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Lithosphere

Sahwave Batholith, NW Nevada: Cretaceous arc flare-up in a basinal terrane

Nicholas J. Van Buer and Elizabeth L. Miller

Lithosphere 2010;2;423-446 doi: 10.1130/L105.1

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Notes

© 2010 Geological Society of America Downloaded from lithosphere.gsapubs.org on October 28, 2010 RESEARCH

Sahwave Batholith, NW Nevada: Cretaceous arc fl are-up in a basinal terrane

Nicholas J. Van Buer1 and Elizabeth L. Miller1 1DEPARTMENT OF GEOLOGICAL AND ENVIRONMENTAL SCIENCES, STANFORD UNIVERSITY, 450 SERRA MALL, BLDG. 320, STANFORD, CALIFORNIA 94305-2115, USA

ABSTRACT

Detailed mapping and sensitive high-resolution ion microprobe (SHRIMP) U-Pb geochronology centered around the Nightingale and Sah- wave Ranges, ~100 km northeast of Reno, Nevada, reveal that most of the Mesozoic basement in this area is composed of predominantly granodiorite-composition plutonic rocks intruded ca. 110–88.5 Ma. These rocks are similar in age, petrology, and composition to the mid- Cretaceous eastern part of the Sierra Nevada Batholith, and are likely related. The youngest plutonic rocks, ca. 93–88.5 Ma, form a large, compositionally zoned intrusive suite, referred to as the Sahwave intrusive suite. This suite is composed of a set of nested, inward-younging intrusions, varying between mafi c, equigranular granodiorite around the periphery to more felsic, K-feldspar–megacrystic granodiorite in the center. The Sahwave intrusive suite is coeval with the Cathedral Range intrusive event along the crest of the Sierra Nevada, including the Tuolumne intrusive suite. The geochemistry and petrology of this intrusion also support similar magma genesis and emplacement. Intrusions of the Cathedral Range intrusive event in the Sierra Nevada were emplaced along the margin of North American continental crust, whereas the Sahwave intrusive suite was intruded into a thick package of basinal metasedimentary rocks that were likely underlain by 87 86 ε transitional crust. More primitive initial Sr/ Sr and Nd values (ca. 0.7047 and –0.2, respectively) refl ect this difference. In light of this likely fundamental difference in lower-crustal character, other factors, possibly related to subducted, water-rich material, must be responsible for creating similar melting conditions among the series of large intrusions that represent the last magmatic fl are-up of the Cretaceous arc.

LITHOSPHERE; v. 2; no. 6; p. 423–446; Data Repository 2010289. doi: 10.1130/L105.1

INTRODUCTION cially scoured Sierra Nevada, the Sahwave and istry. Comparison of data between these intru- Nightingale Ranges, about an hour NE of Reno, sive suites allows us to evaluate whether the The Mesozoic Sierra Nevada Batholith pre- Nevada, form a broad, uplifted horst block of Sierra Nevada Batholith should be considered to serves an extensive record of continental-margin Mesozoic basement that is well suited for inves- extend into the NW Basin and Range (Fig. 1). arc magmatism that serves as a classic, world- tigating the relationship between plutonic rocks Furthermore, differences between these regions wide model, especially for high-intrusive-fl ux in the NW Basin and Range and in the Sierra of high intrusive fl ux may have important impli- magmatism. Previously, however, only recon- Nevada (Figs. 1 and 2). Detailed mapping in the cations for arc fl are-up models. naissance-level studies (e.g., Smith et al., 1971; Sahwave and Nightingale Ranges, combined Barton et al., 1988; Van Buer et al., 2009) have with reconnaissance of the surrounding areas, REGIONAL GEOLOGIC SETTING explored the possibility that this batholith might was used to identify distinct intrusive units for extend past the Sierra Nevada mountains into the further quantitative study. Most of the intrusive Subduction-related arc magmatism in the NW Basin and Range Province (Fig. 1), where units in this area were identifi ed as belonging Cordillera began in the Triassic and continued Mesozoic relationships are obscured by Ceno- to a single, very large, roughly concentrically episodically into the Late Cretaceous (and into zoic volcanism and basin development related zoned intrusive suite, emplaced at ca. 90 Ma, the Paleocene north of the Snake River Plain to extensional faulting. Consequently, many referred to here as the Sahwave intrusive suite and in southern Arizona; Fig. 1). The resulting published fi gures depicting the Sierra Nevada (Fig. 2). Zoned intrusive suites of approximately batholithic belt has been variably disrupted by Batholith are truncated against the edge of the the same age in the Sierra Nevada, such as the Cenozoic extension and translation and now Basin and Range or the Nevada border (e.g., Tuolumne intrusive suite, have received detailed forms several distinct segments, including the Tikoff and de Saint Blanquat, 1997; DeGraaff- geochronological, mineralogical, geochemical, Idaho Batholith, the Sierra Nevada Batholith, Surpless et al., 2002; Lackey et al., 2005), and and structural study due to vigorous and ongo- and the Peninsular Ranges Batholith (Fig. 1). the Sierra Nevada Batholith is often considered ing debate about their petrogenesis and emplace- The fi nal episode of magmatism in California to be restricted to the mountains it was named ment (e.g., Bateman, 1992; Coleman et al., 2004; and Nevada spanned ca. 120–85 Ma, and was for. However, boundaries as recent as the Neo- Žák and Paterson, 2005; Hirt, 2007; Gray et al., particularly voluminous during the latter half gene limit of Basin and Range extension (dotted 2008), and therefore provide an excellent data of this period (e.g., Barton et al., 1988; Ducea, line, Fig. 1), which defi nes the eastern scarp of set for comparison with the Sahwave intrusive 2001). In most of the U.S. Cordillera, the Creta- the Sierra Nevada, would seem to rather arbi- suite. As the fi rst report of its kind in this region, ceous batholith exhibits a regular younging pat- trarily delimit the much older Mesozoic Sierra this paper attempts to set forth several types of tern from west to east that is generally mirrored Nevada Batholith. Although Mesozoic outcrops basic data, from map data and rock descriptions by geochemical trends from more mafi c to more in the Basin and Range are less continuous and to modal mineralogy, U-Pb geochronology, and felsic (e.g., Evernden and Kistler, 1970; Hynd- more deeply weathered than those in the gla- major- and trace-element, and isotope geochem- man, 1983; Silver et al., 1979).

LITHOSPHEREFor permission to| Volumecopy, contact 2 | Number [email protected] 6 | www.gsapubs.org | © 2010 Geological Society of America 423 Downloaded from lithosphere.gsapubs.org on October 28, 2010 VAN BUER AND MILLER

126° W 124° W 122° W 120° W 118° W 116° W 114° W 112° W 110° W 42° N OROOROR MaMMarginalrggini ala Idaho Batholith IDIDIDD 87 86 CACCACAA terranes Sr/ Srr ==0 00.706.7.70. 6 S n in 44° N Figure 1. Plutons of the Mesozoic KlKlamathammatth ake Pla Riivve r magmatic arc (white) are most 40° N RRaRangeangn e NVNVNV prominently exposed in the Idaho Batholith, the Sierra Nevada Batho- lith, and the Peninsular Ranges areaararea ofof Study Batholith. The Sierra Nevada Batho- Fig.Figi ..2 2 42° N W a l k e r L a n e area lith was emplaced across the bound-

Sierra Nevada Batholith ary between the continental litho- a 38° N LFTB UTUTUT sphere of cratonal North America l B a s i n and a variety of marginal terranes k a n d that have oceanic- or transitional- e R a n g e 40° N affi nity lithosphere, as defi ned by the r 87 86 initial Sr/ Sr = 0.706 line (dashed

line; from Farmer and DePaolo,

36° N NoNorthrth 1983). The main part of the Basin

L and Range Province is outlined by a

a dotted line. The Walker Lane accom- AmAmericanericican n 38° N modates right-lateral shear near the

e AZAZAZ western boundary of the Basin and N crcratonatono Range (Wesnousky, 2005). The Lun- 34° N ing-Fencemaker thrust belt (LFTB) is developed in Mesozoic basinal sequences (Oldow, 1984). Distribu- 36° N tion of Mesozoic intrusions is modi- fi ed from King and Beikman (1974). Peninsular 32° N Ranges 500 km Batholith 34° N

122° W 120° W 118° W 116° W114° W 112° W 110° W 108° W

One of the most distinctive features of the boundary between North American continental Peak Group east of the main locus of Cretaceous Sierra Nevada Batholith is the series of large, crust and oceanic terranes to the west, as approx- magmatism (Silberling and Wallace, 1969), but compositionally zoned intrusions of the Cathe- imated by the initial 87Sr/86Sr = 0.706 line (Fig. 1; farther west, the basinal strata exceed 6 km, and dral Range intrusive event, such as the Tuolumne e.g., Gastil, 1975; Saleeby, 1981; Kistler, 1990); no base is exposed (Compton, 1960; Burke and intrusive suite, emplaced along the eastern edge in contrast, the locus of Cretaceous magmatism Silberling, 1973; Speed, 1978). Jurassic short- of the main Sierra Nevada Batholith at the very between the Sierra Nevada and western Idaho ening associated with the Luning-Fencemaker end of Cretaceous arc magmatism between (Fig. 1) does not appear to be adjacent to regular thrust belt (Fig. 1) has folded, thrust, and thick- ca. 94 and 83 Ma (Evernden and Kistler, 1970; continental crust. Wall rocks to the Cretaceous ened this basinal sequence (Oldow, 1984). Kistler et al., 1986; Tikoff and Teyssier, 1992). intrusions in this area include a basinal terrane of The metamorphic and plutonic rocks of Representing a high level of magmatic fl ux early Mesozoic deep-marine strata and the early the northern Sierra Nevada and the northwest (e.g., Ducea, 2001), these intrusions generally Mesozoic arc terranes bounding it to the north- Basin and Range are unconformably overlain exceed 1000 km2 in area, and are characterized west and southwest (Fig. 2; e.g., Speed, 1978; by Eocene, Oligocene, and Miocene volcanic by central megacrystic K-feldspar granites or Quinn et al., 1997; Wyld, 2000). These rocks and sedimentary rocks (Fig. 2). This widespread granodiorites surrounded by more mafi c equi- have regionally been metamorphosed to sub- unconformity represents a profound change granular granodiorites (e.g., Bateman, 1992; greenschist to lower greenschist grade but often from erosion in the latest Cretaceous and early John and Robinson, 1982; Titus et al., 2005; reach amphibolite grade proximal to Meso- Tertiary to active deposition of volcanic and sed- Hirt, 2007; Saleeby et al., 2008). Similar large, zoic intrusions (e.g., Willden, 1964; Bonham, imentary strata in the Eocene to Miocene and is zoned intrusions are also present in the Penin- 1969; Johnson, 1977; Barton et al., 1988). The an important datum for reconstructing geologic sular Ranges Batholith (Fig. 1), although these basinal strata, which belong to the monotonous relationships prior to Miocene extension and are somewhat older (primarily ca. 99–92 Ma) Late Triassic (Norian) to earliest Jurassic Auld related tilting (Van Buer et al., 2009). Uplift and have tonalite and trondhjemite as well as Lang Syne Group, are essentially submarine and erosion of the Tertiary strata have resulted granodiorite compositions (e.g., Gastil, 1983; fan deposits, metamorphosed into slate/phyllite in exposure of the unconformity and underly- Walawender et al., 1990). with subordinate quartzite lenses and rare calc- ing Mesozoic basement in the tilted footwalls The Cretaceous Sierra Nevada and Peninsu- silicate/marble layers (Burke and Silberling, of most major Basin and Range normal faults, lar Ranges Batholiths, which contain these large 1973; Speed, 1978). Correlative, but thinner, leaving a discontinuous Mesozoic outcrop pat- intrusions along their east sides, straddle the strata overlie the shelfal, earlier Triassic Star tern (Figs. 1 and 2).

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120º W 119º W 11 logic or geochemical data have been published OREGON that are adequate to address the magma genesis 42º N NEVADA of these intrusions and their relationship to con- temporaneous intrusions in the Sierra Nevada.

CRETACEOUS PLUTONIC ROCKS OF NORTHWEST NEVADA

Although intrusive rocks can be found scat- Explanation of Map Units 2004 Stanford seismic line tered throughout much of the western Basin and Cenozoic cover (Lerch et al., 2007) shaded by inferred basement Range Province, they constitute a majority of the Inner Sahwave intrusive suite pre-Cenozoic outcrop in an area trending NNE Outer Sahwave intrusive suite BASIN AND RANGE PROVINCE from the Lake Tahoe area across NW Nevada Unexposed Sahwave suite? (Fig. 2; Barton et al., 1988; Van Buer et al., Other Mesozoic intrusions 2009). Plutons in this area are not tightly stitched Other pre-Cenozoic rocks 41º N at the level of exposure, but rather are often Geologic map compiled mainly from Jennings et al., 1977; Irwin and Wooden, 2001. separated by substantial areas of metamorphic outcrop, often more than 10 km across (Fig. 2). Intrusive rocks include quartz monzonite and

e rare diorite/quartz diorite, but are predominantly

g

an granodiorite (cf. Smith et al., 1971). Published R

te

ni geochronology indicates intrusion during the

le

e

NEVADA SSelenite Range NVB Jurassic (ca. 200–160 Ma) and the Cretaceous CALIFORNIA Susanville 212 Bluewing (ca. 115–85 Ma), with the greatest intrusion Mts. fraction between ca. 105 and 90 Ma (Rai, 1969; area of Honey L. Fig. 3 NVB Evernden and Kistler, 1970; Smith et al., 1971; 286 Granite e Morton et al., 1977; Marvin and Cole, 1978; ge gale R. n Springs Pyramid Lake Valley Garside et al., 1992; John, 1992; Oldenburg, ighti rinity Rang N TTrinity Range Sahwave R. 1995; Wyld, 1996; Quinn et al., 1997; Wyld and

Lake RangeLake Range Lake RanRangeLake

40º N Wright, 1997; Wooden et al., 1999; Wyld et al., 2001; Van Buer and Wooden, 2007), although many intrusions remain undated or poorly dated.

S I E R R A N E V A D A A particularly continuous area of Creta- ceous plutonic outcrop occurs in the Sahwave and Nightingale Ranges, which together form a Reno BASIN AND RANGE PROVINCE broadly synclinal horst, with major normal faults along the east side of the Sahwave Mountains and the west side of the Nightingale Range (Fig. 3)1. The bulk of both mountain ranges is granodiorite. This area of intrusive rock is separated from other

Lake plutons on the south and northeast by several Tahoe kilometers of metamorphic wall rocks (Fig. 2), making the Sahwave and Nightingale Ranges a Figure 2. Though disrupted by Basin and Range extension and largely buried by Cenozoic cover well-bounded target for detailed study. However, (uncolored), Mesozoic intrusive rocks (medium gray) comprise most of the pre-Cenozoic rocks because granodiorite outcrops in the Selenite along a belt stretching NNE from the Lake Tahoe region. Rocks of the Sahwave intrusive suite are Range, to the northwest, and the Trinity Range, shown in very dark gray/black. to the east, are potentially contiguous, if not for intervening Cenozoic cover, these areas were also selected for reconnaissance study (Fig. 2). Although the Cretaceous Cordilleran mag- den, 1964; Bonham, 1969; Willden and Speed, The nearest intrusive outcrops to the west, in the matic arc has been traced across NW Nevada 1974; Johnson, 1977). More detailed work has Lake Range, are visually dissimilar, and were (Fig. 1) based on reported pluton ages between been completed on Jurassic and Triassic intru- not closely studied. In the Sahwave and Night- 105 and 85 Ma (e.g., Smith et al., 1971; Barton et sions in western Nevada (e.g., John et al., 1994), ingale Ranges (Fig. 3), several reports and the- al., 1988; Wooden et al., 1999), reconnaissance and on intrusions in the gold-producing region ses include local, more detailed mapping (Smith studies and compilations have not adequately of north-central and northeast Nevada (Fig. 1; and Guild, 1942; East and Trengrove, 1950; Rai, addressed the character of the intrusions across reviewed in du Bray, 2007). For Cretaceous plu- this intervening region. Previous mapping in tons in NW Nevada, some structural and geo- 1GSA Data Repository item 2010289, containing color copies of Figures 3, 4, and 15, is available online northwestern Nevada includes thorough cover- chronological work has been completed (e.g., at www.geosociety.org/pubs/ft2010.htm, or on request age only at 1:250,000 scale, which does not dif- Wyld and Wright, 2001; Ciavarella and Wyld, from [email protected] or Documents Secre- ferentiate between separate plutonic units (Will- 2008; Colgan et al., 2010), but no detailed petro- tary, GSA, P.O. Box 9140, Boulder, CO 80301, USA.

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elevation (km)

3 3 Kse 0 Kjp

A’

JTrm A’ JTrm K U M I V A BLUEWING MTS. N JTrm Kjp Tu NVB-206

V A L L E Y Tu ? Kjp

10km km

Kjp Kjp 1:180,000 scale ? Tu 40° 15’ N Tu

Kpl Kbs

G E Kbs bend Kjp bend Kbs Kpl Tu Kbs

A N

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S A G E H E N V A L L E Y Kpl NVB-208 G Kbs Tu

E H E N V A L L E Y

JC03-SV3 Y E L L A V S G N I R P NVB-207 Kpl verticalno vertical exaggeration exaggeration

JTrm Kjp

Kbs Ks Ks

Ksb

G R A N I T E S P R I N G S V A L L E Y E L L A V S G N I R P S S E E T T I I N N A A R R G G Kbs

JTrm Tu Tu Kjp Kjp S A H A W A V H E R A W N G A E V E R A N G E Tu Kjp

JTrm JTrm

Tu 40° N JTrm

N I G H T I N G A L E JTrm R A N G E Tu Tu Kap

119° W Tu

119° 15’ W Tu A A

3 3

Tu 0 elevatioelevationn (km)

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zoic units (Fig. 3). Together with recent allu- Map Explanation vial deposits, these rocks fi ll part of the area between the Sahwave and Nightingale Ranges, Tertiary as well as Cenozoic extensional basins to the east, west, and north of the Sahwave-Nightin- Volcanic and sedimentary strata TuTuTu Hypabyssal dikes and plugs gale horst (Figs. 2 and 3). The volcanic units Cretaceous Sahwave Intrusive Suite range from basalt fl ows to silicic ignimbrites, Aplite, pegmatite, and the interbedded sediments (not thoroughly KsKsKs Sahwave Grd., 88.5 ± 2.0 Ma and leucogranite intrusions lithifi ed yet) range from landslide deposits and fanglomerates to lacustrine clays (cf. Whitehill, School Bus Grd., 91.2 ± 1.2 Ma KsbKsbKsb (Units shown in lighter shade where inferred to underlie valley sediments) 2009). Additionally, the study area is cut by a KbsKbsKbs Grd. of Bob Spring, 92.8 ± 1.7 Ma few generations of dikes, ranging from rhyolitic to basaltic in composition, which also tend to Grd. of Juniper Pass, 92.7 ± 1.4 Ma KjpKjpKjp Diorite intrusions be more resistant to erosion than the surround- ing rock (Fig. 3). The coarsest are diabase (with Earlier Mesozoic chilled margins), but most have an aphanitic matrix. Although these dikes have not been Selenite Grd., 96.3 ± 0.8 Ma KseKseKse dated, their fi ne-grained nature suggests that Power Line I. C., 104.9 ± 0.8 Ma KplKplKpl they are substantially postmagmatic, and they are compositionally similar to volcanic pack- Auld Lang Syne Group JTrmJTrmJTrm ages in the overlying Tertiary strata. basinal metasedimentary rocks

Symbols Country Rocks

Contact Faults: Inferred Concealed The wall rocks of the Sahwave Batholith are (Balls on downthrown side) mostly metamorphosed mudstone/shale with Gradational interbedded sandstone layers and lenses. A few contact Attitudes: Magmatic Metamorphic Bedding discontinuous, 10–100-m-thick, coarsely crys- Concealed foliation foliation talline marble layers are present south of the contact batholith, but calcareous layers are rare in the Sample locality Mineral lineation metamorphic rocks to the north (Fig. 3). These rocks have been identifi ed as belonging to the Triassic to Early Jurassic Auld Lang Syne Group Figure 3 (on this and previous page). Detailed map of the Sahwave and Nightingale Ranges (location shown with box in Fig. 2), showing distribution of Cretaceous plu- (Johnson, 1977). Away from the batholith, tonic bodies, older wall rocks, and Cenozoic cover. Based on mapping at 1:24,000 metamorphic grade is subgreenschist to lower scale but shown here at 1:180,000 scale. greenschist, and original bedding is clearly seen. Fold axes and foliation in the adjacent Bluewing Mountains (Fig. 3) trend NE-SW, and exhibit 1969; Fanning, 1982; Stager and Tingley, 1988; upland, characterized by a thick blanket of grus, top-to-the-SE vergence, consistent with Juras- Whitehill, 2009). Most of these papers relate to which nourishes the range’s namesake sagebrush sic deformation in nearby parts of the Luning- exploration of the tungsten-mining district along (northern Paiute sai’-wav; Fowler and Fowler, Fencemaker thrust belt (Fig. 1; Oldow, 1984). the southwest margin of the Cretaceous intru- 1971). Map units fall into three basic categories: Adjacent to the batholith, Triassic-Jurassic sive contact, in the southern Nightingale Range the overlying Cenozoic strata, early Mesozoic strata are metamorphosed to siliceous hornfels (Fig. 3), and contain very little data pertaining to metamorphic wall rocks, and Cretaceous intru- or biotite schists, and bedding is often tightly to the igneous rocks themselves. sive rocks. The intrusive rocks are further subdi- isoclinally folded with a subvertical axial-planar vided into two groups: Units that frequently have foliation that is broadly parallel to the intrusive NEW MAPPING IN THE SAHWAVE AND gradational contacts with each other, are more or contact (Fig. 4A). A strong subvertical mineral NIGHTINGALE RANGES less concentrically arranged, and have magmatic lineation is also present within ~100 m of the foliation that is generally weak, absent, or con- intrusive contact, although it is often obscured Mapping of the Sahwave and Nightingale tact-parallel, and are apparently cogenetic, are by a subparallel intersection lineation. In the Ranges was completed at 1:24,000 scale (reduced herein informally named the Sahwave intrusive Bluewing Mountains, along the northern edge of to 1:180,000 in Fig. 3). Each mountain range is suite, whereas units with strong, roughly north- the batholith, the zone of contact-parallel folia- generally more rugged on the side between its south foliation, sharply crosscut by members of tion is only a few hundred meters wide, whereas crest and its bounding normal fault, and the Sah- the aforementioned suite, are considered to be to the southwest, in the Nightingale mining dis- wave Range, in particular, becomes higher and distinct preexisting intrusions. trict, foliation is subparallel to the contact over rockier to the north. However, even the best out- the entire exposed outcrop, up to 5 km away crops in this area are patchy and deeply weath- Cenozoic Strata from the intrusion (Fig. 3). This NW-SE folia- ered as compared to the continuous outcrops of tion is anomalous compared to NE-SW Jurassic the Sierra Nevada crest. The southern Sahwave Oligocene and Miocene volcanic and sedi- structural trends, which tend to dominate in sur- Range (Fig. 3) forms a particularly low-relief mentary rocks unconformably overlie all Meso- rounding areas (e.g., Oldow, 1984).

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A B

Q Q

Q

B B

P K

1 mm

C 1 cm D H B

P

K Q

H

1 mm E F

G K P H

K P P

K P P P K P K B 1 mm 1 cm

Figure 4 (continued on following page).

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I Q J Q P B M B B m B S m m Q

B P K

P S 1 mmm

K B P Q L P

B K P S

N 1 mm M

Figure 4 (on this and previous page). (A) Looking down at tight folds in interbedded shales (dark) and calcareous siltstone layers (light), ~100 m from intru- sive contact in southern Nightingale Range. Deformation is presumed to be Cretaceous since fold axes and lineations are aligned downward, paralleling the contact. Hammer for scale. (B) Thin section of Power Line intrusive complex under crossed polars. Note recrystallized biotite in center, strung out along a wavy foliation plane between feldspar and recrystallized quartz grains. For all thin section images, B—biotite, H—hornblende, K—potassium feld- spar, M—magnetite, P—plagioclase, Q—quartz, S—sphene. (C) Hand sample of the Granodiorite of Juniper Pass. Dark grains are biotite and hornblende. Honey-colored grains are sphene, e.g., near the top left corner. (D) Thin section of Granodiorite of Juniper Pass under crossed polars. Note equigranular texture with biotite (upper right), and hornblende (lower left), in addition to microcline, plagioclase, and quartz. (E) Complex magmatic structures in the Granodiorite of Juniper Pass, ~2 km from outer margin. Note the wavy compositional layering, especially just below left of the hammer. The central, more leucocratic dike also displays complex interfi ngering with a more mafi c phase just left of the hammer handle. Biotite within the lighter phases (black dots) is coarser than in the darker phases. (F) Outcrop of Granodiorite of Juniper Pass ~1 km from outer margin, showing elongated mafi c enclaves and magmatic foliation (parallel to black line). Hammer head for scale at top of rock. (G) Thin section of Granodiorite of Bob Spring under crossed polars. Note the large, poikilitic K-feldspar, and the chloritized biotite (dark) at lower left. (H) Hand sample of Sahwave Granodiorite, showing large K-feldspar phenocryst within a more equigranular matrix. (I) Thin section of Sahwave Granodiorite under crossed polars, showing conspicuous sphene wedges and small, ragged biotites. (J) Megacryst-rich pods in the Sahwave Granodiorite, outlined and labeled “m,” surrounded by relatively leucocratic material. Arrow points to hammer for scale. (K) Thin section of School Bus Granodiorite under crossed polars, showing large biotite (left), conspicuous sphene (center right), and myrmekitic contact between plagioclase and K-feldspar (upper left). (L) Vertical contact between School Bus Granodiorite (right half) and Power Line Complex (left half). Finger for scale. (M) Mingling and mixing relations between diorite and Granodiorite of Juniper Pass. Note interfi nger- ing of darker and lighter units, as well as continuous gradations in color index. The dark splotches at lower right are lichen. Mechanical pencil for scale. (N) Aplite dike. Composite layering can be seen dipping steeply to the left (west). Hammer for scale at very top of rock.

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With some exceptions, the generally quartz- In the very northwestern corner of the study more (Fig. 4F). Mafi c schlieren are common in ofeldspathic composition of the metasedimen- area and throughout the southern Selenite Range the same region. The Granodiorite of Juniper tary rocks is not conducive to the growth of (Figs. 2 and 3), there is a distinct granodiorite, Pass has a discernible magmatic foliation that is diagnostic minerals besides white mica and here referred to as the Selenite Granodiorite defi ned by the alignment of mafi c minerals and occasional biotite. The Nightingale mining dis- (Kse) after the “Selenite pluton” of Smith et al. sometimes subhedral plagioclase, which is gen- trict contains a number of skarn deposits in the (1971). This unit has a conspicuous, generally erally similar to the alignments of mafi c schlie- contact aureole of the batholith where calcare- north-south magmatic foliation defi ned by the ren and mafi c enclaves as well (Fig. 4F). Mag- ous layers have been metamorphosed, yielding alignment of euhedral plagioclase and horn- matic foliation tends to be strongest near the grossular/almandine, clinozoisite/epidote, and blende phenocrysts in rock with a hypidiomor- outer contact, which it often parallels (Fig. 3). more rarely tremolite, diopside, and scheelite, phic igneous texture. Polysynthetic twinning The Granodiorite of Juniper Pass grades in addition to the standard quartz, ± albite, and in the plagioclase is frequently visible to the inward to the more felsic and uniform Grano- calcite. White mica pseudomorphs, apparently unaided eye. This unit is tentatively not included diorite of Bob Spring (Kbs), a medium-grained after both andalusite (square rods) and also in the Sahwave intrusive suite, which intrudes biotite granodiorite or granite, characterized cordierite (dark, mouse-dropping shapes), can it along a sharp contact (Fig. 3) and only rarely by seriate K-feldspar phenocrysts up to ~2 cm. be found in some of the more pelitic layers in contains euhedral plagioclase. Although relative age relations with the Grano- the Bluewing Mountains near the northern mar- diorite of Juniper Pass are diffi cult to determine gin of the batholith (Fig. 3). However, large (to SAHWAVE INTRUSIVE SUITE from the gradational intrusive contact, in map over 5 cm) andalusite crystals remain intact in at pattern, the Granodiorite of Bob Spring appears least one area ~1 km from the northern contact, The metamorphic rocks, the Power Line to cut out the center of the Juniper Pass (Fig. 3) growing in random orientations that cut across complex, and the Selenite Granodiorite are and is presumed to be younger. In the fi eld, this the foliation. intruded by members of the Sahwave intrusive gradational contact is arbitrarily mapped where suite, which consists of three concentric, par- large K-feldspar phenocrysts become more con- Early Intrusive Units tially intergradational intrusive units centered on spicuous than large biotite crystals. Biotite in the Sahwave Range and a distinct lobe-forming the Granodiorite of Bob Spring is more homo- The oldest intrusive unit, informally referred unit that stretches across the central Nightingale geneously distributed, and generally no larger to as the Power Line intrusive complex (Kpl), Range (Fig. 3). Rocks of similar appearance than 1 mm. The K-feldspar phenocrysts are occupies the northwestern Nightingale Range also occur in the western Trinity Range, sepa- poikilitic, mostly surrounding plagioclase and (Fig. 3), and is predominantly a medium-grained rated from the Sahwave Range by Cenozoic fi ll biotite (Fig. 4G), and are occasionally sieve tex- biotite hornblende granodiorite with 5–10 mm in Granite Springs Valley, suggesting that the tured and diffi cult to see. In general, Kbs is fi ner K-feldspar phenocrysts. However, this unit Sahwave intrusive suite may underlie much of grained toward its center, and K-feldspar phe- also includes many unmapped dikes and pods this broad area as well (Fig. 2). The outermost nocrysts are less common. The Granodiorite of of darker granodiorite and diorite ranging from and oldest intrusive unit is a medium- to coarse- Bob Spring bears equant quartz grains that are centimeters to hundreds of meters in dimen- grained equigranular biotite hornblende grano- generally only ~1 mm in size but reach 3–5 mm sion. Some of these are fi ne grained, weathering diorite referred to as the Granodiorite of Juniper in the southern part. Mafi c minerals are often to a blue-grayish color, but all subunits share a Pass (Kjp; Fig. 3). This unit is discernible by its badly chloritized, and feldspars show signs of similar, generally north-south–oriented, steeply conspicuous 4–8 mm biotite crystals. Addition- sericitization. Foliation in this unit is usually dipping solid-state foliation (Fig. 3). This strong ally, large hornblende phenocrysts are common absent or at least too weakly defi ned to measure. foliation distinguishes the Power Line complex around the periphery of this intrusion, giving the The Sahwave Granodiorite (Ks), a K-feldspar– from all other intrusive units, including the Sah- rock a characteristic “Dalmatian” appearance megacrystic biotite granodiorite (Figs. 4H and wave intrusive suite, which intrudes the complex (Figs. 4C and 4D). Hornblende and sphene are 4I), intrudes the central part of the Granodiorite and crosscuts its foliation. Although many of both present throughout the Sahwave intrusive of Bob Spring along a generally shallowly dip- the fi ner-grained mafi c enclaves appear to dem- suite, but only in the Granodiorite of Juniper ping contact that is sharp on the north side but onstrate magma mingling, relationships among Pass does the hornblende form crystals nota- gradational along its south side (Fig. 3). K-feld- these subunits are somewhat obscured by poor bly larger than the 1–3 mm euhedral sphene. In spar megacrysts are 2–4 cm across, somewhat outcrop and the solid-state foliation. In thin sec- detail, the mineral proportions and color index poikilitic, and more abundant (usually 1%–5% by tion, the foliation is defi ned by biotite strung out of this unit vary quite a bit; in places, it can be volume) than in the Granodiorite of Bob Spring. along wavy foliation planes, and the sense of classifi ed as a tonalite or a quartz diorite. Gra- The abundance of K-feldspar megacrysts can shear, if any, is unclear, because the rock bears dational compositional variation can sometimes vary greatly from place to place, and at outcrop no discernible lineation (Fig. 4B). Biotite and be seen across large outcrops; more rarely, inter- scale, it is not uncommon to see distinct string- quartz appear to have been largely recrystallized nal contacts can be discerned where slightly ers and pods enriched in K-feldspar megacrysts, (Fig. 4B), but feldspars remain intact, display- lighter and darker phases occur together. In a rarely up to as much as ~20% (Fig. 4J). The Sah- ing distinct undulatory extinction, suggesting few places, straight or wavy compositional lay- wave Granodiorite forms relatively bold outcrops solid-state deformation at temperatures of ~400– ers, 1 cm to 1 m thick, are bounded by sharp compared to adjacent parts of the Granodiorite of 450 °C or warmer, depending on strain rate. contacts (Fig. 4E). Many of these internal struc- Bob Spring, but the rock is uniformly crumbly This unit also contains many large inclusions of tures are subtle, and only readily seen in fresh and often spheroidally weathered. metamorphic rock, mostly 5–200 m in length but outcrop, so it is possible that they are fairly per- The Nightingale Range contains a distinct including a 4-km-long potential roof pendant as vasive. Mafi c enclaves are found throughout the lobate unit referred to as the School Bus Grano- well (Fig. 3). These are generally elongated in unit, but are only common within 1–2 km of the diorite (Ksb; Fig. 3). This unit is a relatively leu- map view, and aligned subparallel to the folia- exterior contact. Enclaves are typically 5–30 cm cocratic granodiorite, distinguished by scattered tion of the Power Line complex (Fig. 3). in length and fl attened by a ratio of 2:1–5:1 or 1–2 cm K-feldspar phenocrysts and 3–6 mm

430 www.gsapubs.org | Volume 2 | Number 6 | LITHOSPHERE Downloaded from lithosphere.gsapubs.org on October 28, 2010 Sahwave Batholith, NW Nevada | RESEARCH biotite fl akes (Fig. 4K). Unlike the main part Intrusive Contacts published K/Ar hornblende (and biotite) ages of the Sahwave Batholith, this lobe does not are 91 ± 6 (88 ± 4) Ma and 95 ± 6 (92 ± 4) Ma appear to be any more mafi c around its outer The intrusive contacts are generally not for the Granodiorite of Juniper Pass and the edge, and is, in fact, remarkably homogeneous. exposed well enough, or, when gradational, Selenite Granodiorite, respectively (Smith et Magmatic foliation is not generally distinguish- defi ned well enough to measure their attitudes al., 1971). These error bars are about as large as able. The School Bus Granodiorite intrudes both directly, and furthermore they are generally too the total span of ages. To more precisely defi ne the Power Line complex and the Granodiorite irregular where exposed on the outcrop scale the timing and duration of magmatism in the of Juniper Pass along sharp, vertical contacts to make meaningful map-scale measurements study area, samples from each of the six main (Fig. 4L) that are fairly irregular at the map scale directly. Contact attitudes, such as those shown intrusive units were selected for age determina- (Fig. 3). Where it intrudes the Power Line com- on the cross section in Figure 3, have been esti- tion. An additional sample of granodiorite from plex, the units are often separated by metamor- mated from map patterns using three-point con- the Trinity Range, resembling the School Bus phic screens and blobs 20–200 m thick (Fig. 3). straints in areas where the contact appears to be Granodiorite, was dated to investigate whether approximately planar. Where contact orientation the Sahwave intrusive suite might continue this Minor Intrusives is evident, it tends to be steeply dipping and sub- far to the east (Fig. 2). parallel to magmatic foliation, but there are a The southern part of the Granodiorite of couple of notable exceptions. These are the con- U-Pb SHRIMP Methods Juniper Pass contains a number of diorite/quartz tacts along the two largest metamorphic blocks diorite bodies, varying from tens of meters to or pendants at the southern end of the Sahwave Zircons from these seven samples (Table 1) over a kilometer in scale (Fig. 3). These fi ne- to Range, and the shallow contact where the Grano- were analyzed by secondary-ion mass spec- medium-grained intrusions frequently contain diorite of Juniper Pass underlies the Power Line trometry using the Stanford–U.S. Geological ~5 mm euhedral plagioclase phenocrysts, and complex in the northwestern Nightingale Range Survey sensitive high-resolution ion micro- sometimes acicular hornblende crystals as well. (Fig. 3). It is not clear, however, if these cases probe–reverse geometry (SHRIMP-RG) to These diorite bodies appear to be coeval with represent the true roof of the intrusion. In the yield U-Pb age determinations. Zircons were the Sahwave Batholith, often showing magma northwestern Nightingale Range, the low-angle separated from each sample using standard mingling and mixing structures such as lobate portion of the contact terminates westward as the procedures. Sample zircons and chips of R33 and interfi ngering contacts, streaky fi ne-scale top contact of a horizontal dike of the Granodio- standard zircons were mounted in epoxy, intermingling, and outcrop-scale continuous rite of Juniper Pass intruded into the Power Line ground halfway through the grains with compositional variation indicative of wholesale complex (Fig. 3), suggesting that the contact fi ne sandpaper, and polished with diamond mixing (Fig. 4M). in this area may simply surround a fl ap of wall compound. All grains were imaged both in Additionally, the Sahwave Batholith and its rock that was in the process of being stoped off. refl ected light with an optical microscope and country rocks are pervaded by a series of leuco- External contacts of the Sahwave intrusive suite in cathodoluminescence (CL) using a JEOL cratic dikes and sills that tend to be more resis- frequently dike into the metamorphic rocks and 5600 scanning electron microscope to reveal tant to weathering than the surrounding country apparently surround stoped blocks (Fig. 3), sug- zonation as well as cracks, inclusions, and rocks (Fig. 3). Most of these dikes demonstrate gesting that stoping is at least a locally impor- other potential problem areas. U, Th, and Pb wide variations in grain size between aplite and tant process. In other areas, external contacts are isotopes, along with Zr, Hf, La, Ce, Nd, Sm, pegmatite textures, often showing evidence for sometimes quite planar, demonstrating smooth Eu, Gd, Dy, Er, and Yb were analyzed with the repeated intrusion (Fig. 4N). The pegmatites curves that parallel foliation in the adjacent, sub- Stanford-USGS SHRIMP-RG using an oxygen are generally muscovite bearing, and may also vertically lineated wall rocks (Fig. 3), suggesting ion beam between 4 and 6 nA and a spot size contain tourmaline (schorl) and rarely garnet. that the wall rocks were fl attened in pure shear of 20–30 μm. Isotope ratios were normalized The dikes range from 1 cm to 100 m in thick- and fl owed ductilely downward to accommodate using zircon age standard R33 (419 Ma; Black ness and generally strike north-south (Fig. 3). the laterally expanding pluton. et al., 2004) and concentration standard CZ3. Dips are often moderately shallow, but only Age data were reduced using SQUID and ISO- locally consistent in direction of dip. A notable CHRONOLOGY OF EMPLACEMENT PLOT software (Ludwig, 2001, 2003) to yield concentration of leucocratic dikes exists in the 207Pb-corrected 206Pb/238U weighted-average Nightingale Range, intruding the Power Line Although relative ages for the plutons can ages (Table 1; Fig. 5). Complete data tables can complex (Fig. 3). These dikes crosscut the solid- be determined from contact relations, the only be found in Appendix Table A1. state foliation of the Power Line complex and are occasionally composite, containing a phase with scattered large K-feldspar and biotite phe- TABLE 1. SHRIMP U-Pb GEOCHRONOLOGY SAMPLE DATA nocrysts, suggesting that they may be geneti- tinU elpmaS edutitaL.on Longitude Age cally related to the School Bus Granodiorite, (°N) (°W) (±2σ, Ma) which could underlie this area at an unexposed Sahwave Granodiorite JC03-SV3 40°07′56″ 119°04′05″ 88.5 ± 2.0 level. Pegmatite dikes cutting the metamorphic School Bus Granodiorite NVB-207 40°07′37″ 119°16′06″ 91.2 ± 1.2 rocks along the margins of the batholith are fre- Granodiorite of Bob Spring SH-21 40°12′29″ 119°06′02″ 92.8 ± 1.7 quently folded and boudinaged in the foliation Granodiorite of Juniper Pass NVB-206 40°18′47″ 119°01′04″ 92.7 ± 1.4 that is subparallel to the country-rock contact. A Granodiorite in Trinity Range NVB-286 40°10′13″ 118°46′20″ 90.3 ± 0.6 few broader leucogranite intrusions, which are Selenite Granodiorite NVB-212 40°25′58″ 119°16′09″ 96.3 ± 0.8 ′ ″ ′ ″ more uniform in grain size and contain minor Power Line intrusive complex NVB-208 40°08 38 119°13 20 104.9 ± 0.8 biotite, are present near the southern margin of Note: Reported ages are 207Pb-corrected 206Pb/238U weighted-average ages. SHRIMP— the batholith (Fig. 3). sensitive high-resolution ion microprobe.

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238U/206Pb 207 206 238 Pb corrected Pb/ U ages 60 65 70 75 80 100 .07 95 .06

90 .05 .04 85 .03 JC03-SV3 Ks

100 .05

.04 95 .03 90 .02 NVB-207 Ksb

.06 95 .05 90 .04 Pb to 44 Ma 206 NVB-206 Kjp .03

to 139 Ma Pb/ Age (Ma) Age

95 207 .07

90 .06

.05 85 NVB-286 Trinity Range .06

100 .05

95 .04 NVB-212 Kse .03

110 .05

105 .04

.03 100 NVB-208 Kpl .02

95 .05

90 .04 SH-21 Kbs .03 85 2σ errors shown in both types of plot. 110 100 90 80 Age on concordia (Ma) Figure 5. Sensitive high-resolution ion microprobe U-Pb results. At left, selected spot ages used for weighted-mean ages are shown by solid bars. Rejected spot ages are shown by empty bars. Weighted averages are shown by gray lines. Diagrams on right are inverse con- cordia plots, showing accepted spot analyses with solid symbols and rejected spot analyses with empty symbols. Ages along concordia (gray line with tick marks) are shown on the corresponding tick marks at bottom. All errors are 2σ.

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U-Pb SHRIMP Results lation at 109.7 ± 0.8 Ma in NVB-208 (Fig. 5). are similar to many described units in the Sierra However, these rocks lack clear evidence of Nevada Batholith, including units that, for Zircons generally show crisp magmatic older inherited zircons (only one grain out of example, contain conspicuous sphene, euhedral oscillatory zonation under CL and do not con- 77 analyzed was more than ~8 m.y. older than biotite and hornblende, or K-feldspar mega- tain distinct cores (Fig. 6). Only one grain, from the enclosing host rock, at a modest 139 Ma). crysts. Large, concentrically zoned intrusions NVB-286, appeared to have a distinct core and The lack of signifi cant inheritance suggests that are also common in the Sierra Nevada (e.g., rim, but both parts gave exactly the same age. these magmas may have originated at zircon- Bateman, 1992). U-Pb SHRIMP dating in the Individual grain analyses showed a moderately undersaturated conditions. Sahwave and Nightingale area confi rms earlier large amount of scatter, although most analy- SHRIMP U-Pb results (Table 1; Fig. 5) give geochronologic estimation of Late Cretaceous ses spread out along or just above concordia ages for individual units in agreement with the ages simultaneous with major intrusion in the (Fig. 5). Select analyses were dismissed (open relative ages inferred from intrusive relations. Sierra Nevada. Ages spanning from ca. 110 Ma symbols) because of discordance, high com- The Granodiorite of Juniper Pass and the Grano- (represented by inherited zircons in the Power mon Pb, and Pb loss in high-U zircons (Fig. 5; diorite of Bob Spring give indistinguishable Line complex) to ca. 88.5 Ma indicate a long- Table A1, see Appendix). It is diffi cult to tell ages, but the latter is presumed to be younger lived history of repeated intrusion in this part of whether the spread in ages is caused by dis- from crosscutting map relations. These ages the batholith, consistent with prolonged histo- turbed U-Pb systematics or actually represents are also equivalent within error to published ries of magmatism in similarly sized areas of the prolonged periods of crystallization in a large K/Ar hornblende and biotite ages (Smith et al., Sierra Nevada Batholith (e.g., Bateman, 1992; active magma chamber episodically fed by new 1971). Ages from the Sahwave intrusive suite Irwin and Wooden, 2001; Saleeby et al., 2008). batches of magma. Older and younger zircons span from ca. 93 to 88.5 Ma, demonstrating that These lines of evidence all support the idea that from individual samples are not visually differ- this batholith is contemporaneous with the large Cretaceous intrusive rocks in the study area ent or distinguishable in CL images (example intrusions of the ca. 95–83 Ma Cathedral Range formed in a broadly similar arc environment shown in Fig. 6). Some of the signifi cantly older intrusive epoch defi ned in the Sierra Nevada as those in the Sierra Nevada, and represent a ages can be ascribed to scavenging from slightly Batholith (Evernden and Kistler, 1970; Kistler, continuation of the Cretaceous Cordilleran arc older plutonic rocks, such as the distinct popu- 1999). The sample of granodiorite from the across the NW Basin and Range (Fig. 1). western Trinity Range (NVB-286) is also shown Whether or not the Cretaceous intrusions in to have crystallized in this time range, at 90.3 NW Nevada should actually be considered to ± 0.6 Ma, supporting the idea that it is part of be part of the Sierra Nevada Batholith is largely the Sahwave intrusive suite and that these rocks a semantic issue. However, if the boundaries may underlie much of the intervening Granite of this Mesozoic batholith are to be set based Springs Valley as well (Fig. 2). Whereas ages on Mesozoic features, we note that the mostly 105.3 ± 1.4 associated with the Sahwave intrusive suite Late Cretaceous intrusions of our study area are clustered relatively tightly, spanning about lie due east of Early Cretaceous intrusions near 4 m.y., the Selenite Granodiorite and the Power Susanville, in the northernmost Sierra Nevada, Line complex are signifi cantly older, at 96.3 which are generally considered to be part of ± 0.8 and 104.9 ± 0.8 Ma, respectively, justify- the Sierra Nevada Batholith (Fig. 2; Oldenburg, 108.7 ± 1.3 ing their classifi cation as distinct units. 1995). Before Tertiary extension and translation across the Walker Lane (which is considered to CONTINUITY OF THE CRETACEOUS be <30 km at this latitude; Faulds et al., 2005), CORDILLERAN BATHOLITH these two areas would have been even closer (Van Buer et al., 2009), representing the east and Our initial study of batholithic rocks in west edges of the eastward-younging batholith 99.5 ± 1.4 the area around the Sahwave and Nightingale (Figs. 1 and 2). Therefore, we tentatively suggest Ranges in the NW Basin and Range strongly sup- that the Cretaceous intrusions of NW Nevada be ports the suggestion of Smith et al. (1971) and referred to as part of the Sierra Nevada Batho- 105.0 ± 1.2 Barton et al. (1988) that the Cretaceous Cordil- lith. To better clarify the relationship between leran batholith is continuous across NW Nevada intrusions of NW Nevada and the Sierra Nevada, (Figs. 1 and 2). Although obscured by Cenozoic however, we analyzed the magma genesis of the cover, especially under the unbroken volcanic Sahwave intrusive suite using detailed mineral- plateau covering NE California, SE Oregon, ogical and geochemical data, which we com- and part of NW Nevada, Cretaceous batholithic pared to similar data from the most well-studied rocks form a majority of Mesozoic outcrops intrusion of the same age in the Sierra Nevada, along a NNE-trending belt of the northwestern the Tuolumne intrusive suite. Basin and Range (Fig. 2; Barton et al., 1988; Van Buer et al., 2009). The extent of this intrusive MINERALOGY AND GEOCHEMISTRY OF Figure 6. Cathodoluminescence images of rep- belt to the north and west is unclear due to com- THE SAHWAVE INTRUSIVE SUITE resentative zircons from the Power Line intru- plete Cenozoic volcanic cover, but relatively low sive complex (NVB-208), which contains the upper-crustal seismic velocities compatible with Because the main, concentric part of the most antecrystic zircons of any unit. All zircons demonstrate magmatic oscillatory zoning; granitoid rocks persist almost to the NW corner Sahwave intrusive suite appears to be young- younger and older zircons do not show system- of Nevada (Fig. 2; Lerch et al., 2007). Granodio- ing inward, with mafi c units grading into more atic differences. rite units in the Sahwave and Nightingale area felsic units, the rocks along a radial transect

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effectively record the magmatic evolution of the TABLE 2. MINERALOGY AND MAJOR-ELEMENT CHEMISTRY system over its 4 m.y. intrusive history. For this elpmaS atad ladoM ygolarenim reason, the Sahwave intrusive suite was sampled Unit Sample Latitude Longitude Points Quartz K-feldspar Plagioclase Mafi c from center to margin along a transect extending number (°N) (°W) counted (vol%) (vol%) (vol%) (vol%) north from the central Sahwave Granodiorite to the outer edge of the batholith and along a sec- Main Sahwave transect ′ ″ ′ ″ ond, smaller transect through the School Bus Kjp SH-1 40°19 49 119°00 37 1248 23.6 2.6 48.6 25.2 Kjp SH-2 40°19′21″ 119°00′46″ 1058 19.8 6.4 54.8 18.9 lobe in the Nightingale Range (rows of black Kjp NVB-206 40°18′47″ 119°01′04″ 1093 18.7 9.1 52.7 19.5 dots, Fig. 3). Each transect contains samples Kjp SH-5 40°18′29″ 119°01′38″ 1201 21.6 14.2 50.0 14.2 spaced approximately 1 km apart (Table 2), Kjp SH-6 40°18′01″ 119°01′58″ 1051 22.4 11.7 51.8 14.2 chosen from the most pristine outcrops avail- Kjp SH-7 40°17′32″ 119°02′28″ 1061 16.8 11.4 53.3 18.5 able. Along these transects, the mineralogy Kjp SH-8 40°17′06″ 119°02′53″ 856 17.4 2.8 59.7 20.1 ′ ″ ′ ″ records changes in the crystallizing assem- Kjp SH-9 40°16 39 119°03 22 1051 15.8 4.2 60.4 19.6 Kjp SH-10 40°16′10″ 119°03′32″ 208 18.3† 13.0† 48.6† 20.2† blage and determines rock classifi cation under Kjp SH-11 40°15′38″ 119°03′48″ 1039 22.3 11.5 49.7 16.6 the International Union of Geological Sciences grad. SH-12 40°15′08″ 119°03′47″ 1033 21.4 17.6 46.5 14.5 (IUGS) scheme (Streckeisen, 1976). Major- and Kbs SH-14 40°14′04″ 119°04′27″ 1032 25.4 19.2 46.4 9.0 trace-element chemistry responds in detail to Kbs SH-15 40°13′35″ 119°04′48″ 906 23.5 22.7 45.3 8.5 element partitioning and mixing during melting, Kbs SH-16 40°13′08″ 119°05′05″ 1086 27.1 17.9 45.6 9.5 ′ ″ ′ ″ crystal-liquid fractionation, assimilation, and Kbs SH-21 40°12 30 119°06 01 1090 23.3 20.5 49.7 6.5 Kbs SH-22 40°12′12″ 119°06′17″ 865 27.9 22.0 41.4 8.8 other petrogenetic processes (e.g., Hildreth and Kbs SH-23 40°11′49″ 119°06′48″ 940 26.7 20.5 44.1 8.6 Moorbath, 1988). Sr and Nd isotope systems Kbs SH-24 40°11′14″ 119°06′46″ 1010 22.9 23.0 43.2 11.0 are affected by radiogenic decay of Rb and Sm Kbs SH-25 40°10′41″ 119°06′14″ 1006 26.5 33.6 35.6 4.3 isotopes, and are therefore sensitive to the tim- Kbs SH-26 40°09′53″ 119°06′48″ 1065 24.1 17.0 48.0 10.9 ing and extent of differentiation in the source Kbs SH-27 40°09′26″ 119°06′24″ 903 30.3 24.8 37.4 7.4 ′ ″ ′ ″ region. Together, these data provide information Ks SH-29 40°08 26 119°05 11 1129 28.3 16.0 44.7 10.9 Ks SH-30 40°08′20″ 119°04′33″ 827 26.5 16.0 48.1 9.4 on the magma genesis of the system, and are Ks NVB-1 40°07′56″ 119°04′05″ 0n.d.§ n.d.§ n.d.§ n.d.§ appropriate for detailed comparison to similarly School Bus lobe transect sampled coeval intrusions in the Sierra Nevada, ′ ″ ′ ″ such as the Tuolumne intrusive suite (e.g., Bate- Ksb SB-5 40°08 05 119°15 43 877 27.9 24.6 39.5 8.0 Ksb NVB-207 40°07′37″ 119°16′06″ 977 23.2 23.0 46.3 7.5 man, 1992; Hirt, 2007; Gray et al., 2008). Ksb SB-3 40°07′00″ 119°16′18″ 995 24.0 12.0 53.8 10.3 Ksb SB-2 40°06′25″ 119°16′11″ 1069 28.4 25.4 40.2 5.9 Methods Ksb SB-1 40°06′02″ 119°16′30″ 1036 27.1 18.7 48.9 5.2 Aplites For analysis of modal mineralogy, each aplite AP-02 40°02′45″ 119°08′07″ 0n.d.§ n.d.§ n.d.§ n.d.§ 2 sample was sawn into slabs of at least 70 cm , aplite AP-03 40°02′47″ 119°08′00″ 0n.d.§ n.d.§ n.d.§ n.d.§ treated with penetrating epoxy if needed, and aplite AP-04 40°02′50″ 119°07′49″ 0n.d.§ n.d.§ n.d.§ n.d.§ ground fl at. The slabs were etched with con- aplite AP-05 40°02′26″ 119°03′51″ 0n.d.§ n.d.§ n.d.§ n.d.§ centrated hydrofl uoric acid and stained for aplite AP-06 40°02′28″ 119°03′41″ 0n.d.§ n.d.§ n.d.§ n.d.§ ′ ″ ′ ″ § § § § K-feldspar and plagioclase using standard pro- aplite AP-07 40°02 27 119°03 27 0n.d.n.d. n.d. n.d. cedures as outlined by McMonigle et al. (2002). (continued) The stained slabs were sealed with a matte fi n- ish, imaged on a fl atbed scanner at an effective resolution of 1200 dots per inch, and counted by for elemental analysis by X-ray fl uorescence ratios were normalized to 86Sr/88Sr = 0.1194 eye at the intersections of a 2.54 mm grid while (XRF) and inductively coupled plasma–mass and 146Nd/144Nd = 0.7219 to correct for mass- enlarged on screen. Areas of signifi cant crack- spectrometry (Tables 2 and 3). Additionally, dependent fractionation. Initial isotope ratios λ −11 −1 ing, epoxy fi ll, or poor staining were marked six aplite samples from the southern Sahwave were calculated using 87Rb = 1.42 × 10 (yr ) λ −12 −1 143 144 off before counting to avoid spurious results. Range were analyzed by XRF only at the Uni- and 147Sm = 6.54 × 10 (yr ), and Nd/ Ndi ε Sample SH-10 and three samples not listed in versity of California, Santa Cruz. is reported as Nd relative to the chondritic uni- Table 2 were too pervasively cracked to pro- Three samples were analyzed for Sr and Nd form reservoir (CHUR) evolution model of duce enough reliable counting surface. At least isotopes at the Stanford-USGS Micro Analysis Jacobsen and Wasserburg (1980). 800 points were counted for each of the other Center. The samples were prepared by grind- samples (Table 2). Assuming random counting ing picked chips in a tungsten carbide mill, fol- Mineralogy Results σ statistics, this means all 2 errors should be less lowed by a HF-HNO3-HCl dissolution proce- than ~5 vol%, and 2σ errors for modes under dure in Tefl on vials. Sr and Nd fractions were On a ternary quartz–alkali-feldspar– 20% should be less than ~3 vol%. chemically separated using cation exchange plagioclase diagram, samples from the Sahwave For geochemical analysis, aliquots of columns in a clean laboratory before load- intrusive suite (circles) defi ne a trend from the selected samples from the transect were gently ing them into a multicollector Finnegan MAT quartz diorite fi eld to the granite fi eld, with a hammer crushed before handpicking 30–50 g 262 thermal ionization mass spectrometer on majority of the samples falling in the granodio- of fresh chips to be sent to the Washington Ta (single) and Re (double) fi laments, respec- rite fi eld (Fig. 7). These mineralogic trends are State University GeoAnalytical Laboratory tively. Measured 87Sr/86Sr and 143Nd/144Nd quite similar to those of the Tuolumne intrusive

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TABLE 2. MINERALOGY AND MAJOR-ELEMENT CHEMISTRY (continued) Unnormalized major elements

Unit Sample SiO2 TiO2 Al2O3 FeO* MnO MgO CaO Na2O K2O P2O5 Total number (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%) (wt%)

Main Sahwave transect Kjp SH-1 58.74 0.762 18.29 5.33 0.089 2.48 6.01 4.28 1.81 0.265 98.06 Kjp SH-2 60.52 0.839 17.62 5.60 0.095 2.49 5.29 3.95 2.34 0.331 99.07 Kjp NVB-206 62.36 0.599 17.34 4.39 0.085 2.00 5.47 4.10 1.95 0.222 98.50 Kjp SH-5 64.16 0.545 16.81 4.09 0.080 1.83 4.66 3.94 2.51 0.195 98.80 Kjp SH-6 65.27 0.548 17.15 3.69 0.070 1.56 4.63 4.18 2.23 0.179 99.53 Kjp SH-7 62.20 0.698 17.19 4.75 0.094 2.10 5.21 3.93 2.45 0.231 98.86 Kjp SH-8 60.51 0.789 18.16 5.30 0.102 2.22 5.51 4.23 2.12 0.262 99.21 Kjp SH-9 60.86 0.791 18.30 4.96 0.093 1.97 5.61 4.19 2.13 0.272 99.18 Kjp SH-10 63.63 0.589 17.79 4.08 0.077 1.51 5.00 4.16 2.05 0.233 99.12 Kjp SH-11 62.66 0.590 17.57 3.90 0.078 1.54 4.52 3.91 3.28 0.212 98.25 grad. SH-12 65.35 0.442 17.20 2.86 0.057 1.09 3.80 4.38 3.14 0.150 98.48 Kbs SH-14 66.40 0.445 16.65 2.90 0.061 1.05 3.56 4.31 3.09 0.155 98.63 Kbs SH-15 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Kbs SH-16 66.61 0.486 16.31 3.14 0.067 1.10 3.61 4.28 3.06 0.166 98.82 Kbs SH-21 69.10 0.344 15.37 2.25 0.051 0.75 2.85 4.02 3.49 0.123 98.35 Kbs SH-22 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Kbs SH-23 68.55 0.401 15.81 2.40 0.055 0.94 2.92 4.23 3.28 0.130 98.73 Kbs SH-24 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Kbs SH-25 72.42 0.180 14.60 1.26 0.044 0.37 1.79 3.84 4.35 0.060 98.91 Kbs SH-26 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Kbs SH-27 71.14 0.291 14.98 1.92 0.044 0.61 2.59 3.93 3.59 0.113 99.20 Ks SH-29 67.85 0.303 16.28 1.88 0.039 0.60 2.91 4.07 4.02 0.119 98.08 Ks SH-30 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Ks NVB-1 68.03 0.333 16.67 2.07 0.049 0.61 2.75 4.27 4.05 0.124 98.94 School Bus lobe transect Ksb SB-5 70.35 0.226 14.79 1.65 0.052 0.61 2.26 3.39 4.55 0.083 97.95 Ksb NVB-207 68.06 0.283 16.10 1.95 0.046 0.68 2.93 3.85 3.96 0.107 97.97 Ksb SB-3 66.68 0.381 16.32 2.58 0.060 0.92 3.45 3.91 3.54 0.137 97.98 Ksb SB-2 n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ n.d.§ Ksb SB-1 68.30 0.391 15.66 2.49 0.061 0.87 3.01 4.14 3.11 0.126 98.16 Aplites aplite AP-02 78.41 0.041 12.21 0.00 0.001 0.04 0.90 2.76 5.17 0.027 99.65 aplite AP-03 76.84 0.046 13.15 0.13 0.008 0.07 1.12 3.31 4.95 0.025 99.67 aplite AP-04 77.13 0.052 12.82 0.23 0.003 0.03 0.81 3.34 5.19 0.026 99.65 aplite AP-05 76.41 0.045 13.10 0.21 0.009 0.02 0.72 3.35 5.79 0.014 99.67 aplite AP-06 75.47 0.050 13.66 0.33 0.019 0.02 1.15 4.20 4.34 0.016 99.26 aplite AP-07 77.62 0.055 12.82 0.37 0.010 0.11 1.32 3.15 4.64 0.026 100.19 *All Fe is calculated as FeO. †Mineralogy data for sample SH-10 are not used in Figure 7 due to insuffi cient counts. §Not determined.

suite (small squares; Fig. 7). The Sahwave The modal percentages of mafi c minerals and Geochemistry Results intrusive suite has on average a greater modal plagioclase follow a roughly opposite pattern, abundance of mafi c minerals, mainly because except plagioclase actually increases inward Major-element chemistry (Table 2) confi rms mafi c granodiorites compose a larger fraction from the margin to reach its maximum at that the Sahwave intrusive suite represents a of this intrusion than of the Tuolumne intrusive ~6 km. Quartz abundance follows plagioclase’s magnesian, metaluminous to weakly peralumi- suite. In general, plagioclase and mafi c miner- pattern in reverse. The greatest total variation nous, calc-alkaline series, with an alkali-lime als decrease in abundance toward the center occurs within the Granodiorite of Juniper Pass, index of 59.6. Major- and trace-element varia- of the intrusion, while quartz and K-feldspar which is perhaps not surprising given the color tion with respect to silica shows trends consis- increase, as expected from fi eld relations index variations and cryptic contacts seen in tent with fractional crystallization and mixing (Fig. 8). However, these radial modal trends the fi eld, but variation between individual sam- (open symbols, Fig. 9). For example, as differ- are far from monotonic (Fig. 8). For exam- ples seems to increase in the Granodiorite of entiation proceeds to higher % SiO2, the incom- ple, the modal percentage of alkali feldspar Bob Spring (Fig. 8). Despite having a greater patible components Rb and K2O increase. Frac- increases inward for the fi rst 3 km from the abundance of K-feldspar megacrysts, the Sah- tional crystallization of hornblende, sphene, and contact, drops down to almost its starting value wave Granodiorite is modally quite similar to other mafi c minerals can explain the decrease in at ~6 km, and then increases to higher values the Granodiorite of Bob Spring and the School FeO* and Y (not seen in aplite samples, which in the Granodiorite of Bob Spring (Fig. 8). Bus Granodiorite (Fig. 8). may have accumulated a Y-rich phase such as

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TABLE 3. TRACE-ELEMENT CHEMISTRY Sample Unnormalized trace elements number Ni Cr V Ga Cu Zn La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

Main Sahwave transect SH-1 5 18 130 20 34 92 12.51 29.45 4.15 17.65 3.95 1.13 3.15 0.46 2.56 0.48 1.23 SH-2 8 17 136 22 37 105 13.78 32.53 4.54 18.76 4.11 1.14 3.29 0.47 2.57 0.49 1.26 NVB-206 5 13 109 20 24 81 17.85 34.98 4.34 17.00 3.55 0.98 2.88 0.41 2.30 0.43 1.10 SH-5 4 11 95 19 26 82 8.83 20.75 2.97 12.44 2.72 0.81 2.29 0.33 1.85 0.35 0.93 SH-6 3 10 84 20 13 73 27.68 48.55 5.34 18.95 3.50 0.97 2.74 0.39 2.14 0.41 1.11 SH-7 3 11 112 19 19 89 23.44 49.42 6.32 24.70 5.03 1.26 4.05 0.60 3.27 0.62 1.57 SH-8 5 11 122 21 21 100 25.08 51.19 6.04 22.41 4.32 1.20 3.43 0.50 2.80 0.53 1.40 SH-9 4 9 108 21 8 101 16.66 44.59 6.27 26.10 5.60 1.48 4.53 0.64 3.50 0.65 1.66 SH-10 3 7 83 20 18 81 12.89 33.11 4.72 19.65 4.31 1.17 3.49 0.49 2.76 0.51 1.34 SH-11 b.d.* 7 82 19 13 80 18.49 41.31 5.48 21.54 4.45 1.15 3.46 0.49 2.68 0.50 1.30 SH-12 2 4 60 20 20 67 14.14 30.27 3.84 14.96 3.03 0.85 2.33 0.31 1.63 0.30 0.75 SH-14 1 5 62 19 12 68 16.42 33.19 4.05 15.53 3.01 0.84 2.31 0.31 1.64 0.30 0.78 SH-16 1 4 66 19 14 74 14.11 33.00 4.24 16.53 3.19 0.87 2.45 0.32 1.73 0.32 0.82 SH-21 b.d.* 3 46 17 26 51 20.12 33.05 3.67 13.29 2.52 0.68 1.89 0.25 1.36 0.25 0.65 SH-23 1 5 51 20 10 59 21.64 36.94 4.16 15.24 2.90 0.82 2.21 0.30 1.47 0.26 0.67 SH-25 b.d.* 3 24 18 4 42 14.45 25.18 2.79 9.73 1.79 0.45 1.37 0.19 1.05 0.21 0.58 SH-27 b.d.* 3 38 18 8 48 17.60 29.01 3.19 11.58 2.13 0.58 1.56 0.20 1.03 0.19 0.49 SH-29 b.d.* 3 33 18 8 55 13.96 28.34 3.56 13.63 2.64 0.75 1.89 0.26 1.31 0.24 0.63 NVB-1 1 4 35 20 10 67 15.99 32.99 4.22 16.31 3.13 0.81 2.25 0.28 1.48 0.26 0.63 School Bus lobe transect SB-5 1 4 31 14 1 49 12.60 21.78 2.30 7.78 1.40 0.48 1.12 0.16 0.86 0.17 0.45 NVB-207 b.d.* 4 40 18 6 48 10.93 23.48 2.95 11.25 2.25 0.65 1.71 0.24 1.32 0.26 0.68 SB-3 b.d.* 6 51 18 10 57 15.30 32.58 4.06 15.26 3.02 0.84 2.37 0.33 1.82 0.35 0.94 SB-1 1 5 51 18 8 64 16.09 32.06 3.83 14.35 2.88 0.77 2.12 0.29 1.54 0.28 0.72 Aplites AP-02 n.d.† b.d.* 2 n.d.† n.d.† n.d.† 30 56 n.d.† 20 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† AP-03 n.d.† 1 3 n.d.† n.d.† n.d.† 30 27 n.d.† 10 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† AP-04 n.d.† 1 7 n.d.† n.d.† n.d.† 10 19 n.d.† 20 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† AP-05 n.d.† 1 4 n.d.† n.d.† n.d.† 20 16 n.d.† 10 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† AP-06 n.d.† 1 4 n.d.† n.d.† n.d.† 40 13 n.d.† 10 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† AP-07 n.d.† 1 6 n.d.† n.d.† n.d.† 20 44 n.d.† 10 n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† n.d.† (continued)

xenotime), and plagioclase crystallization keeps Compared to the Tuolumne intrusive suite, similar depression in the heavy REEs. The more

Na2O from increasing and removes Sr (Fig. 9). the Sahwave intrusive suite tends to have less felsic units are especially depleted in the middle

Across a radial transect, major elements gener- K2O and Rb, but more Na2O and Sr for any given and heavy REEs compared to the Granodiorite ally track the same patterns seen in the radial amount of SiO2 (Fig. 9). Lower K/Na ratios of Juniper Pass (Fig. 11), presumably due to modal plot (Figs. 8 and 10). On average, major- might partially account for the reduced number greater fractionation of hornblende, in which element chemistry becomes more felsic toward and size of K-feldspar megacrysts. Rubidium and these REEs are compatible (Arth and Barker, the center of the intrusive complex (Fig. 10), but strontium trends with respect to silica in the Sah- 1976). None of the units shows a consistent Eu displays signifi cant variation from this general wave intrusive suite tend to be somewhat more anomaly. Similar REE patterns in the central trend. Because these variations fall into a linear tightly clustered and show stronger correlations Sierra Nevada Batholith have been interpreted array when plotted with respect to silica, much with SiO2 (Fig. 9). Compared to the Tuolumne to refl ect differentiation from a deep-crustal res- of this local variation may be attributed to mix- intrusive suite, radial major-element variations in idue containing garnet (heavy REE compatible) ing between magmas of different composition. the Sahwave intrusive suite extend farther from rather than plagioclase (Eu compatible) as the Evidence for such mixing is actually observed the margin and are less monotonic (Fig. 10). dominant aluminous phase (Ducea, 2001). This (Fig. 4M) between diorite intrusions and the Compared to the Half Dome Granodiorite, the hypothesis is also supported by the relatively Granodiorite of Juniper Pass (which shows the Granodiorite of Juniper Pass is almost uniformly high Sr/Y ratio as compared to primitive mantle greatest variations) in the southern part of the richer in Al2O3, CaO, FeO, MgO, and other ele- melts (Fig. 12), although arc rocks are gener- study area (Fig. 3). The Sahwave intrusive suite ments concentrated in plagioclase and mafi c min- ally enriched in fl uid-mobile large ion lithophile is too long-lived for fractionation of a single large erals (Fig. 10). Trends are more similar between elements as compared to relatively high fi eld batch of magma after the model of Bateman and the Cathedral Peak and Bob Spring granodiorites, strength elements (Fig. 12). Zircon REE pat- Chappell (1979), but trends toward more felsic but the Sahwave intrusive suite contains no equiv- terns (Fig. 11; only Granodiorite of Juniper Pass major- and trace-element compositions (Fig. 9) alent to the Johnson Granite Porphyry (Fig. 10). zircon data shown for simplicity) show small are consistent with mixing between a set of Bulk-rock rare earth element (REE) patterns negative Eu anomalies, but this is probably due increasingly fractionated parental magmas. from this transect (Fig. 11) all show a broadly to the greater incompatibility of Eu in zircon

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TABLE 3. TRACE-ELEMENT CHEMISTRY (continued) Sample Unnormalized trace elements number Tm Yb Lu Ba Th Nb Y Hf Ta U Pb Rb Cs Sr Sc Zr (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)

Main Sahwave transect SH-1 0.18 1.09 0.17 1111 1.96 4.67 12.71 3.70 0.27 1.48 9.86 53.6 2.22 808 10.8 139 SH-2 0.18 1.09 0.18 1007 3.71 6.23 12.87 3.21 0.50 1.91 10.77 75.0 2.89 692 9.9 117 NVB-206 0.16 1.00 0.16 876 6.06 5.04 11.43 3.49 0.38 2.06 11.92 55.6 2.51 720 10.4 127 SH-5 0.13 0.85 0.14 819 3.36 4.56 9.29 3.75 0.38 2.45 14.42 83.0 4.15 624 8.7 129 SH-6 0.16 1.04 0.17 803 12.07 6.61 11.15 3.52 0.75 2.80 13.72 72.8 2.85 653 6.8 120 SH-7 0.23 1.49 0.23 1057 7.87 7.73 16.68 3.69 0.95 2.24 13.45 71.5 3.23 672 10.3 132 SH-8 0.20 1.30 0.22 618 10.35 8.38 14.18 4.18 0.87 2.80 11.54 79.5 4.17 663 9.8 153 SH-9 0.25 1.57 0.24 978 5.24 9.64 17.45 3.88 0.84 2.52 12.20 67.8 3.53 800 8.6 144 SH-10 0.19 1.21 0.19 1008 3.99 7.33 13.80 3.58 0.77 1.88 12.23 64.0 3.33 767 6.8 133 SH-11 0.19 1.18 0.19 1947 4.52 7.00 13.80 3.46 0.67 1.66 15.63 81.1 2.85 745 6.4 124 SH-12 0.11 0.74 0.12 1372 4.60 4.93 8.20 3.04 0.48 1.74 19.29 92.2 3.38 647 4.3 107 SH-14 0.11 0.74 0.12 1218 9.23 5.10 8.31 3.12 0.51 3.51 20.51 86.4 2.56 623 4.6 107 SH-16 0.12 0.87 0.15 963 4.31 6.06 9.10 3.54 0.76 2.14 19.99 105.9 8.46 568 5.2 118 SH-21 0.09 0.62 0.11 872 11.88 4.37 7.02 2.88 0.41 3.09 23.33 118.5 6.62 493 3.6 89 SH-23 0.10 0.67 0.11 897 9.21 4.96 7.51 2.94 0.47 3.82 20.85 114.5 6.12 511 3.9 94 SH-25 0.09 0.68 0.13 784 14.41 6.01 6.19 3.48 0.88 4.72 30.65 172.5 5.71 321 2.0 81 SH-27 0.07 0.47 0.08 999 8.69 3.91 5.31 2.58 0.37 2.75 20.28 105.6 3.70 508 2.9 83 SH-29 0.09 0.55 0.09 1573 4.99 4.45 6.67 2.75 0.37 1.59 22.31 104.2 4.11 662 3.1 92 NVB-1 0.09 0.60 0.09 1532 5.96 5.44 7.29 3.33 0.48 1.91 24.52 125.8 7.35 617 3.1 114 School Bus lobe transect SB-5 0.07 0.49 0.09 985 29.34 3.75 4.79 2.62 0.33 5.99 22.39 138.0 5.62 355 3.9 79 NVB-207 0.10 0.69 0.11 1365 4.11 4.49 7.10 2.63 0.48 1.88 22.55 103.4 3.52 544 3.5 88 SB-3 0.14 0.91 0.15 1447 5.19 6.34 9.82 2.79 0.59 1.81 19.17 95.1 4.42 620 4.3 91 SB-1 0.11 0.73 0.12 893 13.41 5.51 7.99 3.20 0.51 3.85 20.70 106.6 5.63 491 3.9 104 Aplites AP-02 n.d.† n.d.† n.d.† 680 n.d.† 3 22 n.d.† n.d.† 3 18 244 n.d.† 306 1 61 AP-03 n.d.† n.d.† n.d.† 230 n.d.† 4 22 n.d.† n.d.† 5 24 225 n.d.† 251 1 63 AP-04 n.d.† n.d.† n.d.† 60 n.d.† 9 23 n.d.† n.d.† 2 33 225 n.d.† 147 2 50 AP-05 n.d.† n.d.† n.d.† 50 n.d.† 6 23 n.d.† n.d.† 6 37 246 n.d.† 105 1 71 AP-06 n.d.† n.d.† n.d.† n.d.† n.d.† 8 19 n.d.† n.d.† 3 31 183 n.d.† 112 3 49 AP-07 n.d.† n.d.† n.d.† 550 n.d.† 4 17 n.d.† n.d.† 1 20 138 n.d.† 339 3 55 *Below detection. †Not determined.

due to its 2+ charge, much as the positive Ce ing only from 0.7045 to 0.7049 and –0.259 to as well as actual variation in sampled emplace- anomaly is associated with the +4 charge taken –0.173, respectively, indicating a relatively ment depth. When samples containing >5% An by those ions. Figure 11 also shows the range of homogeneous source with a strong mantle com- or >77.8% SiO2 are excluded, one of the remain- hypothetical liquid compositions that would be ponent and little upper-crustal assimilation. ing samples still falls signifi cantly below the 87 86 ε in equilibrium with Granodiorite of Juniper Pass The Sr/ Sr and Nd values are similar to those minimum melt curve, which may suggest that zircon, using the partition coeffi cients for REEs previously measured in the surrounding basinal aplite was extracted before water saturation was in zircon from Sano et al. (2002). Ignoring La, terrane, which is presumably underlain by rela- reached (cf. Nekvasil, 1988), but the other sam- the Granodiorite of Juniper Pass REE pattern is tively mafi c transitional crust (e.g., Farmer and ple (collected 130 m below the Tertiary uncon- within the range of hypothetical liquid compo- DePaolo, 1983), but they are considerably more formity) falls just below the 1 kbar minimum sitions, although it is on the upper side, prob- primitive than those measured in similar intru- (Fig. 14), consistent with an emplacement depth ably because the zircons are frequently included sions along the Sierra Nevada crest (Fig. 13). of 3–4 km. This depth estimate falls within the in hornblende, which competes for the middle Analyses of aplite fall near the water- ~3–10 km range suggested by Van Buer et al. REEs (Fig. 11). saturated 1 kbar haplogranite minimum when (2009) based on the lack of miarolitic cavities Zircon saturation temperatures in the range projected onto a quartz-orthoclase-albite ternary and caldera structures and the presence of anda- of 748–773 °C were calculated from bulk-rock diagram (Fig. 14), consistent with fi eld evi- lusite in the contact aureole. compositions using the model of Watson and dence for the late-stage emplacement of aplite/ Harrison (1983) and provide a likely minimum pegmatite dikes, which likely represent the last A CATHEDRAL RANGE INTRUSIVE temperature range for these granodiorite melts. fraction of residual melt from a fairly water-rich EVENT OUTSIDE THE SIERRA NEVADA 87 86 ε Initial Sr/ Sr and Nd (Table 4) values do magmatic system. Scatter between the samples not differ greatly among the few measured (Fig. 14) may be partially due to varying anor- The Sahwave intrusive suite is similar to the samples from the Sahwave intrusive suite, vary- thite content and postmagmatic silicifi cation, large intrusions of the Cathedral Range intrusive

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epoch in the Sierra Nevada proper (Fig. 15) Portion of IUGS Classification Diagram to Q in terms of its ca. 92.5–88.5 Ma age range, 50 >1000 km2 size, modal and chemical zonation, and internal magmatic structures. It is differ- ent in that it has somewhat lower K/Na ratios, tonalite granite granodiorite smaller abundance and lesser size of K-feldspar megacrysts, a larger proportion of mafi c grano- diorite, more primitive Sr and Nd isotopic ratios, a relatively equant rather than elongate shape, and its location to the north and east of the Sierra Nevada crest (Fig. 15). Additionally, the approx- imately 4 m.y. apparent duration of the Sah- wave intrusive suite is shorter duration than that 20 reported for many of the coeval intrusive suites along the Sierra Nevada crest, but it is similar to quartz quartz quartz the durations represented by the most volumi- monzonite monzodiorite diorite nous phases of those suites (Chen and Moore, 1982; Coleman et al., 2004; Saleeby et al., 2008). Many of these intrusive suites, e.g., the 5 Tuolumne intrusive suite, had shorter reported monzonite monzodiorite to A durations of intrusion before extensive geo- 35 65 90 P chronology campaigns were carried out (e.g., Coleman et al., 2004), so it is possible that the Sahwave suite may also include minor phases Sahwave Granodiorite Granodiorite of Juniper Pass that would extend its reported duration. Despite School Bus Granodiorite Tuolumne intrusive suite some differences, the similarities are compel- ling enough to consider the Sahwave intrusive Granodiorite of Bob Spring (Bateman, 1992) suite a member of the Cathedral Range super- suite. The continuation of this distinctive chain Figure 7. Portion of quartz–alkali-feldspar–plagioclase ternary plot showing samples from Sahwave of intrusions into the NW Basin and Range fur- and Tuolumne intrusive suites, together with International Union of Geological Sciences (IUGS) ther supports the idea of an originally continu- classifi cations. ous Sierra Nevada Batholith later disrupted by Cenozoic extension (Fig. 15). The wide separa- tion between the Sahwave intrusive suite and the Southward distance from intrusion margin (km) Sonora Pass intrusive suite shown in Figure 15 0 5 10 15 20 0 5 70 may suggest the existence of another intrusive P School Bus suite (or suites) in the Reno area, where little- Q studied granitoids of similar age are exposed Granodiorite of Bob Spring Granodiorite 60 A (91–86 Ma K/Ar biotite ages; Marvin and Cole, M 1978; Garside et al., 1992).

50 Emplacement

40 The emplacement mechanisms of these Granodiorite large, long-lived intrusions remain controver- of Juniper Pass sial. In light of detailed geochronology, geo- 30 chemistry, and numerical modeling, a variety Mode (vol. %) Mode (vol. of subtle internal structures have been gener- ally interpreted to suggest that these intrusive 20 complexes were formed by repeated infl ux

Sahwave Granodiorite Sahwave of magma batches into a system kept near its solidus (e.g., Coleman et al., 2004; Hirt, 2007; 10 Saleeby et al., 2008). However, opinions differ greatly on the size, frequency, and emplacement

0 mechanisms of these magmatic replenishment 0.0 0.2 0.4 0.6 0.8 1.0 0.0 1.0 events, varying from frequent re-intrusion of Fraction of radial transect from intrusion margin small dikes (e.g., Glazner et al., 2004) to much Figure 8. Variations in modal mineralogy as a function of distance from intrusion margin, larger batches of magma that remain above their shown at bottom as a fraction of the total distance; Sahwave Range transect on left, School solidi for extended periods of time (e.g., Žák and Bus lobe transect on right. P—plagioclase; Q—quartz; A—alkali feldspar; M—mafi cs. Paterson, 2005). We briefl y evaluate evidence

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Harker variation diagrams for selected major and trace elements 7 300 Granodiorite of Juniper Pass Granodiorite of Bob Spring 6 250 School Bus Granodiorite

5 Sahwave Granodiorite Rb (ppm) Aplites 200 4 Tuolumne intrusive suite 150 3 100 2 FeO* (%) FeO*

1 50

0 0 7 900 800 6 700 Sr (ppm) 5 600 4 500 400

O (%) 3 2 300

K 2 200 1 100

0 0 7 30

6 25

5 Y (ppm) 20 4 15 O (%)

2 3 10

Na 2 5 1

0 0 55 60 65 70 75 80 55 60 65 70 75 80 SiO (%) SiO2 (%) 2

Figure 9. Diagrams showing variation of FeO*, K2O, Na2O, Rb, Sr, and Y as functions of SiO2 in Sahwave and Tuolumne intrusive suites (Tuolumne data from Gray et al., 2008). for different emplacement mechanisms in the ern California suggests that batholithic rocks thin transitional crust, in contrast to the crust Sahwave intrusive suite here. may extend to the base of the crust, although of the southern and central Sierra Nevada The Sahwave intrusive suite generally has large distinct intrusions in the upper crust may Batholith, which is relatively felsic (tonalitic) steep contacts and steep magmatic foliation overlie a complex zone of smaller, vertically to its base (e.g., Saleeby, 1990; Fleidner et al., (Fig. 3); thus, it is unlikely that it is a sill-like sheeted intrusions in the lower crust (Saleeby 2000). Even if the batholithic rocks studied intrusion. Nevertheless, given its 40 km diam- et al., 2003; Barth et al., 2008; Saleeby et al., here extend to only 15 km depth, as shown in eter at a relatively shallow depth of exposure, 2008). Seismic data from farther north along Figure 16, the Sahwave intrusive suite still rep- the intrusion must have been relatively fl at- the arc (Fig. 2; Lerch et al., 2007), how- resents a volume of well over 10,000 km3, such topped (Fig. 16). The downward extent of ever, indicate low velocities compatible with that space accommodation and mechanisms of the batholith is not well defi ned by existing tonalitic/granitic rocks down to ~15 km, sug- its emplacement are nontrivial problems. seismic or gravity data, but comparison to the gesting that the magmatic arc in NW Nevada Given the vast size of the Granodiorite oblique crustal arc sections exposed in south- is underlain by mafi c residua and remnants of of Juniper Pass and the variations in modal

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Sahwave intrusive suite major element transect (with Tuolumne intrusive suite for comparison) Trace-element abundance 1000 100 SiO2 Sahwave intrusive suite SiO2 Tuolumne intrusive suite 100 Granodiorite of Juniper Pass Granodiorite of Bob Spring

10 Al2O3 Al2O3 10 1

Sahwave Granodiorite Sahwave K2O Na2O 2 0.1 K O Large ion Na2O

N-MORB–normalized abundance N-MORB–normalized lithophile High field strength elements CaO elements FeO* CaO 0.01 FeO* Sr KTaRb Ba Th Nb PZr Hf Sm Ti Y 1 Figure 12. Mid-ocean-ridge-basalt (MORB)–nor- malized spider diagram showing abundance of

log(wt. %) MgO trace elements in Sahwave and Tuolumne intru- sive suites (Tuolumne data from Gray et al., TiO2 MgO 2008). Large ion lithophile elements are shown on the left, and high fi eld strength elements TiO2 are on the right, with compatibility increasing P2O5 away from the central dashed line. 0.1

P2O5 MnO dational. This happens gradually along the MnO contact of the Sahwave Granodiorite, but fairly Half Dome Cathedral Peak Granodiorite abruptly where the Granodiorite of Bob Spring Granodiorite intrudes the Granodiorite of Juniper Pass east Porphyry

Johnson Granite of the Power Line complex in the Nightingale 0.01 Quartz Lake of May Diorite Range (Fig. 3). 0.0 0.2 0.4 0.6 0.8 1.0 Fraction of radial transect from intrusion margin Sharp internal contacts likely refl ect areas Figure 10. Logarithmic plot showing major-element concentrations as a function of fractional dis- where new magma batches “eroded” their way tance along the radial transect from the outside to the center of the intrusion for the Sahwave into older magma that had partially cooled to and Tuolumne intrusive suites (Tuolumne data from Bateman and Chappell, 1979). Note that the the point where it behaved as a solid, perhaps Tuolumne data are from a shorter, east-west transect of about half the length of the Sahwave tran- even experiencing brittle fracture and stoping sect, but have been expanded as a fraction of radial distance. in places. Conversely, arcuate, gradational con- tacts likely formed where the previous batch of magma was either still partially molten, or at least close enough to its solidus to experi- Rare earth element abundance 10,000 mineralogy and chemistry it contains, it is ence defrosting and partial to complete mixing Granodiorite of Juniper Pass bulk rock All other Sahwave intrusive suite bulk rock entirely possible that this unit was emplaced along its contact. The apparent lack of inter- 1000 Granodiorite of Juniper Pass zircon over time as a series of smaller intrusive events. nal contacts within the Granodiorite of Bob Hypothetical liquid in equilibrium with zircons from Granodiorite The cryptic internal structures and contacts Spring, the School Bus Granodiorite, and the of Juniper Pass within the Granodiorite of Juniper Pass are dif- Sahwave Granodiorite (with the exception of a 100 fi cult to interpret, but the general smoothness few contacts surrounding leucocratic segrega- of compositional variation within the sampled tions), combined with the general homogeneity 10 part of this unit suggests that individual batches of these units, suggests that each may repre- of magma generally stayed hot long enough sent a single phase of rapid magma input into 1 to partially mix with their successors. Other a large, partially molten magma chamber. The

Chondrite-normalized abundance contacts within and around the Sahwave intru- concentric arrangement of these units further 0.1 sive suite also vary greatly in style. Although suggests that the central part of each unit was La Ce Pr SmNd Eu Gd Tb Dy Ho Er Tm Yb Lu often poorly exposed, contacts between units not fully mechanically and/or thermally stabi- Figure 11. Chondrite-normalized rare-earth- can be both sharp, such as where the School lized before its successor intruded, and possi- element diagram comparing whole-rock analy- Bus Granodiorite intrudes the Granodiorite bly fl owed back downward after defrosting to ses from the Granodiorite of Juniper Pass with of Juniper Pass, or gradational over hundreds accommodate the new magma. The concentric zircons from the same unit and the modeled of meters, such as where the Granodiorite of arrangement of successively more homoge- composition of the liquid that would have been in equilibrium with the zircons. Data from the Bob Spring intrudes the Granodiorite of Juni- neous (and generally more differentiated) units rest of the Sahwave Intrusive Suite are grouped per Pass (Fig. 3). In certain places, contacts (Fig. 16) also suggests that the system was together for comparison. are observed to transition from sharp to gra- warming over time, allowing larger and longer-

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TABLE 4. Sr AND Nd ISOTOPIC DATA lived magma chambers to be formed at both

87 86 σ) 87 86 σ) 143 144 σ) ε σ) the level of exposure and perhaps at the deeper Sample Sr/ Sr (±2 Rb Sr Age Sr/ Sri (±2 Nd/ Nd (±2 Sm Nd Nd (±2 number (ppm) (ppm) (Ma) (ppm) (ppm) level of magma production. Warming over SH-1 0.70499 ± 2 53.6 808 92.6 0.70473 ± 2 0.512514 ± 6 3.95 17.65 –0.173 ± 6 time in the southern Nightingale Range due SH-11 0.70528 ± 2 81.1 745 92.6 0.70486 ± 2 0.512466 ± 8 4.45 21.54 –0.259 ± 8 to re-intrusion of the School Bus Granodiorite SH-29 0.70538 ± 2 104.2 662 88.5 0.70480 ± 2 0.512479 ± 9 2.64 13.63 –0.223 ± 9 so close to the contact already heated once by S109-6* n.r.† n.r.† n.r.† 92.6 0.7047§ n.r.† n.r.† n.r.† n.r.† the Granodiorite of Juniper Pass may also be † † † § † † † † S110-6* n.r. n.r. n.r. 88.5 0.7045 n.r. n.r. n.r. n.r. responsible for the extensive shouldering-aside

*Sri data for S109-6 and S110-6 (same locations as NVB-206 and NVB-1, respectively) are from Wooden et al. (1999). implied by the anomalous orientation of the †Not reported. wall rocks in this area (Fig. 3). § Corrections to the reported Sri values, based on the ages from this study and Rb/Sr ratios from co-located samples, are insignifi cant at the reported precision. Basinal Setting and Implications for Arc Flare-Up

In light of the extensive similarities between Sr and Nd isotopic variation the Sahwave intrusive suite and coeval mag- 6 matic systems to the south, it is interesting to 4 note that the crustal environments of these Figure 13. Sr and Nd iso- intrusions are very different (Figs. 1 and 15). 2 tope systematics for Sah- Whereas the other massive intrusions of the wave and Tuolumne intru- Cathedral Range intrusive epoch are interpreted sive suites (Tuolumne data 0 to lie along the margin of North American con-

( t ) from Gray et al., 2008).

tinental crust, as marked by scattered roof pen- Nd -2 Also shown are data from 87 86 ε nearby intrusive rocks dants of the miogeocline and initial Sr/ Sr -4 within 150 km of the center >0.706 (Fig. 1; e.g., Saleeby, 1981; Kistler, Granodiorite of Juniper Pass of the Sahwave intrusive 1990), the Sahwave intrusive suite is posi- -6 Sahwave Granodiorite suite (data from Farmer and tioned in a deep stack of basinal muds thought analyses within 150 km DePaolo, 1983). to overlie transitional or oceanic crust (Speed, -8 Tuolumne intrusive suite 1978; Farmer and DePaolo, 1983; Elison et al., 0.704 0.705 0.706 0.707 1990). Because of its unique position relative 87 86 Initial Sr/ Sr to the other members of the Cathedral Range event, the Sahwave intrusive suite can be used to examine hypotheses about the potential causes for the massive magmatic fl are-up represented Q Quartz-albite-orthoclase system: by these intrusions. It has been suggested that measured aplite compositions and this particular pulse of major magmatic activity minimum melt relations may have been due to westward underthrusting of North American lower crust beneath the mag- matic arc, which is hypothesized to have been near the western edge of a massive orogenic wedge (DeCelles and Coogan, 2006; DeCelles et al., 2009). The voluminous magmatism in the best aplite analyses Sahwave and Nightingale Ranges at this time, aplite analyses with > 5% An or > 77.8% SiO however, demonstrates very primitive isotopic 2 87 86 ε − ratios of Sr/ Sri ~0.7047 and Nd ~ 0.2, which are not compatible with incorporation of a large crustal component. Similar or more primitive 1 2 isotope ratios in the penecontemporaneous La 5 Posta events of the Peninsular Ranges Batho- lith (Fig. 1; Walawender et al., 1990) corrobo- 10 rate this. Furthermore, modest reconstructed Cretaceous crustal thicknesses near the Sahwave Batholith (~38 km; e.g., Colgan et al., 2006) would suggest that the orogenic wedge did not continue this far west in northern Nevada. Ab Or Since the availability of continental lower Figure 14. Quartz-orthoclase-albite (Q-Or-Ab) ternary diagram comparing measured aplite com- crust does not appear to have been the main positions to experimentally determined minimum-melt compositions (black dots) and phase rela- control on high magmatic fl ux in the arc at this tions (lines) in a water-saturated system (Johannes and Holtz, 1996), at the pressures labeled in time, it seems that a more regionally extensive kilobars. Aplite samples were collected from dikes in the granodiorite of Juniper Pass. and consistent triggering mechanism must be

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121º W 120º W OREGON 119º W 118º W Figure 15. The mid- to Late Cretaceous Sierra NEVADA 42º N Nevada Batholith (darker gray shades) was 2004 Stanford seismic line emplaced across metamorphic rocks and the (Lerch et al., 2007) Jurassic arc (lightest gray). Compositionally shaded by inferred basement zoned intrusions emplaced during the Cathe- dral Range intrusive epoch (95–83 Ma) are shown as dark gray and black. D—Domelands intrusive suite, JM—John Muir intrusive suite, SP—Sonora Pass intrusive suite, T—Tuolumne intrusive suite, W—Mount Whitney intrusive 41º N suite, S—Sahwave intrusive suite of this study.

R.

invoked. A widespread fl are-up in the arc Selenite could have been related to the tectonic under- S plating of Franciscan subduction accretionary Trinity R. material (Saleeby et al., 2008), a change in 40º N subduction rate and/or obliquity, age, or com- position of underthrust oceanic lithosphere, or the stress regime accompanying intrusion. Reno Alternatively, subduction of thicker oceanic Lake B A S I N crust in the Late Cretaceous could potentially Tahoe be called upon to both induce a magmatic fl ux A N D event and subsequently terminate magma- tism. Very shallow subduction of a large and S I E R R A N E V A D A 39º N R A N G E thick oceanic plateau is hypothesized to have disrupted the Mojave-Salinia segment of the Sacramento arc (Saleeby, 2003), but modestly thickened oceanic crust in adjacent segments might have G R E A T V A L L E Y led to moderately shallow subduction and the SP ? CALIFNEVADAO observed cessation of magmatism. Thicker oceanic crust might incorporate and react with RNIA 38º N a greater volume of seawater (especially if pil- T low basalts represent a disproportionate share

Yosemite of crustal thickening in oceanic plateaus; e.g., Village Gladczenko et al., 1997). Dragged downward by previously subducted, denser oceanic litho- JM sphere, the leading edge of this thickened oce- anic crust could have released its fl uids into the mantle wedge, creating a massive, fl uid- 37º N rich basaltic fl ux that might have remelted any stack of older basalt left underplated at the base of the arc crust by prior arc activity. Triggered by the same cause as the incipient W fl at-slab subduction, magmatic fl ux would Explanation of Map Units increase until crowding from the increasingly buoyant oceanic lithosphere caused stagnation Cenozoic cover of the mantle wedge, halting magmatism. 36º N 94-83 Ma zoned plutons, inner CONCLUSIONS 94-83 Ma zoned plutons, outer D

Unexposed zoned plutons? New mapping, geochronology, petrology, and geochemistry in the Sahwave and Nightin- Other Mesozoic intrusions gale Ranges of western Nevada document the Other pre-Cenozoic rocks northward continuation of the Cretaceous Cor- dilleran arc across the NW Basin and Range Geologic map compiled mainly from Jennings et Garlock fault and form the groundwork for more detailed al., 1977; Irwin and Wooden, 2001; Bateman, San Andreas fault 50 km 1992; John, 1983; Tikoff and de Saint Blanquat, future study. Intrusive activity in the Sahwave 1997; Hirt, 2007; Saleeby et al., 2008. Ages are and Nightingale area continued from ca. 110 from many sources. to 88.5 Ma, and included the emplacement of

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Crustal-scale cartoon a large, concentrically zoned intrusive suite at 0 ca. 93–88.5 Ma, during the culminating mag- matic fl are-up of the Sierra Nevada Batholith. Sahwave Mineralogy and geochemistry support the cor- Granodiorite Granodiorite relation of the Sahwave intrusive suite with Granodiorite of Bob Spring members of the Cathedral Range intrusive 10 Figure 16. Cartoon cross of Juniper Pass section of Sahwave intru- event along the Sierra Nevada crest. The oldest sive suite after intrusion in unit of the Sahwave intrusive suite, the Grano- the Late Cretaceous. A few diorite of Juniper Pass, is marked by signifi cant large, nested plutons in the compositional variations, which may indicate upper crust are hypoth- 20 formation from multiple smaller intrusions, but esized to overlie a mix- the later, K-feldspar–porphyritic Granodiorite ture of smaller, vertically aligned intrusive remnants of Bob Spring and Sahwave Granodiorite are in the lower crust, follow- more homogeneous and may represent rela- ing the model of Saleeby et tively large magma-mush chambers that were Depth (km) 5 km 30 al. (2008). The later, central continuously maintained above their solidi. plutons were able to reach Concentric arrangement and gradational con- larger sizes while remain- tacts between different units imply that parts ing mushy and homoge- neous because the system of the system remained near the solidus during basaltic underplating and partial 40 much of the 4 m.y. it was active. Despite differ- remelting (minor assimilation), warmed over time. Dashed storage, and hybridization? line indicates present level ences in the lower crust beneath the Sahwave of erosion. intrusive suite and intrusions along the crest of the Sierra Nevada (as indicated by more 87 86 ε primitive Sr/ Sri and Nd values to the north), striking similarities between these segments of thick root of mafic residua the arc suggest that a regionally developed sub- crustal mechanism, such as the subduction of thicker and wetter oceanic crust or Franciscan mélange, may have been responsible for gen- eration of the intrusions that punctuate the end APPENDIX TABLE A1. U-Pb SHRIMP ANALYTICAL DATA of Cretaceous magmatism along much of the Spot number Common 206Pb U Th 232Th/238U 206Pb/238U age Total 238U/206Pb Total 207Pb/206Pb U.S. Cordilleran arc. (%) (ppm) (ppm) (±1σ, Ma) (±% err) (±% err)

JC03-SV03: Sahwave Granodiorite ACKNOWLEDGMENTS SV3-1 0.12 623 286 0.47 84.8 ± 1.3 75.4 ± 1.5 0.0486 ± 3.3 SV3-2 0.08 667 241 0.37 87.3 ± 1.3 73.3 ± 1.5 0.0484 ± 3.2 This research was partially sponsored by SV3-3 0.28 497 106 0.22 86.3 ± 1.4 74.0 ± 1.6 0.0499 ± 3.8 National Science Foundation (NSF) Tec- SV3-4 0.13 750 245 0.34 87.7 ± 1.3 72.9 ± 1.5 0.0488 ± 3.1 tonics grant 0809226, two Stanford McGee SV3-5 0.11 669 199 0.31 87.9 ± 1.3 72.8 ± 1.5 0.0486 ± 3.2 Grants, and a Geological Society of America SV3-6 0.37 601 180 0.31 90.1 ± 1.4 70.8 ± 1.6 0.0508 ± 3.3 SV3-7 0.11 867 348 0.42 91.4 ± 1.3 70.0 ± 1.5 0.0487 ± 2.8 (GSA) Student Research Grant. Van Buer was SV3-8 –0.40 753 244 0.33 91.6 ± 1.4 70.1 ± 1.5 0.0447 ± 3.1 partially supported by a Burt and DeeDee SV3-9 0.25 529 161 0.31 89.9 ± 1.4 71.0 ± 1.6 0.0498 ± 3.4 McMurtry Fellowship. Special thanks are due NVB-207: School Bus Granodiorite to Joe Wooden for help acquiring and analyz- NVB207-7 –0.10 2081 457 0.23 98.9 ± 1.4 64.9 ± 1.4 0.0472 ± 1.6 ing sensitive high-resolution ion microprobe NVB207-8 0.30 225 120 0.55 93.7 ± 1.8 68.3 ± 1.9 0.0503 ± 5.0 (SHRIMP) data, to Bettina Wiegand for mea- NVB207-9 0.05 1015 232 0.24 90.9 ± 1.4 70.6 ± 1.5 0.0482 ± 2.4 suring Sr and Nd isotopes, and to other helpful NVB207-10 –0.01 1285 392 0.32 93.9 ± 1.4 68.3 ± 1.5 0.0478 ± 2.0 folks at the Stanford-USGS Micro-Analysis NVB207-11 –0.41 357 94 0.27 92.4 ± 1.6 69.8 ± 1.7 0.0446 ± 4.1 Facility. We also thank Gail Mahood, Robinson NVB207-12 –0.36 314 56 0.18 91.6 ± 1.6 70.3 ± 1.8 0.0450 ± 4.4 NVB207-13 0.50 232 55 0.25 88.6 ± 1.7 72.1 ± 1.9 0.0518 ± 4.8 Cecil, and Sandra Wyld for helpful reviews. NVB207-14 –0.03 419 127 0.31 90.5 ± 1.5 70.9 ± 1.7 0.0476 ± 3.8 NVB-206: Granodiorite of Juniper Pass REFERENCES CITED NVB206-1 0.66 152 76 0.52 94.8 ± 1.8 67.0 ± 1.9 0.0532 ± 6.0 Arth, J.G., and Barker, F., 1976, Rare-earth partitioning NVB206-2 0.50 346 183 0.55 91.8 ± 1.3 69.4 ± 1.4 0.0518 ± 5.0 between hornblende and dacitic liquid and implica- NVB206-3 0.07 224 66 0.31 94.2 ± 1.5 67.9 ± 1.6 0.0485 ± 4.8 tions for the genesis of trondhjemitic-tonalitic mag- NVB206-4 0.89 1420 187 0.14 43.9 ± 0.6 145.0 ± 1.3 0.0593 ± 4.9 mas: Geology, v. 4, p. 534–536, doi: 10.1130/0091-7613( NVB206-5 0.09 437 181 0.43 88.5 ± 1.2 72.2 ± 1.3 0.0485 ± 3.5 1976)4<534:RPBHAD>2.0.CO;2. NVB206-6 –0.44 230 112 0.51 90.9 ± 1.4 70.7 ± 1.5 0.0444 ± 4.9 Barth, A.P., Anderson, J.L., Jacobsen, C.E., Paterson, S.R., and Wooden, J.L., 2008, Magmatism and tectonics in a NVB206-7 –0.16 271 153 0.58 92.8 ± 1.4 69.1 ± 1.5 0.0444 ± 4.4 tilted crustal section through a continental arc, eastern NVB206-8 –0.02 475 186 0.41 91.7 ± 1.2 69.8 ± 1.3 0.0477 ± 3.5 Transverse Ranges and southern Mojave Desert: Geo- NVB206-9 0.34 364 147 0.42 89.1 ± 1.3 71.6 ± 1.4 0.0505 ± 3.9 logical Society of America Field Guide 11, p. 101–117, (continued) doi: 10.1130/2008.fl d011(05).

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APPENDIX TABLE A1. U-Pb SHRIMP ANALYTICAL DATA (continued) Barton, M.D., Battles, D.A., Debout, C.E., Capo, R.C., Chris- tensen, J.N., Davis, S.R., Hanson, R.B., Michelson, C.J., Spot number Common 206Pb U Th 232Th/238U 206Pb/238U age Total 238U/206Pb Total 207Pb/206Pb and Trim, H.G., 1988, Mesozoic contact metamorphism (%) (ppm) (ppm) (±1σ, Ma) (±% err) (±% err) in the western United States, in Ernst, W.G., ed., Meta- morphism and Crustal Evolution of the Western United NVB-206: Granodiorite of Juniper Pass (continued) States, Rubey Volume 7: Englewood Cliffs, New Jer- NVB206-10 0.43 253 76 0.31 92.8 ± 1.5 68.6 ± 1.6 0.0513 ± 4.7 sey, Prentice Hall, p. 110–178. NVB206-11 0.65 1010 453 0.46 84.2 ± 1.0 75.5 ± 1.2 0.0528 ± 2.6 Bateman, P.C., 1992, Plutonism in the Central Part of the Sierra Nevada Batholith, California: U.S. Geological NVB206-12 0.10 728 398 0.56 93.3 ± 1.1 68.6 ± 1.2 0.0486 ± 2.8 Survey Professional Paper 1483, 186 p. NVB206-13 0.29 235 69 0.30 94.1 ± 1.5 67.8 ± 1.5 0.0502 ± 4.7 Bateman, P.C., and Chappell, B.W., 1979, Crystallization, NVB-286: Granodiorite in the Trinity Range fractionation, and solidifi cation of the Tuolumne intru- sive series, Yosemite National Park, California: Geolog- 286-1 0.20 765 286 0.39 84.6 ± 0.7 75.6 ± 0.8 0.0493 ± 2.9 ical Society of America Bulletin, v. 90, p. 465–482, doi: 286-2 0.64 557 376 0.70 89.9 ± 0.8 70.7 ± 0.9 0.0529 ± 3.2 10.1130/0016-7606(1979)90<465:CFASOT>2.0.CO;2. 286-3 0.18 523 214 0.42 90.2 ± 0.8 70.8 ± 0.9 0.0492 ± 3.3 Black, L.P., Kamo, S.L., Allen, C.M., Davis, D.W., Aleinikoff, 286-4 0.13 954 497 0.54 90.7 ± 0.6 70.5 ± 0.7 0.0488 ± 3.9 J.N., Valley, J.W., Mundil, R., Campbell, I.H., Korsch, 286-5 0.17 1140 200 0.18 90.2 ± 0.6 70.9 ± 0.6 0.0492 ± 2.2 R.J., Williams, I.S., and Foudolis, C., 2004, Improved 206Pb/238U microprobe geochronology by the monitor- 286-6 2.01 1040 278 0.28 92.1 ± 0.6 68.1 ± 0.6 0.0638 ± 2.1 ing of a trace-element–related matrix effect: SHRIMP, 286-7 0.13 1833 681 0.38 90.6 ± 0.4 70.5 ± 0.5 0.0489 ± 1.9 ID-TIMS, ELA-ICP-MS, and oxygen isotope docu- 286-8 0.07 664 210 0.33 95.3 ± 0.9 67.1 ± 0.9 0.0485 ± 3.2 mentation for a series of zircon standards: Chemical 286-9 2.39 408 116 0.29 88.3 ± 1.6 70.8 ± 1.5 0.0667 ± 11.8 Geology, v. 205, p. 115–140, doi: 10.1016/j.chemgeo 286-10 0.51 1999 164 0.08 138.9 ± 0.6 45.8 ± 0.5 0.0528 ± 1.1 .2004.01.003. 286-11 0.03 1576 1368 0.90 93.3 ± 0.5 68.5 ± 0.5 0.0481 ± 1.9 Bonham, H.F., 1969, Geology and Mineral Deposits of Washoe and Storey Counties, Nevada: Nevada Bureau 286-12 0.03 574 258 0.46 92.2 ± 0.8 69.4 ± 0.9 0.0481 ± 1.9 of Mines Bulletin 70, 140 p. 286-13 0.44 622 222 0.37 88.1 ± 0.8 72.3 ± 0.9 0.0513 ± 3.2 Burke, D.B., and Silberling, N.J., 1973, The Auld Lang Syne 286-14 0.17 942 624 0.68 90.1 ± 0.7 70.9 ± 0.8 0.0491 ± 2.5 Group, of Late Triassic and Jurassic(?) age, north-cen- 286-15 0.13 432 172 0.41 90.2 ± 1.1 70.9 ± 1.2 0.0488 ± 3.8 tral Nevada: Contributions to Stratigraphy, U.S. Geo- logical Survey Bulletin 1394-E, 14 p. NVB-212: Selenite Granodiorite Chen, J.H., and Moore, J.G., 1982, Uranium-lead isotopic NVB212-1 0.69 547 196 0.37 95.0 ± 1.5 67.1 ± 1.6 0.0534 ± 2.9 ages from the Sierra Nevada Batholith, California: NVB212-2 –0.37 622 154 0.26 94.2 ± 1.5 68.4 ± 1.6 0.0450 ± 2.9 Journal of Geophysical Research, v. 87, p. 4761–4784, NVB212-3 0.15 1462 446 0.32 97.1 ± 1.4 66.0 ± 1.5 0.0492 ± 1.8 doi: 10.1029/JB087iB06p04761. Ciavarella, V., and Wyld, S.J., 2008, Wall rocks as recorders NVB212-4 –0.07 479 110 0.24 95.6 ± 1.6 67.2 ± 1.6 0.0474 ± 3.3 of multiple emplacement mechanisms—Examples NVB212-5 0.16 3479 1485 0.44 98.6 ± 1.4 64.9 ± 1.4 0.0493 ± 1.1 from Cretaceous intrusions of northwest Nevada, in NVB212-6 4.01 531 118 0.23 96.3 ± 1.6 64.0 ± 1.6 0.0798 ± 5.3 Wright, J.E., and Shervais, J.W., eds., Ophiolites, Arcs, NVB212-9 0.37 615 185 0.31 98.8 ± 1.6 64.7 ± 1.6 0.0509 ± 2.7 and Batholiths: Geological Society of America Special NVB212-10 0.06 686 153 0.23 97.2 ± 1.5 65.9 ± 1.5 0.0484 ± 2.7 Paper 438, p. 517–550, doi: 10.1130/2008.2438(19). NVB212-11 0.11 1219 320 0.27 94.2 ± 1.4 68.0 ± 1.5 0.0487 ± 2.1 Coleman, D.S., Gray, W., and Glazner, A.F., 2004, Rethink- ing the emplacement and evolution of zoned plutons; NVB212-12 –0.26 784 205 0.27 99.7 ± 1.5 64.5 ± 1.5 0.0459 ± 2.7 geochronologic evidence for incremental assembly of NVB212-13 –0.18 296 77 0.27 96.6 ± 1.7 66.5 ± 1.7 0.0465 ± 4.2 the Tuolumne intrusive suite: California Geology, v. 32, NVB212-16 0.19 282 103 0.38 96.7 ± 1.7 66.2 ± 1.7 0.0494 ± 4.0 no. 5, p. 433–436. NVB212-17 –0.03 1434 356 0.26 101.6 ± 1.5 63.1 ± 1.5 0.0478 ± 1.8 Colgan, J.P., Dumitru, T.A., Reiners, P.W., Wooden, J.L., and NVB212-18 2.80 503 131 0.27 100.5 ± 1.6 62.1 ± 1.6 0.0702 ± 2.6 Miller, E.L., 2006, Cenozoic tectonic evolution of the Basin and Range Province in northwestern Nevada: NVB-208: Power Line Complex American Journal of Science, v. 306, p. 616–654, doi: NVB208-1 –0.04 2244 236 0.11 110.0 ± 1.6 58.3 ± 1.4 0.0479 ± 1.5 10.2475/08.2006.02. NVB208-2 –0.06 4127 1250 0.31 110.2 ± 1.6 58.2 ± 1.4 0.0477 ± 1.1 Colgan, J.P., Wyld, S.J., and Wright, J.E., 2010, Geologic Map of the Vicksburg Canyon Quadrangle, Humboldt NVB208-3 –0.05 908 857 0.98 105.8 ± 1.6 60.6 ± 1.5 0.0478 ± 2.3 County, Nevada: Nevada Bureau of Mines and Geol- NVB208-4 4.26 624 157 0.26 102.7 ± 1.6 59.8 ± 1.5 0.0819 ± 2.1 ogy Map 169, scale 1:24,000. NVB208-5 0.31 753 169 0.23 99.8 ± 1.5 64.1 ± 1.5 0.0504 ± 3.3 Compton, R.R., 1960, Contact metamorphism in Santa Rosa NVB208-6 –0.16 744 153 0.21 104.7 ± 1.7 61.4 ± 1.6 0.0468 ± 2.9 Range, Nevada: Geological Society of America Bul- NVB208-7 0.19 1218 311 0.26 105.2 ± 1.6 60.8 ± 1.5 0.0496 ± 2.0 letin, v. 71, p. 1383–1416, doi: 10.1130/0016-7606(1960 )71[1383:CMISRR]2.0.CO;2. NVB208-8 0.11 766 179 0.24 105.5 ± 1.6 60.7 ± 1.5 0.0490 ± 2.5 DeCelles, P.G., and Coogan, J.C., 2006, Regional structure NVB208-9 0.08 1117 329 0.30 109.0 ± 1.6 58.8 ± 1.5 0.0488 ± 2.1 and kinematic history of the Sevier fold-and-thrust NVB208-10 2.63 961 254 0.27 100.3 ± 1.5 62.2 ± 1.5 0.0689 ± 1.8 belt, central Utah: Geological Society of America Bul- NVB208-11 –0.10 4772 750 0.16 110.0 ± 1.5 58.3 ± 1.4 0.0474 ± 1.0 letin, v. 118, p. 841–864, doi: 10.1130/B25759.1. NVB208-12 –0.05 555 121 0.23 106.6 ± 1.7 60.2 ± 1.6 0.0477 ± 2.9 DeCelles, P.G., Ducea, M.N., Kapp, P., and Zandt, G., 2009, NVB208-13 0.06 690 169 0.25 103.9 ± 1.6 61.7 ± 1.5 0.0486 ± 2.6 Cyclicity in Cordilleran orogenic systems: Nature Geo- science, v. 2, p. 251–257, doi: 10.1038/ngeo469. NVB208-14 0.23 666 177 0.27 104.0 ± 1.6 61.5 ± 1.5 0.0499 ± 2.6 DeGraaff-Surpless, K., Graham, S.A., Wooden, J.L., and SH-21: Granodiorite of Bob Spring McWilliams, M.O., 2002, Detrital zircon provenance analysis of the Great Valley Group, California: Evolu- SH21-1 0.16 481 193 0.41 91.7 ± 1.6 69.7±1.7 0.0491 ± 3.1 tion on an arc-forearc system: Geological Society of SH21-2 –0.13 524 181 0.36 93.1 ± 1.6 68.9 ± 1.7 0.0468 ± 3.1 America Bulletin, v. 114, p. 1564–1580, doi: 10.1130/0016 SH21-3 0.08 354 79 0.23 96.3 ± 1.7 66.4 ± 1.8 0.0486 ± 3.9 -7606(2002)114<1564:DZPAOT>2.0.CO;2. SH21-4 0.02 340 68 0.21 92.3 ± 1.6 69.3 ± 1.8 0.0480 ± 3.9 du Bray, E.A., 2007, Time, space, and composition relations SH21-5 0.12 850 376 0.46 93.3 ± 1.5 68.5 ± 1.6 0.0488 ± 3.2 among northern Nevada intrusive rocks and their SH21-6 0.14 848 402 0.49 92.0 ± 1.5 69.5 ± 1.6 0.0490 ± 2.4 metallogenic implications: Geosphere, v. 3, no. 5, p. 381–405, doi: 10.1130/GES00109.1. 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