinting zation of the right stepover geometry of the along its length. Clear Lake basin, another com- older structures. Along-strike and succes- Rodgers Creek–Maacama fault system, when plex extensional strike-slip basin (Hearn et al., sional changes in fault and basin geometry the maturely evolved overlapping geometry 1988), is bounded by northwest-trending faults at the southern end of the fault system prob- of the northern Rodgers Creek and Maa- that have pre-basin compressional strike-slip ably are adjustments to frequent fault zone cama fault zones was overprinted by a less histories (Fig. 1). re organizations in response to Mendocino evolved, non-overlapping stepover geometry. The mixed histories of transtension and Triple Junction migration and northward The Rodgers Creek–Maacama fault sys- transpression associated with the wide trans- transit of a major releasing bend in the tem has contributed at least 44–53 km of form boundary east of the San Andreas fault are northern San Andreas fault. right-lateral displacement to the East Bay the consequence of processes operating along The earliest Rodgers Creek fault zone dis- fault system south of San Pablo Bay since the Pacifi c, Gorda–Juan de Fuca, and North placement is interpreted to have occurred 7 Ma, at a minimum rate of 6.1–7.8 mm/yr. American plate boundaries since the Late Mio- ca. 7 Ma along extensional basin-forming cene (ca. 10 Ma), and in some instances since faults that splayed northwest from a west- GEOLOGIC SETTING OF THE much earlier in the Tertiary. These processes northwest proto-Hayward fault zone, open- RODGERS CREEK–MAACAMA include northward-migrating slab window– ing a transtensional basin west of Santa Rosa. FAULT SYSTEM related volcanism associated with migration After ca. 5 Ma, the early transtensional basin of the Mendocino Triple Junction (Dickinson was compressed and extensional faults were The transform boundary between the Pacifi c and Snyder, 1979; Fox et al., 1985; Stanley, reactivated as thrusts that uplifted the north- and North American plates in northern Califor- 1987; McLaughlin et al., 1994, 1996; Graymer east side of the basin. After ca. 2.78 Ma, the nia (United States) is a wide zone that refl ects et al., 2002); large-scale block rotations and Rodgers Creek fault zone again splayed from eastward migration into the North American plate motions (Argus and Gordon, 2001; the earlier extensional and thrust faults to plate and lengthening since the late Tertiary Wells and Simpson, 2001); and northward- steeper dipping faults with more north- (Fig. 1). East of the San Andreas fault (the west- migrating restraining and releasing bends in northwest orientations. In conjunction with ern boundary of the transform margin) and south the northern San Andreas fault (Fox, 1976; the changes in orientation and slip mode, the of the subducting Gorda–Juan de Fuca plate, Wakabayashi et al., 2004; Wilson et al., 2005). this wide transform boundary is composed of Other processes that may have indirectly infl u- *Present address: Lettis Consultants Int., Inc., Wal- mixed structural domains dominated in places enced the long-term evolution of the transform nut Creek, California 94596, USA. by active extensional right-lateral faults associ- boundary include partial coupling between Geosphere; April 2012; v. 8; no. 2; p. 342–373; doi:10.1130/GES00682.1; 17 fi gures; 3 tables. 342 For permission to copy, contact [email protected] © 2012 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/2/342/3342741/342.pdf by guest on 23 September 2021 Evolution of the Rodgers Creek–Maacama fault system AB 12 41° GORDA- Eureka 41° JUAN DE NORTHAMERICANPLATE Eureka 36 a Weavervillee FUCA Redding Redding Cape PLATE 20 Mendocinon Cape Mendocino f Mendocino Fracture Zone Red Bluff Garberville MENDOCINO COAST RANGES 40° Point South RedBluff Delgada S FRACTUREZONE (Jachens edge,e, Gorda and Griscom, – Ju 1983) B A n an dee Fuca Plate RESTRAINING BEND R T 1 L SACRAMENTO 40° Point Delgada E T Fort Braggg 51 S T PACIFIC A Willits N CoveloS MFZ ca. 0.3 Ma P Valley R 39° PointPoiinti MAFZ IN Arenae G S Lake Pillsbury SantaS RRosa MFZ ca. 2.0 Ma A F 11 AREA OF N A Sutter OCEAN D U Sutter FIGURE 2 MA L R Ukiah T Buttes E A Valley FZ Z S 30 Clear O 38° Lake N Point Reyes 39° E Dunnigan Hills PointArena San Franciscor MAFZ MFZ ca. 5 – 6 Ma 42 0 20 40 60 km San Lake Jose Berryessa AREA OF SCALE RELEASING BEND Santa FIGURE 2 Rosa VALLEY 37° F RCFZ A Santa Cruz U MFZ ca. 8 – 9 Ma L T Montereye PACIFIC Salinas BMV 11 H 38° AYW Point Reyes COAST RANGES PLATE 125° 124° 123° 122° A San RD FAULT 51 Francisco S A EXPLANATION N ZONE A CASCADIA SUBDUCTION MARGIN N D SanJose MFZ ca. 11–12 Ma R E A S CF SAN ANDREAS FAULT (main boundary between Pacific and North American Plates) 37° FAULT FAULTS EAST OF SAN ANDREAS FAULT SantaCruz QSV East Bay Fault System-Includes Hayward + Proto-Hayward fault zones Calaveras + other fault zones Monterey Rodgers Creek-Maacama Fault System-Includes Rodgers Creek, Maacama + related 0 20 40 60 km fault zones 36° 125° 124° 123° 122° Figure 1. Maps showing the regional setting of the Rodgers Creek–Maacama fault system and the San Andreas fault in northern Califor- nia. (A) The Maacama (MAFZ) and Rodgers Creek (RCFZ) fault zones and related faults (dark red) are compared to the San Andreas fault, former and present positions of the Mendocino Fracture Zone (MFZ; light red, offshore), and other structural features of northern California. Other faults east of the San Andreas fault that are part of the wide transform margin are collectively referred to as the East Bay fault system and include the Hayward and proto-Hayward fault zones (green) and the Calaveras (CF), Bartlett Springs, and several other faults (teal). Fold axes (dark blue) delineate features associated with compression along the northern and eastern sides of the Coast Ranges. Dashed brown line marks inferred location of the buried tip of an east-directed tectonic wedge system along the boundary between the Coast Ranges and Great Valley (Wentworth et al., 1984; Wentworth and Zoback, 1990). Dotted purple line shows the underthrust south edge of the Gorda–Juan de Fuca plate, based on gravity and aeromagnetic data (Jachens and Griscom, 1983). Late Cenozoic volcanic rocks are shown in pink; structural basins associated with strike-slip faulting and Sacramento Valley are shown in yellow. Motions of major fault blocks and plates relative to fi xed North America, from global positioning system and paleomagnetic studies (Argus and Gordon, 2001; Wells and Simpson, 2001; U.S. Geological Survey, 2010), shown with thick black arrows; circled numbers denote rate (in mm/yr). Restrain- ing bend segment of the northern San Andreas fault is shown in orange; releasing bend segment is in light blue. Additional abbreviations: BMV—Burdell Mountain Volcanics; QSV—Quien Sabe Volcanics. (B) Simplifi ed map of color-coded faults in A, delineating the principal fault systems and zones referred to in this paper. Geosphere, April 2012 343 Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/8/2/342/3342741/342.pdf by guest on 23 September 2021 McLaughlin et al.