GSA Bulletin: from Jurassic Shores to Cretaceous Plutons

Home , Alabama Hills, Metavolcanic rock

From Jurassic shores to Cretaceous plutons: Geochemical evidence for paleoalteration environments of metavolcanic rocks, eastern California

Sorena S. Sorensen* Department of Mineral Sciences, NHB-119, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560 George C. Dunne Department of Geological Sciences, California State University, Northridge, Northridge, California 91330-8266 R. Brooks Hanson† Science, 1200 New York Avenue, N.W., Washington, D.C. 20005

Mark D. Barton Department of Geosciences, University of Arizona, Tucson, Arizona 85721 Jennifer Becker } Othmar T. Tobisch Earth Science Board, University of California, Santa Cruz, California 95604 Richard S. Fiske Department of Mineral Sciences, NHB-119, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560

ABSTRACT and nonmarine (Alabama Hills, Inyo Moun- metavolcanic rocks is important because in fresh tains) settings display similar degrees of K for volcanic rocks this property is used to: (1) clas- Volcanic and plutonic rocks exposed in Na (or Ca) exchange that were affected by iso- sify magma series (e.g., Gill, 1981; Le Maitre et east-central California record a long history of topically distinct fluids. Some alkali-metaso- al., 1989; Müller and Groves, 1995), (2) interpret metasomatism and/or metamorphism within matism of Jurassic metavolcanic rocks is re- tectonic regimes of eruption or emplacement the Mesozoic Cordilleran continental arc. We lated to Cretaceous plutonism. In the Ritter (e.g., Miller, 1978; Christe and Hannah, 1990), use whole-rock and mineral elemental compo- Range and Alabama Hills, these effects are lo- and/or (3) address properties of mantle sources sitions, along with standard and cathodolumi- calized around pluton contacts, appear to be (e.g., Luhr, 1992; Stolper and Newman, 1994). nescence petrography to characterize alter- more vein related than pervasive, and over- Because abundances of alkali and alkaline-earth ation histories of Late Triassic to Middle print K-metasomatized assemblages. elements in volcanic rocks are readily changed Jurassic metavolcanic rocks in the Ritter under a variety of posteruptive pressure (P)-T Range, White-Inyo Mountains, and Alabama INTRODUCTION fluid conditions (e.g., Lipman, 1965; Noble, Hills. Although alkali-metasomatism is wide- 1967; Scott, 1971; Hart et al., 1974), identifying spread and pervasive, ratios and abundances Economic and petrologic concerns offer rea- alkali-metasomatic effects is a logical prerequi- of Ce, Th, Tb, and Ta suggest that mafic pro- sons to study the alteration of arc volcanic rocks. site to determining if metavolcanic rocks had al- toliths from the White-Inyo Mountains were The emplacement of magmas into colder country kaline protoliths. shoshonitic, whereas those from the Ritter rocks drives hydrothermal systems in volcanoplu- Geochemically and mineralogically similar Range were calc-alkaline. Alkali exchange ap- tonic arcs. Some of these systems create economic styles of alkali-metasomatism of volcanic rocks parently modified the compositions of many mineralization, such as porphyry base-metal and can occur in different environmental settings. metavolcanic rocks. Much of this metasoma- skarn deposits. Others may metasomatize and For example, low-T (<200 ¡C) K-metasomatism tism may have occurred at low-temperature metamorphose significant volumes of rock, yet of felsic volcanic rocks has been attributed to: (T) conditions, and attended or shortly post- produce only minor amounts of economic miner- (1) density-driven downward flow of brines in dated deposition of the volcanic protoliths. alization (e.g., Barton et al., 1988, 1991a, 1991b). playa-lake hydrologic systems (e.g., Chapin and High δ18O values for K-rich metatuffs from In long-lived arcs, volcanic rocks may undergo Lindley, 1986; Dunbar et al., 1994; Leising et the Ritter Range suggest that the K-metaso- fluid-rock interactions when (or shortly after) they al., 1995), (2) distal parts of epithermal mag- matizing fluid was low-T seawater. In contrast, are deposited, or during later thermal and/or hy- matic and meteoric fluid-flow systems (e.g., low δ18O values for K-rich metatuffs from the drothermal events (e.g., Seyfried et al., 1988; Criss Barton et al., 1991a, 1991b), and (3) sea-floor Alabama Hills and Inyo Mountains seem to re- and Taylor, 1986; Barton et al., 1991a, 1991b; weathering mechanisms (e.g., Munha et al., flect rock interaction with meteoric water Hanson et al., 1993; Battles and Barton, 1995). 1980; Staudigel et al., 1981, 1995; Alt et al., prior to contact metamorphism. Jurassic Because metasomatism changes igneous rock 1986). The variety of fluid sources and settings metatuffs deposited in marine (Ritter Range) compositions, identifying the alteration histories that produce low-T K-metasomatism in rela- of metavolcanic rocks may be needed to assess tively young and otherwise unmetamorphosed *e-mail: [email protected] the geochemical characteristics of their pro- volcanic rocks underscores a need to document †[email protected] toliths. For example, assessing the alkalinity of paleoalteration environments in terranes that

GSA Bulletin; March 1998; v. 110; no. 3; p. 326Ð343; 11 figures; 3 tables.

326 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS have more complex thermal and fluid histories. Alabama Hills (Fig. 1; Dunne and Walker, 1993). et al., 1992). In contrast, volcanism in the Creta- Conversely, determining alteration histories Localities in the White Mountains, Ritter Range, ceous arc was entirely subaerial (Fiske and may help to identify paleogeographic and paleo- Alabama Hills, and southern Inyo Mountains al- Tobisch, 1978, 1994). Roughly coeval Jurassic tectonic settings of volcanism. low us to contrast metavolcanic rocks deposited in volcanic sequences were deposited in a marine Evidence for low-T alteration may be pre- marine versus nonmarine settings, and to study setting in the Ritter Range, and subaerially in the served even if volcanic rocks are affected by protolith geochemical variations across the conti- Alabama Hills and southern Inyo Mountains. Al- later contact metamorphism, a common phe- nental margin, as described in the following. though the depositional setting of much of the nomenon in long-lived arcs (Hanson et al., 1993; The depositional environments of volcanic White Mountains sequence is unknown, it ap- Dunn and Valley, 1992; Franklin et al., 1981). rocks changed during the lifetime of the pears to be marine at its base (Early Jurassic Hanson et al. (1993) delineated alteration styles Cordilleran arc. In Early to Middle Jurassic time, time?) and is clearly subaerial at its top (Late of metavolcanic rocks from the Ritter Range, a paleoshoreline separated marine from subaerial JurassicÐEarly Cretaceous time). Sierra Nevada, California, on the basis of whole- depositional settings of volcanic rocks (e.g., These localities allow us to study igneous geo- rock and mineral major and minor chemical Busby-Spera, 1985; 1986; 1988; 1990; Saleeby chemical variations across an autochthonous seg- compositions, along with stable isotope data. Al- though these rocks were contact metamorphosed during Late Cretaceous time by the Sierra Nevada batholith, they preserve geochemical evidence of earlier, lithostratigraphically con- trolled, pervasive alteration. Some alteration effects were attributed to low-T (<200 ¡C) reaction between Jurassic volcanic rocks and seawater shortly after deposition, 50 to 100 m.y. before contact metamorphism (Hanson et al., 1993). This paper documents metasomatism and metamorphism of volcanic rocks from an approximately east to west transect across the central Sierra Nevada segment of the Cordilleran arc, in order to deduce settings of alteration and likely protoliths.

GEOLOGY OF THE CENTRAL SIERRA NEVADA SEGMENT OF THE CORDILLERAN ARC

Eastern California is well suited for comparing Jurassic and Cretaceous alteration of metavolcanic rocks because (1) thick sections of approximately contemporaneous Jurassic metavolcanic rocks are preserved there, and each shows a range of protolith compositions; (2) exposures cross both the inferred Early to Middle Jurassic shoreline and the distal part of the Paleozoic continental margin; and (3) the intensity of contact metamorphism, which accompanied either Middle to Late Jurassic, or mid- to Late Cretaceous plutonism, or both, varies among the sections. The Cordilleran arc contains a long and areally exten- sive record of Mesozoic magmatism (Fig. 1, Saleeby et al., 1992; Saleeby and Busby, 1993; Schweickert and Lahren, 1993). In east-central California, Jurassic metavolcanic and plutonic rocks occur as pendants or screens within the northwest-trending, mostly Cretaceous Sierra Nevada batholith. Prominent localities of metavolcanic rocks are the Saddlebag Lake, Ritter Range, Mount Morrison, Goddard, and Oak Creek pendants (e.g., Saleeby, 1981; Schweickert Figure 1. The Jurassic arc in eastern California. Localities of metavolcanic rocks are shown in and Lahren, 1993). East of the Sierra Nevada, black in the inset. Abbreviations: SL—Saddlebag Lake; RR—Ritter Range; MM—Mount Jurassic metavolcanic and plutonic rocks are ex- Morrison; WM—White Mountains; G—Goddard; OC—Oak Creek; AH—Alabama Hills; posed in the White-Inyo Mountains and the IM—southern Inyo Mountains.

Geological Society of America Bulletin, March 1998 327 SORENSEN ET AL. ment of the Jurassic arc in a transect from the Local Geology of Jurassic Volcanic Sections U-Pb age of 154 Ma, and a hypabyssal intrusion edge of the Paleozoic continental margin to the at White Mountain Peak has an age of 137 Ma shelf-slope boundary, and thus presumably from In the White Mountains, a lower, predomi- (Fig. 2; Hanson et al., 1987). The depositional thinner to thicker continental crust. In the Ritter nantly volcanic sequence is overlain by an up- setting of these rocks is unknown, owing to a Range and Mount Morrison pendants, Late Tri- per, predominantly epiclastic sequence. (Fig. 2; lack of sedimentary intercalations. Most of the assic and Early Jurassic metavolcanic rocks un- Hanson et al., 1987). The oldest part of the sec- overlying sequence consists of metamorphosed conformably overlie metamorphosed Paleozoic tion consists of interbedded marble and felsic alluvial fan and fluvial deposits exposed in sedimentary rocks (Fiske and Tobisch, 1978; cf. metavolcanic rocks that compose a small pen- down-faulted blocks along the crest and western Greene and Schweickert, 1995). The latter rocks dant within the 165 Ma Barcroft Granodiorite side of the range (Fates, 1985; Hanson et al., correlate with strata in the White-Inyo Moun- (Gillespie, 1979; Stern et al., 1981). Marble lay- 1987). Lithosomes within this interval include tains, which pin the basement of this segment of ers as thick as 50 m were likely deposited in a conglomerate, volcanic rocks, volcanogenic the Jurassic arc to the North American continent marine environment (Hanson, 1986; cf. Fiske sandstone, siltstone, and a few tuffs. The White (Stevens and Greene, 1995; cf. Kistler, 1990). A and Tobisch, 1978). An approximately 3-km- Mountains section was intruded by a Late Cre- submarine channel sequence has been traced thick package of metamorphosed ash-flow tuffs, taceous batholith beginning ca. 100 Ma (Stern from the westernmost Inyo Mountains into the hypabyssal intrusions, and mafic volcanic flows et al., 1981; Hanson et al., 1987; McKee and Mount Morrison pendant (Stevens and Greene, is exposed along the range crest. Its base is lo- Conrad, 1996). 1995). Right-lateral offset of this channel by cally intruded by the Barcroft Granodiorite, but In the Ritter Range, a faulted section consists of cryptic Mesozoic faults is ~65 km (Kistler, 1990; at least part of this package is younger than 165 Late Triassic to Late Jurassic or Early Cretaceous Stevens and Greene, 1995). Ma: an ash-flow tuff within it yielded a zircon metavolcanic rocks, interlayered with more than

Figure 2. Pseudostrati- graphic columns for the Rit- ter Range, White Mountains, southern Inyo Mountains, and Alabama Hills. New U-Pb radiometric ages of zircons for Ritter Range units (J. Saleeby, E. Warner Holt, O. Tobisch, R. Fiske, unpublished data) are indicated by dots. Both these and other zircon ages are noted in bold italics. New values of δ18O for samples from the Ritter Range, Alabama Hills, and southern Inyo Mountains are indicated by triangles; published data for Ritter Range units (Hanson et al., 1993) are shown in parentheses.

328 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

40 thin but laterally continuous beds of calc- RESULTS in both the Ritter Range (Hanson et al., 1993); silicate rocks and marble (Fig. 2; Fiske and and the Alabama Hills, the presence of an- Tobisch, 1978; Hanson et al., 1993). Marine fos- Contact Metamorphism of Volcanic Rocks dalusite + K-feldspar in metaÐash-flow tuff units sils have been found in marble layers near the ge- within 20 to 200 m of pluton contracts indicates ographic center of and western edge of the pen- Metavolcanic rocks of the Ritter Range and a maximum metamorphic T = ~610 ¡C, at a dant (Reinhardt et al., 1959; Fiske and Tobisch, Alabama Hills were contact metamorphosed at maximum P = ~2 kbar (Chatterjee and Johannes, 1978). The former locality contains the pelecypod hornblende-hornfels to transitional pyroxene- 1974). In the latter area, a few blocks of metaÐ Weyla. In western North America, Weyla is found hornfels facies conditions, whereas those of the ash-flow tuff in a complex mixed-rock zone are in Sinemurian to possibly middle Toarcian strata White and southern Inyo Mountains were meta- immersed in the Alabama Hills Granite. These (Damborenea and Manceñido, 1979); its presence morphosed at albite-epidote-hornfels facies con- blocks contain sillimanite + K-feldspar, an as- indicates an Early Jurassic age (202 to 186 Ma, ditions (Fig. 3). In all localities, felsic rocks con- semblage suggesting T > ~610 ¡C in the border Gradstein et al., 1995). The metavolcanic rocks tain less amphibole, epidote, biotite, and apatite, zone. In both the Ritter Range and Alabama are of mafic to felsic compositions and consist of and more muscovite, quartz, K-feldspar, zircon, Hills, metamorphic plagioclase ranges from lava flows, ash-flow tuffs, tuff breccias, bedded and tourmaline than mafic rocks (Fig. 3). These An20Ð40, and K-feldspar (Or>95) has pseudo- tuffs, and lapilli tuffs. The section is cut by five variations reflect protolith compositions. morphed alkali-feldspar phenocrysts. granitic plutons and minor dikes, all of which Most of these metavolcanic rocks lack min- Most metavolcanic rocks in the White Moun- range from 100 to 86 Ma in age (Bateman and eral assemblages that allow precise estimates of tains were probably metamorphosed in the biotite Nokleberg, 1978; Bateman and Chappell, 1979; contact metamorphic P-T conditions. However, zone of the albite-epidote-hornfels facies, and Stern et al., 1981; Bateman, 1983, 1988, 1992). In the southern Inyo Mountains, three intervals of metavolcanic and metavolcaniclastic rocks make up a 3.1-km-thick section (Fig. 2; Dunne and Walker, 1993). The lowest interval consists of basal limestone-clast conglomerate, overlain by volcanogenic conglomerate, sandstone, and siltstone, mafic lava flows, and minor tuff. The middle interval is composed primarily of felsic ash-flow tuff and intermediate to felsic lava flows, and minor volcanic breccia, conglomerate, and sandstone. Most of the upper interval consists of sandstone and siltstone and less abundant conglomerate. All three intervals contain abundant sedimentary structures (e.g., raindrop im- pressions, mud-crack casts) that indicate deposition in flood plain, alluvial fan, and lacustrine environments (Garvey et al., 1993). The upper interval contains metavolcanic rocks that have a minimum age of about 150 Ma; it is intruded by dikes of inferred Late Jurassic and earliest Creta- ceous ages. Minimum ages for the metavolcanic rocks of the middle interval are 168Ð169 Ma (Dunne and Walker, 1993). In the Alabama Hills, metavolcanic strata are exposed in two intervals (Fig. 2; Dunne and Walker, 1993). The 2-km-thick lower interval consists of felsic ash-flow tuff overlying volcanogenic sedimentary rocks, both of which are cut by numerous (~60 vol %) hypabyssal pods, dikes, and sills. A 0 to 10-m-thick unit of shale, quartz arenite, and conglomerate separates this interval from an overlying, >450-m-thick interval of felsic ash-flow tuff. Both intervals are intruded by the 85 Ma Alabama Hills Granite, and by a 148 Ma dike of the Independence dike swarm (Chen and Moore, 1979). The tuff of the upper Figure 3. The mineral assemblages of analyzed metavolcanic rocks, grouped by field and interval yielded a minimum age of 170 Ma, sim- whole-rock chemical constraints on likely protoliths (Tables 1 and 2; retrograde minerals were ilar to a provisionally determined age for the ignored). Because only three samples from the Alabama Hills were analyzed, mineral assem- lower interval (Fig. 2; Dunne and Walker, 1993; blages were combined with data for five additional samples from this locality (for which chem- unpublished data). ical data are not reported).

Geological Society of America Bulletin, March 1998 329 SORENSEN ET AL. hornblende-hornfels facies assemblages are re- The metavolcanic rocks of the southern Inyo 5.3‰, respectively; quartz and K-feldspar from stricted to ~50 m of contacts with the Barcroft Mountains also may have been metamorphosed AH95Ð02 display values of 6.0‰ and 3.4‰. Granodiorite. Albite-epidote-hornfels facies meta- during Jurassic and/or Cretaceous plutonism. Mineral fractionations are 2.7‰ and 2.6‰. morphic conditions are evidenced by: (1) the pres- However, Inyo Mountains metavolcanic rocks are Quartz (8.7‰), plagioclase (7.2‰), and alkali- ence of albite in most mineral assemblages rocks so feebly recrystallized that even if they were feldspar (7.8‰) separates from the deuterically (although a few analyses of plagioclase from sam- heated by two episodes of plutonism, the com- altered Alabama Hills Granite resemble δ18O val- ples collected within ~50 m of the Barcroft Gran- bined thermal input of these events left little ex- ues for the Sierra Nevada batholith (Table 3; cf. odiorite contact display up to An15; Hanson, 1986); pression in their mineral assemblages and textures. Taylor, 1986, p. 297). (2) a lack of metamorphic hornblende, again except The ca. 169 Ma metaÐash-flow tuff from the within ~ 50 m of the Barcroft Granodiorite contact; Geochemistry of Metavolcanic Rocks Inyo Mountains was sampled ∼5 km away from and (3) the presence of biotite in most samples of pluton contacts. Both samples contain the low-T appropriate bulk composition (Fig. 3). Some chemical features of the metavolcanic metamorphic mineral assemblage chlorite + mus- Instead of biotite, metavolcanic rocks of the rocks are evidently of igneous origin, whereas covite. Quartz and alkali-feldspar separates from southern Inyo Mountains contain muscovite and others attest to metasomatic additions or losses sample IM95Ð09 yield typical igneous δ18O val- chlorite, which coexist with albite (Ab>95; Fig. 3). (Tables 1 and 2; the Appendix describes sampling ues (9.5‰ and 8.8‰, respectively; Table 3). Some ash-flow tuff units preserve relict igneous and analytical methods). Ranges and covariations Quartz from IM95Ð07A also shows a typical ig- δ18 alkali feldspar compositions of Or45Ð80 in grains of SiO2 with TiO2,Al2O3, and MgO resemble neous value (9.2‰), but the O for alkali that mostly yield Or>95. A meta-andesitic lava those for calc-alkaline, basaltic andesite to rhyo- feldspar (4.0‰) is lower than most igneous values contains relict igneous alkali feldspar remnants in lite suites from continental arcs (Fig. 4). However, (cf. Taylor and Sheppard, 1986). Inyo Mountains

Or>95 K-feldspar, as well as relict phenocrysts CaO, Na2O, and K2O contents of the metavol- mineral pairs show fractionations of 0.7‰ for that locally preserve An45 plagioclase. The latter canic suite are scattered compared to data for sample IM95Ð09, and 5.2‰ for IM95–07A. The phenocrysts are partially replaced by albite calc-alkaline, alkaline, and peralkaline arc rocks fine-grained matrix of sample IM95Ð07A yields a δ18 (Ab>95) and K-feldspar (Or>95). (Fig. 4). O value of 5.1‰, similar to its alkali-feldspar The age of contact metamorphism is well con- The metavolcanic rocks resemble young, calc- phenocrysts. The matrix of IM95Ð09, which has a strained in the Ritter Range, inferred in the Al- alkaline volcanic rocks from continental arcs in δ18O value of 9.8‰, resembles the sample’s abama Hills, and somewhat speculative in the their contents of many minor and trace elements quartz phenocrysts. White-Inyo Mountains. Sharp et al. (1993) re- (Figs. 5 and 6). Although some rocks have K, Rb, ported an 40Ar/39Ar age of 85 Ma for metamor- Ba and Th values similar to those of calc-alkaline Cathodoluminescence Petrography of phic hornblende from a mafic metavolcanic rock volcanic rocks, others are much richer in these el- Metavolcanic Rocks in the Ritter Range pendant. This age is only ements and poorer in Sr (or vice versa) than the slightly less than the crystallization ages of the latter suite (Fig. 5). Rocks from the Ritter Range Many minerals luminesce when bombarded youngest granitoid rocks that cut the pendant generally show less enriched light rare earth ele- by cathode rays, and quartz and feldspar minerals (e.g., Bateman, 1992; also see below). We inter- ments (LREE) patterns than the other suites of in hydrothermally altered and/or metamorphosed pret the 85 Ma date to approximate the age of metavolcanic rocks. Most rocks from the Ritter volcanic rocks commonly display cathodolumi- contact metamorphism of the pendant. Despite Range and White Mountains display slight nega- nescence (CL; e.g., Marshall, 1988). CL colors the high-T metamorphic assemblages of most tive Eu anomalies, whereas many rocks from the generally result from different trace element acti- Ritter Range metavolcanic rocks, classic hornfels Inyo Mountains and Alabama Hills show slight vators. For example, small amounts of Fe3+ pro- textures are mostly restricted to within 50 to 200 positive Eu anomalies (Fig. 6). duce red CL in albite, Fe2+ and Mn2+ yield yel- m of pluton contacts (Sorensen et al., 1993). Sim- low and green CL in more calcic plagioclase, and ilar relationships of texture to pluton contacts are Oxygen Isotope Systematics of Metatuffs trace Ti4+ (or intrinsic CL intensified by this acti- seen in the Alabama Hills. There, coarsening of vator) causes blue CL in K-feldspar (Marshall, the metaÐash-flow tuff of the upper interval Quartz and K-feldspar phenocrysts from 1988, and references cited). The intensities and (Dunne and Walker, 1993) appears within ~20 m metaÐash-flow tuffs exposed in the Alabama hues of CL in Figure 7 cannot be compared among of its contact with the 85 Ma Alabama Hills Hills, southern Inyo Mountains, and Ritter Range samples, owing to the vicissitudes of photo- Granite. This texture and the absence of older were separated and analyzed for δ18O values graphic processing. Nevertheless, information granitoid plutons suggest Cretaceous contact (Table 3; Appendix). Two 164 Ma metaÐash-flow about alteration and metamorphism can be metamorphism. tuff units of the Ritter Range were each sampled gleaned from each image. In the White Mountains, metamorphic horn- >200 m from contacts with Cretaceous plutons. Except for the Inyo Mountains, most of the blende is found in metavolcanic rocks only The average δ18O values for K-feldspar (+10.0‰ original igneous phenocrysts in the metavolcanic within ~50 m of the 165 Ma Barcroft Granodio- to +10.2‰) are fractionated by 2.1‰ with re- rocks have been replaced by other minerals. To- rite. Its presence is the most reliable indicator of spect to quartz (+12.1‰ to +12.3‰). gether with scanning electron microscope (SEM) Jurassic contact metamorphism. However, much The 170 Ma metaÐash-flow tuff of the Al- imagery and microprobe analyses, CL petrogra- of the metavolcanic section is younger than 165 abama Hills was sampled near its highest ex- phy sheds some light on the nature of these phe- Ma (Hanson et al., 1987), and thus deposited af- posed stratigraphic level (sample AH95Ð06A) nocryst replacements, along with the distribution ter Barcroft Granodiorite emplacement. Such and near its base (sample AH95Ð02; Fig. 2; Table and textural relations of albite, calcic plagioclase, rocks were likely metamorphosed by the 90 to 3). Because the unit is cut out by the 85 Ma Al- and K-feldspar in rock matrices. In samples from 100-Ma Pellisier Flats Granite. Albitization of abama Hills Granite, sample AH95Ð06A was the southern Inyo and White Mountains (Fig. 7, A some of the Jurassic section is related to contacts collected ~10 m and AH95Ð02 ~450 m from the and B) extremely fine grained, blue-luminescent with this pluton (Anderson, 1937; Crowder and pluton contact. Quartz and K-feldspar from K-feldspar has replaced delicate matrix textures Ross, 1972). AH95Ð06A yield δ18O values of 8.0‰ and that resemble those of igneous ash or glass. In

330 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

TABLE 1. WHOLE-ROCK ANALYSES OF MAJOR AND MINOR ELEMENTS, IN WT% OXIDES Ritter Range RR90- RR90- RR90- HT OH F71-12 F71-13 F71-14 F71-15 F71-42 F71-43 F71-44 F71-46 F71-47 F71-48 F71-51 F71-68 09A 09B 09C

SiO2 70.7 71.0 69.6 72.0 72.4 66.4 54.8 71.3 69.2 58.0 60.2 72.0 76.3 70.0 72.0 65.7 70.7 Al2O3 14.3 13.5 14.6 14.3 13.4 16.0 18.9 14.3 14.8 20.0 18.2 14.1 13.0 14.5 13.8 15.0 14.6 Fe2O3 1.8 1.2 0.8 2.6 1.3 3.6 7.1 2.2 2.3 5.7 5.7 2.3 1.1 2.3 1.9 4.8 3.2 FeO 0.4 0.8 0.5 1.0 1.6 0.3 1.4 1.0 0.7 0.8 0.6 0.2 0.2 0.3 0.2 0.2 0.3 MgO 0.3 0.6 0.1 1.6 0.4 1.7 3.3 0.3 0.5 1.8 1.7 0.9 0.2 0.3 0.1 1.8 0.2 CaO 1.2 1.0 0.7 1.2 1.1 1.8 6.0 0.5 1.2 0.8 2.7 2.3 0.0 0.9 1.0 3.9 2.4 Na2O 0.9 0.3 1.8 1.7 3.7 6.7 4.5 5.4 8.0 5.6 7.7 2.8 1.7 4.1 3.7 3.2 3.2 K2O 9.0 7.7 8.9 3.5 4.4 2.6 2.4 3.2 0.3 5.5 1.4 4.5 6.0 5.5 6.6 3.0 5.0 TiO2 0.3 0.3 0.2 0.3 0.1 0.4 0.7 0.4 0.6 0.7 0.6 0.2 0.2 0.3 0.2 0.7 0.4 P2O5 0.09 0.10 0.04 0.11 0.07 0.07 0.26 0.14 0.26 0.31 0.27 0.07 0.03 0.12 0.10 0.24 0.21 MnO 0.04 0.07 0.04 0.12 0.12 0.10 0.14 0.08 0.08 0.07 0.14 0.09 0.03 0.06 0.03 0.14 0.06 Total 99.03 96.57 97.28 98.43 98.59 99.67 99.50 98.82 97.94 99.28 99.21 99.46 98.76 98.38 99.63 98.68 100.27

Ritter Range (continued) Northern White Mountains F71-69 F71-70 F71-73 F71-75 F73-01 F73-04 F73-05 F73-07 82784-27 72984-3 82484-18 WMP-2 82184-11B 71683-10 7484-17

SiO2 51.6 50.4 61.0 51.0 76.0 69.0 66.6 70.7 65.6 58.9 68.1 69.2 68.3 76.8 49.7 Al2O3 16.8 18.0 17.3 19.9 12.8 14.7 16.2 13.8 16.8 22.6 14.8 14.1 15.9 13.0 18.2 Fe2O3 7.7 6.1 2.7 4.6 1.9 1.0 1.1 0.4 3.2 3.7 2.7 3.6 2.6 0.9 9.3 FeO 2.2 4.2 4.2 6.4 0.6 2.6 3.0 3.5 N.D. N.D. N.D. N.D. N.D. N.D. N.D. MgO 5.2 4.4 2.0 4.2 1.7 1.4 1.6 0.5 0.7 0.9 0.3 0.9 0.5 0.4 6.5 CaO 7.5 6.9 4.1 2.6 2.1 3.0 1.5 3.0 0.9 0.4 0.5 1.3 0.3 0.2 5.6 Na2O 3.2 3.4 4.1 6.5 1.7 1.5 4.9 2.1 2.2 3.4 2.3 5.5 3.9 4.7 5.2 K2O 3.5 3.4 3.4 1.4 2.4 5.1 3.5 3.2 9.8 9.2 8.9 4.2 6.4 2.2 2.7 TiO2 0.9 1.0 0.8 1.0 0.2 0.3 0.4 0.3 0.6 0.5 0.5 0.6 0.5 0.2 1.0 P2O5 0.37 0.36 0.30 0.36 0.21 0.14 0.13 0.12 0.11 0.05 0.14 0.23 0.10 0.02 0.43 MnO 0.20 0.18 0.12 0.15 0.33 0.14 0.14 0.11 0.07 0.10 0.02 0.05 0.05 0.01 0.07 Total 99.17 98.34 100.02 98.11 99.94 98.88 99.07 97.73 99.98 99.75 98.26 99.68 98.55 98.43 98.70

Northern White Mountains (continued) Alabama Hills Southern Inyo Mountains 81784-4 7484-21 81283-8 82583-11 71483-25 SI-87-22 SI-87-23b SI-87-23a SI-87-6X SI-87-19b SI-87-19c SI-87-11

SiO2 56.6 51.8 53.9 57.5 58.6 68.5 73.5 74.0 52.4 55.7 57.5 57.6 Al2O3 18.0 17.5 18.3 16.5 17.7 14.8 13.6 13.3 16.9 20.0 19.0 16.4 Fe2O3 7.5 8.3 10.4 7.9 6.8 3.1 1.7 1.8 7.7 6.4 6.3 6.6 FeO N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. MgO 2.8 6.4 4.9 3.0 3.2 2.5 0.3 0.3 0.9 0.8 0.5 1.5 CaO 2.7 5.1 1.3 2.9 2.9 1.6 1.0 1.1 5.9 1.9 2.3 3.4 Na2O 5.6 5.8 5.2 6.4 5.1 1.8 3.0 3.0 5.0 4.8 3.1 6.3 K2O 3.2 2.7 4.0 2.6 3.6 4.3 5.4 5.6 3.4 6.1 7.8 3.1 TiO2 1.0 0.8 1.2 0.9 0.9 0.4 0.2 0.2 1.0 0.5 0.7 0.8 P2O5 0.37 0.38 0.46 0.40 0.30 0.14 0.08 0.07 0.43 0.47 0.45 0.35 MnO 0.08 0.07 0.05 0.12 0.11 0.12 0.09 0.07 0.16 0.12 0.05 0.16 Total 97.85 98.85 99.71 98.22 99.21 97.26 98.87 99.44 93.79 96.79 97.70 96.21

Southern Inyo Mountains (continued) SI-85-6 SI-87-7 SI-87-3bx SI-D20-9 SI-87-3x SI-87-21a SI-87-21b SI-87-20a SI-87-6 IM95-07A IM95-09

SiO2 66.5 68.5 68.8 69.0 69.6 71.4 71.6 71.9 73.6 73.1 73.5 Al2O3 16.8 14.9 14.1 15.7 14.4 13.9 14.0 14.5 13.3 13.2 13.3 Fe2O3 3.2 2.1 2.0 2.9 2.1 2.0 2.1 1.2 1.9 1.8 1.6 FeO N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. N.D. 0.1 0.3 MgO 0.2 0.1 0.1 0.3 0.1 0.2 0.3 0.1 0.1 0.2 0.2 CaO 0.2 0.8 1.2 0.5 0.7 0.5 0.5 0.9 0.1 0.6 0.8 Na2O 4.9 3.3 2.0 4.2 1.9 2.7 2.5 3.8 1.6 1.8 2.0 K2O 6.3 7.8 7.9 5.6 8.3 6.4 6.4 6.1 7.8 6.5 5.4 TiO2 0.6 0.4 0.4 0.4 0.4 0.3 0.3 0.2 0.3 0.3 0.2 P2O5 0.12 0.06 0.06 0.09 0.06 0.09 0.09 0.04 0.07 0.09 0.08 MnO 0.01 0.03 0.07 0.03 0.06 0.05 0.06 0.03 0.01 0.08 0.02 Total 98.83 97.99 96.63 98.72 97.62 97.54 97.85 98.77 98.78 97.78 97.40 Note: N.D. = not determined.

contrast, matrices of tuffs from the Ritter Range luminescent K-feldspar (Or>95) has replaced within the blue-luminescent K-feldspar replace- and Alabama Hills (Fig. 7, C and D) consist of alkali-feldspar phenocrysts in samples from the ments of phenocrysts in the Ritter Range sample coarser-grained mosaics of K-feldspar, nonlumi- White Mountains, Ritter Range, and Alabama (Fig. 7C). nescent (black) quartz, and yellow-green lumi- Hills (Fig. 7, BÐD). Brownish-purple-luminescent The luminescence of former plagioclase phe- nescent metamorphic plagioclase. K-feldspar has replaced phenocrysts and crystal nocrysts varies among samples. In the Inyo Moun- Pseudomorphs of alkali-feldspar phenocrysts fragments of alkali feldspar in the Inyo Mountains tains sample (Fig. 7A) plagioclase phenocrysts show two main types of luminescence. Blue- sample (Fig. 7A), and also appears as patches consist of relict igneous plagioclase (green specks),

Geological Society of America Bulletin, March 1998 331 1.711.50 0.242.20 0.22 192.10 0.32 N.D.2.10 0.31 N.D. N.D. N.D. 1.60 0.31 N.D. N.D. 1.70 0.27 N.D. N.D. 3.90 0.25 N.D. N.D. 3.60 0.57 N.D. N.D. 2.60 0.52 N.D. N.D. 2.10 0.37 N.D. N.D. 1.50 0.32 N.D. N.D. 2.00 0.23 N.D. N.D. 2.10 0.33 N.D. N.D. 1.80 0.30 N.D. N.D. 3.80 0.28 N.D. N.D. 1.40 0.57 N.D. N.D. 1.90 0.20 N.D. N.D. 2.30 0.36 N.D. N.D. 2.60 0.32 N.D. N.D. 2.70 0.49 N.D. N.D. 2.20 0.53 N.D. N.D. 1.50 0.33 N.D. N.D. 1.90 0.24 N.D. N.D. 1.70 0.31 N.D. N.D. 0.27 N.D. N.D. 2.67 N.D. N.D. 5.80 0.41 N.D. 2.85 0.82 N.D.2.80 0.41 N.D. N.D. 3.39 0.43 N.D. N.D. 3.29 0.50 N.D. N.D. 1.95 0.46 N.D. N.D. 2.31 0.32 N.D. N.D. 1.60 0.36 N.D. N.D. 2.74 0.26 N.D. N.D. 1.90 0.43 N.D. N.D. 2.05 0.29 N.D. N.D. 0.31 N.D. N.D. 1.90 N.D. N.D. 2.80 N.D. 0.411.90 0.51 201.70 0.42 282.80 0.44 16 222.90 0.63 23 192.10 0.55 22 252.40 0.48 13 211.70 0.39 30 131.80 0.41 25 261.50 0.42 26 2.00 11 0.33 17 131.30 0.52 24 122.09 0.27 13 192.00 0.32 12 0.30 8 17 201.70 20 12 0.60 20 0.411.10 13 0.19 15 0.30 7 11 12 12 14 TABLE 2. WHOLE-ROCK ANALYSES OF TRACE ELEMENTS OF ANALYSES 2. WHOLE-ROCK TABLE Ba Co Cr Cs Hf Rb Sr Sb Ta Th U Zn Zr Sc La Ce Nd Sm EuYYb Lu Tb Nb N.D. = not determined. All measurements in ppm. N.D. = not determined.

Note: Ritter Range RR90-09ARR90-09BRR90-09C 2534HT 929OH 1.9 2934F71-12 <1.7 1.4F71-13 0.9F71-14 <1.9 7.3 <1.3F71-15 11.5 1380 4.2F71-42 5.9 1060 674 4.0 1080 7.2F71-43 283 4.3 3.7 8.5 27.4F71-44 353 859 47.3 90F71-46 261 147 84.4 12.5 11.0 26.6 1060 1.9 40F71-47 4.9 156 3.5 3.2 13.5 4.5 9.4F71-48 3.7 497 1.0 1350 8.1 6.3F71-51 1.05 3.2 13.1 6.1 2.1 171 4.9 3.4F71-68 1.1 924 2.9 2.7 1.2 16.3 1770 206 129F71-69 5.9 99 0.9 66 8.2 1800 14.5 0.9 6.0F71-70 17.6 2.9 1.5 2.9 15.7 1270 94 239 601 5.5 4.5 3.5F71-73 1.7 7.6 1240 2.8 6.0 80 0.98F71-75 1.1 5.5 1.4 3.2 10 5.0 5.8 3.1 204 2.8F73-01 812 5.4 7 2.5 5.3 14.0 99 14 231 0.97 0.84 0.39 3.3F73-04 738 9.5 63 29.8 84 162 8 1620 170 3.5 2.2 11.5F73-05 2.9 4.3 1.5 15.3 11.7 27.1 105 5.2 24.7 1210 451 161 38.9 2.9 11.4F73-07 2.1 3.9 210 4.4 2.8 1660 1.39 0.52 55 10.7 171 30.7 4.5 2.9 2.3 0.8 37 0.9 4.1White Mountains 10.6 8.2 1.4 1590 1.18 39.4 182 2.9 15.7 60 117 10.882784-27 20.7 4.2 136 20.8 2180 3.2 33.4 0.46 0.69 4.1 140 2.3 47 84 105 108 67.872984-3 5.7 136 2.2 0.7 1210 2.1 596 9.7 40.7 5.3 3.4 4.0 45.8 63.382484-18 5.3 22.4 2.8 1.7 127 333 5.0 3.7 64.0 8.9 90 121 23.5 3130 97 3.9 81 1.40 1.10WMP-2 4.3 3.2 149 127 5.0 18.7 81.5 4.2 34.8 21.2 135 6.2 685 596 36 1.2182184-11B 122.0 2.2 1.3 2.4 1460 9.1 17.2 3.3 364 22.7 0.81 3.9 15.8 14.9 27.0 4.5 2110 0.85 25571683-10 34 2.7 33 11.2 1.7 1.5 136 0.63 17.0 128 101 24 4.8 16 0.62 1.3 1.97484-17 61 5.1 1070 51 2.3 32 2.5 268 1.0 0.45 2.6 7.4 221 1011 2.9 8.9 230 13.6 268 0.3381784-4 0.20 2.2 0.82 121 0.38 8.0 0.84 123 1.0 N.D. 108 155 4.3 1.7 43 297484-21 125 23 32 23 4.0 497 34 7.6 10.5 33 4.9 57 2.2 13.9 0.44 267 3.9 7.481283-8 3.2 10 2.7 N.D. 0.5 155 0.70 9.3 437 36 3.4 0.5 N.D. 175 0.4 17 13.3 3.982583-11 0.98 15 92 9.1 1430 21 93 0.7 22 62 216 61 1.6 1.6 1.5 158 19.9 6.671483-25 0.62 12 2.4 N.D. 31 293 19.2 7.1 0.82 11.3 N.D. 393 174 3.8 3.2 3.3 177 0.8 72 0.98 105 1870 2.4 4.4Inyo Mountains 8.1 33.8 31 38 164 0.95 31 74 7.4 1780 126 3.4 131 58.6 15.1 8.7 0.33 N.D. 56 1.9 2.0 44 N.D. 18.3 0.63 1.02 52 25.9 12.1 32SI-87-6X 1520 196 0.43 N.D. 170 34 12.8 N.D. 38 113 6.2 1.57 N.D. 75 6.6 50.6 6.6 9.4 20SI-87-19b 2.4 113 34 7.2 79 140 53.6 0.30 0.43 3.3 18.9 N.D. 126 44 3.2 3.30 0.54 74 18 4.8 217SI-87-19c 3.9 7.2 26.1 1.36 N.D. 16.4 51 1.56 52.2 27 27.7 1.46 4.1 N.D. 16.0 82 67.5 64 154 115 N.D. 27SI-87-11 N.D. 31.6 65 3.2 59 23 1.50 3.1 N.D. 81 1.01 90 25 0.96 5.6 4.2 64 44SI-85-6 433 1.90 523 19 31 840 29.8 1.17 15.6 N.D. 21 1.61 108 46 220 23 4.5 6.6SI-87-7 420 0.61 650 1.04 109 103 32 4.7 N.D. N.D. N.D. 17.4 26 4.7 4.1 N.D. 40 0.56 38 3.5 14.8SI-87-3bx 590 3.6 1000 96 35 51 N.D. 254 2.03 4.8 0.51 3.9 0.32 76 N.D. 19 27 N.D.SI-D20-9 27 N.D. 7.8 0.87 7.8 98 4.2 N.D. 299 0.44 1850 0.85 2.7 N.D. 52 22 14 N.D.SI-87-3ax N.D. 235 29 20.0 3.8 0.69 N.D. N.D. 23 24 542 500 30 0.52 3.7 3.8 1.66 0.54 SI-87-21a 460 N.D. 1.01 2.0 860 0.37 N.D. N.D. 49 36 4.0 N.D. N.D. 309 33 36 7.4 5.0 0.45 28 3.1 N.D. 1680SI-87-21b 0.94 5.2 N.D. 5.0 49 1.06 4.0 N.D. 1.2 41.5 N.D. 0.84 5.0 120 N.D. N.D. 50 180 287SI-87-20a 0.81 1.38 6.6 450 4.0 17 306 N.D. 1.6 78.4 N.D. N.D. 1.53 6.0 1.18 0.43 52 14 160 78 420SI-87-6 N.D. 690 950 N.D. 19 10.0 37 2.1 144 43.5 7.1 0.63 N.D. N.D. 19 1.6 N.D.IM95-07A N.D. 970 N.D. 640 9.2 3.4 1.34 N.D. 0.78 60 N.D. 0.65 47 N.D. 229 1470 N.D. 190 20.0 57.5 82 32.0 N.D.IM95-09 150 3.4 N.D. 45.4 7.0 7.0 31 1.8 48.9 N.D. 2.00 680 2.00 0.63 3.6 N.D. 0.87 104 69 1.9 3.6 237 6.2 170 N.D. 8.3 N.D. N.D. N.D.Alabama Hills 9.9 86 0.72 2.00 190 220 N.D. N.D. 31.0 500 N.D. 119 N.D. 662 0.80 17.4 0.41 6.0 79 48.5 N.D. 0.77 6.2 260 1.41 N.D. 157SI-87-22 N.D. 41.0 56 26.3 6.2 1.32 1.00 140 N.D. 15.3 0.34 2.0 36 3.00 N.D. 30.8 N.D. 678SI-87-23b 0.20 200 N.D. 93 2.5 35.8 2.0 222 7.4 0.39 222 0.70 2.8 2.0 N.D. 52 N.D. 150 1.23 1.08 11.1SI-87-23a 210 4.0 6.4 N.D. 32.7 2.1 N.D. 170 33.5 N.D. 71 53.9 1.9 1.13 N.D. 2.00 200 1.6 N.D. 1060 28.3 N.D. 100 2.00 N.D. 0.69 170 1.17 N.D. 55 103 25.7 3.2 N.D. 1.00 N.D. 240 830 29.8 6.6 5.5 0.78 100 130 24.7 2.0 28.0 N.D. 2.0 3.5 36.7 N.D. 5.9 460 23.9 2.00 740 260 0.69 N.D. 66 21.0 N.D. 42.0 N.D. 9.3 N.D. 0.57 5.7 N.D. 2.00 190 N.D. 67 N.D. 3.5 N.D. 4.6 7.5 1.36 28.0 200 4.8 N.D. 4.4 8.6 N.D. 2.00 59.5 480 N.D. N.D. 35.6 1.36 0.61 2.00 23.6 2.9 27.6 194 3.6 28 N.D. 0.71 109 50.1 N.D. 27.4 N.D. N.D. 4.4 3.0 1.03 2.05 N.D. 22.8 71 4.5 N.D. 0.64 14.6 N.D. N.D. 390 N.D. 3.8 171 1.0 5.5 78.2 97 80 440 220 N.D. 0.50 0.92 78.8 46.6 3.6 1.0 1.10 2.00 364 140 3.4 32.3 220 N.D. 1.26 90 145 N.D. 1.3 8.5 360 410 N.D. 40.5 220 N.D. 27.5 0.47 5.3 65.3 2.1 140 110 N.D. N.D. 73.7 N.D. 0.61 1.42 2.70 6.8 37.3 N.D. 56.9 119 170 110 46.8 133 N.D. 2.50 170 2.6 1.52 1.00 N.D. 83.1 6.3 9.0 23.2 2.40 1.20 N.D. 2.00 88 N.D. 37.6 146 43.9 0.90 25.7 22.3 N.D. N.D. 47.2 2.60 3.10 2.00 1.00 3.0 36.4 6.4 24.2 68 51.0 100 6.5 43.2 2.6 4.6 55.6 0.90 1.20 26.3 67 1.90 15 91 7.1 4.7 1.60 8.6 N.D. 22.7 N.D. 39 4.4 0.80 34.4 1.42 22.2 107 N.D. 3.7 1.00 1.60 170 32.9 N.D. 3.6 112

332 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

Quartz phenocrysts and crystal fragments luminesce reddish-purple in the Inyo Mountains sample (Fig. 7A), but are nonluminescent (black) in the other samples (Fig. 7, BÐD). Because quartz phenocrysts in Inyo Mountains samples display igneous δ18O values, their luminescence may also be a relict igneous feature that survived both K-metasomatism and metamorphism.

DISCUSSION

Alkali Abundances in Metavolcanic Rocks: Protolith or Alteration Features?

Many of the metavolcanic rocks from eastern California show much higher or lower K/Na than young, fresh, calc-alkaline arc volcanic rocks (Table 1, Fig. 4). To what extent are such alkali- element ratios of primary igneous origin? Follow- ing work by Miller (1978), Christe and Hannah (1990) grouped metavolcanic rocks of the White- Inyo Mountains in a “high-K lower Mesozoic magmatic province.” Christe and Hannah (1990) concluded that the alkali abundances and elevated K/Na of Jurassic metavolcanic rocks from both this region and ones from the Kettle Rock sequence of the northern Sierra Nevada reflect protolith characteristics. Fresh alkaline volcanic rocks from arcs are much richer in K, Rb, Ba, Na, and Sr than calc-alkaline ones (e.g., Gill, 1981),

and are typically identified by plots of SiO2 versus K2O or versus (K2O + Na2O). Because such cor- relations can be disturbed by alkali alteration, less mobile elements should be used to detect alkaline protoliths of metavolcanic rocks (e.g., Pearce, 1982). High-K (shoshonitic) basalts are enriched in other large ion lithophile elements (e.g., Th) and light REE (e.g., Ce) with respect to heavy REE (e.g., Yb) and high field strength elements (e.g., Ta) compared with calc-alkaline basalts. Figure 4. Variation diagrams of major and minor elements for metavolcanic rocks from eastern Ratios of these elements may discriminate be- California. Symbols indicate localities, as noted: squares—Ritter Range, triangles—White Moun- tween the two magma series (Pearce, 1982). tains, diamonds—Inyo Mountains, hexagons—Alabama Hills. All analyses are recalculated on an However, even moderate igneous fractionation anhydrous basis. A solid line bounds the field for 133 analyses of young volcanic rocks from the can change Ce/Yb, Th/Yb, and Ta/Yb enough to Mexican volcanic belt, compiled from Luhr and Carmichael (1980), Mahood (1981), Nelson and “confuse” the plotted field boundaries, which are Livieres (1986), Luhr et al. (1989), Nelson and Hegre (1990), and some unpublished analyses by based on basalt compositions. In the eastern Cali- J. F. Luhr (1996, personal commun.), along with data for other calc-alkaline suites from conti- fornia localities basalts are rare, but basaltic nental arcs (Jakes and Smith, 1970; Mackenzie and Chappell, 1972; Keller, 1974; Smith et al., andesites are not, so we have stretched the applic- 1977, 1979; Smith and Johnson, 1981). The solid lines with arrowheads indicate trends defined by ability of the discriminant diagrams a bit by us- calc-alkaline volcanic rocks from the Mexican Volcanic Belt. ing analyses of the latter rocks (Fig. 8). With this caveat in mind, values for the Ritter Range rocks are within calc-alkaline fields, whereas the partially replaced by albite (reddish blotches), K- few albite grains display thin selvages or patches of White and Inyo Mountains rocks show alkaline feldspar (blue specks), and calcite (bright orange blue-luminescent K-feldspar (Fig. 7, B and C). In (shoshonitic) affinities (Fig. 8, A and B). Christe specks). In the White Mountains sample, plagio- the Alabama Hills sample, former plagioclase phe- and Hannah (1990) did not report data for Ta, so clase phenocrysts are replaced by strongly CL- nocrysts are now aggregates of dull yellow-green- comparison samples from the Kettle Rock se- zoned albite that luminesces brownish- to dull- luminescent An20Ð40 plagioclase, bright-orange- quence are not plotted. reddish-purple (Fig. 7B). Dull-red-luminescent luminescent calcite specks, and blue-luminescent Can the degree of alkali and alkaline earth ele- albite has replaced plagioclase phenocrysts in the K-feldspar (Fig. 7D). The plagioclase is likely of ment enrichment observed in the metavolcanic Ritter Range sample (Fig. 7C). In both samples, a metamorphic origin. rocks of eastern California be due solely to a

Geological Society of America Bulletin, March 1998 333 SORENSEN ET AL.

Figure 5. “Spider diagrams” of minor and trace elements for metavolcanic rocks from eastern California. Symbols are as in Figure 4. All analyses are recalculated on an anhydrous basis and normalized to values for average mid-oceanic-ridge basalt (MORB) of Pearce (1982). The stippled pattern in D defines a field of 86 analyses of young calc-alkaline volcanic rocks of the Mexican Volcanic Belt (for references, see the caption for Fig. 4). The outlined, unshaded region in D represents values for the Ritter Range (shown in A).

high-K igneous protolith assemblage? We think sociated calc-alkaline rocks. However, data for ement data show evidence for mildly alkaline not. Na and Sr contents of the metavolcanic rocks alkaline and peralkaline rhyolites show little protoliths of mafic rocks from the White-Inyo anticorrelate with those of K and Rb, which overlap with values for the felsic metavolcanic Mountains, but the associated felsic rocks lack points to alkali exchange as a means to produce rocks. At a given K/Al and Ti content, the strong evidence of alkaline or peralkaline pro- the values seen in the suite (Figs. 9 and 10). Com- metavolcanic rocks are much richer in Ba than toliths. This result is not paradoxical; Pleistocene parison with suites of modern fresh igneous are alkaline or peralkaline rhyolites. A compari- to Recent volcanoes in New Guinea and active rocks with the metavolcanic rocks and K-meta- son with data for K-metasomatized Tertiary vol- volcanoes in the Mexican Volcanic Belt (Smith somatized Tertiary igneous rocks show that alkali canic rocks of the southwestern United States and Johnson, 1981; Mackenzie and Chapell, exchange is not an important igneous fraction- (Fig. 10A) suggests that the extreme Ba-enrich- 1972; Nelson and Liveres, 1986; Luhr et al., ation process (Figs. 9 and 10). Instead, the alter- ment seen in the felsic metavolcanic rocks more 1989) have erupted calc-alkaline and alkaline se- ation trends defined by pairs of fresh (or less al- likely reflects metasomatism than igneous frac- ries lavas in close spatial proximity more or less tered) and K-altered Tertiary igneous rocks are tionation. REE patterns of alkaline and peralka- contemporaneously. mimicked by the data for the metavolcanic rocks line rhyolites tend to display very large negative (Figs. 9 and 10). Eu anomalies (e.g., Jakes and Smith, 1970; Replacement Mineralogy of Metavolcanic There is little evidence that the felsic metavol- Mackenzie and Chappell, 1972; Keller, 1974; Rocks canic rocks of eastern California had alkaline or Smith et al., 1977;1979; Smith and Johnson, peralkaline protoliths (Figs. 9 and 10). Alkaline 1981), a feature not seen in the REE patterns of CL petrography provides evidence for: (1) and peralkaline rhyolites from the Aeolian arc, the felsic metavolcanic rocks. widespread and abundant development of K- Papua New Guinea, and the Mexican Volcanic We conclude that the alkali systematics and feldspar in rocks that show varying intensities of Belt show variable but dramatic enrichments in much of the alkali abundances in the metavol- contact metamorphic recrystallization; (2) rem- Zr/Ti and depletions in Ba/Ti with respect to as- canic rock suites reflect metasomatism. Trace el- nants of igneous plagioclase in relict phenocrysts

334 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

Figure 6. Rare earth element patterns for metavolcanic rocks from eastern California. Symbols are as in Figure 4. All analyses are recalculated on an anhydrous basis and normalized to average values for C1 chondrite values (Anders and Ebihara, 1982), multiplied by a factor of 1.31. The stippled pattern in D defines a field for 86 analyses of young calc-alkaline volcanic rocks of the Mexican Volcanic Belt (for references, see the caption for Fig. 4). The outlined, unshaded region in D represents the values for the Ritter Range shown in A.

from the Inyo Mountains; (3) the presence of red- TABLE 3. OXYGEN ISOTOPE DATA FOR luminescent, probably igneous quartz only in the ASH-FLOW TUFF UNITS low-T metamorphosed rocks of the Inyo Moun- Quartz K-Feldspar Others* tains; and (4) growth of metamorphic An Alabama Hills 20Ð40 plagioclase in samples from the Ritter Range and 85 Ma Granite 8.7 7.8 plg 7.2 170 Ma Ash-flow Tuff Alabama Hills. These results parallel the varia- AH95-02 6.0 3.4 tions of metamorphic grade expressed by the AH95-06A 8.0 5.3 overall mineral assemblages of the localities. The Southern Inyo Mountains CL images also reveal possible mechanisms for 169 Ma Ash-flow Tuff alkali-metasomatism and phenocryst replace- IM95-07A 9.2 4.0 mat 5.1 ment in the Inyo and White Mountains. In those IM95-09 9.5 8.8 mat 9.8 samples, the preservation of delicate igneous tex- Ritter Range tures by K-feldspar suggests that volume changes 164 Ma, Structurally Lower Ash-flow Tuff during K-metasomatism were probably minor. † Average 12.1 10.2 This is consistent with alkali exchange mecha- 164 Ma, Structurally Higher Ash-flow Tuff Average¤ 12.3 10.0 nisms that essentially balance K gain with Ca and Note: Values are of δ18O, relative to standard mean ocean water Na loss, and/or Na gain with Ca or K loss. Only (SMOW). the Alabama Hills sample, which was obtained *plg = plagioclase, mat = matrix. †Quartz from 8 samples; alkali feldspar from 9 samples. within 20 m of a pluton contact, shows evidence ¤Quartz from 8 samples; alkali feldspar from 7 samples. for much matrix grain growth (Fig. 7D, cf. Fig. 11, A and B). This suggests that some meta-

Geological Society of America Bulletin, March 1998 335 Abbreviations: plg—plagioclase, qz—quartz, ksp—K-feldspar, alb—albite, apt—apatite. additional explanation. See text for Figure 7. Cathodoluminescence of samples from the Inyo Mountains (A; sample SI- the Inyo 7. Cathodoluminescence of samples from Figure 87Ð21A), White Mountains (B; sample 72984Ð3), Ritter Range (C; sample F71Ð46), and images is 1.6 mm. The long dimension in all four Alabama Hills (D; sample SI-87Ð23A).

336 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

Quartz and whole-rock δ18O values for 12 of 13 lower-section rocks range from +11.1‰ to +16.0‰ (sample B87–37a has a δ18O of +7.4‰; Table 3 of Hanson et al., 1993). These δ18O values could reflect protoliths like the high-δ18O tuffs from the Tuscan magmatic province (Tay- lor and Turi, 1976). However, the wide areal extent of high-δ18O rocks in the pendant and oc- currence of the highest δ18O values in oxidized and locally Mn- and Sr-rich units of piemontite- and braunite-bearing ash-flow tuff argue against these being igneous values (Hanson et al., 1993). Units with similar field aspects and silica contents (and thus of likely protoliths) to these high δ18O rocks are also present in the other two structural settings of the Ritter Range. Four of five whole-rock and quartz δ18O values for the “lower-section rocks near Nydiver Lakes” range from +4.1‰ to +4.8‰; the fifth (sample F85Ð7) has a δ18O of +7.5‰ (Table 3 of Hanson et al., 1993). Whole-rock δ18O values for four of five samples of metaÐash-flow tuff from the upper section range from +2.1‰ to +6.2‰; the fifth (sample F77Ð17) has a δ18O of +7.5‰. Whole- rock and quartz δ18O values for the Kuna Crest granodiorite are +9.0‰ and +7.9‰, respectively, and whole-rock δ18O for the Shellen- barger granite is +7.5‰ (Table 3 of Hanson et al., 1993). The data for these plutonic rocks agree fairly well with the δ18O values (+5.5‰ to +8.5‰) that Taylor (1986) reported for the Sierra Nevada batholith. Very high (>+10‰) δ18O values in ash-flow tuffs are attributed to assimilation of large Figure 8. Variations of Ce/Yb versus Ta/Yb and of Th/Yb versus Ta/Yb in mafic metavolcanic amounts of metasedimentary rock, whereas as- rocks. No data are shown for the Alabama Hills, because only analyses with SiO < 62 wt% are 2 similation of meteoric-waterÐaltered roof rocks of plotted. Pearce (1982) proposed the discriminant between shoshonitic (sho) and calc-alkaline calderas is thought to produce very low (<+5‰) (ca) basalts, shown as fields separated by the dashed line. RR—Ritter Range; WM—White δ18O values in both ash-flow tuffs and associated Mountains; IM—Inyo Mountains. Symbols are as in Figure 4. plutonic rocks (e.g., Taylor and Sheppard, 1986; Larson and Geist, 1995). It seems geologically implausible that both of these mechanisms oper- volcanic rocks may preserve textures that reflect values of metasomatized and/or contact-meta- ated in close proximity to produce numerous units lower T and/or earlier alkali-metasomatic effects morphosed volcanic rocks may reflect both mag- of felsic rocks with observed δ18O values >+10‰ rather than contact metamorphism. Albite and matic and fluid-rock effects (e.g., Taylor and throughout a 20 km2 area in structural setting 1 K-feldspar should be stable phases in K- and/or Sheppard, 1986; Criss and Taylor, 1986). Our in- (including the 164 Ma metaÐash-flow tuff units of Na-rich bulk compositions even over the wide terpretation of the somewhat small set of δ18O Table 3) along with felsic rock units that show range of contact metamorphic temperatures data presented here is supported by a larger data δ18O <+5‰ in setting 2. The contrast between the recorded by the mineral assemblages of these set and additional geological constraints for δ18O value of +7.5‰ for the Schellenbarger gran- rocks. Grains of these minerals that formed by the Ritter Range (Hanson et al., 1993). There, ite porphyry, which is interpreted to be a hypa- relatively low-T alkali-metasomatism might per- metavolcanic rocks are found in three structural byssal subcaldera intrusion, and values of +2.1‰ sist during later, higher T contact metamorphism, settings: (1) nearly vertical layers of a Triassic to to +6.2‰ for coeval upper section rocks that rep- barring penetrative deformation or significant Early Cretaceous “lower section”; (2) fault- resent caldera fill and collapse deposits (Fiske and fluid infiltration. bounded slivers of vertical layers of Triassic to Tobisch, 1994), argues against a magmatic origin Oxygen Isotope Evidence for Fluid Sources. Jurassic rocks (the “lower-section rocks near for the low δ18O values in structural setting 3 (cf. Ritter Range. The abundant alkali-metasomatism Nydiver Lakes” of Hanson et al., 1993); and (3) a Larsen and Geist, 1995). Furthermore, Late Cre- of the metavolcanic sections testifies to interac- gently dipping mid-Cretaceous “upper section.” taceous plutonic rocks and at least one sample tions between these rocks and fluids. Oxygen iso- Rocks in all three settings are alkali altered and from each structural setting all show δ18O values tope data can help constrain temperatures and en- intruded by the Late Cretaceous Kuna Crest typical of the Sierra Nevada batholith. It seems vironments of fluid-rock interactions (e.g., Criss granodiorite. The upper section is also intruded unlikely that most of the magmas that produced and Taylor, 1986; Valley, 1986). However, δ18O by the mid-Cretaceous Shellenbarger granite. the Jurassic to Early Cretaceous Ritter Range vol-

Geological Society of America Bulletin, March 1998 337 SORENSEN ET AL.

The 2.1‰ fractionation between average δ18O values for Ritter Range quartz and K-feldspar pairs (Table 3) suggests high-T (i.e., igneous or contact metamorphic) rather than low-T (<200 ¡C) equilibration. However, K-feldspar “phe-

nocrysts” of Or>95 are clearly not of igneous origin. Many single-crystal quartz phenocrysts: (1)

are typically riddled with H2O ± CO2-, (l + v)- bearing fluid inclusions; (2) show no cathodoluminescence; and (3) contain pseudomorphs of melt inclusions that consist of metamorphic minerals. Furthermore, many “quartz phenocrysts” in hand sample consist of polycrystalline aggregates of quartz grains that display polygonal or ragged boundaries in thin section. Because we interpret both quartz and K-feldspar to pseudo- morph or replace original igneous phenocrysts, we conclude that the fractionation of δ18O values between quartz and K-feldspar reflects high-T reequilibration of high δ18O whole-rock values imposed at lower-T conditions. Alabama Hills and Inyo Mountains. Although we have analyzed relatively few samples from the Alabama Hills and Inyo Mountains, their δ18O values contrast with those for the lower section rocks of the Ritter Range (Table 3). The 170 Ma metaÐash-flow tuff of the Alabama Hills shows fractionations of δ18O that suggest that quartz and K-feldspar equilibrated under high-T (>~600 ¡C) conditions. However, one of the quartz and both of the K-feldspar samples show lower δ18O values than are typical of felsic volcanic rocks (Table 3, cf. Taylor and Sheppard, 1986). Because the two samples are from different parts of the same ash-flow tuff unit and the K-

feldspar phenocryst compositions are Or>95,it seems unlikely that these low values are of igneous origin. Meteoric-hydrothermal water cir- culation systems centered upon granitoid plutons can produce nonigneous δ18O values in altered Figure 9. Alkali and alkaline-earth element systematics for metavolcanic rocks from eastern volcanic rocks, but such rocks generally display California. All analyses are recalculated on an anhydrous basis. Symbols are as in Figure 4. disequilibrium mineral-pair fractionations (e.g., Fields for analyses of calc-alkaline, alkaline, and peralkaline volcanic rocks from continental Criss and Taylor, 1986). Sample AH95Ð02, arcs (Mexican Volcanic Belt, Aeolian arc, Papua New Guinea) are outlined in solid lines. The which shows the lower of the δ18O values for stippled pattern denotes a field for K-metasomatized Tertiary volcanic rocks from California quartz and K-feldspar, was collected farthest and Arizona (Glazner, 1988; Roddy et al., 1988; Hollocher et al., 1994). Barbless arrows connect from the pluton contact. The pluton, which dis- analyses of probable protolith and alteration product reported by Glazner (1988); barbed ar- plays mineralogical effects of hydrothermal al- row connects less- with more-K-metasomatized volcanic rocks as per Hollocher et al. (1994). A teration, exhibits magmatic values for quartz, pla- shows Rb/Sr versus K/Al; B shows K/Na versus Rb/Sr. References for the comparison data for gioclase, and alkali feldspar. These features are unaltered igneous rocks are in the caption for Figure 4. atypical of meteoric-hydrothermal systems, in which the lowest δ18O values are centered on the pluton and increase in country rocks with dis- canic section were highly contaminated by crust igneous values. Hanson et al. (1993) attributed the tance from pluton contacts. Accordingly, we sug- that had locally heterogeneous δ18O values, yet high δ18O values of lower section rocks to low-T gest that the δ18O values for sample AH95Ð06A the Late Cretaceous, pluton-producing magmas (<200 ¡C) interaction with seawater, and con- record the release of magmatic fluids from the emplaced into the volcanic section were not. For cluded that meteoric water infiltration produced Alabama Hills Granite into the metaÐash-flow all of these reasons, Hanson et al. (1993) inter- low δ18O values along the bounding fault zone of tuff unit, which had earlier been K-metasoma- preted most of the δ18O values of metavolcanic an Early Cretaceous caldera complex (the Ny- tized by water with a meteoric signature. Because rocks from the Ritter Range to reflect pre-Late diver section), and within coeval caldera deposits models of fluid flow around cooling plutons (e.g., Cretaceous alteration regimes rather than primary (the upper section). Hanson et al., 1993; Hanson, 1995) show that this

338 Geological Society of America Bulletin, March 1998 PALEOALTERATION ENVIRONMENTS OF METAVOLCANIC ROCKS

Tertiary ash-flow tuffs near Socorro, New Mex- ico, to reflect infiltration of brines from overlying playa lake systems, and Leising et al. (1995) extended this interpretation to K-metasomatized Tertiary volcanic rocks from the Harcuvar Mountains of southwestern Arizona. Potassi- cally altered Tertiary ash-flow tuffs typically display whole-rock δ18O values >+11‰ (Chapin and Lindley, 1986; Roddy et al., 1988; Glazner, 1988; Dunbar et al., 1994). The low δ18O values for quartz and K- feldspar in K-metasomatized ash-flow tuffs of the Inyo Mountains and Alabama Hills contrast with the high δ18O values reported for terranes that are interpreted to have been infiltrated by nonmagmatic, low-T brines in terrigenous fluid- rock systems (Chapin and Lindley, 1986; Glazner, 1988; Roddy et al., 1988; Dunbar et al., 1994). What if somewhat higher T hydrothermal systems produced the K-alteration seen in the Inyo Mountains and the Alabama Hills? Fox and Miller (1990) documented abundant sodic alteration of Jurassic plutons in southeastern Califor- nia. If coeval plutons were being albitized at depth beneath the volcanic sections of the Inyo Mountains and Alabama Hills, meteoric- hydrothermal fluids enriched by Na-for-K exchange at depth could potentially rise and potas- sically alter an overlying volcanic section, a mechanism similar to that proposed for the Ann- Mason porphyry copper deposit (Dilles and Einaudi, 1992). However, the presence of unit- scale, alternating Na- and K-metasomatism in in- tercalated units argues against fluid-rock interactions in a simple meteoric-hydrothermal system. Figure 10. Ba/Ti (A) and Zr/Ti (B) versus K/Al in metavolcanic rocks. All analyses are re- A spatial association between zones of K- and calculated on an anhydrous basis. Symbols are as in Figure 4. Patterning, fields, and arrows are Na-metasomatism and Jurassic pluton contacts defined in the caption for Figure 9. References for comparison data are in the captions of Fig- has been noted at Yerington, Nevada, and else- ures 4 and 9. where in the Jurassic Cordilleran arc, in which heat from plutons has driven reactions between sequence of events is unlikely in a single plutonic phenocrysts (e.g., Lindley, 1985). Despite a very rocks and metasomatic fluids from various episode, we interpret the low δ18O values of sam- low-T contact-metamorphic overprint, the δ18O sources (Carten, 1986; Dilles and Einaudi, 1992; ple AH95Ð02 to reflect a pre-Cretaceous alter- and compositional effects of arrested or incom- Battles and Barton, 1995). However, unit-scale ation event. The very low-T contact-metamor- plete Jurassic K-metasomatism may be preserved K- and Na-metasomatism in the Inyo Mountains phosed metatuffs of the Inyo Mountains may in some metatuffs of the Inyo Mountains. is not obviously spatially organized with respect record an arrested alteration process. Sample to (the admittedly distant) contacts of either IM95Ð09 seems to have largely retained what are From Jurassic Shores . . . Jurassic or Cretaceous plutons. Although K- presumably its original igneous δ18O values metasomatism of metatuffs from the Inyo Moun- (Table 3). This is consistent with the local preser- The infiltration of alkali-rich fluids from vari- tains and Alabama Hills may have been driven by vation of igneous K-feldspar and plagioclase ous sources at low-T conditions has been called plutonic or volcanic heat, it need not represent the compositions and the apparent magmatic growth upon to explain widespread, pervasive Na and K lower T parts of focused hydrothermal systems zoning of CL seen in quartz phenocrysts and alteration of volcanic rocks (e.g., Chapin and related to Jurassic plutonism. crystal fragments in many of the Inyo Mountains Glazner, 1983; Liesing et al., 1995; Battles and For all of these reasons, we interpret the high rocks. In contrast, the matrix and K-feldspar phe- Barton, 1995; Barton and Johnson, 1996). Battles δ18O values observed for K-metasomatized nocrysts of sample IM95Ð07A show δ18O values and Barton (1995) attributed sodic alteration of metaÐash-flow tuffs of the Ritter Range and the that suggest alteration by meteoric water. It is in- Permian to Jurassic rocks of the Cordilleran arc low δ18O values measured in similar rocks from teresting to note that low-T K-alteration of un- to isotopically heavy, moderately to highly the Inyo Mountains to reflect different fluid metamorphosed Tertiary ash-flow tuffs is typi- saline fluids of marine, formational, and/or sources: namely, seawater and meteoric water. cally manifested first in the matrix, then in meteoric origin. Dunbar et al. (1994) interpreted We conclude that the K-metasomatic effects in plagioclase phenocrysts, and finally in sanidine pervasive, regional, low-T, K-metasomatism of Jurassic metavolcanic rocks of eastern California

Geological Society of America Bulletin, March 1998 339 SORENSEN ET AL. to in effect “track” the Jurassic shoreline in this overprints. In summary, the alkali-metasomatism APPENDIX. SAMPLING AND ANALYTICAL METHODS USED IN THIS STUDY region by preserving the δ18O values of waters that accompanied Cretaceous plutonism appears that altered the rocks. to be either restricted to rocks within at most a Sampling few hundred meters of pluton contacts, or vein . . . to Cretaceous Plutons related. It is distinguishable from the effects of Somewhat ironically, the samples discussed in this earlier alkali-metasomatism by its relatively re- paper were collected specifically to avoid alteration. Most of the Ritter Range samples were collected by Modest amounts of alkali metasomatism of the stricted scale and vein-related style. R. S. Fiske and O. T. Tobisch in 1970Ð1971, as part of metavolcanic rocks are linked to mid- and Late a U.S. Geological Survey regional mapping study Cretaceous plutonism. Such alteration is predom- CONCLUSIONS aimed at characterizing the protoliths of the lower sec- inantly sodic (Na) or sodic-calcic (NaCa). In the tion. For this reason, they avoided samples with obvious evidence of alteration, as manifested by veining and White Mountains, it is expressed by albitization 1. Trace element data suggest that mafic patchy mineralization. Samples from the White Moun- centered on the Cretaceous Pellisier Flat Granite metavolcanic rocks of the White-Inyo Moun- tains were collected by R. B. Hanson in 1983Ð1985. (Anderson, 1937; Crowder and Ross, 1972). In tains, which were erupted continentward of their His goals were to represent the range of mafic-to-felsic the Ritter Range and Alabama Hills, Na and calc-alkaline counterparts in the Ritter Range, lithologies and the stratigraphy, and to achieve geo- NaCa alteration of Cretaceous plutons and coun- had shoshonitic protoliths. graphic coverage from south to north on the range crest. He also avoided collecting rocks with obvious veining try rocks is generally manifested by sparse, 2. Much of the Jurassic metavolcanic sections or replacement features. Samples from the southern centimeter-scale alteration haloes around veins. in the Ritter Range, White-Inyo Mountains, and Inyo Mountains and Alabama Hills were collected in Such veins are widespread in the Ritter Range, but Alabama Hills are pervasively alkali metasoma- 1985Ð1987 by G. C. Dunne and J. D. Walker as part of less common in the Alabama Hills. Although tized. Rhyolitic ash-flow tuffs from these locali- a structural study of the section in conjunction with a program of U/Pb radiometric dating of zircons. They pervasive K-for-Na exchange is seen in some ties tend to be K-metasomatized. collected samples that appeared to be the least altered metaÐash-flow tuffs of the Ritter Range, it only 3. Much of the alkali-metasomatism seen in and representative of major units in these two areas, affects rocks within ~50 to 200 m of contacts with Jurassic metavolcanic rocks of eastern California from outcrops that were not immediately adjacent to in- the Kuna Crest granodiorite (Sorensen et al., is likely related to syndepositional or slightly trusive contacts. 1993). This Cretaceous metasomatism produced postdepositional fluid-rock interaction, rather δ18 Analytical Methods An>97 plagioclase, andalusite, and Or>95 micro- than to Cretaceous plutonism. The O values of cline in rocks that evidently underwent significant K-metasomatized ash-flow tuffs may reflect ma- Because this report uses data obtained in several labs growth of matrix grains and concomitant grain- rine (Ritter Range) versus nonmarine (Alabama over a 20+ year period, we include an explanation of size reduction of relict phenocrysts (Sorensen et Hills, Inyo Mountains) depositional and alter- the analytical methods. al., 1993). ation environments, and thus “track” the Jurassic Mineral Analyses. Electron probe microanalyses of feldspar from the Ritter Range and White Moun- Cathodoluminescence illuminates the replace- shoreline. tains were carried out by R. B. Hanson, and those of ment style of NaCa alteration of the 170 Ma 4. Alkali metasomatism associated with Creta- feldspar from the Inyo Mountains and Alabama Hills metaÐash-flow tuff of the Alabama Hills (Figs. 2 ceous plutonism ranges from local Na for K ex- were carried out by S. S. Sorensen. These results are and 11). Veining and attendant alteration of this change in the Alabama Hills, to albitization in the quoted in the section on contact metamorphism and unit are common only within ~20 m of the con- White Mountains, to local K for Na exchange in the discussion, but are not presented in tables or figures. Hanson used the ARL-EMX and Cameca tact with the Alabama Hills Granite. There, as the Ritter Range. All appear to be restricted in Camebax microprobes at the University of California, shown by sample AH95Ð06A, veins of dark scale compared with earlier alkali-metasomatic Los Angeles, for his analyses of minerals from the green hornblende and brown biotite are sur- effects and/or related to veining and contact- White Mountains. He recalculated analyses from the rounded by alteration haloes about two to three metamorphic recrystallization. ARL-EMX using Bence and Albee (1968) corrections, whereas data from the Cameca Camebax were reduced vein widths wide (Figs. 11, A and C). Within with ZAF corrections. Hanson and Sorensen obtained these haloes, An20Ð40 plagioclase has replaced ACKNOWLEDGMENTS mineral data for the Ritter Range, Inyo Mountains, and K-feldspar of both phenocrysts and matrix. Two Alabama Hills with the ARL-SEMQ microprobe in the blue-luminescent K-feldspar phenocryst pseudo- Field and laboratory work by Sorensen was Department of Mineral Sciences, National Museum of morphs farther from the vein show incipient re- supported by the Smithsonian Institution’s Natural History, Smithsonian Institution. The acceler- ating voltage was 15 kV, and the sample current placement along cracks by yellow-green-lumi- Sprague and Becker Funds, and Scholarly 0.025 mA; data were reduced using the corrections nescent An20Ð40 plagioclase grains that have Studies Program. Financial support for analy- method of Albee and Ray (1970). magenta-luminescent albite rims. In the black ses of samples from the Inyo Mountains and Whole-Rock, Major Element Analyses. X-ray and white SEM backscattered electron image, the Alabama Hills was provided to Dunne by a Cal- fluorescence (XRF) analyses of major elements for samples from the Ritter Range were carried out in the phases are shown as white to light gray horn- ifornia State University at Northridge (CSUN) now-defunct XRF and rapid rock analysis facilities of blende and biotite, medium gray K-feldspar, and Faculty Research Grant, and by the CSUN De- the former analytical laboratories of the U.S. Geologi- darker gray An20Ð40 plagioclase. Such plagioclase partment of Geological Sciences. Part of the cal Survey in the mid- to late 1970s. Reports made to is rare and sporadic in samples distant from the work by Barton was funded by National Science the submitters and a database search conducted in 1996 contact. For example, sample AH95Ð02, sampled Foundation grant EAR-95-27009. Work by Fiske indicate that that method was essentially that described in U.S. Geological Survey Bulletin 1144-A, supple- ~450 m from the contact (Fig. 11B), lacks biotite and Tobisch was supported by the U.S. Geologi- mented by atomic absorption analyses. XRF analyses + hornblende veins and attendant NaCa alter- cal Survey, and by the Sprague and Becker Funds of samples from the White Mountains were carried out ation, and also shows lesser amounts of matrix of the Smithsonian Institution. We thank Jason at the University of California, Los Angeles, using grain growth than does sample AH95Ð06A (Fig. Saleeby, Elizabeth Warner Holt, William Melson, “museum piece” Phillips XRF equipment in a now- defunct analytical facility. Analytical methods were 11 A and C). This comparison shows that Na and and Howard Wilshire for their comments on ear- cited in Hanson (1986). XRF analyses of samples from NaCa alteration related to Cretaceous pluton lier drafts, and Bulletin reviewers John Dilles and the southern Inyo Mountains and the Alabama Hills contacts in the Alabama Hills is fairly easily dis- Peter Schiffman and associate editor Samuel were carried out by X-Ray Assay Laboratories, 1885 tinguished from the pervasive K-alteration that it Mukasa for their helpful comments. Leslie Street, Don Mills, Ontario, Canada.

340 Geological Society of America Bulletin, March 1998 cathodoluminescence in sample AH95Ð02,cathodoluminescence in sample the same pluton contact. collected ~450 m from electron backscattered The black and white photo (C) is a scanning electron microscope further explanation. A. See text for of right area image of the central plagioclase extends ~2 mm outward from a 0.5 mm biotite- from plagioclase extends ~2 mm outward 20Ð40 Figure 11. Sodic-calcic alteration of metaÐash-flow tuff related to Cretaceous plutonism, to Cretaceous tuff related of metaÐash-flow 11. Sodic-calcic alteration Figure hornblende vein in sample AH95Ð06A, in sample vein hornblende a pluton contact. B illustrates collected ~20 m from Alabama Hills. The color images (A and B) show cathodoluminescence. In A, In cathodoluminescence. The color images (A and B) show Alabama Hills. an envelope An of yellow-luminescent

Geological Society of America Bulletin, March 1998 341 SORENSEN ET AL.

Whole-Rock, Trace Element Analyses. Instrumen- western United States (Rubey Volume VII): Englewood Weyla (Bivalvia, Lower Jurassic): Palaeogeography, tal neutron activation analyses (INAA) of samples from Cliffs, New Jersey, Prentice Hall, p. 110Ð178. Palaeoclimatology, Palaeoecology, v. 27, p. 85Ð102. the Ritter Range and White Mountains were performed Barton, M. D., Ilchik, R. P., and Marikos, M. A., 1991a, Meta- Dilles, J. H., and Einaudi, M. T., 1992, Wall-rock alteration and at the now-defunct U.S. Geological Survey radiochem- somatism, in Kerrick, D. M., ed., Contact metamorphism: hydrothermal flow paths about the Ann-Mason porphyry Reviews in Mineralogy, v. 26, p. 321Ð345. copper deposit, Nevada; a 6-km vertical reconstruction: istry laboratory at Reston, Virginia. Aliquants (200Ð500 Barton, M. D., Staude, J.-M., Snow, E. A., and Johnson, D. A., Economic Geology, v. 87, p. 1963Ð2001. mg) of powdered rock samples were irradiated in the 1991b,Aureole systematics, in Kerrick, D. M., ed., Contact Dunbar, N. W., Chapin, C. E., Ennis, D. J., and Campbell, A. R., TRIGA reactor at the U.S. Geological Survey, Denver, metamorphism: Reviews in Mineralogy, v. 26, p. 723Ð821. 1994, Trace element and mineralogical alteration associ- Colorado, at a flux of ~2 × 1012 n/cm2/s for 8 hr. For Bateman, P. C., 1983, A summary of critical relations in the ated with moderate and advanced degrees of K-meta- both sets of samples, the standard was a powdered ob- central part of the Sierra Nevada batholith: Geological So- somatism in a rift basin at Socorro, New Mexico: New sidian spiked with a variety of elements. Samples were ciety of America Memoir 159, p. 241Ð254. Mexico Geological Society, 45th Field Conference Guide- counted on Ge(Li) intrinsic Ge, and low-energy photon Bateman, P. C., 1988, Construction and genesis of the central book, p. 225Ð232. detectors between 1 and 8 weeks after irradiation. The part of the Sierra Nevada batholith, California: U.S. Geo- Dunn, S. R., and Valley, J. W., 1992, Calcite-graphite isotope logical Survey Open File Report 88Ð382, 188 p. thermometry; a test for polymetamorphism in marble, data were reduced using the SPECTRA program mod- Bateman, P. C., 1992, Plutonism in the central part of the Sierra Tudor Gabbro, Ontario, Canada: Journal of Metamorphic ified for interactive plotting of photopeaks (Grossman Nevada batholith: U.S. Geological Survey Professional Geology, v. 10, p. 487Ð501. and Baedecker, 1987), and were also corrected for Paper 1483, 186 p. Dunne, G. C., and Walker, J. D., 1993, Age of Jurassic volcan- spectral and fission-product interferences (Baedecker Bateman, P. C., and Chappell, B. W., 1979, Crystallization, ism and tectonism, southern Owens Valley area, east- and McKown, 1987). Estimated precision of most of fractionation, and solidification of the Tuolomne Intrusive central California: Geological Society of America Bul- the INAA data is better than ±10% based on counting Series, Yosemite National Park, California: Geological letin, v. 105, p. 1223Ð1230. statistics, and control samples run as unknowns agreed Society of America Bulletin, v.90, p. 465Ð492. Fates, D. G., 1985, Mesozoic (?) metavolcanic rocks northern within the analytical uncertainties. INAA analyses of Bateman, P. C., and Nokleberg, W. J., 1978, Solidification of White Mountains, California: Structural style, lithology, the Mt. Givens Granodiorite, Sierra Nevada, California: petrology, depositional setting, and paleogeographic sig- trace elements for samples from the southern Inyo Journal of Geology, v. 86, p. 563Ð579. nificance [Master’s thesis]: Los Angeles, University of Mountains and Alabama Hills were carried out at X- Battles, D. A., and Barton, M. D., 1995, Arc-related sodic hy- California, 225 p. Ray Assay Laboratories. drothermal alteration in the western United States: Geol- Fiske, R. S., and Tobisch, O. T., 1978, Paleogeographic signif- Oxygen Isotope Analyses. Quartz and alkali feld- ogy, v. 23, p. 913Ð916. icance of volcanic rocks of the Ritter Range Pendant, spar phenocrysts were removed from ash-flow tuff units Bence, A. E., and Albee, A. L., 1968, Empirical correction fac- central Sierra Nevada, California, in Howell, D. G., and of the Ritter Range, Inyo Mountains, and Alabama Hills tors for the electron probe microanalysis of silicates and McDougall, K. A., eds., Mesozoic paleogeography of the by handpicking coarse fractions of the crushed rock oxides: Journal of Geology, v. 76, p. 382Ð403. western United States: Pacific Section, Society of Eco- sample. 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The data for quartz were corrected andesitic volcaniclastic rocks of the Mineral King subma- cal Society of America Bulletin, v. 106, p. 582Ð593. by adding 0.75‰ to the analytical results, based on data rine caldera complex, Sierra Nevada, California: Journal Fox, L. K., and Miller, D. M., 1990, Jurassic granitoids and re- for a variety of in-house and published standards that of Volcanology and Geothermal Research,v. 27, p. 43Ð76. lated rocks of the southern Bristol Mountains, southern were run along with the unknowns. The analyses are re- Busby-Spera, C., 1988, Speculative tectonic model for the Providence Mountains, and Colton Hills, Mojave Desert, producible within ±0.5‰ of δ18O. lower Mesozoic arc of the southwest Cordilleran United California, in Anderson, J. L., ed., The nature and origin States: Geology, v. 16, p. 1121Ð1125. of Cordilleran magmatism: Geological Society of Amer- Cathodoluminescence Petrography. 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J., 1988, Cathodoluminescence of geological ma- of Geology, v. 79, p. 100Ð110. MANUSCRIPT ACCEPTED JULY 26, 1997

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