Data Series 439

U.S. Department of the Interior

U.S. Geological Survey

Geochemical Database for Igneous Rocks of the

Ancestral Cascades Arc—Southern Segment, 

California and Nevada
Cover photograph: Miocene volcanic rocks of the ancestral Cascades arc, southern segment,

host epithermal precious metal deposits on Bodie Bluff, east of historic Bodie, California.
Geochemical Database for Igneous Rocks 

of the Ancestral Cascades Arc—

Southern Segment, California and Nevada

By Edward A. du Bray, David A. John, Keith Putirka, and Brian L. Cousens

Data Series 439

U.S. Department of the Interior

U.S. Geological Survey
U.S. Geological Survey, Reston, Virginia: 2009

Version 1.0

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Suggested citation:

du Bray, E.A., John, D.A., Putirka, Keith, and Cousens, B.L., 2009, Geochemical database for igneous rocks of the 

ancestral Cascades arc—Southern segment, California and Nevada: U.S. Geological Survey Digital Data Series 

439, 1 CD-ROM. [Available at URL http://pubs.usgs.gov/ds/439]

ISBN 978-1-4113-2405-3

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director
Contents

Introduction ................................................................................................................................................... 1

Acknowledgments ....................................................................................................................................... 1

Igneous Rocks of the Southern Cascades Arc Segment—Constituents of the Database ............. 3

Data Compilation Methods ......................................................................................................................... 4

Data Fields ..................................................................................................................................................... 4

field_number ........................................................................................................................................ 5

lithology ................................................................................................................................................ 5

ign_form ................................................................................................................................................ 5

alteration .............................................................................................................................................. 5

longitude and latitude ........................................................................................................................ 5

SiO2, TiO2, Al2O3, FeO*, MnO, MgO, CaO, Na2O, K2O, and P2O5 ............................................... 5

LOI, H2O+, H2O-, CO2, Cl, F, and S .................................................................................................... 6

total_I ................................................................................................................................................... 6

vol_sum ................................................................................................................................................. 6

Ba, Be, Cs, Rb, Sr, Y, Zr, Hf, Nb, Th, U, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, 

Lu, Ag, Au, Co, Cr, Ni, Sc, V, Cu, Mo, Pb, Zn, Sn, W, Ta, As, Sb, and B .......................... 6

chem_src ............................................................................................................................................ 10

rad_age ............................................................................................................................................... 11

uncert ................................................................................................................................................. 11

age_src ............................................................................................................................................... 12

geol_age ............................................................................................................................................. 12

geol_age_src ..................................................................................................................................... 12

strat_name ......................................................................................................................................... 12

Isotopic Data ...................................................................................................................................... 13

δO18 ........................................................................................................................................ 13

87Sr/86SrI .................................................................................................................................. 13

206Pb/204Pb .............................................................................................................................. 13

207Pb/204Pb ...............................................................................................................................13

208Pb/204Pb .............................................................................................................................. 13

143Nd/144Nd ............................................................................................................................. 13

References Cited ........................................................................................................................................ 13

iii
iv

Figures

1. Index map showing approximate distribution of Cenozoic igneous rocks and analyzed 

samples, southern Cascades arc segment................................................................................. 2

2. Total alkali-silica variation diagram showing compositions of ancestral Cascades—southern 

arc segment rocks........................................................................................................................... 7

3. FeO/(FeO+MgO) variation diagram showing the composition of ancestral Cascades—southern arc segment rocks.................................................................................................................... 8

4. Na2O+K2O-CaO versus SiO2 variation diagram showing the composition of ancestral Cascades—southern arc segment rocks.......................................................................................... 9

5. Trace-element, tectonic-setting–discrimination variation diagram showing the composition of 

ancestral Cascades—southern arc segment rocks .............................................................. 10
Geochemical Database for Igneous Rocks of the Ancestral 

Cascades Arc—Southern Segment, California and Nevada

By Edward A. du Bray, David A. John, Keith Putirka, and Brian L. Cousens

Introduction Abundant Tertiary igneous rocks preserved in the study area 

are demonstrably products of subduction-related arc magmatism that prevailed along the west edge of the North American The importance of Cenozoic subduction and magmatism plate during the Cenozoic (Putirka and Busby, 2007; Busby associated with the Cascades magmatic arc in understanding and others, 2008a, b; and Cousens and others (2008). the geologic evolution of western North America is widely Decades of geologic investigations in the study area, recognized. Cenozoic volcanic rocks of the Cascades mag- including those by Thompson and White (1964), O’Neil and matic arc have been traditionally divided into two components: others (1973), Silberman and McKee (1973), Ashley and (1) those derived from Pliocene to Quaternary volcanoes of Silberman (1976), Whitebread (1976), Vikre (1989), and John the active High Cascades arc (McBirney, 1978; Hildreth, (2001), for example, have highlighted the association between 2007) and (2) those associated with deeply dissected Tertiary igneous rocks and mineral deposits in the southern segment (mostly Eocene to late Miocene) volcanoes of the ancestral of the ancestral Cascades arc. These associations suggest that Cascades arc. In Oregon and Washington, ancestral Cascades many deposits, representing diverse mineral deposit types, arc rocks form the well-studied (see du Bray and others, 2006) are spatially, temporally, and probably genetically related to Western Cascades (Callaghan, 1933; Thayer, 1937; Peck and ancestral Cascades magmatic arc processes. Although many others, 1964), whereas the southern extension of the ances- local studies have been conducted, including Master’s and tral Cascades arc along the California-Nevada border was Doctoral theses, volcanic rocks of the southern Cascades arc first suggested by Noble (1972) and verified by Christiansen segment have not been as thoroughly studied as have been the and Yeats (1992). Although subsequent work by Putirka and products of modern arc volcanism. Despite the abundance and Busby (2007), Busby and others (2008a, b), and Cousens and importance of igneous rocks in the study area, geochemical others (2008) has added considerably to our understanding of data available for these rocks have been neither compiled nor the ancestral arc segment between just north of Lake Tahoe synthesized. The geochemical database presented here repre- and Mono Lake, California, much of the rest of this diffuse arc sents the first phase of an effort to synthesize and interpret the remains poorly studied. geochemistry of igneous rocks that constitute the southern seg- Data presented in this report pertain to the geochemistry ment of the ancestral Cascades arc. The ultimate goal of this of igneous rocks that constitute the southern segment of the effort is an evaluation of the time-space-compositional evolu- ancestral Cascades magmatic arc and were compiled as part of tion of magmatism associated with the southern Cascades arc the Mineral Systems of the Ancestral and Modern Cenozoic segment and identification of genetic associations between Cascades Arcs and central California Coast Ranges project magmatism and mineral deposits in this region. conducted by the U.S. Geological Survey. A previously 

completed companion compilation (du Bray and others, 2006) 

pertains to igneous rocks that constitute the northern segment 

of the ancestral Cascades arc in Washington and Oregon. The Acknowledgments

geographic area addressed in this compilation extends south 

between lats 42°N. (the California-Oregon border) and 37°N. We would like to thank a number of individuals who 

throughout the northwest-elongate region that spans the Cali- helped make this effort possible. The staff of the USGS 

fornia-Nevada border (fig. 1). The area is covered by volu- Denver library, who used the interlibrary loan process to 

minous accumulations of Cenozoic volcanic rock. Although obtain many of the geologic reports on which this compilation 

Tertiary phaneritic intrusive rocks are essentially absent in is based, were critical to the success of this compilation. We 

this arc segment, shallowly emplaced dikes, sills, intrusive thank Tatanisha Pettes for her efforts; data from many sources 

lava dome complexes, and small plugs are relatively common. were available only in analog form and had to be painstakingly 
Reno

Elko

Fresno

Redding

SACRAMENTO

CARSON

 CITY

San Francisco

NEVADA

CALIFORNIA

123° 122° 121° 120° 119° 118° 117° 116°

42°

41°

40°

39°

38°

37°

0 50 100 MILES

0 50 100 200 KILOMETERS

Sample locations

EXPLANATION

High Cascades, modern arc 

Bimodal basalt-rhyolite 

Western andesite, ancestral arc 

Interior andesite-rhyolite 

Pacific

Ocean

STUDY

AREA

OREGON IDAHO

CALIFORNIA

NEVADA

Figure 1. Index map (compiled from King and Beikman, 1975, and Ludington and others, 1996) showing approximate distribution of Cenozoic igneous rocks and analyzed samples, southern Cascades arc segment.

 Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada
Igneous Rocks of the Southern Cascades Arc Segment—Constituents of the Database 

typed. Many geologic researchers tracked down missing bits 4. Calc-alkaline compositions (though some samples, 

of information that allow this database to be as complete as it especially from the Warner Range, the Pyramid 

is. These individuals include Matthew Granitto, C.D. Henry, Range, and other isolated locales, have a tholeiitic G.R. Priest, P.G. Vikre, A.B. Wallace, M.W. Ressel, M.F. Dig- affinity). gles, J.G. Smith, and R.P. Ashley. We also thank J.C. Hagan, 

M.M. Jean, Dylan Rood, and R.K. Sharma for their consider- 5. Lava flows or lahars—rock types consistent with erupable efforts in the X-ray fluorescence lab at California State tion from composite stratovolcanoes that predominate University, Fresno; they helped generate a significant part of in subduction-related magmatic arcs. Otherwise, age- the data contained in this compilation. Finally, we gratefully appropriate ash-flow tuffs exposed within the study acknowledge technical reviews by D.L. Fey and S.A. Giles area are considered far-traveled, interior andesite- that helped improve this report.

rhyolite assemblage rocks unrelated to southern Cascades arc segment magmatism. Data for the Eureka 

Igneous Rocks of the Southern Valley tuff (erupted from the Little Walker caldera) 

Cascades Arc Segment—Constituents are included in the database because Priest (1980) 

suggested an arc-related source; however, Busby and 

of the Database others (2008b) proposed an origin related to Basin and 

Range magmatism and associated structural controls.

No clear-cut definition distinguishes constituents of the 6. Miocene to Pliocene tholeiitic, high alumina (low southern segment of the ancestral Cascades magmatic arc. 

The identity of rocks that are unequivocally part of this arc, potassium) olivine basalts in the Modoc plateau of 

as opposed to those that (1) clearly pre- or post-date the arc, northern California and southern Oregon are considor (2) represent geospatially coincident rocks whose genesis ered to represent magmatism associated with backis unrelated to magmatic arc processes, is not well delineated. arc spreading or continental extension and are not Based on the work of Christiansen and Yeats (1992), Lud- included in the database (Hildreth, 2007). ington and others (1996) assigned Tertiary volcanic rocks of 

Nevada to one of three assemblages: (1) 43–19 Ma interior 7. Middle Miocene volcanic rocks temporally and 

andesite-rhyolite, (2) 20–0 Ma bimodal basalt-rhyolite, or (3) chemically equivalent to the voluminous Columbia 31–12 Ma western andesite (fig. 1). In Nevada, rocks asso- River Basalt Group, including the Steens and Lovejoy ciated with the southern Cascades arc segment are broadly Basalts, are not related to southern Cascades arc mag- equivalent to those of the western andesite assemblage. For matism and are not included in the database. the purposes of this compilation we used the following criteria 

to differentiate plausible constituents of the southern Cascades 8. Tertiary potassic and ultra-high potassium basalts, arc segment from other volcanic rocks exposed in the compila- mostly in the Sierra Nevada (Moore and Dodge, tion area:

1980), are not related to southern Cascades arc mag- 1. Tertiary igneous rocks exposed between lats 42°N. and matism and are not included in the database. 37°N. The eastern limit of the southern arc segment 

is approximately coincident with the east side of the 9. Samples of lava flows, debris flows, intrusions, and Walker Lane belt (Stewart, 1988); to the west, these some pyroclastic deposits are included in the database, rocks, especially lavas and lahars that are presumably whereas data for volcaniclastic sedimentary rocks are products of stratovolcanoes and domes aligned along 

not. the crest of the ancestral arc, extend down the gently 

sloping west flank of the Sierra Nevada. 10. Samples of rocks from volcanoes that retain primary 

2. Generally spatially coincident with the distribution constructional morphology are considered related to 

of the western andesite assemblage of Ludington and Quaternary High Cascades magmatism and are not 

others (1996) and conversely spatially distinct from included in the database.

the distributions of bimodal basalt-rhyolite and interior Considerable efforts have been made to consistently andesite-rhyolite assemblage rocks.

apply the criteria just outlined. However, because some geo- 3. Ages mostly between 25 and about 4 Ma, but may chemical data sources present incomplete sample documenta- include rocks as young as 3 Ma in the area immedi- tion, it has not been possible to prevent inclusion of potentially ately around Lake Tahoe (Cousens and others, 2008) inappropriate data. The amount of inappropriate data inadver- and as old as 30 Ma in the Warner Range of northeastern California (Duffield and McKee, 1986; Carmichael tently included in the database is probably small and should 

and others, 2006). not significantly affect data interpretation.
 Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada

Data Compilation Methods the “db no cens or alt” tab and included in the data accessed 

via the tab labeled “alt.” In addition, samples with initial 

Copies of original data source materials (subsequently analytic totals greater than 102 percent or less than 98 percent 

referred to as sources), including published reports and (in samples for which at least some volatile abundances were 

Master’s and Doctoral theses, were used to add data to the determined) or less than 96 percent (in samples for which 

database. Reference lists contained in sources of data were no volatile abundances were determined) were identified 

examined and used to identify additional data sources. In and removed from the data accessed via the “db no cens or 

this way, data for more than 2,000 samples from 82 sources alt” tab; samples with these characteristics probably indicate 

were identified and incorporated into the database. We unusable, inaccurate analyses and were also included in the 

believe that this process has probably resulted in identifica- data accessed via the tab labeled “alt.” Row entries in the data 

tion and incorporation of most of the compositional data that accessed via the “alt” tab are sorted into subsets of samples 

have been produced for magmatic-arc related igneous rocks that share the same alteration characteristic (in red, at the top in the study area. In order for a sample to be included in the of each subset of data rows). database, at least a sample number and major oxide analysis 

were required; most available trace element and (or) isotopic 

data for these samples were also included in the database. 

Samples for which only trace element or isotopic data were Data Fields

available were not included in the database. Small amounts of 

additional geochemical data can be gleaned by consulting the Data fields presented and described herein represent 

appropriate data sources. Data presented in source materials those considered most critical to addressing questions conwere included in the database, without modification (with the cerning the tectonic, petrologic, and metallogenic evolution 

exception of recalculation of major oxide data, as described of magmatism in the study area. Data for each of these fields 

in the section pertaining to major oxide data), and all input constitute a column, or set of related columns, in the database. 

subsequently verified. No effort was made to exclude hydro- Data in these columns can be sorted, queried, and interpreted thermally altered samples from the compilation. Rather, all to address questions concerning the history, development, and igneous rock compositional data were compiled and samples implications of magmatic activity in the study area. Sample known to be altered were coded accordingly. number records are aggregated in blocks of data that share a Data were compiled using Microsoft Excel and can be primary geochemical data source. accessed using software compatible with .xls files. The data- Blank cells in the database indicate that no data are base release (file, SW Casc geochem DB.xls) includes several available for the corresponding column. Some sources report worksheets that are accessed using tabs arrayed along the values of zero for some database fields. These values indicate base of the spreadsheet screen display. The tab labeled “Main 

that an abundance determination was attempted but that the SWCasc db” accesses the primary data compilation. The tab 

labeled “db no cens or alt” accesses a worksheet that contains constituent was not detected in the sample. Similarly, some 

a copy of the primary data compilation in which censored data sources present qualified data. In particular, records for some 

(data coded as less than some specified value) and samples samples include less than (<) symbols. These data indicate 

that violate the filtering criteria defined in the next paragraph that the constituent was detected but that its concentration was 

have been deleted. The tab labeled “alt” accesses a worksheet unquantifiable beyond the fact that its concentration is less 

that contains data for altered samples, as defined in the next than the indicated value. Actual analytical precision (number 

paragraph, and can be used to evaluate the geochemistry of of significant figures) associated with each database entry is 

alteration processes. The database release also includes a portrayed by each displayed onscreen value. Data in some 

tab-delimited, text file version of the database (file, cells appear to be more precise than displayed values, but SW Casc geochem DB.txt). this is a misleading artifact of computational processes (for For the purposes of this compilation, hydrothermally instance, recalculation to 100 percent volatile free), which altered samples are those samples with any of the following may have been used to create data cell contents. Precision characteristics: SiO2

 abundances greater than 78 or less than varies within individual columns in accordance with specific 47 percent; total volatile content greater than 4 percent; Al2

O3 analytical protocols and the way data are reported in individual abundances greater than 22 or less than 10 percent; total iron sources. In most cases, the number of significant figures abundances (as FeO) greater than15 percent; MnO abundances defined in data sources was retained. However, in some cases, greater than 0.6 percent; CaO abundances greater than 15 perthe level of precision implied is implausible given either the cent; Na2

O abundances greater than 7 or less than 1 percent; 

K O ab analytical protocol or the corresponding analytical state of the 2 undances greater than 7.5 or less than 0.15 percent; or 

values of Na O/K O less than 0.5. Samples with any of these art; accordingly, some numeric data contained in the database 2 2

characteristics probably do not preserve primary igneous rock have been rounded to indicate a plausible level of analytical 

compositions and were removed from the data accessed via precision.
field_number

Identifiers for analyzed sample materials were compiled 

from sources and presented without modification; except, all 

blank spaces were removed from sample identifiers.

lithology

In most cases, the composition of analyzed samples was 

compiled from information contained in the sources. All volcanic rock compositional names derived from the source were 

evaluated and updated as necessary, relative to the volcanic 

rock total alkalis versus silica nomenclature grid (LeBas and 

others, 1986). Many sources also classify the composition 

of intrusions (dikes, sills, stocks, and so forth) using volcanic 

rock nomenclature. These designations suggest that these 

shallowly solidified, and therefore, fine-grained rocks were 

not evaluated by modal analysis, and that subsequent name 

assignment using the nomenclature of Streckeisen (1973) for 

intrusive igneous rocks was not possible. In accordance with 

procedures defined by the International Union of Geological 

Sciences, composition names for intrusive rocks are defined 

using the relative modal proportions of quartz, alkali feldspar, 

and plagioclase relative to the classification scheme of Streckeisen (1973).

ign_form

The form of the igneous rock represented by each sample 

is given where known. In some cases, source materials do 

not specify whether the sample represents lava, a pyroclastic 

deposit, or some form of intrusion; in these situations, lava 

is presumed. Samples coded as representing dikes or sills 

represent thin tabular bodies that are discordant and concordant with enclosing rocks, respectively. Larger intrusive 

bodies, generally discordant to enclosing rocks, are coded as 

plutons, stocks, and plugs depending on their size; plutons are 

the largest of these bodies, whereas plugs are the smallest. In 

most cases, samples from intrusions coded as plutons represent bodies that cooled slowly, at the greatest depths, and are 

phaneritic, whereas samples from intrusions coded as plugs 

represent the subvolcanic environment, many have a quenched 

groundmass, and some may represent parts of endogenous to 

exogenous volcanic flow domes.

alteration

Many sources explicitly indicate that some analyzed 

samples are altered. Other sources provide sufficient descriptive information about samples that alteration can be inferred. 

Some sources simply indicate that samples are altered; these 

samples are simply coded as “Yes” in the “alteration” column. Other alteration terms used to code altered samples are 

advanced argillic, argillic, deuteric, hydrated glass, opalized, 

oxidation, potassic, propylitic, sericitic, and silicification. 

Each of these terms is applied in accordance with their standard usage, defined for instance by Guilbert and Park (1986). 

These terms are appended with a “?” when the proper alteration nomenclature is ambiguous due to the nature of available 

descriptive information.

longitude and latitude

An effort was made to obtain location data for all samples 

with composition data. Most sources contain some form of 

location information. Missing sample location data were 

requested from authors, most of whom were able to provide 

missing information. Accordingly, location data are available 

for all but a very few samples. Latitude and longitude data are 

reported as decimal degrees (relative to the North American 

Datum of 1927). In the study area, longitude is reported as a 

negative value (western hemisphere) and latitude as a positive 

value (northern hemisphere).

Location data are of variable quality as a consequence of 

the manner in which they were initially acquired and subsequently reported. The number of significant figures presented 

as part of location data in the “longitude” and “latitude” 

columns indicates relative levels of sample location precision, 

as follows:

• four significant figures indicate that the given location 

is accurate within tens of meters,

• three significant figures indicate that the given location 

is accurate within hundreds of meters,

• two significant figures indicate that the given location 

is accurate within thousands of meters, and

• one significant figure indicates that the given location 

is accurate within tens of thousands of meters.

Some sources report sample location in terms of Township, Range, and Section values, usually to the closest quarter 

of a section. Township-Range-Section data were digitized to 

obtain decimal degree location; within the appropriate quarter 

section quadrilaterals, digitized points were usually selected 

to coincide with a road, trail, stream bottom, quarry, or natural 

cliff, any of which might represent a likely sampling location. 

Some sources do not include numerical sample location data 

but do contain sample maps. Location data for these samples 

were obtained by digitizing sample sites. A very few sources 

merely describe sample locations; these were used to estimate 

a sample location, which was then digitized.

SiO2, TiO2, Al2O3, FeO*, MnO, MgO, CaO, Na2O, 

K2O, and P2O5

Sources report whole rock, major oxide data in a variety 

of formats. In addition, these data were produced by a wide 

array of analytical procedures, each with its own associated 

Data Fields   
 Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada

analytical precision and accuracy. Compositions for some Several sources present data for H2

O and do not specify 

of the samples included in the database are presented in their whether this species is bound water (+) or nonessential moissources already recalculated to 100 percent, volatile free. ture (-). These data have been included in the H2

O+ column of 

Some information loss occurs when data are reported solely the database. Cell entries of “bdl” indicate that the abundance 

in this fashion. Compiling analytical methods and associ- of the indicated constituent is below detection limit.

ated estimates of precision and accuracy associated with the 

reported data was beyond the scope of this effort. Analytical total_I protocols, precision, and accuracy were highly variable among 

sources. Fortunately, most sources document these parameters One measure of major oxide analytical accuracy is how so that associated questions can be resolved by reference to the nearly the sum of the determined constituents approaches 100 appropriate data source. The database includes columns for percent. Consequently, the database includes a column that the abundances of SiO2

, TiO2, Al2O3, FeO, MnO, MgO, CaO, reports initial oxide sum analytical totals as reported by the Na2

O, K2O, and P2O5. However, because diverse analyti- source. Some sources do not include totals; totals for these 

cal protocols were used to analyze samples, not all sources samples were computed and added to the database. Initial contain data for each of these constituents. Cell entries of analytical totals reported in the sources were spot checked for “bdl” indicate that the abundance of the indicated constituent accuracy; discrepancies were noted and corrected in a num- is below detection limit. ber of cases. Many sources present abundances for the major Several different schemes are possible for reporting iron oxides but include no abundance data for volatile constitucontents. In addition, reported abundances of ferrous versus ents. Initial analytical totals for these samples tend to be from 

ferric iron in many of these rocks are unlikely to represent several to 5 or 6 percent less than 100 percent. It is imposmagmatic values, because of oxidation during late- to post- sible to determine whether these low initial totals result from 

magmatic hydrothermal processes. Consequently, total inaccurate analyses and (or) unreported volatile constituent 

iron abundances were recalculated as ferrous iron oxide and abundances.

denoted as FeO*. Interaction with postmagmatic fluids caused 

compositions of many rocks of the study area to change in 

other ways as well. In particular, many of these rocks were vol_sum

hydrothermally altered (as indicated by secondary clay miner- The total volatile content of igneous rocks in the study als, sericite, and (or) chlorite). Both processes caused volatile area can provide some insight concerning whether abundances contents of the affected samples to increase, and correspond- of other constituents accurately represent primary magmatic ingly caused relative abundances of all other constituents to values. Samples with elevated volatile contents, for example decrease. Therefore, to facilitate meaningful oxide abundance greater than 3 weight percent, are likely to have experienced comparisons among samples, all analyses were recalculated some fluid-mediated, postmagmatic chemical modification. to 100 percent on a volatile-free basis. The resulting data are Given the wide range of analytical protocols used in analysis reported in columns identified by SiO2

, TiO2, Al2O3, FeO*, of these samples, the best possible measure of sample vola- MnO, MgO, CaO, Na2

O, K2O, and P2O5. All these data are tile content is total volatile content. For the purposes of the reported as weight percent. To facilitate comparison of ances- compilation, if LOI data are the only information contained tral Cascades—southern arc segment major oxide data to those in source data compilations concerning volatile content, LOI for other magmatic arc rocks, the compiled data are presented values were designated as total volatile content. Alternatively, on several standard variation diagrams (figs. 2, 3, 4 ). if the source includes data for H2

O+, H2O-, CO2, Cl, F, or S, 

these data were summed to yield total volatile content. All 

LOI, HO+, HO-, CO, Cl, F, and S data are presented as weight percent.

The data sources report volatile constituent contents of Ba, Be, Cs, Rb, Sr, Y, Zr, Hf, Nb, Th, U, Ga, La, Ce, igneous rock samples in widely disparate ways. In order to 

capture important information concerning the volatile contents Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ag, 

of these rocks, an array of data columns was designated to Au, Co, Cr, Ni, Sc, V, Cu, Mo, Pb, Zn, Sn, W, Ta, 

account for various analytical protocols and data reporting for- As, Sb, and B

mats. Volatile constituents whose abundances are commonly 

determined include LOI (loss on ignition), H2

O+ (structurally The sources present data for inconsistent sets of trace 

bound), H2

O- (nonessential moisture), CO2, Cl, F, and S. Of elements. Of these, data for Ba, Be, Cs, Rb, Sr, Y, Zr, Hf, Nb, 

these, few sources contain halogen and S abundance data. Th, U, Ga, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, 

Similarly, data for H2

O+, H2O-, and CO2 are rarely and non- Yb, Lu, Ag, Au, Co, Cr, Ni, Sc, V, Cu, Mo, Pb, Zn, Sn, W, Ta, 

systematically reported. However, given the potential impor- As, Sb, and B were compiled; all data are in parts per million. 

tance of these constituents in hydrothermal processes, compil- These constituents are among those for which sources most 

ing all available data for these components seems warranted. often contain data and also are considered sufficient to address 
0

2468

10121416

35 40 45 50 55 60 65 70 

Basalt Basaltic

andesite

Dacite

Latite/

hawaiite

Andesite

Trachyte/trachydacite

benm oreite

Shoshonite/

m ugearite

Potassic trachybasalt/

SiO2 , IN W EIGHT PERCENT

Na O+K O, IN WEIGHT PERCENT 2 2

Figure 2. Total alkali-silica variation diagram showing compositions of ancestral Cascades—southern arc segment rocks. Field boundaries from Le B
0.3

0.40.50.60.70.80.91.0

50 55 60 65 70 75 

Ferroan

Calc-alk

M agnesian

Tholeiitic

SiO , 2 IN WEIGHT PERCENT

FeO*/(FeO*+MgO)

Figure 3. FeO/(FeO+MgO) variation diagram showing the composition of ancestral Cascades—southern arc segment rocks relative to boundaries betnesian rocks as well as between tholeiitic and calc-alkaline rocks. Ferroan versus magnesian boundary (black line) from Frost and others (2001), tholboundary (red line) from Miyashiro (1974).
-8

-6-4-2

02468

1012

50 55 60 65 70 75 

Alkalic

Calcic

Calc-alkalic

Alkali-calcic

NaO+KO-CaO,INWEIGHTPERCENT

2

2

SiO2 , IN WEIGHT PERCENT

Figure 4. Na2O+K2O-CaO versus SiO2 variation diagram showing the composition of ancestral Cascades—southern arc segment rocks relative to boualkali-calcic, calc-alkalic, and calcic rock series. Boundaries between various rock series from Frost and others (2001).
1

10

100

1,000

1 10 100 1,000

Syn-collisional W ithin plate

O cean ridge Volcanic arc 

Y + Nb, IN PARTS PER M ILLION

Rb, IN PARTS PER M ILLION

10 Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada

many petrologic, tectonic, and metallogenic questions. Cell following list. Sources of geochemical information include 

entries of “bdl” indicate that the abundance of the indicated publications of the U.S. Geological Survey, unpublished data 

constituent is below detection limit. To facilitate comparison contained in the U.S. Geological Survey National Geochemiof ancestral Cascades—southern arc segment trace element cal Database, Master’s theses, Doctoral dissertations, articles 

data and their tectonic implications to those for other mag- published in journals, and publications of the Nevada Bureau 

matic arc rocks, the compiled data are plotted on a Rb versus of Mines and Geology.

Y + Nb variation diagram (fig. 5). Entries in the “chem_src” column of the database are 

keyed numerically to sources identified below:

chem_src 1. King (2006)

 2. Noble and others (1976)

Chemical and location data for each sample included 3. Ransome (1898)

in the database were compiled from primary data sources, 4. Priest (1980)

in most cases a single source. For a few samples, data were 5. Brem (1977)

culled from two or more sources; for example, major oxide 6. John (2001)

data may have been compiled from one source and trace ele- 7. Crowder and others (1972)

ment data from another. Entries in the “chem_src” column of 8. Ross (1961)

the database are keyed numerically to sources identified in the 9. O’Neil and others (1973)

Figure 5. Trace-element, tectonic-setting–discrimination variation diagram showing the composition of ancestral Cascades—southern 

arc segment rocks. Tectonic setting-composition boundaries from Pearce and others (1984).
10. Knopf (1918)

11. Halsey (1953)

12. Spurr (1901)

13. Curtis (1951)

14. Bonham and Garside (1979)

15. Putirka, Keith, University of California, Fresno, unpublished data, 2007

16. Cornwall (1972)

17. Thompson and White (1964)

18. Ransome (1909)

19. Busby and others (2008a)

20. Busby and others (2008b)

21. Cousens, B.L., Carleton University, unpublished data 

(#1), 2007

22. Whitebread (1976)

23. Schwartz (2001)

24. Garrison (2004)

25. John (1992)

26. Latham (1985)

28. Al-Rawi (1969)

29. Chesterman and others (1986)

30. Osborne (1985)

31. Carmichael and others (2006)

32. Garside and Bonham (2006)

33. Henry and others (2004)

34. Garside and others (2003)

35. Egger, A.E., Stanford University, unpublished data 2008

36. Garside and Nials (1998)

37. John, D.A., U.S. Geological Survey, unpublished data 

(#1) 2007

38. Bingler (1978)

39. Schoen and White (1967)

40. Castor and Henry (2000)

41. Vikre (1989)

42. Ekren and others (1971)

43. Robinson (1972)

44. Silberman and Chesterman (1995)

45. Keith (1977)

46. Wallace (1975)

47. Pullman (1983)

48. Luethe (1974)

49. John, D.A., U.S. Geological Survey, unpublished data 

(#2), 2007

50. Mallin (1989)

51. Hudson (1977)

52. Garside (1979)

53. Bosma-Douglas (1987)

54. du Bray, E.A., U.S. Geological Survey, unpublished data, 

2008

55. Ressel (1996)

56. Kistler (1974)

57. Bartow (1980)

58. Dodge and Calk (1986)

59. Tooker and others (1970)

60. Wilshire (1957)

61. John, D.A., U.S. Geological Survey, unpublished data 

(#3), 2008

62. Grose and McKee (1986)

63. Putirka and Busby (2007)

64. Grose and others (1992)

65. Youngkin (1980)

66. Bean (1980)

67. Tuppan (1981)

68. Grose and others (1990)

69. Diggles, M.F., U.S. Geological Survey, unpublished data, 

2008

70. Finn (1987)

71. Jean (2007)

72. Vikre, P.G., U.S. Geological Survey, unpublished data, 

2008

73. U.S. Geological Survey, National Geochemical Database, 

2008

74. Ormerod (1988)

75. John, D.A., and Colgan, J.P., U.S. Geological Survey, 

unpublished data (#1), 2008

76. John, D.A., U.S. Geological Survey, unpublished data 

(#4), 2008

77. Hudson and others (2009)

78. Sharma (2008)

79. John, D.A., and Colgan, J.P., U.S. Geological Survey, 

unpublished data (#2), 2008

80. John, D.A., U.S. Geological Survey, unpublished data 

(#5), 2008

81. du Bray, E.A., and John, D.A., U.S. Geological Survey, 

unpublished data, 2008

82. Cousens, B.L., Carleton University, unpublished data 

(#2), 2009

rad_age

The ages of the igneous rocks in the study area have been 

of considerable interest and many age determinations have 

been made. The database column titled “rad_age” contains 

radiometric ages, in millions of years, for samples of Tertiary 

igneous rocks in the study area. Multiple geochronologic age 

determinations have been obtained for some samples. Ages 

recorded in the “rad_age” column are the best possible estimates based on information contained in the age sources.

uncert

The database column titled “uncert” contains data, in 

millions of years, for the analytical uncertainties (as presented 

in the source) associated with each of the age determinations 

reported in the “rad_age” column.

Data Fields 11
age_src

Sloan and others (2003) have recalculated ages using 

currently accepted decay constants, as appropriate, and compiled most of the isotopic age data available for rocks in the 

southern Cascades arc segment. This compilation was used 

to identify the primary data sources (identified in the database 

column titled “age_src”) from which geochronologic data for 

the study area’s igneous rocks were extracted to compile ages 

of samples included in the database. In many cases, geochemical and geochronologic data are contained in the same source; 

the age source for each of these samples is numerically keyed 

to a previously identified source of geochemical data (database column “chem_src”). For the relatively small number of 

samples for which geochemical and geochronologic data have 

different sources, age source(s) data are keyed to alpha-coded 

citations listed below:

A. Noble and others (1974)

B. Silberman and Chesterman (1972)

C. Silberman, Bonham, and others (1979)

D. Silberman and McKee (1972)

E. Castor and others (2005)

F. Silberman, White, and others (1979)

G. Saucedo and Wagner (1992)

H. Wise, W.S., University of California, Santa Barbara, 

unpublished data, 2007

I. Henry, C.D., Nevada Bureau of Mines and Geology, 

unpublished data, 2007

J. McKee and John (1987)

K. John and others (1989)

L. Faulds and others (2000)

M. Chesterman and Gray (1975)

N. Smailbegovic (2002)

O. Smith, J.G., U.S. Geological Survey, unpublished data, 

2008

P. Fleck, R.J., U.S. Geological Survey, unpublished data, 

2008

Q. Kleinhampl and others (1975)

R. Garside and Silberman (1978)

S. Diggles and others (1989)

T. Pullman (1984)

U. Robinson and others (1968)

V. Crafford (2007)

W. Krauskopf and Bateman (1977)

X. Ashley and Silberman (1976)

Y. Gilbert and Reynolds (1973)

Z. Larsen (1979)

AA. Marvin and Cole (1978)

AB. Chesterman (1968)

AC. Dalrymple (1963)

AD. Huber and Rinehart (1967)

AE. Dalrymple (1964)

AF. Marvin and others (1977)

AG. Gilbert and others (1968)

AH. Morton and others (1977)

AI. Reheis and Block (2007)

geol_age

Radiometric ages have not been determined for most 

samples included in the database. However, identified age 

determinations and geologic and geochronologic reasoning 

were used to develop preferred geologic age estimates for 

many of the Tertiary igneous rock units in the study area. 

Geologic ages where given in years are rounded to the nearest 

million. No systematic effort was made to establish geologic 

ages for samples of dikes, sills, and other volumetrically insignificant intrusions. No entry is recorded in the “geol_age” 

column when the associated sample has been radiometrically 

dated.

geol_age_src

Estimates of geologic age for many of southern Cascades 

arc segment rocks rely upon geologic inference, correlations, 

and other diverse data sources; these sources are identified in 

the “geol_age_src” column of the database. Digits to the left 

of the “\” symbol identify the principal source used to establish geologic age. These digits are keyed to entries previously 

identified in either the “chem_src” or “age_src” discussions. 

Digits to the right of the “\” symbol identify the rationale used 

to establish geologic age. Entries coded as “\1” indicate that 

a correlation of map units figure or some discussion of age in 

the source provide the basis for the geologic age assignment. 

In contrast, entries coded as “\2” indicate that the radiometric 

age of sample(s) that are not part of the database, but representative of the same intrusion as sample(s) that are included in 

the database, was used to establish geologic age.

strat_name

Some sources associate either formal or informal 

stratigraphic nomenclature with samples for which they 

include geochemical data. These names were compiled in 

the database field titled “strat_name” in order to facilitate 

sorting of database contents by stratigraphic unit. Entries 

in this field are shortened from full stratigraphic designation (for instance, Eureka Valley Tuff) to entries that denote 

just the geographic feature included in the full stratigraphic 

designation (for instance, Eureka Valley). Coding samples by 

assigned stratigraphic name allows grouping of samples from 

a particular stratigraphic unit. Grouped in this way, geochemical characteristics of units can be identified and interpreted 

and comparisons to similar stratigraphic units can be made. 

Among the regionally most important stratigraphic designations of this sort are Kate Peak, Alta, Eureka Valley, Relief 

Peak, Table Mountain, Disaster Peak, Mehrten, Carson Pass, 

Stanislaus, Milltown, Lousetown, Coal Valley, Boca Ridge, 

Aurora, Warner Range, Pyramid, Potato Peak, Willow Springs, 

and Mt. Biedeman. Unfortunately, many data sources do not 

assign specific formal or informal stratigraphic names; these 

12  Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada
sources assign samples names that are entirely lithologic, such 

as basalt, basaltic andesite, or andesite.

Hudson and others (2009) have refined stratigraphic 

nomenclature for Tertiary volcanic rocks in the Virginia 

City, Nev., area. Stratigraphic designations compiled in 

the “strat_name” column for samples collected during their 

geologic mapping in the Virginia City area are in accord with 

their new nomenclature for the sampled units. Their stratigraphic refinements also affect names assigned to previously 

collected and analyzed samples from this area. Entries in the 

“strat_name” column of the form Kate Peak (Flowery Peak) 

give the stratigraphic name of the sampled unit, as assigned by 

the individual who collected the sample, followed (in parentheses) by the new stratigraphic name, as defined by Hudson 

and others (2009), for the sampled unit.

Isotopic Data

Stable and (or) radiogenic isotope data are available for 

a relatively small fraction of southern Cascades arc segment 

geochemical database samples. Data of this sort provide 

additional geologic framework information that can help constrain magma sources and the processes that contributed to the 

petrogenesis of these rocks. Compiled isotopic data pertain 

to ratios of various isotopes of oxygen, strontium, lead, and 

neodymium, as described next.

δO18

Stable isotope ratio of 18O to 16O relative to the same ratio 

in a standard (usually SMOW, standard mean ocean water).

87Sr/86SrI

Initial isotope ratio of 87Sr (generated by radioactive 

decay of 87Rb) to 86Sr; except data from Ormerod (1988) 

(source=74), which are measured 87Sr/86Sr ratios. Initial ratios 

are calculated from measured 87Sr/86Sr ratios and determined 

sample ages.

206Pb/204Pb

Isotope ratio of 206Pb (generated by radioactive decay of 238U) to 204Pb.

207Pb/204Pb

Isotope ratio of 207Pb (generated by radioactive decay of 235U) to 204Pb.

208Pb/204Pb

Isotope ratio of 208Pb (generated by radioactive decay of 232Th) to 204Pb.

143Nd/144Nd

Isotope ratio of 143Nd (generated by radioactive decay of 

147Sm) to 144Nd.

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18  Geochemical Database for Igneous Rocks of the Ancestral Cascades Arc—Southern Segment, California and Nevada

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