Stratigraphy, paleomagnetism, and anisotropy of magnetic susceptibility of the Miocene Stanislaus Group, central Sierra Nevada and Sweetwater Mountains, California and Nevada Nathan M. King* Geology Department, California State University, Sacramento, California 95819, USA John W. Hillhouse U.S. Geological Survey, 345 Middlefi eld Road, Menlo Park, California 94025, USA Sherman Gromme 420 Chaucer Street, Palo Alto, California 94301-2201, USA Brian P. Hausback Geology Department, California State University, Sacramento, California 95819, USA Christopher J. Pluhar Earth Sciences Department, University of California, Santa Cruz, California 95064-1077, USA ABSTRACT and in the Anchorite Hills, we infer clock- Lava fl ows and ash-fl ow tuffs of the Stanislaus wise, vertical-axis rotations of ~10° to 26° to Group (Table 1) were deposited in a series of Paleomagnetism and anisotropy of mag- be a consequence of dextral shear. The AMS west-draining canyons, such as the Cataract netic susceptibility (AMS) reveal pyroclastic results from 19 sites generally show that the Channel (Ransome, 1898; Lindgren, 1911) in fl ow patterns, stratigraphic correlations, and Eureka Valley Tuff fl owed outward from its the Sierra Nevada, which may have connected tectonic rotations in the Miocene Stanislaus proposed source area, the Little Walker Cal- with highlands in western Nevada. Outcrops of Group, an extensive volcanic sequence in the dera, although several indicators are trans- the Stanislaus Group (ca. 9.5 Ma) on the west- central Sierra Nevada, California, and in the verse to radial fl ow. AMS-derived fl ow pat- ern slope of the central Sierra Nevada are rem- Walker Lane of California and Nevada. The terns are consistent with mapped channels in nants of deposits that once choked the Miocene Stanislaus Group (Table Mountain Latite, the Sierra Nevada and Walker Lane. paleovalley system. Eureka Valley Tuff, and the Dardanelles For- Today, the high eastern scarp of the Sierra mation) is a useful stratigraphic marker for Keywords: ash-fl ow tuff, Miocene, California, Nevada separates the western volcanic fl ows understanding the post–9-Ma major fault- paleomagnetism, magnetic anisotropy from the proposed caldera source, with the base ing of the easternmost Sierra Nevada, uplift of the fl ows now standing 1500 m above the of the mountain range, and transtensional INTRODUCTION caldera. Whether the high scarp, which formed tectonics within the central Walker Lane. since 5 Ma, is the product of rapid uplift of the The Table Mountain Latite has a distinc- The late Miocene Stanislaus Group consists Sierra Nevada (Unruh, 1991; Wakabayashi and tively shallow reversed-polarity direction (I of widespread volcanic units that extend from Sawyer, 2001) or collapse of a high-standing − ° ° α ° = 26.1 , D = 163.1 , and 95 = 2.7 ) at sam- the western foothills of the Sierra Nevada in plateau (Wolfe et al., 1997; Mulch et al., 2006) pling sites in the foothills and western slope California, across the crest of the Sierra Nevada, remains a matter for debate. The paleotopogra- of the Sierra Nevada. In ascending order, the and into the Basin and Range Province of west- phy of the Miocene volcanic rocks and the under- Eureka Valley Tuff comprises the Tollhouse ern Nevada (Fig. 1). Just east of the drainage lying Eocene gold-bearing gravels is critical to − ° ° α Flat Member (I = 62.8 , D = 159.9 , 95 = divide at Sonora Pass, the volcanic succession arguments concerning paleoelevation, isostasy, 2.6°), By-Day Member (I = 52.4°, D = 8.6°, is very thick and bears proximal features that and midcrustal dynamics of the region. α 95 = 7.2°), and Upper Member (I = 27.9°, D = have been interpreted as being part of a caldera East of the Sierra Nevada, the Stanislaus α 358.0°, 95 = 10.4°). The Dardanelles Forma- rim. The Little Walker Caldera, which under- Group is in the tectonically active, central tion has normal polarity. From the magneti- lies a roughly circular valley in this area, is the Walker Lane (Stewart, 1988). Late Cenozoic zation directions of the Eureka Valley Tuff in proposed source of the Stanislaus Group (Slem- and contemporary movement of the Pacifi c the central Walker Lane north of Mono Lake mons, 1966; Noble et al., 1974; Priest, 1979). plate relative to North America is partially *Current address: San Francisco Bay Regional Water Quality Control Board, 1515 Clay St., Oakland, CA 94612, USA Geosphere; December 2007; v. 3; no. 6; p. 646–666; doi: 10.1130/GES00132.1; 16 fi gures; 6 tables. 646 For permission to copy, contact [email protected] © 2007 Geological Society of America Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/646/854730/i1553-040X-3-6-646.pdf by guest on 23 September 2021 on 23 September 2021 by guest Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/646/854730/i1553-040X-3-6-646.pdf Geosphere, December2007 647 120.5 W 120 119.5 119 Sweetwat KM SCM B&R er M Nevada CR 38.5 Walker ou South ntains River 395 Sister 4 Map Area Dardanelles Mount Patterson k es For SN rs Cone Figure 3 Wheeler Peak ell GV B&R Stanislaus Red Peak ttake rk hi la Dardan C W Sonora Peak DardanelleRiver Bald Peak Neva CR California Donnell Sonora da Little Walkerl California ork 108 Pass F Lake Dorrington laus Leavitt Caldera Bridgeport nis Mount ta Peak Reservoir S Emma Arnold California Nevada, Sierra owtuffs, ofMioceneash-fl Magnetism McKays Beardsley Relief Peak Bridgeport Point Pinecrestnenec st Riverr Bodie ills Lake LakeL H th Fork Nor Middle us Rattlesnake nisla Pinecrest te Murphys Sta Hill hori Anc Angels 167 ork Conway uth F Camp So Summit Yosemite Mono Lake 38 N Hetch Melones Hetchy Lake Lee Vining Sonora Reservoir 0 Table Mountain 10 20 30 km 395 120 0 10 20 30 mi 120 Explanation Geologic Index Map 120.5 W 120 119.5 119 1. Wagner et al., 1987 Probable extent of the 5 2. Huber, 1983a 38.5 7 Little Walker Caldera 3. Huber, 1983b Stanislaus Group, undivided 2 4 8 4. Giusso, 1981 Dardanelles Formation 1 6 9 5. Halsey, 1953 6. Priest, 1979 Eureka Valley Tuff, undivided 3 7. King, 2006 Upper Member, Eureka Valley Tuff 8. Brem, 1984 9. Kleinhampl et al., 1975 By-Day Member, Eureka Valley Tuff 38 N 11 10 12 10. Huber et al., 1989 Tollhouse Flat Member, Eureka Valley Tuff 11. Wagner et al., 1990 12. Al-Rawi, 1969 Table Mountain Latite Figure 1. Geologic map and index to mapping of the Stanislaus Group in California and western Nevada. Inset shows physiographic provinces: B&R—Basin and Range; CR—Coast Ranges; GV—Great Valley; KM—Klamath Mountains; SCM—Southern Cascade Mountains; SN—Sierra Nevada. King et al. TABLE 1. EVOLUTION OF STRATIGRAPHIC NOMENCLATURE OF THE STANISLAUS GROUP, CALIFORNIA AND NEVADA Ransome (1898) Slemmons (1966) Noble et al. (1974); used in this study Dardanelle Flow Dardanelles Member Dardanelles Formation Upper Member Eureka Valley Member By-Day Member Eureka Biotite-augite latite Valley Tuff Tollhouse Flat Member Table Mountain Flow Table Mountain Latite Member Stanislaus Group Table Mountain Latite Stanislaus Formation Note: Modified from Noble et al. (1974), in which Tollhouse Flat Member and Table Mountain Latite are equivalent to Ransome’s (1898) biotite-augite latite and Table Mountain Flow, respectively. accommodated (20%) across the Walker Lane, of AMS as a fl ow indicator in well-known chan- PREVIOUS WORK with the rest of the strain being taken up by the nel-fi lling deposits and, if successful, to apply San Andreas fault system (Argus and Gordon, the method elsewhere to delineate the broader The volcanic rocks now known as the Stan- 1991; Hearn and Humphreys, 1998; Atwater channel system in isolated volcanic remnants. islaus Group (Table 1; Noble et al., 1974) have and Stock, 1998; Wernicke and Snow, 1998; Also, we wanted to test whether the pattern of captured the interest of geologists for 150 yr. Thatcher et al., 1999; Bennett et al., 2003; fl ow is consistent with a source area centered Trask (1856) and Whitney (1865) were early McQuarrie and Wernicke, 2005). Beds of the on the Little Walker Caldera. Establishment observers of the “Table Mountain Flow” near Stanislaus Group and other late Cenozoic depos- of a radial fl ow pattern outward from the cal- Sonora, California. They noted the inverted its within the Walker Lane are broken and tilted dera would confi rm the proposed source of the position of the “basalt” within an older stream by a complex of strike-slip and normal faults Eureka Valley Tuff. channel positioned above the current drainages. that formed in response to northward move- A necessary complement to the AMS study Ransome (1898) described the Table Mountain ment of the Sierra Nevada block, Basin-and- was the measurement of natural remanent Flow in more detail, defi ning the stratigraphy as Range extension, and dextral shear (Stewart, magnetization at sites within the Stanislaus a lower latite (Table Mountain Flow), a middle 1988; Faulds et al., 2005; Wesnousky, 2005). Group. Vertical-axis rotation is likely within biotite-augite latite, and an upper latite (Dar- Understanding the original distribution of the the tectonically active areas east of the east- danelle fl ow). The sinuous lava fl ows of Table Stanislaus Group provides important reference ern Sierra Nevada escarpment (Cashman and Mountain fi lled a paleovalley known as the datum for reconstructing the regional tectonic Fontaine, 2000); therefore, it was necessary Cataract Channel (Ransome, 1898; Slemmons, history since 9.5 Ma. Therefore, we undertook to account for any rotations in the interpreta- 1953), and the fl ows probably originated from this study of magnetic properties to provide tion of the AMS fl ow directions.