Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
00729 1st pages / page 1 of 15 Magmatic growth and batholithic root development in the northern Sierra Nevada, California M.R. Cecil1,*, G. Rotberg2, M.N. Ducea2, J.B. Saleeby1, and G.E. Gehrels2 1 California Institute of Technology, Division of Geological and Planetary Sciences, Pasadena, California 91125, USA University of Arizona, Department of Geosciences, Tucson, Arizona 85721 USA 2 ABSTRACT In contrast to the much-studied central and southern Sierra Nevada, relatively little is known about the growth and petrogenesis of the batholith in its northern reaches, making it difficult to evaluate range-wide, spatiotemporal trends in batholithic development and the regional extent of eclogite root production and/or loss. New U-Pb ages from northern Sierra plutons reveal a shift between the age of Cretaceous magmatism recorded in the northern Sierra and the timing of an apparent flare-up in the main batholith, indicating: (1) that the northern batholith was more spatially dispersed and emplaced into regions beyond the modern topographic range; and (2) that the Cretaceous high-flux event may have occurred over a longer period of time than previously suggested. Relative to the southern Sierra, Nd and Sr isotopic signatures in northern plutons are more primitive, mimicking the predominantly juvenile nature of the terranes into which the plutons are built. Despite differences in isotopic character, however, major and trace element trends are remarkably similar between northern plutons and the rest of the batholith, suggesting that emplacement into juvenile and/or oceanic lithosphere does not inhibit the generation of evolved, arc-type magmatic products. Northern plutons have relatively high La/Yb and Sr/Y and steep rare-earth element patterns, with small to no Eu anomalies. Taken together, these trends are interpreted to indicate deep processing of magmas in equilibrium with a feldspar-poor, amphibolite-rich residue, containing modest amounts of garnet. It is therefore likely that *Present address: California State University, Northridge, Department of Geosciences, Northridge, California 91330-8266, USA; robinson.cecil@csun .edu. the northern Sierra Nevada batholith was emplaced into relatively thick crust and developed a dense mafic to ultramafic root. Because it is not seismically imaged today, we posit that the root was subsequently lost, perhaps in response to encroachment of protoCascade arc volcanism. INTRODUCTION The Sierra Nevada, one of the largest batholiths in North America, strikes NNW and can be traced ~600 km along the eastern spine of California, varying in width between ~80 and 120 km. The batholith comprises mainly subduction-related intermediate to felsic intrusive rocks and associated metamorphic screens and pendants (Bateman and Wahrhaftig, 1966; Evernden and Kistler, 1970; Ducea, 2001; Saleeby et al., 2003). Although the Sierra Nevada is commonly classified as a single, exhumed continental mega-plutonic complex, major lateral (W to E) changes in the age (Kistler and Peterman, 1973, 1978; Stern et al., 1981; Chen and Moore, 1982), composition (Moore, 1959; Bateman, 1992), and isotopic signature (Doe and Delevaux, 1973; DePaolo, 1980, 1981; Masi et al., 1981; Saleeby et al., 1987a; Kistler, 1990; Kistler and Ross, 1990; Chen and Tilton, 1991; Kistler and Fleck, 1994; Ducea, 2001; Lackey et al., 2005, 2008) of the batholith have long been recognized. These changes are largely attributed to the flaring up and migration of magmatism across heterogeneous crustal and upper mantle domains. In addition to significant transverse changes, the Sierra Nevada also changes along strike in several important ways: (1) plutonic rocks are volumetrically more significant in the central and southern Sierra Nevada (between ~35 °N and 37.5 °N; Fig. 1), comprising nearly the entire exposed arc in those portions of the range; (2) Eocene–Miocene clastic sedimentary and volcanic rocks are preserved in the northern Sierra Nevada (N of 38 °N), whereas they are conspicuously absent in other parts of the range (Fig. 1); (3) the estimated depths of pluton emplacement become shallower toward the north (Ague and Brimhall, 1988; Pickett and Saleeby, 1993; Ague, 1997; Nadin and Saleeby, 2008); (4) the basement into which the batholith is built changes from mainly late Proterozoic continental and transitional lithosphere in the south to a tapestry of accreted Phanerozoic belts in the north (Kistler, 1990; Fig. 1); and (5) the southern and central part of the batholith had a documented dense root that has recently delaminated from the base of the crust (e.g., Ducea and Saleeby, 1998b; Zandt et al., 2004), whereas the development and/or loss of such a root in the northern Sierra is unclear (Frassetto et al., 2011). Although a wealth of information exists about the main batholithic body of the Sierra Nevada in its southern and central extents, much less is known about the age and petrogenesis of granitic plutons in the north. Because of the northsouth changes enumerated above, we examined the geochronologic, geochemical, and isotopic character of northern plutons with the aim of (1) describing their petrology and emplacement history, (2) identifying range-wide spatial and temporal patterns in batholith genesis, and (3) identifying fundamental differences, if any, between magma sources regions in the north and other parts of the range. This work was conducted as part of a larger, interdisciplinary project—the Sierra Nevada Earthscope Project (SNEP)—aimed at resolving the nature and complexity of the Sierran lithosphere. Of particular interest to principal investigators were: the presence or absence of a dense residue at the base of the felsic crust, the distribution of that residue through both time and space, and its influence on recent volcanism and surface deformation. In light of the greater context of this work, the isotopic and geochemical data presented herein are interpreted with an eye toward understanding the evolution of the lower crust and mantle lithosphere in the northern Sierra Nevada. Geosphere; June 2012; v. 8; no. 3; p. 1–15; doi:10.1130/GES00729.1; 11 figures; 3 tables; 1 supplemental file. MANUSCRIPT RECEIVED 15 JUNE 2011 ◊ REVISED MANUSCRIPT RECEIVED 17 JANUARY 2012 ◊ MANUSCRIPT ACCEPTED 14 FEBRUARY 2012 ◊ FIRST PUBLISHED ONLINE XX MONTH 2012 For permission to copy, contact [email protected] © 2012 Geological Society of America 1 00729 1st pages / page 2 of 15 Cecil et al. 122°W 121°W 120°W 119°W 118°W 87 Sr/86Sri = 0.706 isopleth Tertiary volcanics Sierra Nevada batholith G05 39.5°N G08 Sutter Buttes G01 a Yub Panthalassan (oceanic) affinity N. American (continental) affinity Pendant rocks 0 25 G06 G02 2 G03 G12 R. G10 G11 T 39°N G22 Sample location G02 Sample name Km 50 100 G20 G19 G23 G17 G21 Sacramento G16 G18 . Con st es R n sum cre 38.5°N N Basin and Range G12 Sierra Nevada a at V Gre 38°N Rivers Mafic/ultramafic rocks G04 G09 117°W lley NV 37°N CA NV CA o nt te ex ith rn hol ste at we .N. b S s ge R an 706 >0. 6 70 <0. ast Co 37.5°N f Fresno 36.5°N Mt. Whitney Figure 1. Generalized geologic map of the central and northern Sierra Nevada, modified after Irwin and Wooden (2001), Saucedo and Wagner (1992), and Wagner et al. (1987). Sample locations (and their corresponding names) are shown in white. The Sri 0.706 line is modified after Kistler and Peterman (1978) and Kistler (1990). Belts of metamorphic rocks in the northern Sierra foothills have been grouped according to the two different interpreted lithosphere types (Panthalassan and North American) of Kistler (1990). The western extent of the Great Valley is based on the presence of tonalitic and gabbroic arc-related basement sampled in well cores (Williams and Curtis, 1977; Saleeby, 2007). GEOLOGIC BACKGROUND The Sierra Nevada batholith formed as a result of long-lived subduction of the Pacific plate beneath western North America (Dickinson, 1981). Magmatism was in general continuous from ca. 248 to 80 Ma, but most active during episodic events in the Late Jurassic (165–145 Ma) and Late Cretaceous (100–85 Ma), building a thick Mesozoic crustal column—at least in the central and southern Sierra—composed of ~35 km of batholithic rocks (Pickett and Saleeby, 1993; Ducea, 2001). In general, plutons making up the batholith tend to become younger, more silicic, and more voluminous toward the east. Unlike in the central and southern stretches of the Sierra Nevada, where batholithic rocks comprise the vast majority of the crust, the northern Sierra Nevada batholith is a loosely assembled patch- 2 work of quartz diorite, granodiorite, and tonalite plutons. In the north, plutons are more variable in their composition and size, collectively comprising less than 50% of the exposed surface geology north of latitude 38.5 °N. Prebatholithic Rocks of the Northern Sierra Nevada Granitoid rocks of the northern Sierra are intruded across range-parallel, accretionary tectonostratigraphic packages of Paleozoic and Mesozoic metamorphic rocks, which are juxtaposed along Late Jurassic and older faults (Saleeby, 1982; Edelman and Sharp, 1989; Snow and Scherer, 2006). We have grouped these packages into a western, Panthalassan (oceanic) belt and a central, North American (continental) belt, after the two different lithosphere types defined Geosphere, June 2012 by Kistler (1990) (Fig.1). The western belt of Panthalassan affinity is composed mainly of Jura–Triassic metavolcanic arc rocks and associated Upper Jurassic accretionary metasediments. Basement rocks to this belt are primarily midocean ridge basalt (MORB)–affinity Paleozoic ophiolitic rocks (Saleeby, 1982; Sharp, 1988; Ernst et al., 2008). Rocks of the North American belt consist primarily of the early Paleozoic Shoo Fly Complex, which contains mostly deep marine siliciclastic rocks deposited in proximity to a continental source (e.g., Girty et al., 1996; Harding et al., 2000). Although derived from a continental source, the Shoo Fly and associated assemblages are floored by oceanic or transitional lithosphere, as inferred from their relatively juvenile isotopic nature. In the southern Sierra Nevada, the western boundary of the Precambrian continental 00729 1st pages / page 3 of 15 Northern Sierra Nevada magmatism Sample Northern transect G01 G02 G03 G04 G05 G06 G08 G09 G10 G11 G12 Latitude Longitude 39.2978 39.3307 39.3219 32.3247 39.4433 39.3334 39.3782 39.3436 39.3276 39.3123 39.3061 –121.0882 –120.1947 –120.633 –120.5981 –120.0112 –120.2906 –120.671 –120.3385 –120.3901 –120.4946 –120.6328 TABLE 1. SAMPLE INFORMATION AND U-Pb GEOCHRONOLOGY Distance E of range crest (km) Rock type Location or unit –59.5 –68.6 –18.3 –17.7 25 8.5 –18.1 4.4 0 –8.9 –20.7 Granodiorite Granodiorite Granodiorite Quartz monzonite Granite Tonalite Granite Granodiorite Granodiorite Granodiorite Diorite Southern transect G14 38.3721 –120.5542 –39.6 Granodiorite G16 38.4356 –120.5509 –39.3 Granodiorite G17 38.5463 –120.352 –22.2 Granodiorite G18 38.561 –120.2663 –20.5 Granodiorite G19 38.6457 –120.1343 –3.8 Tonalite G20 38.7048 –120.0899 0 Granodiorite G21 38.6945 –119.9956 8.0 Tonalite G22 38.776 –119.8968 16.5 Granodiorite G23 38.7648 –119.8484 20.6 Granodiorite Note: n.d.—not determined; MSWD—mean standard of weighted deviates. margin is geochemically outlined by the classic 87Sr/86Sri = 0.706 isopleth, which bisects the west-central part of the batholith (Kistler and Peterman, 1978; Kistler, 1990) (Fig. 1). Eastward transition into older continental lithosphere is evidenced by more evolved isotopic signatures in the batholith (Chen and Tilton, 1991; Sisson et al., 1996; Coleman and Glazner, 1998) and the presence of ancient, continentderived miogeoclinal rocks in metamorphic screens and pendants (Saleeby and Busby, 1993). To the north, that boundary becomes less well defined and the zone that is inferred to separate the more juvenile, accreted metamorphic belts from the ancient continental margin is generally thought to lie well east of the Sierra Nevada batholith (Davis et al., 1978). We present new geochemical and isotopic data from the northern Sierra, which is used to elucidate the influence of strikingly different prebatholithic lithospheric conditions on the magmatic development of the batholith. SAMPLE SELECTION, PREPARATION, AND ANALYSIS Plutons were sampled from 20 locations along two range-perpendicular transects in the northern Sierra Nevada: a northerly transect at the latitude of the Yuba River (~39.25 °N), and another at the approximate latitude of the Consumnes River (~38.5 °N) (Fig. 1). Only samples with no visible weathered surfaces and/or secondary minerals were crushed and pulverized to a coarse-sand size. The bulk of the crushed material was processed for zircon separation using standard density and magnetic Pb/ 238U age (±2σ) MSWD Yuba River pluton Pleasant Valley pluton Lake Spaulding (S) Lake Spaulding (E) N. Flonston Donner Lake Bowman Lake Donner Pass Soda Springs Cascade Lake (W) Emigrant Gap 162.2 (2.2) 162.0 (3.0) 166.5 (2.6) 145.3 (3.0) n.d. 109.0 (2.5) 372.0 (6.0) 116.4 (2.6) 111.6 (2.3) 120.8 (2.8) n.d. 2.8 1.7 1.8 3.0 — 5.5 1.9 3.3 4.0 0.5 — West Point (N) West Point (S) Cooks Station Bear River Reservoir Silver Lake (W) Caples Lake (W) Carson Pass (W) Freel Peak Freel Peak 166.3 (2.0) 163.2 (3.2) 148.7 (2.4) 121.5 (1.3) 105.2 (1.5) 101.7 (1.5) 109.8 (2.1) 90.2 (1.7) 106.8 (1.9) 2.1 1.5 2.9 4.6 2.5 1.4 5.3 3.8 2.4 techniques, and small aliquots were set aside and powdered in an Al2O3-lined shatter box for whole-rock geochemical and isotopic analysis. Zircons separated from each sample were picked and mounted, along with Sri Lanka and R33 standards, in 2.5 cm epoxy discs. U-Pb zircon geochronology data were collected via laser ablation–multicollector–inductively coupled plasma mass spectrometry (LA-MC-ICPMS) (GV Isoprobe) at the Arizona LaserChron Center (see Gehrels et al., 2008, for instrumentation and methodology details). Sample information, location, and U-Pb age data are summarized in Table 1. Individual U-Pb measurements and concordia plots are provided in the Supplemental File1. Some samples (G06 and G10, for example) show a high scatter in individual zircon U-Pb ages. These are attributed to analytical error, as opposed to meaningful geologic heterogeneity, due to the fact that: (1) zircon age standards analyzed in the same session show similar scatter, and (2) there is no observed relationship between calculated age and U concentration, U/Th, or any other geologic indicator. Major and trace element analyses were performed at the GeoAnalytical Laboratory in the School of Earth and Environmental Sciences at Washington State University using X-ray fluorescence (XRF) (Johnson et al., 1999) and ICPMS. Major and trace element data are summarized in Table 2. Isotopic analyses were per1 Supplemental File. Weighted mean plots and Concordia diagrams for all reported U-Pb analyses. If you are viewing the PDF of this paper or reading it offline, please visit http://dx.doi.org/10.1130/GES00729.S1 or the full-text article on www.gsapubs.org to view the Supplemental File. Geosphere, June 2012 206 formed at the University of Arizona via isotopedilution–thermal ionization mass spectrometry (ID-TIMS), using both an automated VG Sector multicollector instrument with adjustable 1011 Ω Faraday collectors and a Daly photomultiplier (Otamendi et al., 2009) and a VG Sector 54 instrument (Ducea, 2002) (see Appendix for details of Sm-Nd and Rb-Sr isotopic measurements). All isotope data are summarized in Table 3. RESULTS U-Pb Geochronology U-Pb zircon ages of plutons from the northern Sierra Nevada record the presence of a Late Jurassic arc, active between 167 and 145 Ma, and a mid-Cretaceous arc, with magmatism continuous between 125 and 90 Ma. The distribution of ages presented here is similar to range-wide estimates of magmatic flux, in that both reveal pronounced magmatic episodes in the Jurassic and in the Cretaceous, but they differ in that: (1) the Jurassic event is apparently more significant in the north; and (2) the distribution of ages from the northern Sierra is offset from the apparent intrusive flux curve for the greater Sierra Nevada, as defined by Ducea (2001) (Fig. 2). Although the similarities and differences between these trends are significant, it is important to note that magmatic rocks in general comprise a much smaller proportion of the crust in the northern Sierra Nevada and that much of which is presumably underlain by granitic rocks in the higher, eastern reaches of the range, is presently covered by younger volcanic and clastic deposits (e.g., Saucedo and Wagner, 3 00729 1st pages / page 4 of 15 Cecil et al. TABLE 2. MAJOR AND TRACE ELEMENT CHEMISTRY* Northern transect G01 G02 G03 SiO2 67.82 69.66 65.73 TiO2 0.28 0.53 0.4 Al2O3 16.63 15.06 16.55 FeO† 3.48 3.86 4.24 MnO 0.09 0.09 0.09 MgO 1.26 1.23 2.03 CaO 4.12 4.11 4.73 Na2O 4.17 3.98 3.57 K2O 2.16 1.35 2.53 P2O5 0.09 0.13 0.15 Total 100.1 100 100.1 La 11.47 10.96 15.81 Ce 20.27 20.85 30.01 Pr 2.45 2.58 3.51 Nd 9.35 10.62 13.34 Sm 2.02 2.75 2.71 Eu 0.67 1.04 0.77 Gd 1.83 3.03 2.19 Tb 0.28 0.53 0.32 Dy 1.67 3.35 1.82 Ho 0.34 0.71 0.35 Er 0.96 2.04 0.99 Tm 0.15 0.33 0.14 Yb 0.98 2.18 0.93 Lu 0.17 0.37 0.15 Ba 753.1 472.0 886.1 Th 2.67 2.33 4.44 Nb 4.14 2.67 4.28 Y 9.47 18.87 9.28 Hf 2.38 4.29 2.96 Ta 0.37 0.4 0.3 U 0.99 0.77 1.19 Pb 9.18 2.96 11.2 Rb 47.84 35.41 65.68 Cs 1.75 0.88 2.14 Sr 405.2 218.9 691.9 Sc 6.61 12.08 9.3 Zr 84.52 162.3 108.3 Southern transect G14 G16 G17 SiO2 63.13 62.38 78.31 TiO2 0.71 0.53 0.12 Al2O3 16.63 17.29 11.53 † FeO 6.01 5.96 1.75 MnO 0.12 0.11 0.02 MgO 2.0 1.98 0.01 CaO 4.43 4.79 0.07 Na2O 2.51 2.84 3.84 K2O 4.19 3.88 4.33 P2O5 0.28 0.24 0.01 Total 100.1 100 99.98 La 30.2 27.85 55.39 Ce 68.87 56.07 121.2 Pr 8.11 6.54 14.85 Nd 31.78 24.9 51.66 Sm 6.95 5.11 11.17 Eu 1.41 1.27 0.18 Gd 6.0 4.18 9.61 Tb 0.92 0.59 1.88 Dy 5.23 3.19 12.29 Ho 1.02 0.6 2.59 Er 2.71 1.61 7.38 Tm 0.39 0.23 1.11 Yb 2.44 1.43 6.95 Lu 0.38 0.22 1.07 Ba 979.5 988.2 17.08 Th 14.67 14.13 17.34 Nb 20.68 9.48 24.28 Y 26.77 16.13 70.54 Hf 6.96 4.74 15.22 Ta 1.62 0.76 1.75 U 3.65 3.53 3.59 Pb 13.47 13.24 18.99 Rb 165.9 135.7 156.7 Cs 5.95 8.06 0.47 Sr 560.7 699.2 7.54 Sc 13.55 10.73 1.67 Zr 276.5 181.2 595.7 *All values are unnormalized, given in wt%. † All Fe is calculated as FeO. 4 G04 60.02 0.93 19.43 4.16 0.09 1.33 2.81 5.28 5.58 0.26 99.89 56.02 6.46 24.2 4.21 2.02 3.44 0.48 2.69 0.54 1.46 0.22 1.44 0.27 0.27 1630 1.98 8.75 13.33 16.28 0.35 0.74 13.75 45.73 0.37 415.8 6.91 867.9 G05 78.95 0.06 12.09 0.5 0.04 0.07 0.43 3.3 4.55 0.01 100 13.65 24.7 2.72 9.14 2 0.14 1.87 0.35 2.21 0.48 1.44 0.24 1.75 0.3 97.46 20.91 6.58 14.44 2.95 1.03 27.8 32.75 244.6 7.88 34.86 1.24 60.48 G06 66.55 0.51 16.28 4.05 0.08 1.72 4.2 3.75 2.73 0.12 99.8 17.47 35.95 4.36 16.57 3.36 0.85 2.95 0.45 2.57 0.51 1.36 0.2 1.3 0.21 825.9 12.41 6.75 13.75 3.18 0.79 2.46 10.83 79.27 3.91 431.3 7.89 106.1 G08 76.09 0.16 13.16 2.2 0.04 0.14 1.97 2.91 3.32 0.03 100.1 44.57 66.31 10.26 36.89 7.25 1.12 6.58 1.08 6.49 1.29 3.61 0.54 3.45 0.53 720.3 13.53 8.03 33.39 4.71 0.72 3.05 14.34 114.2 1.03 187.0 10.37 158.3 G09 67.87 0.44 15.86 3.65 0.08 1.51 3.61 3.57 3.25 0.12 99.9 14.53 29.13 3.59 14.01 3.03 0.75 2.64 0.43 2.65 0.54 1.52 0.24 1.61 0.27 763.8 10.4 7 14.58 4.27 0.81 4.04 13.1 111.8 4.5 362.2 7.91 143.9 G10 63.21 0.68 16.87 5.4 0.1 2.63 5.22 3.43 2.43 0.16 100.2 18.41 37.58 4.58 17.86 3.73 0.92 3.29 0.51 3.08 0.61 1.66 0.25 1.61 0.26 829.8 8.73 6.77 16.17 3.27 0.65 2.78 9.02 86.34 3.4 461.8 12.06 112.6 G18 76.66 0.11 13.03 1.05 0.06 0.12 0.6 3.74 4.51 0.03 99.92 18.65 56.02 6.46 24.2 4.21 2.02 3.44 0.48 2.69 0.54 1.46 0.22 1.44 0.31 270.2 20.33 18.87 18.79 3.84 1.6 5.05 21.88 168.7 1.53 49.55 2.43 105.4 G19 62.35 0.79 16.92 5.61 0.1 2.68 5.57 3.38 2.47 0.15 100.1 19.06 34.45 3.87 14.44 3.17 1.22 2.91 0.44 2.51 0.5 1.29 0.18 1.11 0.18 1187 12.7 12.19 12.19 4.72 0.71 3.25 9.98 78.91 2.38 414.3 15.78 180.0 G20 69.49 0.43 15.33 3.28 0.07 0.12 3.21 3.47 3.38 0.12 100.1 27.6 50.85 5.53 18.69 3.2 0.78 2.54 0.39 2.27 0.45 1.27 0.2 1.35 0.23 784.6 17.7 12.89 12.89 3.72 0.95 4.84 17.23 121.2 4.89 337.1 6.02 121.6 G21 66.97 0.53 15.78 4.27 0.07 1.67 4.02 3.45 2.99 0.14 99.89 25.63 46.77 5.2 18.18 3.36 0.85 2.61 0.38 2.17 0.41 1.08 0.16 1.0 0.16 831.7 13.85 10.98 10.98 3.98 0.78 3.5 11.15 85.94 2.57 453.3 8.28 138.4 G22 70.42 0.37 15.46 2.48 0.05 0.83 2.69 4.05 3.53 0.11 99.9 20.07 35.65 3.9 13.69 2.45 0.67 1.76 0.24 1.3 0.23 0.58 0.08 0.56 0.1 865.8 15.39 6.5 6.5 3.45 0.5 3.83 18.58 110.5 2.84 432.6 3.58 109.3 G23 67.1 0.52 16.69 3.65 0.11 1.08 3.1 5.17 2.41 0.17 100 21.13 42.34 5.29 21.0 4.65 1.06 4.22 0.69 4.16 0.84 2.22 0.32 2.01 0.32 783.1 6.58 21.71 21.71 5.38 0.41 2.24 11.72 80.84 3.63 315.1 7.52 209.6 Geosphere, June 2012 G11 66.13 0.51 16.21 4.23 0.09 2.01 4.54 3.66 2.45 0.14 99.7 16.27 32.44 3.95 15.22 3.19 0.82 2.75 0.42 2.47 0.5 1.36 0.21 1.34 0.22 659.3 7.48 6.87 13.36 3.75 0.7 3.0 12.25 83.32 2.97 444.5 9.45 128.8 G12 54.77 0.68 16.38 8.57 0.16 6 9.03 2.73 1.49 0.18 99.9 10.13 19.85 2.6 10.95 2.56 0.92 2.48 0.39 2.27 0.46 1.26 0.19 1.2 0.19 476.7 1.97 2.74 11.83 1.08 0.18 0.63 5.58 33.41 1.45 601.5 30.17 33.66 00729 1st pages / page 5 of 15 Northern Sierra Nevada magmatism TABLE 3. Nd AND Sr ISOTOPE DATA 87 147 Sr/ 86Sr Sr/ 86Sri Sm/144Nd 143Nd/144Nd 87 Sample Rb/ 86Sr Northern transect G01 0.6852 G02 0.4816 G03 0.2743 G04 0.3137 G05 17.875 G06 0.4667 G08 0.5423 G09 0.7513 G10 0.5082 G11 0.4817 G12 0.1078 Southern transect G14 0.919 G16 0.488 G17 134.614 G18 8.8334 G19 0.712 G20 0.9927 G21 0.5254 G22 0.6417 G23 0.783 87 143 Nd/144Ndi εNdi 0.70448 0.70451 0.70548 0.70545 0.73463 0.70562 0.70568 0.70722 0.70629 0.70666 0.70500 0.70293 0.70340 0.70483 0.70480 0.70798 0.70489 0.70283 0.70598 0.70549 0.70584 0.70476 0.1241 0.1489 0.063 0.1086 0.1284 0.1111 0.1165 0.1334 0.1209 0.1197 0.1381 0.51275 0.51293 0.51250 0.51243 0.51266 0.51248 0.51261 0.51245 0.51245 0.51234 0.51255 0.51262 0.51277 0.51243 0.51238 0.51257 0.51239 0.51233 0.51231 0.51236 0.51225 0.51241 –0.31 2.7 –3.9 –5.1 –1.2 –4.6 –6.0 –6.3 –5.3 –7.5 –4.3 0.70752 0.70615 1.04810 0.72381 0.70649 0.70736 0.70644 0.70639 0.70616 0.70538 0.70501 0.70668 0.70807 0.70542 0.70593 0.70562 0.70557 0.70498 0.1229 0.1162 0.1233 0.1325 0.1219 0.1078 0.1133 0.1013 0.1009 0.51248 0.51258 0.51256 0.51234 0.51244 0.51234 0.51237 0.51242 0.51258 0.51235 0.51246 0.51244 0.51223 0.51236 0.51226 0.51228 0.51236 0.51248 –5.5 –3.4 –3.7 –7.9 –5.4 –7.2 –6.8 –5.4 –2.9 8 n = 17 Northern transect 3 × 104 Southern transect 6 Number S. Sierra intrusive flux 5 2 × 104 4 3 1 × 104 2 1 0 50 Apparent intrusive flux (km2/My) 7 370 Ma 100 206 150 Figure 2. Histogram of Jurassic–Cretaceous U-Pb zircon ages from the northern Sierra Nevada. Apparent intrusive flux in the southern Sierra Nevada (dotted black line) is from Ducea (2001). A single Devonian age (370 Ma) from the Bowman Lake batholith is not plotted. 200 238 Pb/ U age (Ma) 1992; Busby and Putirka, 2009) (Fig. 1). Thus, the ages we present may not accurately reflect the relative volumes of magmatic pulses in this part of the range. For example, a comparison of the age histogram from this study with the estimated age-area distribution of previously dated plutons from the northern Sierra Nevada (between 39 °N and 40 °N; Cecil et al., 2010) suggests that the large ca. 165 Ma age peak is overrepresented. In addition to revealing temporal variability (periods of high and low magmatic flux), U-Pb zircon ages are also spatially variable. In both the northern and southern transects, Cretaceous plutons become systematically younger to the east (Fig. 3). This is similar to trends previously reported in the southern and central Sierra Nevada (Chen and Moore, 1982; Nadin and Saleeby, 2008), the Coast Mountain batholith of British Columbia (Gehrels et al., 2009), and the Peninsular Ranges (Silver et al., 1979; Silver and Chappell, 1988). Jurassic plutons are restricted to the western parts of both transects, and their ages have no apparent migratory trends. A single Late Devonian age (370 Ma) from the Bowman Lake pluton was also measured, and is in good agreement with previously published zircon ages from the same composite batholith (Saleeby et al., 1987b; Hanson et al., 1988). Because its petrogenetic history is not related to that of the other Mesozoic intrusions, it is not considered in subsequent sections. Major and Trace Element Geochemistry In this and subsequent sections and figures, northern Sierra plutons from this study are compared with a range-wide suite of Jurassic and Cretaceous intrusive rocks, compiled from the crest Age (Ma) 60 Figure 3. Arc migratory trends for the Sierra Nevada batholith. U-Pb ages for the central and southern Sierra Nevada (small circles) 80 are from Saleeby and Sharp (1980), Stern et al. (1981), Chen and 2 Moore (1982), Saleeby et al. (1987a, 2008), Chen and Tilton (1991), 100 Tobisch et al. (1995), Clemens-Knott and Saleeby (1999), and Cole3 1 man et al. (2004). U-Pb zircon ages from plutons in north-central 120 Nevada (large red circles) are from Van Buer and Miller (2010). Ar-Ar ages from plutons in north-central Nevada (black crosses) are U-Pb ages from the southern and central Sierra Nevada from Smith et al. (1971). U-Pb ages from the Great Valley basement 140 U-Pb ages from the northern Sierra are from Saleeby (2007); location of batholithic rocks in the Great Nevada (this study) U-Pb ages from north central Nevada Valley subsurface at the latitude of the northern Sierra Nevada from 160 Williams and Curtis (1977). Migratory trend 1 (wide-dashed line) = Ar-Ar ages from north central Nevada 2.7 km/My (from Chen and Moore, 1982; at latitude ~37 °N). MigraU-Pb ages from the Great Valley 180 basement tory trend 2 (dotted line) = 2.0 km/My. This is a fit to Cretaceous data from the northern Sierra Nevada (38.5 °N–39.5 °N) presented 200 -100 -50 0 50 100 150 200 in this study. Migratory trend 3 (dot-dash line) = 4.7 km/My. This is Distance east of the range crest (km) a fit to early to mid-Cretaceous ages of batholithic rocks in the Great Valley subsurface (Saleeby, 2007), Cretaceous ages (this study), and U-Pb ages from north-central Nevada (Van Buer and Miller, 2010). This eastward migration rate is a minimum, because it uses maximum estimates of Neogene east-west extension across northwestern Nevada and the northeastern Sierra Nevada (35%; from Surpless et al., 2002; Colgan et al., 2006a). Geosphere, June 2012 5 00729 1st pages / page 6 of 15 Cecil et al. western North American volcanic and intrusive rock database (NAVDAT; see Fig.4 caption for a list of references). For discussions of elemental and isotopic geochemistry, the northern Sierra Nevada plutons investigated in this study are divided into a Jurassic and a mid-Cretaceous group, based on the distribution of ages presented. Both groups are similar compositionally, but differ in some of their geochemical and/or isotopic trends. In general, Jurassic intrusions tend to have greater compositional heterogeneity, showing greater scatter and less well defined trends, both geochemically and isotopically. Plutons of the northern Sierra are calc-alkaline to slightly calcic and form a trend that is nearly identical to all other Sierra Nevada intrusive rocks when plotted as Na2O + KO-CaO versus SiO2 (Fig. 4A). With the exception of few, high SiO2 (>70%) samples, northern Sierra plutons are metaluminous to mildly peraluminous (Fig. 4B). With the except of K2O, most major oxides in both age groups form linear arrays and are negatively correlated with silica content, which varies between 54 and 78 wt% SiO2, trending toward higher values in mid to Late Cretaceous rocks (Fig. 5). In both Jurassic and Cretaceous plutons, FeO is higher than that of most Sierra Nevada intrusions, across all values of SiO2. Trace element compositions are generally characterized by enrichments in large ion lithophile elements (LILE) and strong depletions in Nb and Ti (Fig. 6). Jurassic plutons show greater depletion in high field strength elements (HFSE), which is reflected in higher average Ba/Th ratios (average Jurassic Ba/Th = 235; average Cretaceous Ba/Th = 65). Like most major and trace element patterns, chondrite-normalized, rare-earth element K2O + Na2O - CaO 12 Figure 4. General classification of northern Sierra Nevada pluA tons. (A) Plot of K2O + Na2O – 8 CaO versus SiO2. Major element alic data from northern plutons Alk 4 ic (this study) are compared here, alc li-c a and in subsequent figures, with Alk data from a range-wide suite lic 0 ka -al of Jurassic and Cretaceous c l Ca lcic plutons, compiled from North Ca –4 American volcanic and intrusive rock database (NAVDAT; All Sierra Nevada data Cretaceous plutons –8 www. navdat.org). Data are Jurassic plutons from: Kistler and Peterman (1978); Bateman and Chappel –12 45 50 55 60 65 70 75 80 (1979); Bateman et al. (1984, 1988); Saleeby et al. (1987a); SiO2 Ague and Brimhall (1988); 3 Moore (1991); Clemens-Knott B low SiO2 (1992); Coleman et al. (1992); Peraluminous Sisson (1992); Sisson et al. FG (1996); Macias (1996); Truschel 2 (1996); Ratajeski et al. (2001); Gray (2003); Hirt (2007); Pater- A/NK T SB son et al. (2008). (B) A/CNK Metaluminous High SiO2 1 (Al2O3 /(CaO + Na2O3 + K2O) mol%) versus A/NK (Al 2 O 3 / Peralkaline (Na2O3 + K2O) mol%) diagram for discriminating between 0 metaluminous, peraluminous, 0.6 0.8 1 1.2 1.4 and peralkaline compositions. A/CNK Most plutons from the northern Sierra are metaluminous to mildly peraluminous. Three samples plot as outliers to the main trend and correspond with those samples having unusually high or low SiO2 contents. Samples overlap most closely with data from plutons of the Fine Gold intrusive suite (central Sierra Nevada foothills) and the Sahwave batholith (north-central Nevada). T (light-green field)— Tuolumne intrusive suite (Bateman and Chappell, 1979); SB (gray-striped field)—Sahwave batholith, Nevada (Van Buer and Miller, 2010); FG (blue horizontal–striped field)—Fine Gold intrusive suite (Truschel, 1996). 6 Geosphere, June 2012 (REE) patterns are also similar to those of the greater Sierra Nevada batholith (Figs. 7A and 7B). Rare-earth element patterns show enrichment in the light rare-earth elements (LREE) (up to >100× chondrite) and relative depletion in heavy rare-earth elements (HREE), which have flat to slightly concave trends. La/Yb ratios range from 5 to 35, but are slightly higher (steeper REE slope) and more homogeneous in mid-Cretaceous plutons. Most samples have small to no Eu anomalies, with the exception of rare high SiO2 intrusions, which have large negative anomalies (Fig. 7C). Sr and Nd Isotopes Strontium and neodymium isotope systematics of northern Sierra Nevada plutons were investigated in order to identify any spatial and temporal patterns in magmatic source and to estimate the degree to which magmas interacted with older, preexisting crust. Initial 87Sr/86Sr ratios in most plutons range between 0.7047 and 0.7059, with the notable exceptions of samples G01 and G02, which have more primitive ratios (0.7029 and 0.7034, respectively). G01 and G02 are from Jurassic plutons emplaced into Panthalassan lithosphere of the northwestern Sierra Nevada foothills, the significance of which will be discussed in subsequent discussion sections. Additionally, samples from high SiO2 intrusions have low Sr, high Rb/Sr ratios, and high 87Sr/86Sri ratios (0.7070–0.7081). Initial εNd values for most northern Sierra plutons are negative and vary between –7.5 and –2.9 and show expected negative correlation with initial Sr ratios (Fig. 8). Low 87Sr/86Sri samples (G01 and G02) have correspondingly high εNd(i) values (–0.3–2.7). High SiO2 (>75%) rocks with high 87Sr/86Sri (indicated by asterisks in Fig. 8), however, have εNd(i) values within the normal range. These anomalously high 87Sr/86Sri values likely reflect minor contamination by crustal components, such as Calaveras Formation wall rocks (Fig. 8), or, potentially, seawater-altered metabasalts. Given the exceptionally low Sr concentrations in these rocks (<49 ppm), only very small degrees of contamination are necessary to greatly elevate 87Sr/86Sri ratios. DISCUSSION Flare-ups and Migration of the Magmatic Arc Plutons of the northern Sierra Nevada are mainly calc-alkaline, subduction-related products that were generated episodically during intrusive events in the Middle to Late Jurassic and the mid-Cretaceous. Although there are plutons 00729 1st pages / page 7 of 15 Northern Sierra Nevada magmatism 15 3 All Sierra Nevada data Cretaceous plutons Jurassic plutons 2 TiO2 FeO 5 1 0 8 0 7 Rock / Chondrite 10 Cretaceous plutons Jurassic plutons 100 10 All Sierra Nevada data A 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb 6 K2O 5 4 4 100 NaO2 3 2 2 1 Rock / Chondrite 6 B 0 15 0 80 10 1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb 2.0 60 10 CaO 5 20 0 40 50 60 80 70 SiO2 40 50 60 70 0 80 1.0 1000 G20 101.7 Ma; Ba/Th = 60; Sr/Y = 41; La/YbN = 18 G01 162.2 Ma; Ba/Th = 282; Sr/Y = 42; La/YbN = 9 Sample / N-MORB 100 10 1 0.1 Rb Ba Th K U Nb Ta La Ce Sr Nd Sm Zr Ti Hf Eu Gd Dy Y Er Yb Lu of this general age in the main body of the batholith to the south, the distribution of ages reported here is offset from recognized major, range-wide apparent high-flux events (Ducea, 2001; Fig. 2). There is an observed paucity of post–100 Ma plutons in north compared with great volumes of batholithic material emplaced into the central and southern Sierra during the mid- to Late Cre- taceous flare-up (ca. 100–85 Ma). Likewise, the observed pulse of northern magmatism between ca. 130 and 100 Ma (Fig. 2) is not as prevalent in the southern and central parts of the batholith. This could be explained by a southward shift in magmatism through time, although intermediate arc-related basement rocks that are early to mid-Cretaceous in age have been identified in Geosphere, June 2012 Average = 0.93 ± 0.25 0.5 C SiO2 Figure 5. Harker diagrams showing the variation of major oxides and Mg # (MgO/[MgO + FeO]) with SiO2. All iron is represented as FeO. Figure 6. Normal–mid-ocean ridge basalt (N-MORB)–normalized trace element abundance diagrams for representative samples from the northern Jurassic Sierra Nevada (G01) and the northern Cretaceous Sierra Nevada (G20). Both show large-ion–lithophile element (LILE) enrichment, relative high field strength element (HFSE) depletion, and strong depletions in Ti and Nb. The N-MORB values are from Sun and McDonough (1989). 1.5 Eu/Eu* Mg # 40 0.0 50 55 60 65 70 75 80 SiO2 Figure 7. (A and B) Rare-earth element (REE) abundance diagrams normalized to chondrite values (Sun and McDonough, 1989) for Cretaceous (A) and Jurassic (B) plutons of the northern Sierra Nevada. Shaded curve encompasses all REE data available for batholithic rocks of the central and southern Sierra Nevada (see Fig. 4 caption for a list of references). (C) Plot of europium anomaly (Eu/Eu*) versus SiO2. Dashed lines indicate the average and 2σ standard deviation of Eu/Eu* for all samples except for the high (>70 wt%) SiO2 rocks outlined. well cores from the eastern Great Valley at central to southern Sierra latitudes (Saleeby, 2007). Alternatively, the age distribution presented here, together with new insights from the Great Valley subsurface, could be indicating that the Cretaceous flare-up event was less punctuated and occurred over a longer period of time than previously estimated (Fig. 2). The apparent north-south difference in the timing of Cretaceous high-volume magmatism could be due in part to the covering of younger plutons in the northeastern Sierra by 7 00729 1st pages / page 8 of 15 Cecil et al. 15 5 Jurassic plutons DM y rra ea ntl Ma 10 Cretaceous plutons Average Nd-Sr of Sahwave batholith, NV SN wallrocks (Calaveras Fm) εNd(i) 0 EM * –5 T Y * –10 Crustal contamination –15 0.700 0.702 0.704 0.706 0.708 0.710 0.712 0.714 87 Sr/86Sr(i) Figure 8. Initial 87Sr/ 86Sr versus initial εNd for northern Sierra Nevada plutons, compared with initial Nd-Sr fields from the Tuolumne intrusive suite (T; Bateman and Chappell, 1979), Yosemite (Y; Ratajeski et al., 2001), and the Sahwave batholith, north-central NV (yellow diamond; Van Buer and Miller, 2010). Sierra Nevada wallrock data are from the Late Paleozoic Calaveras Formation (DePaolo, 1981). DM—depleted mantle reservoir. EM—enriched (slab + pelagic sediments) mantle reservoir. late Cenozoic volcanic and clastic deposits. It is more likely, however, to be due to the widening of the batholith to the north. In the southernmost Sierra Nevada (35.5 °N), the width of the exposed batholith is ~60 km, and it widens gradually along strike to the north such that at the latitudes of this study, it is roughly 100 km, from outcroppings of Jura–Cretaceous plutons in the western foothills to exposed granites east of the range crest. In the north, the locus of Late Cretaceous (post–100 Ma) magmatism coeval with large intrusive suites of the eastern Sierra Nevada (e.g., the Sonora Pass, Tuolumne, John Muir, and Mount Whitney suites) is shifted to the northeast, up to 200 km east of the modern range crest (Smith et al., 1971; Barton et al., 1988; Van Buer and Miller, 2010). Because of its age, presumed volumetric significance (covering an area of >1000 km2), geochemistry, and zonation pattern, the Sahwave batholith of NW Nevada is considered part of the greater Sierra Nevada batholith, suggesting that it is continuous across the modern divide and into Nevada (Van Buer and Miller, 2010). Even accounting for maximum amounts of Cenozoic extension across northern California and northwestern Nevada (~35%; Surpless et al., 2002; Colgan et al., 2006a, 2006b), the eastern extent of the magmatic Sierra in the north is far greater than it is in south, stretching the batholith to ~180 km in width at 40 °N. Subsurface sampling of the north-central Great 8 Valley basement near Sutter Buttes (Fig. 1) reveals that it is underlain by mafic and intermediate batholithic products (Williams and Curtis, 1977). Similar rocks have been observed in cores from other parts of the eastern Great Valley and, where dated, yield early Cretaceous ages ranging from ca. 140 to 130 Ma (Saleeby, 2007). This further increases the overall dispersion of the northern Sierra Mesozoic batholith to ≥200 km. However, the width of the arc at any given 10 My time period was probably not more than 60 km, similar to the modern frontal arcs of the Andes (e.g., Mamani et al., 2010). The presence of Cretaceous Sierran magmatism both east and west of the modern topographic range helps account for the apparent reduction in batholithic volume in the northern Sierra Nevada, while highlighting the difference between voluminous, spatially-concentrated magmatism in the south and dispersed magmatism in the north. Because of the northward widening of the batholith, the apparent rate of eastward migration of Cretaceous magmatism in the north is also greater (Fig. 3). In the central Sierra, Chen and Moore (1982) estimate eastward propagation of the arc at 2.7 km/Ma, whereas in the northern Sierra, that estimate increases to 4.8 km/Ma. The widening of the batholith to the north coincides with the widening and dispersal of the Mesozoic thrust belt in the retroarc. At the latitudes of the southern Sierra Nevada (~35 °N–37.5 °N), the eastern Geosphere, June 2012 Sierra thrust belt is confined to a narrow belt of folds and mylonitic thrusts along the eastern margin of the batholith (Dunne et al., 1978, 1983; Walker et al., 1990; Dunne and Walker, 1993). This narrow belt transitions to a wider belt to the north, where the westernmost zone of Mesozoic deformation, the Luning-Fencemaker fold and thrust belt, defines a broader zone of mainly thin-skinned imbricate thrusts (Wyld, 2002; DeCelles, 2004). This pattern suggests that the delivery of continental lithosphere components from the foreland region into the magma source region by retroarc thrusting was more vigorous in the south, potentially driving a more spatially concentrated pattern of magma genesis and resulting composite batholith growth. High-Flux Events in the Northern Sierra Nevada The northern Sierra Nevada arc was assembled in a non-steady state, with times of higher fluxes separated by magmatic lulls (Fig. 2), similar to the southern Sierra Nevada and most other Cordilleran arcs studied in some detail to date (e.g., Gehrels et al., 2009; Coast Mountains batholith). What stands out for the northern Sierra Nevada transects is the high apparent intrusive flux during the earlier, Jurassic stage of magmatism. This is similar to the Coast Mountains batholith, where the initial stages of magmatism were characterized by high apparent fluxes, intermediate to felsic compositions, and high δ18O (Wetmore and Ducea, 2011), suggesting in that case, that the fertile framework represented by continental miogeoclinal rocks provided an important mass contribution to the magmatic budget. We suggest a similar scenario for the northern Sierra Nevada, where the arc was built from its inception onto the continental margin, albeit one comprising some accreted (and primitive) terranes. This contrasts with various peri–American island arcs of Jurassic age that are primitive and more mafic in composition (e.g., the Talkeetna arc in Alaska; DeBari and Sleep, 1991) or the Jurassic arc segments found along the western margin of South America in Chile (Oliveros et al., 2007). There are no good estimates of magmatic fluxes for those arcs, but there is every indication that they were built as island arcs away from the continental margin and were subsequently docked. The northern Sierra Nevada example supports a previous suggestion that arcs developing along a continental margin have high magmatic fluxes initially because they are inevitably built on a meltfertile sequence of passive margin (miogeoclinal) assemblages (Ducea et al., 2010). The later, mid-Cretaceous flare-up in the northern 00729 1st pages / page 9 of 15 Northern Sierra Nevada magmatism 8 Sierra Nevada and the latest Cretaceous one east of the range, represent more typical mature arc events that formed in response to the overall cyclic nature of foreland deformation, crustal thickening, and magmatism (DeCelles et al., 2009), which are superimposed on the constant baseline flux of hydrous melting from the mantle wedge (Grove et al., 2003). 6 Cretaceous plutons Jurassic plutons Central Sierra plutons 4 εNd(i) 2 0 ~ –0.2, 100 km E –2 –4 –6 Emplacement of the Northern Sierra Nevada Batholith into Primitive and Heterogeneous Crust –8 –10 0.707 0.705 ~ 0.7048, 100 km E Sri 0.706 line 87 Strontium and neodymium isotopes from both Jurassic and Cretaceous plutons in the northern Sierra Nevada are variable but trend toward more primitive values than those in the south. The distribution of Sr-Nd signatures from northern plutons is consistent with a twocomponent mixing of depleted, mantle-derived magmas with evolved metasedimentary wall rocks (Fig. 8). The Jurassic Yuba River (G01) and Pleasant Valley (G02) plutons intruding Panthalassan lithosphere in the western foothills have distinctively primitive 87Sr/86Sri (0.7030–0.7035) and εNd(i) (–0.3–+2.7), limiting the reservoir to isotopically juvenile oceanic arc rocks and/or altered MORB. Large, Late Cretaceous intrusive suites of the central and southern Sierra show a greater enrichment in radiogenic strontium than Cretaceous plutons in the northern Sierra and northwest Nevada, indicative of a major along-strike change in magma source, which incorporates older, continental material in the south. Initial εNd and 87Sr/86Sri plotted along rangeperpendicular transects reveal a trend toward more evolved isotopic compositions from the foothills east to near the range crest, and a trend toward more primitive values eastward from the range crest (Fig. 9). This is in contrast to the central and southern Sierra, which was emplaced across a presumed boundary between accreted Phanerozoic rocks to the west and Proterozoic continental lithosphere to the east, such that isotopic values evolve consistently eastward toward more continental values (Fig. 9B). New investigation of pendant rocks in the central and southern Sierra indicates that that portion of the batholith was likely emplaced into transitional lithosphere and the western margin of continental lithosphere coincided with the location of the eastern Sierra thrust belt (J. Saleeby, 2011, personal commun.). The close proximity to, and underthrusting of, continental lithosphere from the retroarc imparts the eastward progressive and more evolved isotopic signatures in the south. To the north, the boundary between Panthalassan and continental lithosphere not only becomes more diffuse, but is truncated by Sr/86Sr(i) 0.709 0.703 0.701 –100 –50 0 50 Distance east of the range crest (km) Figure 9. Initial εNd and 87Sr/ 86Sr plotted as a function of distance across the range. Nd and Sr both show systematic eastward trend toward more evolved values, which are most pronounced immediately west of the range crest (gray zone). East of the range crest, values trend back toward more primitive values, mimicking the pronounced bend in the Sr 0.706 isopleth in the northern Sierra Nevada (see Fig. 1). At ~100 km east of the range crest (accounting for postmagmatic extension), isotopic values of the Sahwave batholith are yet more primitive than those from the northeastern Sierran (Sri ≅ 0.7045; εNdi ≅ 0). With regard to Sr, this is in contrast to the central (and southern; not shown) parts of the batholith, shown in black squares. Central Sierra Sr data are from a range perpendicular transect at ~36.5 °N (compiled by Lackey et al., 2008; data from Chen and Tilton, 1991; Sisson et al., 1996; Coleman and Glazner, 1998; Wenner and Coleman, 2004). ). strike-slip faults in the backarc (e.g., Oldow, 1983), thereby apparently bending the Sri 0.706 line and imparting an appendage-like shape to the isotope data. Ignoring the ca. 162 Ma Yuba River and Pleasant Valley plutons, there is no correlation between age and isotopic character of plutons, suggesting that observed isotopic variability is controlled by heterogeneity in relatively primitive crustal and upper mantle magma source regions. Despite clear along-strike changes in the character of magmatic source, as evidenced from changing isotopic values, major and trace element data are remarkably similar along all segments of the Sierran batholith. This can be seen via comparison of major element trends (Figs. 4 and 5), REE element trends (Fig. 7), and selected trace element ratios (Fig. 10). This Geosphere, June 2012 indicates that the juvenile nature of the lithosphere in the northern Sierra Nevada (its age, chemistry, mineralogy, thickness, etc.) does not preclude the generation of significant volumes of fractionated granitoids. This has been documented in other geologic settings and is perhaps best exemplified by the generation of the great Coast Mountains batholith of British Columbia and southeast Alaska (e.g., Mahoney et al., 2009; Wetmore and Ducea, 2011). The non-dependence of source lithosphere type on granitoid melt production can be seen in plots showing no relationship between Sr/Y and La/Yb, proxies for depth of melting, and initial 87 Sr/86Sr, a proxy for type and/or maturity of preexisting lithosphere (Fig. 11). The geochemical similarity of plutons emplaced into fertile continental lithosphere (southern Sierra), an amalga- 9 00729 1st pages / page 10 of 15 Cecil et al. 40 120 10 100 7% garnet amphibolite 30 La/Yb 20 80 Sr/Y Cretaceous plutons Jurassic plutons Sahwave Batholith Yosemite Intrusives SW Sierra foothills A Cretaceous plutons Jurassic plutons Average metabasalts (Smartville Complex, SN) 30% garnet amphibolite 20 30 60 20 10 Hi Sr/Y “Adakite” field 120 40 30 60 50 20 100 Normal intermediate arc field B 80 Sr/Y 60 0 0 10 20 30 40 50 Y 20 Figure 10. Plot of Sr/Y versus Y for northern Sierra Nevada plutons (large circles) and regional data for the entire Sierran batholith. High Sr/Y (“adakite”) and normal intermediate (dacite-andesite) arc fields are from Drummond and Defant (1990). Partial-melting trends from an amphibolite source with variable garnet abundances (7%–30%) are from Petford and Atherton (1996). Yellow star is the average of metabasaltic basement rocks of the Smartville complex (part of the Panthalassan belt; see Fig. 1) (Beard, 1998) and is similar to source compositions used by Petford and Atherton (1996) in their modeling. mation of accreted Phanerozoic belts (northern Sierra), and basinal terranes (northwest Nevada; Van Buer and Miller, 2010), attests to alongstrike similarity in style of Sierran batholithic petrogenesis. Constraints on Depth of Melting and Associated Batholithic Residues Plutons of the northern Sierra Nevada are interpreted to have been generated through melting of deep crustal sources, based on REE fractionation patterns, the absence of Eu anomalies, and elevated La/Ybnorm and Sr/Y ratios, all of which are discussed in detail below. Rare-earth element patterns for northern Sierra plutons are moderately steep, characterized by both enrichment in LILE and relative depletion in HREE, and show mildly concave upward “dished” middle-REE depletion (Fig. 7). These trends are consistent with low to moderate degrees of partial melting in equilibrium with a residue rich in amphibole, which preferentially incorporates middle-REE, and modest amounts of garnet. The above described REE trends are evident in both Jurassic and Cretaceous plutons, although REE patterns of 10 40 0 0.702 0.704 0.705 0.706 0.707 0.708 0.709 87 Sr/86Sr(i) Figure 11. Plots revealing a lack of correlation between La/Yb (A) and Sr/Y (B) and initial 87Sr/ 86Sr. Data are from Van Buer and Miller (2010; Sahwave batholith); Ratajeski et al. (2001; Yosemite); and Clemens-Knott (1992; SW Sierra foothills). Jurassic rocks are more variable and tend to be slightly less steep (average Jurassic La/Ybnorm ≅ 9; average Cretaceous La/Ybnorm ≅ 11). Given that average Gd/Yb ratios (a measure of HREE differentiation) are the same, but La/Sm (a measure of LREE differentiation) are higher in Cretaceous plutons, the observed difference in overall steepness is apparently due to greater LREE enrichment in Cretaceous plutons. This is similar to REE trends for the Peninsular Ranges batholith observed by Gromet and Silver (1987), who document increases eastward and through time in La/Ybnorm and LREE enrichment. The difference in La/Ybnorm between Jurassic and Cretaceous magmatic episodes could be due to a decrease in the degree of partial melting, and/or a change in the mineralogy of the source residua over time. All rocks, with the exception of the high SiO2 plutons, have very small Eu anomalies (average Eu/Eu* = 0.93; Fig. 7C). Eu2+ can substitute for inter-tetrahedral cations in feldspars and is strongly partitioned by plagioclase (Weill and Drake, 1973) and alkali feldspars (e.g., Ren, 2004). It does not, however, have an affinity for occupying Ca sites in amphibole or clinopyroxene. In fact, partition coefficient patterns of REE Geosphere, June 2012 0.703 between amphibole and silicic melts show negative Eu anomalies (e.g., Sisson, 1994). Thus, the lack of a large Eu depletion signal in Sierran granitoids indicates the generation of granitoid melts in equilibrium with a relatively feldsparpoor source. Some residual feldspar is certainly permissible, however, given the competing effects of feldspar (Eu relatively compatible) and amphibole (Eu relatively incompatible). In addition to having small to no Eu anomalies, most northern Sierran intrusives have high Sr concentrations (average ≅ 450 ppm), high Sr/Y ratios (up to 75), and low Y concentrations (average ≅ 14 ppm) (Fig. 10). Relative depletion in the HREE, high Sr/Y, high Sr, and low Y are all characteristics of magmas produced at depth from the melting of a subducting mafic slab (Kay, 1978; Defant and Drummond, 1990). They are also characteristic of magmas produced via melting of amphibolite in the deep subarc crust in equilibrium with a garnet + amphibole + clinopyroxene residue (Petford and Atherton, 1996; Stevenson et al., 2005; Mahoney et al., 2009). A plot of Sr/Y against Y concentration in northern Sierra Nevada plutons reveals trends consistent with those from experimental batch partial-melts of source 00729 1st pages / page 11 of 15 Northern Sierra Nevada magmatism amphibolite with garnet abundance ranging between 7% and 30% (Petford and Atherton, 1996) (Fig. 10). Batholithic residua likely to be amphibole rich, relatively feldspar poor, and to have modest amounts of garnet, are consistent with high pressure (>10 kbar) melting experiments of a basaltic source (e.g., Rapp et al., 1991; Wolf and Wyllie, 1993, 1994). The production of northern Sierra Nevada granodiorites and tonalites is therefore loosely constrained to depths ≥35 km and is interpreted to result from the processing of metabasaltic sources in the lower arc crust. The Presence and Fate of a Dense Batholithic Root in the North Studies of the southern Sierra Nevada suggest that it was composed of a thick (35–40 km; Pickett and Saleeby, 1993, 1994; Ducea, 2001) column of felsic and intermediate rocks underlain by a dense, garnet and clinopyroxene-rich residue (Ducea and Saleeby, 1996, 1998a; Saleeby et al., 2003). This deep residue, on the basis of its mineralogy, was termed an “eclogitic” root (Saleeby et al., 2003), also informally known as “arclogite.” Fundamental changes between lower crustal and upper mantle xenoliths entrained in Miocene basalts and those entrained in Plio– Quaternary basalts, provide evidence that such an eclogitic root existed at the base of the felsic batholith in the Miocene, but was subsequently lost from beneath the southeastern Sierra by ca. 3.5 Ma (Ducea and Saleeby, 1996, 1998a, 1998b; Farmer et al., 2002; Saleeby et al., 2003). Foundering of the eclogite root accounts for the present-day modest crustal thickness (~35 km) of the southern Sierra Nevada (Park et al., 1995; Jones et al., 1994; Zandt et al., 2004), and its replacement by hot asthenosphere has been called upon to explain recent uplift and high topography in the southern Sierra (Jones et al., 2004) and Cenozoic basaltic volcanism (Manley et al., 2000; Farmer et al., 2002). The continued attachment of the root beneath the west-central Sierra Nevada has likewise been associated with tectonic subsidence there (Saleeby and Foster, 2004). As such, the development and removal of an eclogitic root has played a fundamental role in the evolution of the central and southern Sierra. Much less understood in this context, however, is the northern Sierra, which may have had a much different tectonic history, as inferred from the different ages and distribution of plutons and the lower and more subdued topography. Indeed, a major focus of SNEP was to image the lithospheric structure of the northern Sierra Nevada and to learn more about the potential development and/or loss of a high-density batholithic root there. In terms of the exposure of batholithic rocks within the modern topographic range, the northern Sierra Nevada appears to have volumetrically less material than the main batholith to the south. Xenolith studies, as well as experimental studies of partial melts derived from hydrous mafic lithologies, indicate that only magmatic arcs producing large volumes and thick (>25 km) columns of felsic material will generate gravitationally unstable roots (e.g., Ducea, 2002). Similarly, it has been suggested that sourcing of melts in oceanic lithosphere reduces the potential for generating garnet-rich lithologies (e.g., Ducea and Saleeby, 1998a). It could be argued, therefore, that the northern batholith was less likely to have developed a dense residual root. The lack of lower crustal and/or mantle xenoliths in the northern Sierra Nevada prevents direct sampling of the batholith at depth there. However, diagnostic trace elements evidence presented here for deep processing of magmas in the northern Sierra implies: (1) that the crust was reasonably thick (>>35 km) in the Mesozoic; and (2) that a dense mafic residue was produced during batholith generation. Thus, despite the patchy exposure of northern Sierra plutons and their emplacement into relatively juvenile lithosphere, it is likely that the bulk of the crustal column there was composed of a thick section of intermediate to felsic batholithic products floored by a dense residual root. This is in contrast to proposed estimates of thin crust during Mesozoic time in northwestern Nevada, based on limited Cenozoic crustal extension there (Colgan et al., 2006a, 2006b). Seismic receiver-function analysis of crust and upper mantle structure in the Sierra Nevada reveals a bright, “delamination” Moho at ~30 km depth in the southern and eastern parts of the range, which is interpreted to be tectonic in origin and generated by a large step in wave speed between relatively homogeneous continental crust and asthenosphere below (Zandt et al., 2004; Frassetto et al., 2011). This delamination Moho is thought to result from the foundering of dense, negatively buoyant lithosphere, and its replacement by asthenosphere at shallow levels. The Moho dips westward, becoming deep and significantly weaker, in seismic expression, beneath the central and western portions of the Sierra Nevada. Areas where the Moho appears weak correlate well with a tomographically imaged, high-speed anomaly at depth (Gilbert et al., 2008; Reeg et al., 2008; Schmandt and Humphreys, 2010). Together, these observations have been interpreted as a dense root, which is attached to the base of the Sierran crust and presently in the process of foundering into the mantle. This explains the high-speed anomaly at depth, as well as the weak Moho, since the Geosphere, June 2012 crustal root appears seismically fast and similar to the mantle with which it is in contact. Seismic imaging (e.g., Zandt et al., 2004; Schmandt and Humphreys, 2010; Frassetto et al., 2011), together with heat-flow measurements (Saltus and Lachenbruch, 1991) and studies of xenoliths (Ducea and Saleeby 1996, 1998a, 1998b) and young volcanics (Manley et al., 2000; Farmer et al., 2002), form a coherent picture of evolving lithosphere through time and space in the southern and eastern Sierra Nevada region. Conversely, the crustal structure and lithospheric evolution of the northern Sierra Nevada has remained ambiguous. Large-scale tomographic studies of the western United States reveal the absence of dense, over-thickened crust in the northern Sierra Nevada region (e.g., Yang et al., 2008). A recent study using receiver-function analysis (Frassetto et al., 2011) shows a continuous Moho at ~35 km depth beneath the northern Sierra Nevada that dips shallowly westward and appears stepped (deeper to the east) at the approximate eastern margin of the metamorphic foothills belt. Although brighter than the weak Moho recognized in the central and western Sierra, the amplitude of the northern Moho is not as high as that of the delamination Moho to the south and east, and has been interpreted as resulting from extension and volcanism associated with the westward encroachment of the Basin and Range (Frassetto et al., 2011). Given the geochemical evidence supporting the development of a dense, mafic batholithic residue beneath the northern Sierra, we propose that the observed northern Moho is the result of sharpening due to post-Mesozoic removal of that residue. We accept, however, that this assertion is problematic in the absence of volcanism attributable to convective removal of the lithosphere and replacement by hot asthenosphere and/or geomorphic signals that can be clearly related to a specific tectonic event or events. Although marked incision of river channels in the central and northern Sierra (e.g., Wakabayashi and Sawyer, 2001; Stock et al., 2004) indicate relative base-level changes in the Pliocene, it is not clear whether or not such baselevel changes were generated by a climatic or a tectonic perturbance. It is also not clear what the triggering mechanism for root loss would have been. The northern Sierra Nevada batholith is more dispersed and likely less voluminous than the southern part of the batholith. It is plausible that instead of a singular, large plug of dense material at the base of the felsic crust, there developed multiple, but smaller lenses of maficultramafic cumulates. Given appropriate thermal and rheological conditions not uncommon in arc settings, it is possible for those cumulates 11 00729 1st pages / page 12 of 15 Cecil et al. to be convectively removed shortly after they are formed (Jull and Kelemen, 2001). These downwellings would have occurred in Mesozoic time and may not require a dramatic, wholesale overturning of the upper mantle, potentially explaining the lack of delamination-driven geomorphic and volcanic features in the northern Sierra region. Alternatively, the northern Sierra Nevada could have developed a dense eclogitic root similar to that proposed for the southern Sierra, but it was thermally destabilized by eruptive events of the proto–Cascade arc at ca. 15 Ma, which initiated along the eastern margin of the northern Sierra Nevada batholith (Busby et al., 2008a, 2008b). It is conceivable that proto–Cascade arc volcanism weakened the lithosphere, leading to a delamination event, the formation of the Sierra Nevada microplate (Busby et al., 2008b; Busby and Putirka, 2009), and eruption of the Table Mountain latite at ca. 10.4 Ma (e.g., Pluhar et al., and references therein). In such a scenario, modification of the northern Sierra Nevada landscape and/or volcanism resulting from foundering of the dense root could be attributed to Basin and Range extension and the development of the ancestral Cascades. garnet residua. On this basis, we propose that the northern Sierra Nevada developed a dense, “arclogitic” root similar to the one sampled by Miocene lower crustal xenoliths in the southern Sierra, even though the greater spatial distribution of plutons in the north implies a more dispersed and thinner root mass there. Because the crust is only ~35 km thick today and is underlain by a seismically strong Moho, we suggest that the northern dense root was convectively recycled back into the mantle, perhaps in response to the initiation of proto–Cascade arc volcanism and the initiation of the Sierra Nevada microplate. ACKNOWLEDGMENTS The authors thank Victor Valencia for help in the University of Arizona LaserChron laboratory. We are grateful to Craig Jones and an anonymous reviewer for their thorough and thoughtful reviews, which greatly improved the manuscript. This research was supported by National Science Foundation (NSF) awards EAR0606967 (Continental Dynamics Program) to Ducea, EAR-0732436 for support of the Arizona LaserChron Center (Gehrels), and by the George and Betty Moore Foundation, Caltech Tectonics Observatory Number 171 (Saleeby and Cecil). APPENDIX CONCLUSIONS The data presented here afford new insights into the petrogenetic and tectonic development of the northern segment of the Sierra Nevada batholith. Documentation of the geochemical and isotopic character of a regional suite of northern plutons allows for the identification of spatial and temporal variations in a longlived continental magmatic arc system. New U-Pb geochronology data argue for the widening and dispersal of the batholith to the north, which has important tectonic implications for the spatial concentration of magmatic products and their related residues. A preponderance of early to mid-Cretaceous pluton ages further suggests that the documented Cretaceous flare-up event was less punctuated and longer-lived than previously estimated. Principal findings, based on new major and trace element chemistry, and Nd-Sr isotopes, are that plutons of the northern Sierra Nevada were sourced from—and emplaced into—Phanerozoic oceanic and juvenile lithospheric terranes, but are nonetheless geochemically very similar to those emplaced into less heterogeneous and more evolved lithosphere in the southern Sierra. This suggests that younger and/or thinner lithosphere does not preclude the development of thick crust or dense residual phases. Perhaps most interesting is the recognition that northern plutons have clear geochemical signatures consistent with equilibration of magmas at depth (>35 km) with amphibole + 12 Concentrations of Rb, Sr, Sm, and Nd were determined by isotope dilution, with isotopic compositions determined on the same spiked runs. An off-line manipulation program was used for isotope-dilution calculations. Typical runs consisted of acquisition of 100 isotopic ratios. The mean result of ten analyses of the Rb standard NRbAAA performed during the course of this study is: 85Rb/ 87Rb = 2.61199 ± 20. Fifteen analyses of the Sr standard Sr987 yielded mean ratios of: 87Sr/ 86Sr = 0.710285 ± 7 and 84Sr/ 86Sr = 0.056316 ± 12. The mean results of five analyses of the Sm standard nSmb performed during the course of this study are: 148Sm/147Sm = 0.74880 ± 21, and 148 Sm/152Sm = 0.42110 ± 6. Fifteen measurements of the La Jolla Nd standard were performed during the course of this study. The standard runs yielded the following isotopic ratios: 142Nd/144Nd = 1.14184 ± 2, 143 Nd/144Nd = 511853 ± 2, 145Nd/144Nd = 0.348390 ± 2, and 150Nd/144Nd = 0.23638 ± 2. The Sr isotopic ratios of standards and samples were normalized to 86 Sr/ 88Sr = 0.1194, whereas the Nd isotopic ratios were normalized to 146Nd/144Nd = 0.7219. The estimated analytical ±2σ uncertainties for samples analyzed in this study are: 87Rb/ 86Sr = 0.35%, 87Sr/ 86Sr = 0.0011%, 147 Sm/144Nd = 0.2%, and 143Nd/144Nd = 0.0010%. Procedural blanks averaged from five determinations were: Rb 6 pg, Sr 110 pg, Sm 2.7 pg, and Nd 5.0 pg. REFERENCES CITED Ague, J.J., 1997, Thermodynamic calculation of emplacement pressures for batholithic rocks, California: Implications for the aluminum-in-hornblende barometer: Geology, v. 25, p. 563–566, doi:10.1130/0091-7613 (1997)025<0563:TCOEPF>2.3.CO;2. Ague, J.J., and Brimhall, G.H., 1988, Magmatic arc asymmetry and distribution of anomalous plutonic belts in the batholiths of California: Effects of assimilation, crustal thickness, and depth of crystallization: Geological Society of America Bulletin, v. 100, p. 912–927, doi:10.1130 /0016-7606(1988)100<0912:MAAADO>2.3.CO;2. Geosphere, June 2012 Barton, M.D., Battles, D.A., Debout, G.E., Capo, R.C., Christensen, J.N., Davis, S.R., Hanson, R.B., Michelson, C.J., and Trim, H.E., 1988, Mesozoic contact metamorphism in the western United States, in Ernst, W.G., ed., Metamorphism and Crustal Evolution of the Western United States, Volume 7: Englewood Cliffs, New Jersey, Prentice-Hall, p. 110–178. Bateman, P.C., 1992, Plutonism in the central part of the Sierra Nevada batholith, California: U.S. Geological Survey Professional Paper 1483, 186 p. Bateman, P.C., and Chappell, B.W., 1979, Crystallization, fractionation, and solidification of the Tuolumne Intrusive Series, Yosemite National Park, California: Geological Society of America Bulletin, v. 90, p. 465–482, doi: 10.1130/0016-7606(1979)90<465:CFASOT>2.0.CO;2. Bateman, P.C., and Wahrhaftig, C., 1966, Geology of the Sierra Nevada, in Bailey, E.H., ed., Geology of Northern California: San Francisco, California, California Division of Mines and Geology, p. 107–172. Bateman, P.C., Dodge, F.C.W., and Bruggman, P., 1984, Major oxide analyses, CIPW norms, modes, and bulk specific gravities of plutonic rocks from the Mariposa 1° × 2° sheet, central Sierra Nevada, California: U.S. Geological Survey Open-File Report 84-0162, 59 p. Bateman, P.C., Chappell, B.W., Kistler, R.W., Peck, D.L., and Busacca, A.J., 1988, Tuolumne Meadows quadrangle, California: Analytical data: U.S. Geological Survey Bulletin 1918, 43 p. Beard, J.S., 1998, Polygenetic tonalite-trondhjemite-granodiorite (TTG) magmatism in the Smartville Complex, northern California with a note on LILE depletion in plagiogranites: Mineralogy and Petrology, v. 64, p. 15–45, doi:10.1007/BF01226562. Busby, C.J., and Putirka, K., 2009, Miocene evolution of the western edge of the Nevadaplano in the central and northern Sierra Nevada: Paleocanyons, magmatism, and structure: International Geology Review, v. 51, p. 670–701, doi:10.1080/00206810902978265. Busby, C.J., DeOreo, S.B., Skilling, I., Gans, P.B., and Hagan, J.C., 2008a, Carson Pass-Kirkwood paleocanyon system: Paleogeography of the ancestral Cascades arc and implications for landscape evolution of the Sierra Nevada (California): Geological Society of America Bulletin, v. 120, p. 274–299, doi:10.1130 /B25849.1. Busby, C.J., Hagan, J.C., Putirka, K., Pluhar, C.J., Gans, P.B., Wagner, D.L., Rood, D., DeOreo, S.B., and Skilling, I., 2008b, The ancestral Cascades arc: Cenozoic evolution of the central Sierra Nevada (California) and the birth of the new plate boundary, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 331–378, doi:10.1130 /2008.2438(12). Cecil, M.R., Ducea, M.N., Reiners, P.R., Gehrels, G.E., Mulch, A., Allen, C., and Campbell, I., 2010, Provenance of Eocene fluvial deposits from the centralnorthern Sierra Nevada and implications for paleotopography: Tectonics, v. 29, doi:10.1029/2010TC002717. Chen, J.H., and Moore, J.G., 1982, Uranium-lead isotopic ages from the Sierra Nevada batholith: California Journal of Geophysical Research, v. 87, p. 4761–4784, doi:10.1029/JB087iB06p04761. Chen, J.H., and Tilton, G.R., 1991, Applications of lead and strontium isotopic relationships to the petrogenesis of granitoid rocks, central Sierra Nevada batholith, California: Geological Society of America Bulletin, v. 103, p. 439–447, doi:10.1130/0016-7606(1991)103 <0439:AOLASI>2.3.CO;2. Clemens-Knott, D., 1992, Geologic and isotopic investigations of the Early Cretaceous Sierra Nevada batholith, Tulare County, California, and the Ivrea Zone, Northwest Italian Alps: Examples of interaction between mantle-derived magma and continental crust [Ph.D. thesis]: California Institute of Technology, 359 p. Clemens-Knott, D., and Saleeby, J.B., 1999, Impinging ring dike complexes in the Sierra Nevada batholith, California: Roots of the Early Cretaceous volcanic arc: Geological Society of America Bulletin, v. 111, p. 484–496, doi: 10.1130/0016-7606(1999)111<0484:IRDCIT>2.3.CO;2. Coleman, D.S., Frost, T.P., and Glazner, A.F., 1992, Evidence from the Lamarck granodiorite for rapid Late Creta- 00729 1st pages / page 13 of 15 Northern Sierra Nevada magmatism ceous crust formation in California: Science, v. 258, p. 1924–1926, doi:10.1126/science.258.5090.1924. Coleman, D.S., and Glazner, A.F., 1998, The Sierra crest magmatic event: Rapid formation of juvenile crust during the Late Cretaceous in California, in Ernst, W.G., and Nelson, C.A., eds., Integrated Earth and Environmental Evolution of the Southwestern United States: Geological Society of America Special Volume: Columbia, Maryland, Bellwether, p. 253–272. Coleman, D.S., Gray, W., and Glazner, A.F., 2004, Rethinking the emplacement and evolution of zoned plutons: Geochronologic evidence for incremental assembly of the Tuolumne Intrusive Suite, California: Geology, v. 32, p. 433–436, doi:10.1130/G20220.1. Colgan, J.P., Dumitru, T.A., Reiners, P.W., Wooden, J.L., and Miller, E.L., 2006a, Cenozoic tectonic evolution of the basin and range province in northwestern Nevada: American Journal of Science, v. 306, p. 616–654, doi:10.2475/08.2006.02. Colgan, J.P., Dumitru, T.A., McWilliams, M., and Miller, E.L., 2006b, Timing of Cenozoic volcanism and Basin and Range extension in northwestern Nevada: New constraints from the northern Pine Forest Range: Geological Society of America Bulletin, v. 118, p. 126– 139, doi:10.1130/B25681.1. Davis, G.A., Monger, J.W.H., and Burchfiel, B.C., 1978, Mesozoic construction of the Cordilleran collage, central British Columbia to central California, in Howell, D.G., and McDougall, K.A., eds., Mesozoic paleogeography of the western United States: Society of Economic Paleontologists and Mineralogists, Pacific Section, Pacific Coast Paleogeography Symposium 2, p. 137–156. Day, H.W., and Bickford, M.E., 2004, Tectonic setting of the Jurassic Smartville and Slate Creek complexes, northern Sierra Nevada, California: Geological Society of America Bulletin, v. 116, p. 1515–1528, doi:10.1130 /B25416.1. DeBari, S.M., and Sleep, N.H., 1991, High-Mg, low-Al bulk composition of the Talkeetna island arc, Alaska: Implications for primary magmas and the nature of arc crust: Geological Society of America Bulletin, v. 103, p. 37–47, doi:10.1130/0016-7606(1991)103<0037: HMLABC>2.3.CO;2. DeCelles, P.G., 2004, Late Jurassic to Eocene evolution of the Cordilleran thrust belt and foreland basin system, western USA: American Journal of Science, v. 304, p. 105–168, doi:10.2475/ajs.304.2.105. DeCelles, P.G., Ducea, M.N., Kapp, P., and Zandt, G., 2009, Cyclicity in Cordilleran orogenic systems: Nature Geoscience, v. 2, p. 251–257, doi:10.1038/ngeo469. Defant, M.J., and Drummond, M.S., 1990, Derivation of some modern arc magmas by melting of young subducted lithosphere: Nature, v. 347, p. 662–665, doi: 10.1038/347662a0. DePaolo, D.J., 1980, Sources of continental crust—Neodymium isotope evidence from the Sierra Nevada and Peninsular ranges: Science, v. 209, p. 684–687, doi:10.1126/science.209.4457.684. DePaolo, D.J., 1981, A neodymium and strontium isotopic study of the Mesozoic calc-alkaline granitic batholiths of the Sierra Nevada and Peninsular ranges, California: Journal of Geophysical Research, v. 86, p. 10,470– 10,488, doi:10.1029/JB086iB11p10470. Dickinson, W., 1981, Plate tectonics and the continental margin of California, in Ernst, W.G., ed., The Geotectonic Development of California: Englewood Cliffs, New Jersey, Prentice-Hall, p. 1–28. Doe, B.R., and Delevaux, M.H., 1973, Variations in lead isotopic compositions in Mesozoic granite rocks of California—Preliminary investigation: Geological Society of America Bulletin, v. 84, p. 3513–3526, doi:10.1130 /0016-7606(1973)84<3513:VILCIM>2.0.CO;2. Drummond, M.S., and Defant, M.J., 1990, A model for trondhjemite-tonalite-dacite genesis and crustal growth via slab melting: Archean to modern comparisons: Journal of Geophysical Research, v. 95, p. 21,503– 21,521, doi:10.1029/JB095iB13p21503. Ducea, M.N., 2002, Constraints on the bulk composition and root foundering rates of continental arcs: A California arc perspective: Journal of Geophysical Research, v. 107, doi:10.1029/2001JB000643. Ducea, M.N., and Saleeby, J.B., 1996, Buoyancy sources for a large, unrooted mountain range, the Sierra Nevada, California: Evidence from xenolith thermobarometry: Journal of Geophysical Research. Solid Earth, v. 101, p. 8229–8244, doi:10.1029/95JB03452. Ducea, M.N., and Saleeby, J.B., 1998a, The age and origin of a thick mafic-ultramafic keel from beneath the Sierra Nevada batholith: Contributions to Mineralogy and Petrology, v. 133, p. 169–185, doi:10.1007 /s004100050445. Ducea, M.N., and Saleeby, J.B., 1998b, A case for delamination of the deep batholithic crust beneath the Sierra Nevada, California: International Geology Review, v. 40, p. 78–93, doi:10.1080/00206819809465199. Ducea, M.N., Otamendi, J.E., Bergantz, G., Stair, K.M., Valencia, V.A., and Gehrels, G.E., 2010, Timing constraints on building an intermediate plutonic arc crustal section: U-Pb zircon geochronology of the Sierra Valle Fertil–La Huerta, Famatinian arc, Argentina: Tectonics, v. 29, doi:10.1029/2009TC002615. Dunne, G.C., and Walker, J.D., 1993, Age of Jurassic volcanism and tectonism, southern Owens Valley region, east-central California: Geological Society of America Bulletin, v. 105, p. 1223–1230, doi:10.1130/0016-7606 (1993)105<1223:AOJVAT>2.3.CO;2 Dunne, G.C., Gulliver, R.M., and Sylvester, A.G., 1978, Mesozoic evolution of the White, Inyo, Argus, and Slate ranges, eastern California, in Howell, D.G., and McDougall, K.A., eds., Mesozoic Paleogeography of the Western United States: Pacific Coast Section, Society of Economic Paleontologists and Mineralogists, Pacific Coast Paleogeography Symposium 2, p. 189–207. Dunne, G.C., Moore, S.C., Gulliver, R.M., and Fowler, J., 1983, East Sierran thrust system, eastern California: Geological Society of America Abstracts with Programs, v. 15, p. 322.. Edelman, S.H., and Sharp, W.D., 1989, Terranes, early faults, and pre-Late Jurassic amalgamation of the western Sierra Nevada metamorphic belt, California: Geological Society of America Bulletin, v. 101, p. 1420–1433, doi:10.1130/0016-7606(1989)101<1420: TEFAPL>2.3.CO;2. Ernst, W.G., Snow, C.A., and Scherer, H.H., 2008, Contrasting early and late Mesozoic petrotectonic evolution of northern California: Geological Society of America Bulletin, v. 120, p. 179–194, doi:10.1130/B26173.1. Evernden, J.F., and Kistler, R.W., 1970, Chronology of Emplacement of Mesozoic Batholithic Complexes in California and Western Nevada: U.S. Geological Survey Professional Paper, v. 623, p. 42. Farmer, G.L., Glazner, A.F., and Manley, C.R., 2002, Did lithospheric delamination trigger late Cenozoic potassic volcanism in the southern Sierra Nevada, California?: Geological Society of America Bulletin, v. 114, p. 754–768, doi:10.1130/0016-7606(2002)114<0754: DLDTLC>2.0.CO;2. Frassetto, A., Zandt, G., Gilbert, H., Owens, T.J., and Jones, C.H., 2011, Structure of the Sierra Nevada from receiver functions and implications for lithospheric foundering: Geosphere, v. 7, p. 898–921, doi:10.1130 /GES00570.1. Gehrels, G.E., Valencia, V.A., and Ruiz, J., 2008, Enhanced precision, accuracy, efficiency, and spatial resolution of U-Pb ages by laser ablation–multicollector– inductively coupled plasma mass spectrometry: Geochemistry Geophysics Geosystems, v. 9, doi: 10.1029/2007GC001805. Gehrels, G., Rusmore, M., Woodsworth, G., Crawford, M., Andronicos, C., Hollister, L., Patchett, J., Ducea, M., Butler, R., Klepeis, K., Davidson, C., Friedman, R., Haggart, J., Mahoney, B., Crawford, W., Pearson, D., and Girardi, J., 2009, U-Th-Pb geochronology of the Coast Mountains batholith in north-coastal British Columbia: Constraints on age and tectonic evolution: Geological Society of America Bulletin, v. 121, p. 1341–1361, doi:10.1130/B26404.1. Gilbert, H., Yang, Y., Forsyth, D.W., Jones, C., Owens, T.J., and Zandt, G., 2008, Bounds of foundering in the southern Sierra Nevada: Eos (Transactions, American Geophysical Union), v. 89, p. 53. Girty, G.H., Lawrence, J., Burke, T., Fortin, A., Gallarno, C.S., Wirths, T.A., Lewis, J.G., Peterson, M.M., Ridge, Geosphere, June 2012 D.L., Knaack, C., and Johnson, D., 1996, The Shoo Fly Complex: Its origin and tectonic significance, in Girty, G.H., et al., eds., The Northern Sierra Terrane and Associated Mesozoic Magmatic Units: Implications for the Tectonic History of the Western Cordillera, Volume 81: Pacific Section, Society of Economic Paleontologists and Mineralogists, p. 1–24. Gray, W., 2003, Chemical and thermal evolution of the Late Cretaceous Tuolumne intrusive suite, Yosemite National Park, California [Ph.D. thesis]: Chapel Hill, University of North Carolina. Gromet, P., and Silver, L.T., 1987, REE variations across the Peninsular Ranges batholith: Implications for batholithic petrogenesis and crustal growth in magmatic arcs: Journal of Petrology, v. 28, p. 75–125. Grove, T.L., Elkins-Tanton, L.T., Parman, S.W., Chatterjee, N., Muntener, O., and Gaetani, G.A., 2003, Fractional crystallization and mantle-melting controls on calcalkaline differentiation trends: Contributions to Mineralogy and Petrology, v. 145, p. 515–533, doi:10.1007 /s00410-003-0448-z. Hanson, R.E., Saleeby, J.B., and Schweickert, R.A., 1988, Composite Devonian island-arc batholith in the northern Sierra Nevada, California: Geological Society of American Bulletin, v. 100, p. 446–457. Harding, J.P., Gehrels, G.E., Harwood, D.S., and Girty, G.H., 2000, Detrital zircon geochronology of the Shoo Fly Complex, northern Sierra terrane, northeastern California, in Soreghan, M.J., and Gehrels, G.E., eds., Paleozoic and Triassic Paleogeography and Tectonics of Western Nevada and Northern California, Volume 347: Boulder, Colorado, Geological Society of America Special Paper 347, p. 43–55, doi:10.1130/0-8137 -2347-7.43. Hirt, W.H., 2007, Petrology of the Mount Whitney intrusive suite, eastern Sierra Nevada, California: Implications for the emplacement and differentiation of composite felsic intrusion: Geological Society of America Bulletin, v. 119, p. 1185–1200, doi:10.1130/B26054.1. Irwin, W.P., and Wooden, J.L., 2001, Plutons and accreted terranes of the Sierra Nevada, California: U.S. Geological Survey Open-File Report 99-0374. Johnson, D.M., Hooper, P.R., and Conrey, R.M., 1999, XRF analysis of rocks and minerals for major and trace elements on a single low dilution Li-tetraborate fused bead: Advances in X-ray Analysis, v. 41, p. 843–867. Jones, C.H., Kanamori, H., and Roecker, S.W., 1994, Missing roots and mantle drips—Regional P(N) and teleseismic arrival times in the southern Sierra Nevada and vicinity, California: Journal of Geophysical Research, Solid Earth, v. 99, p. 4567–4601, doi:10.1029/93JB01232. Jones, C.H., Farmer, G.L., and Unruh, J., 2004, Tectonics of Pliocene removal of lithosphere of the Sierra Nevada, California: Geological Society of America Bulletin, v. 116, p. 1408–1422, doi:10.1130/B25397.1. Jull, M., and Kelemen, P.B., 2001, On the conditions for lower crustal convective instability: Journal of Geophysical Research. Solid Earth, v. 106, p. 6423–6446, doi:10.1029/2000JB900357. Kay, R.W., 1978, Aleutian magnesian andesites; melts from subducted Pacific Ocean crust: Journal of Volcanology and Geothermal Research, v. 4, p. 117–132, doi:10.1016/0377-0273(78)90032-X. Kistler, R.W., 1990, Two different lithosphere types in the Sierra Nevada, California, in Anderson, L., ed., The Nature and Origin of Cordilleran Magmatism: Geological Society of America Memoir 174, p. 271–281. Kistler, R.W., and Fleck, R.J., 1994, Field guide for a transect of the central Sierra Nevada, California: Geochronology and isotope geology: U.S. Geological Survey Open-File Report 94-0267, 50 p. Kistler, R.W., and Peterman, Z.E., 1973, Variations in Sr, Rb, K, Na, and initial Sr87/Sr86 in Mesozoic granitic rocks and intruded wall rocks in central California: Geological Society of America Bulletin, v. 84, p. 3489–3512, doi: 10.1130/0016-7606(1973)84<3489:VISRKN>2.0.CO;2. Kistler, R.W., and Peterman, Z.E., 1978, Reconstruction of crustal blocks of California on the basis of initial strontium isotopic compositions of Mesozoic granitic rocks: U.S. Geological Survey Professional Paper 1071, 17 p. Kistler, R.W., and Ross, D.C., 1990, A strontium isotopic study of plutons and associated rocks of the southern 13 00729 1st pages / page 14 of 15 Cecil et al. Sierra Nevada and vicinity, California: U.S. Geological Survey Bulletin 1920, p. 20. Lackey, J.S., Valley, J.W., and Saleeby, J.B., 2005, Supracrustal input to magmas in the deep crust of Sierra Nevada batholith: Evidence from high δ18O zircon: Earth and Planetary Science Letters, v. 235, p. 315– 330, doi:10.1016/j.epsl.2005.04.003. Lackey, J.S., Valley, J.W., Chen, J.H., and Stockli, D.F., 2008, Dynamic magma systems, crustal recycling, and alteration in the central Sierra Nevada batholith: The oxygen isotope record: Journal of Petrology, v. 49, p. 1397–1426, doi:10.1093/petrology/egn030. Macias, S., 1996, The Sonora Intrusive Suite: Constraints on the assembly of a Late Cretaceous, concentricallyzoned granitic pluton of the Sierra Nevada batholith [M.S. thesis]: Seattle, University of Washington. Mahoney, J.B., Gordee, S.M., Haggart, J.W., Friedman, R.M., Diakow, L.J., and Woodsworth, G.J., 2009, Magmatic evolution of the eastern Coast Plutonic Complex, Bella Coola region, west-central British Columbia: Geological Society of America Bulletin, v. 121, p. 1362–1380, doi:10.1130/B26325.1. Mamani, M., Wörner, G., and Sempere, T., 2010, Geochemical variations in igneous rocks of the Central Andean orocline (13°S to 18°S): Tracing crustal thickening and magma generation through time and space: Geological Society of America Bulletin, v. 122, p. 162–182, doi:10.1130/B26538.1. Manley, C.R., Glazner, A.F., and Farmer, G.L., 2000, Timing of volcanism in the Sierra Nevada of California: Evidence for Pliocene delamination of the batholithic root?: Geology, v. 28, p. 811–814, doi:10.1130/0091 -7613(2000)28<811:TOVITS>2.0.CO;2. Masi, U., Oneil, J.R., and Kistler, R.W., 1981, Stable isotope systematics in Mesozoic granites of central northern California and southwestern Oregon: Contributions to Mineralogy and Petrology, v. 76, p. 116–126, doi:10.1007/BF00373691. Moore, J.G., 1959, The quartz diorite boundary line in the western United States: The Journal of Geology, v. 67, p. 198–210, doi:10.1086/626573. Moore, J.G., 1991, Marion Peak Quadrangle, Fresno County, California: Analytic data: U.S. Geological Survey Bulletin 1986, 23 p. Nadin, E.S., and Saleeby, J.B., 2008, Disruption of regional primary structure of the Sierra Nevada batholith by the Kern Canyon fault system, California, in Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 429–454. Oldow, J.S., 1983, Tectonic implications of a late Mesozoic fold and thrust belt in northwestern Nevada: Geology, v. 11, p. 542–546, doi:10.1130/0091-7613(1983)11 <542:TIOALM>2.0.CO;2. Oliveros, V., Morata, D., Aguirre, L., Feraud, G., and Fornari, M., 2007, Jurassic to Early Cretaceous subduction-related magmatism in the Coastal Cordillera of northern Chile (18°30′, 24° S): Geochemistry and petrogenesis: Revista Geológica de Chile, v. 34, p. 209–232. Otamendi, J.E., Ducea, M.N., Tibaldi, A.M., Bergantz, G.W., de la Rosa, J.D., and Vujovich, G.I., 2009, Generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the Famatinian magmatic arc, Argentina: Journal of Petrology, v. 50, p. 841–873, doi:10.1093/petrology/egp022. Park, S., Clayton, M., Ducea, M., Jones, C., Wernicke, B., and Ruppert, S., 1995, Project combines seismic and magnetotelluric surveying to address the Sierran root question: Eos (Transactions, American Geophysical Union), v. 76, p. 297–298, doi:10.1029/95EO00177. Paterson, S.R., Zak, J., and Janousek, V., 2008, Growth of complex sheeted zones during recycling of older magmatic units into younger: Sawmill Canyon area, Tuolumne batholith, Sierra Nevada, California: Journal of Volcanology and Geothermal Research, v. 177, p. 457–484, doi:10.1016/j.jvolgeores.2008.06.024. Petford, N., and Atherton, M., 1996, Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru: Journal of Petrology, v. 37, p. 1491–1521, doi:10.1093/petrology/37.6.1491. 14 Pickett, D.A., and Saleeby, J.B., 1993, Thermobarometric constraints on the depth of exposure and conditions of plutonism and metamorphism at deep levels of the Sierra Nevada batholith, Tehachapi Mountains, California: Journal of Geophysical Research. Solid Earth, v. 98, p. 609–629, doi:10.1029/92JB01889. Pickett, D.A., and Saleeby, J.B., 1994, Nd, Sr, and Pb isotopic characteristics of Cretaceous intrusive rocks from deep levels of the Sierra Nevada batholith, Tehachapi Mountains, California: Contributions to Mineralogy and Petrology, v. 118, p. 198–215, doi:10.1007/BF01052869. Rapp, R.P., Watson, E.B., and Miller, C.F., 1991, Partial melting of amphibole/eclogite and the origin of Archean trondhjemites and tonalites: Precambrian Research, v. 51, p. 1–25, doi:10.1016/0301-9268(91)90092-O. Ratajeski, K., Glazner, A.F., and Miller, B.V., 2001, Geology and geochemistry of mafic to felsic plutonic rocks in the Cretaceous intrusive suite of Yosemite Valley, California: Geological Society of America Bulletin, v. 113, p. 1486–1502, doi:10.1130/0016-7606 (2001)113<1486:GAGOMT>2.0.CO;2. Reeg, H., Jones, C.H., Gilbert, H., Owens, T.J., and Zandt, G., 2008, Tomographic observations connecting convective downwellings with lithospheric source regions, Sierra Nevada, California: Eos (Transactions, American Geophysical Union), v. 89, p. 53. Ren, M., 2004, Partitioning of Sr, Ba, Rb, Y, and LREE between alkali feldspar and peraluminous silicic magma: The American Mineralogist, v. 89, p. 1290–1303. Saleeby, J.B., 1982, Polygenetic ophiolite belt of the California Sierra Nevada: Geochronological and tectonostratigraphic development: Journal of Geophysical Research, v. 87, p. 1803–1824, doi:10.1029 /JB087iB03p01803. Saleeby, J., 2007, Western extent of the Sierra Nevada batholith in the Great Valley basement: Eos (Transactions, American Geophysical Union), v. 88, p. F2186. Saleeby, J., and Busby, C., 1993, Paleogeographic and tectonic setting of axial and western metamorphic framework rocks of the southern Sierra Nevada, California, in Dunn, G., and MacDougall, K., eds., Mesozoic Paleogeography of the Western United States, Volume II: Pacific Section, SEPM (Society for Sedimentary Geology), book 71, p. 197–226. Saleeby, J., and Foster, Z., 2004, Topographic response to mantle lithosphere removal in the southern Sierra Nevada region, California: Geology, v. 32, p. 245–248, doi:10.1130/G19958.1. Saleeby, J., and Sharp, W., 1980, Chronology of the structural and petrologic development of the southwest Sierra Nevada foothills, California: Summary: Geological Society of America Bulletin, v. 91, p. 317–320, doi: 10.1130/0016-7606(1980)91<317:COTSAP>2.0.CO;2. Saleeby, J.B., Sams, D.B., and Kistler, R.W., 1987a, U/Pb zircon, strontium, and oxygen isotopic and geochronological study of the southernmost Sierra Nevada batholith, California: Journal of Geophysical Research, v. 92, p. 10,443–10,466, doi:10.1029/JB092iB10p10443. Saleeby, J., Hannah, J.L., and Varga, R.J., 1987b, Isotopic age constraints on middle Paleozoic deformation in the northern Sierra Nevada, California: Geology, v. 15, p. 757–760, doi:10.1130/0091-7613(1987)15<757: IACOMP>2.0.CO;2. Saleeby, J., Ducea, M., and Clemens-Knott, D., 2003, Production and loss of high-density batholithic root, southern Sierra Nevada, California: Tectonics, v. 22, 24 p., doi:10.1029/2002TC001374. Saleeby, J.B., Ducea, M.N., Busby, C.J., Nadin, E.S., and Wetmore, P.H., 2008, Chronology of pluton emplacement and regional deformation in the southern Sierra Nevada batholith, California, in Wright, J.E., Shervais, J.W., ed., Ophiolites, Arcs, and Batholiths: A Tribute to Cliff Hopson: Geological Society of America Special Paper 438, p. 397–427. Saltus, R.W., and Lachenbruch, A.H., 1991, Thermal evolution of the Sierra Nevada: Tectonic implications of new heat flow data: Tectonics, v. 10, p. 325–344, doi:10.1029/90TC02681. Saucedo, G.J., and Wagner, D.L., 1992, Geologic map of the Chico quadrangle, California, California Division of Mines and Geology, Regional Geologic Map Series, Map 7A, scale 1:250,000. Geosphere, June 2012 Schmandt, B., and Humphreys, E., 2010, Seismic heterogeneity and small-scale convection in the southern California upper mantle: Geochemistry Geophysics Geosystems, v. 11, doi:10.1029/2010GC003042. Sharp, W.D., 1988, Pre-Cretaceous crustal evolution of the Sierra Nevada region, in Ernst, W.G., ed., Metamorphism and Crustal Evolution of the Western United States: Englewood Cliffs, New Jersey, Prentice-Hall, p. 824–864. Silver, L.T., and Chappell, B.W., 1988, The Peninsular Ranges batholith: An insight into the evolution of the Cordilleran batholiths of southwestern North America: Royal Society of Edinburgh Transactions: Earth Science, v. 79, p. 105–121. Silver, L.T., Taylor, H.P., and Chappell, B.W., 1979, Some petrological, geochemical and geochronological observations of the Peninsular Ranges batholith near the international border of the U.S.A. and Mexico, in Abbott, P.L., and Todd, V.R., eds., Mesozoic Crystalline Rocks, Peninsular Ranges Batholith and Pegmatites: Point Sal Ophiolite: San Diego, California, San Diego State University, Department of Geological Sciences, p. 83–110. Sisson, T.W., 1992, Triple Divide Peak Quadrangle, Fresno and Tulare counties, California: Analytical data: U.S. Geological Survey Bulletin 2026, 18 p. Sisson, T.W., 1994, Hornblende-melt trace-element partitioning measured by ion microprobe: Chemical Geology, v. 117, p. 331–344, doi:10.1016/0009-2541(94)90135-X. Sisson, T.W., Grove, T.L., and Coleman, D.S., 1996, Hornblende gabbro sill complex at Onion Valley, California, and a mixing origin for the Sierra Nevada batholith: Contributions to Mineralogy and Petrology, v. 126, p. 81–108, doi:10.1007/s004100050237. Smith, J.G., McKee, E.H., Tatlock, D.B., and Marvin, R.F., 1971, Mesozoic granitic rocks in northwestern Nevada—Link between Sierra Nevada and Idaho batholiths: Geological Society of America Bulletin, v. 82, p. 2933–2944, doi:10.1130/0016-7606(1971)82 [2933:MGRINN]2.0.CO;2. Snow, C.A., and Scherer, H., 2006, Terranes of the western Sierra Nevada Foothills metamorphic belt, California: A critical review: International Geology Review, v. 48, p. 46–62, doi:10.2747/0020-6814.48.1.46. Stern, T.W., Bateman, P.C., Morgan, B.A., Newell, M.F., and Peck, D.L., 1981, Isotopic U-Pb ages of zircon from the granitoids of the central Sierra Nevada, California: U.S. Geological Survey Professional Paper 1185, 17 p. Stevenson, J.A., Daczko, N.R., Clarke, G.L., Pearson, N., and Klepeis, K.A., 2005, Direct observation of adakite melts generated in the lower continental crust, Fiordland, New Zealand: Terra Nova, v. 17, p. 73–79, doi:10.1111/j.1365-3121.2004.00586.x. Stock, G.M., Anderson, R.S., and Finkel, R.C., 2004, Pace of landscape evolution in the Sierra Nevada, California, revealed by cosmogenic dating of cave sediments: Geology, v. 32, p. 193–196, doi:10.1130/G20197.1. Sun, S.S., and McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts; implications for mantle composition and processes, in Saunders, A.D., and Norry, M.J., eds., Magmatism in the Ocean Basins: The Geological Society of London Special Publication 42, p. 315–345. Surpless, B.E., Stockli, D.F., Dumitru, T.A., and Miller, E.L., 2002, Two-phase westward encroachment of Basin and Range extension into the northern Sierra Nevada: Tectonics, v. 21, doi:10.1029/2000TC001257. Tobisch, O.T., Saleeby, J.B., Renne, P.R., McNulty, B., and Tong, W.X., 1995, Variations in deformation fields during development of a large volume magmatic arc, central Sierra Nevada, California: Geological Society of America Bulletin, v. 107, p. 148–166, doi:10.1130 /0016-7606(1995)107<0148:VIDFDD>2.3.CO;2. Truschel, J., 1996, Petrogenesis of the Fine Gold intrusive suite, Sierra Nevada batholith, California [M.S. thesis]: Northridge, California State University, 137 p. Van Buer, N.J., and Miller, E.L., 2010, Sahwave Batholith, NW Nevada: Cretaceous arc flare-up in a basinal terrane: Lithosphere, v. 2, p. 423–446, doi:10.1130/L105.1. Wagner, D.L., Jennings, C.W., Bedrossian, T.L., and Bortugno, E.J., 1987, Geologic map of the Sacramento quadrangle, California, California Division and Mines and Geology, Regional Geologic Map Series, Map 1A, scale 1:250,000. 00729 1st pages / page 15 of 15 Northern Sierra Nevada magmatism Wakabayashi, J., and Sawyer, T.L., 2001, Stream incision, tectonics, uplift, and evolution of topography of the Sierra Nevada, California: The Journal of Geology, v. 109, p. 539–562, doi:10.1086/321962. Walker, J.D., Martin, M.W., Bartley, J.M., and Coleman, D.S., 1990, Timing and kinematics of deformation in the Cronese Hills, California, and implications for Mesozoic structure of the southwestern Cordillera: Geology, v. 18, p. 554–557, doi:10.1130/0091-7613 (1990)018<0554:TAKODI>2.3.CO;2. Weill, D.F., and Drake, M.J., 1973, Europium anomaly in plagioclase feldspar: Experimental results and semiquantitative model: Science, v. 180, p. 1059–1060, doi:10.1126/science.180.4090.1059. Wenner, J.M., and Coleman, D.S., 2004, Magma mixing and Cretaceous crustal growth: Geology and geochemistry of granites in the Central Sierra Nevada Batholith, Cali- fornia: International Geology Review, v. 46, p. 880– 903, doi:10.2747/0020-6814.46.10.880. Wetmore, P., and Ducea, M.N., 2011, Geochemical evidence of a near-surface history for source rocks of the central Coast Mountain Batholith, British Columbia: International Geology Review, v. 53, p. 230–260, doi:10.1080 /00206810903028219. Williams, H., and Curtis, G.H., 1977, The Sutter Buttes of California: A study of Plio-Pleistocene volcanism: University of California Publications in Geological Sciences, v. 116, p. 1–71. Wolf, M.B., and Wyllie, P.J., 1993, Garnet growth during amphibolite anatexis—Implications of a garnetiferous restite: The Journal of Geology, v. 101, p. 357–373, doi:10.1086/648229. Wolf, M.B., and Wyllie, P.J., 1994, Dehydration-melting of amphibolite at 10 kbar: The effects of temperature and Geosphere, June 2012 time: Contributions to Mineralogy and Petrology, v. 115, p. 369–383, doi:10.1007/BF00320972. Wyld, S.J., 2002, Structural evolution of a Mesozoic backarc fold-and-thrust belt in the U.S. Cordillera: New evidence from northern Nevada: Geological Society of America Bulletin, v. 114, p. 1452–1468, doi:10.1130 /0016-7606(2002)114<1452:SEOAMB>2.0.CO;2. Yang, Y., Ritzwoller, M.H., Lin, F.-C., Moschetti, M.P., and Shapiro, N.M., 2008, Structure of the crust and uppermost mantle beneath the western Unites States revealed by ambient noise and earthquake tomography: Journal of Geophysical Research, v. 113, doi:10.1029 /2008JB005833. Zandt, G., Gilbert, H., Owens, T.J., Ducea, M., Saleeby, J., and Jones, C.H., 2004, Active foundering of a continental arc root beneath the southern Sierra Nevada in California: Nature, v. 431, p. 41–46, doi:10.1038/nature02847. 15