UC Berkeley Archaeological X-ray Fluorescence Reports

Title X-Ray Fluorescence (XRF) Analysis Major Oxide and Trace Element Concentrations of Mainly Volcanic Rock Artifacts from a Number of Sites in Central Arizona

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Author Shackley, M. Steven

Publication Date 2013-07-10

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GEOARCHAEOLOGICAL X-RAY FLUORESCENCE SPECTROMETRY LABORATORY 8100 WYOMING BLVD., SUITE M4-158 ALBUQUERQUE, NM 87113 USA

X-RAY FLUORESCENCE (XRF) ANALYSIS MAJOR OXIDE AND TRACE ELEMENT CONCENTRATIONS OF MAINLY VOLCANIC ROCK ARTIFACTS FROM A NUMBER OF SITES IN CENTRAL ARIZONA

Probable Cienega Large and San Pedro points from the collection

by

M. Steven Shackley Ph.D., Director Geoarchaeological XRF Laboratory Albuquerque, New Mexico

Report Prepared for

Dr. Anna Neuzil EcoPlan Associates, Inc. Tucson, Arizona

10 July 2013 www.escholarship.org/uc/item/7pt4r7vt

INTRODUCTION

The analysis here of artifacts mainly produced from high silica rhyolite is an attempt to provide a beginning data base for further artifact provenance studies in central Arizona. An intensive oxide and trace element analysis of the artifacts indicates a strong preference for high silica volcanics for the production of stone tools including dart points such as the ones figured on the cover page. None of the artifacts can be assigned to source at this time. The assemblage appears to be a Late Archaic/Cienega Phase assemblage rather typical of the region (Sliva 2...).

Many of the rhyolite and silicified rhyolite samples are finished tools and some biface thinning flakes indicating a large range of tool types. These high silica volcanic rocks resemble the

Picacho Mountains "felsite" described in the Picacho Reservoir Archaic Project report (Bayham et al. 1986; Most 1986; Shackley 1986). Only a direct comparison of the geochemistry between source standards from the Picacho Mountains and these artifacts will verify this assumption.

LABORATORY SAMPLING, ANALYSIS AND INSTRUMENTATION

All archaeological samples are analyzed whole. The results presented here are

quantitative in that they are derived from "filtered" intensity values ratioed to the appropriate x-

ray continuum regions through a least squares fitting formula rather than plotting the proportions

of the net intensities in a ternary system (McCarthy and Schamber 1981; Schamber 1977). Or

more essentially, these data through the analysis of international rock standards, allow for inter-

instrument comparison with a predictable degree of certainty (Hampel 1984; Shackley 2011a).

Trace Element Analyses

Trace element analyses were conducted to provide data for future comparisons with

sources that may be discovered. All analyses for this study were conducted on a

ThermoScientific Quant’X EDXRF spectrometer, located in the Geoarchaeological XRF

Laboratory, Albuquerque, New Mexico. It is equipped with a thermoelectrically Peltier cooled

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solid-state Si(Li) X-ray detector, with a 50 kV, 50 W, ultra-high-flux end window

bremsstrahlung, Rh target X-ray tube and a 76 µm (3 mil) beryllium (Be) window (air cooled),

that runs on a power supply operating 4-50 kV/0.02-1.0 mA at 0.02 increments. The

spectrometer is equipped with a 200 l min−1 Edwards vacuum pump, allowing for the analysis of

lower-atomic-weight elements between sodium (Na) and titanium (Ti). Data acquisition is

accomplished with a pulse processor and an analogue-to-digital converter. Elemental

composition is identified with digital filter background removal, least squares empirical peak deconvolution, gross peak intensities and net peak intensities above background.

The analysis for mid Zb condition elements Ti-Nb, Pb, Th, the x-ray tube is operated at

30 kV, using a 0.05 mm (medium) Pd primary beam filter in an air path at 200 seconds livetime to generate x-ray intensity Ka-line data for elements titanium (Ti), manganese (Mn), iron (as

T Fe2O3 ), cobalt (Co), nickel (Ni), copper, (Cu), zinc, (Zn), gallium (Ga), rubidium (Rb),

strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), lead (Pb), and thorium (Th). Not all

these elements are reported since their values in many volcanic rocks are very low. Trace

element intensities were converted to concentration estimates by employing a least-squares

calibration line ratioed to the Compton scatter established for each element from the analysis of

international rock standards certified by the National Institute of Standards and Technology

(NIST), the US. Geological Survey (USGS), Canadian Centre for Mineral and Energy

Technology, and the Centre de Recherches Pétrographiques et Géochimiques in France

(Govindaraju 1994). Line fitting is linear (XML) for all elements but Fe where a derivative fitting is used to improve the fit for iron and thus for all the other elements. When barium (Ba) is analyzed in the High Zb condition, the Rh tube is operated at 50 kV and up to 1.0 mA, ratioed to the bremsstrahlung region (see Davis 2011; Shackley 2011a). Further details concerning the petrological choice of these elements in Southwest obsidians is available in Shackley (1988,

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1995, 2005; also Mahood and Stimac 1991; and Hughes and Smith 1993). Nineteen specific pressed powder standards are used for the best fit regression calibration for elements Ti-Nb, Pb,

Th, and Ba, include G-2 (basalt), AGV-2 (andesite), GSP-2 (granodiorite), SY-2 (syenite),

BHVO-2 (hawaiite), STM-1 (syenite), QLO-1 (quartz latite), RGM-1 (obsidian), W-2 (diabase),

BIR-1 (basalt), SDC-1 (mica schist), TLM-1 (tonalite), SCO-1 (shale), NOD-A-1 and NOD-P-1

(manganese) all US Geological Survey standards, NIST-278 (obsidian), U.S. National Institute of Standards and Technology, BE-N (basalt) from the Centre de Recherches Pétrographiques et

Géochimiques in France, and JR-1 and JR-2 (obsidian) from the Geological Survey of Japan

(Govindaraju 1994).

Major and Minor Oxide Analysis

Analysis of the major oxides of Na, Mg, Al, Si, P, K, Ca, Ti, Mn, and Fe is performed under the multiple conditions elucidated below. The composition of alkalis Na2O and K2O, and silica

(SiO2) in these rocks allows for elemental determination of rock type (LeBas et al. 1986; Table 1 and Figure 1 here).

The fundamental parameter analysis (theoretical with standards), while not as accurate as destructive analyses (pressed powder and fusion disks) is usually within a few percent of actual, based on the analysis of USGS RGM-1 obsidian standard (see also Shackley 2011a). The fundamental parameters (theoretical) method is run under conditions commensurate with the elements of interest and calibrated with four USGS standards (RGM-1, rhyolite; AGV-2, andesite; BHVO-1, hawaiite; BIR-1, basalt), and one Japanese Geological Survey rhyolite standard (JR-1).

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Conditions of Fundamental Parameter Analysis1

Low Za (Na, Mg, Al, Si, P) Voltage 6 kV Current Auto2 Livetime 100 seconds Counts Limit 0 Filter No Filter Atmosphere Vacuum Maximum Energy 10 keV Count Rate Low Mid Zb (K, Ca, Ti, V, Cr, Mn, Fe) Voltage 32 kV Current Auto Livetime 100 seconds Counts Limit 0 Filter Pd (0.06 mm) Atmosphere Vacuum Maximum Energy 40 keV Count Rate Medium High Zb (Sn, Sb, Ba, Ag, Cd) Voltage 50 kV Current Auto Livetime 100 seconds Counts Limit 0 Filter Cu (0.559 mm) Atmosphere Vacuum Maximum Energy 40 keV Count Rate High Low Zb (S, Cl, K, Ca) Voltage 8 kV Current Auto Livetime 100 seconds Counts Limit 0 Filter Cellulose (0.06 mm) Atmosphere Vacuum Maximum Energy 10 keV Count Rate Low 1 Multiple conditions designed to ameliorate peak overlap identified with digital filter background removal, least squares empirical peak deconvolution, gross peak intensities and net peak intensities above background. 2 Current is set automatically based on the mass absorption coefficient.

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The data from the WinTrace software were translated directly into Excel for Windows and

SPSS software for statistical manipulation and the oxides plotted against the TAS plot to determine rock type. In order to evaluate these quantitative determinations, machine data were compared to measurements of known standards during each run. RGM-1 a USGS rhyolite standard is analyzed during each sample run for obsidian artifacts to check machine calibration

(Table 1).

Analytic Trajectory

In an effort to understand the rock types in the assemblage the following trajectory was followed. After acquiring the trace elements and oxides, the alkali/silica data were "plotted" on the TAS plot. The rock type determination was then added in the rock type column in the spreadsheet and the spreadsheet loaded into SPSS for statistical analysis. First a Ward's method

Euclidean hierarchical cluster analysis was calculated to generate groups using the two alkalis and silicon dioxide as variables, the same used to plot in the TAS system (Figure 2). Then these seven clusters were used as priors in a Mahalanobis discriminant analysis using the same elements as variables (Table 2 and Figure 3). The cross-validated classification results are over

95% correct classification indicating high classification success with these variables.

DISCUSSION

More than 61% of the raw materials at these sites is rhyolite or a highly silicified rhyolite

(>77% SiO2; see Table 2 and Figures 1 and 2). A few of these artifacts are actually relatively

low silica ultrabasic rocks such as foidite, phonolite, or phonotephrite. These rocks are generally

difficult to knap, but were likely expedient sources in the absence of better toolstone.

Interestingly, very few basalt rocks were used as raw materials in these sites, although there were

quite a few relatively high silica intermediate rocks used to produce tools (dacite, andesite,

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trachyandesite, trachydacite; Table 3 and Figure 4). The knapping difference between dacite and

trachydacite is very small. The dominance of silicic volcanic rocks here is likely due to the

prevalence of rhyolites and high silica rhyolites in the mountains to the east of these sites, and

the general lack of basic volcanic rocks such as basalt. As geochemical investigations into

volcanic raw materials increase, it is becoming increasingly evident that raw materials that were

called "basalt" in the past are actually dacite and related relatively high silica volcanic rocks

(Shackley 2011b). Major sources of dacite used from Paleoindian through late periods are at the

base of the Mogollon Rim in northern Arizona, and sources in northern New Mexico (Shackley

2011b). This assemblage appears to verify this procurement pattern.

The next step would be to obtain samples of the Picacho Mountain "felsite" which is likely the source of much of the rhyolite and perhaps silicified rhyolite in this assemblage.

These "quarries" at Picacho are quite extensive, but the analytic technology in the early 1980s was not such that an elemental and oxide analysis was feasible. This project provides the data to move a larger raw material study forward.

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REFERENCES CITED

Davis, K.D., T.L. Jackson, M.S. Shackley, T. Teague, and J.H. Hampel 2011 Factors Affecting the Energy-Dispersive X-Ray Fluorescence (EDXRF) Analysis of Archaeological Obsidian. In X-Ray Fluorescence Spectrometry (XRF) in Geoarchaeology, edited by M.S. Shackley, pp. 45-64. Springer, New York.

Govindaraju, K. 1994 1994 Compilation of Working Values and Sample Description for 383 Geostandards. Geostandards Newsletter 18 (special issue).

Hampel, Joachim H. 1984 Technical Considerations in X-ray Fluorescence Analysis of Obsidian. In Obsidian Studies in the Great Basin, edited by R.E. Hughes, pp. 21-25. Contributions of the University of California Archaeological Research Facility 45. Berkeley.

Hildreth, W. 1981 Gradients in Silicic Magma Chambers: Implications for Lithospheric Magmatism. Journal of Geophysical Research 86:10153-10192.

Hughes, Richard E., and Robert L. Smith 1993 Archaeology, Geology, and Geochemistry in Obsidian Provenance Studies. In Scale on Archaeological and Geoscientific Perspectives, edited by J.K. Stein and A.R. Linse, pp. 79-91. Geological Society of America Special Paper 283.

Lebas, M.J., Lemaitre, R.W., Streckeisen, A. and Zanettin, B. 1986 A Chemical Classification of Volcanic-Rocks Based on the Total Alkali Silica Diagram. Journal of Petrology 27(3): 745-750.

Mahood, Gail A., and James A. Stimac 1990 Trace-Element Partitioning in Pantellerites and Trachytes. Geochemica et Cosmochimica Acta 54:2257-2276.

McCarthy, J.J., and F.H. Schamber 1981 Least-Squares Fit with Digital Filter: A Status Report. In Energy Dispersive X-ray Spectrometry, edited by K.F.J. Heinrich, D.E. Newbury, R.L. Myklebust, and C.E. Fiori, pp. 273-296. National Bureau of Standards Special Publication 604, Washington, D.C.

Schamber, F.H. 1977 A Modification of the Linear Least-Squares Fitting Method which Provides Continuum Suppression. In X-ray Fluorescence Analysis of Environmental Samples, edited by T.G. Dzubay, pp. 241-257. Ann Arbor Science Publishers.

Shackley, M. Steven 1988 Sources of Archaeological Obsidian in the Southwest: An Archaeological, Petrological, and Geochemical Study. American Antiquity 53(4):752-772.

1995 Sources of Archaeological Obsidian in the Greater American Southwest: An Update and Quantitative Analysis. American Antiquity 60(3):531-551.

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2005 Obsidian: Geology and Archaeology in the North American Southwest. University of Arizona Press, Tucson.

2011a An Introduction to X-Ray Fluorescence (XRF) Analysis in Archaeology. In X-Ray Fluorescence Spectrometry (XRF) in Geoarchaeology, edited by M.S. Shackley, pp. 7- 44. Springer, New York.

2011b Sources of Archaeological Dacite in Northern New Mexico. Journal of Archaeological Science 38:1001-1007.

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Table 1. Elemental concentrations for the artifacts and USGS RGM-1 by site. Measurements in parts per million (ppm) or percent by weight as noted.

Sample Site (AZAA:12) Fe Zn Rb Sr Y Zr Nb Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 MnO Fe2O3 Rock Type ppm ppm ppm ppm ppm ppm ppm % % % % % % % % % % 1181 16 12778 51 185 203 29 114 13 2.894 1.266 11.599 74.914 0 5.54 2.075 0.247 0.037 1.282 rhyolite 1612 16 13717 37 149 102 26 219 7 1.75 1.096 8.179 80.22 0 6.912 0.836 0.192 0.024 0.667 silicified rhyolite 2420 16 30364 96 220 160 40 204 15 3.151 0.349 4.875 48.674 2.662 7.601 29.436 0.266 0.18 2.522 phonotephrite 1171-1 16 10075 19 95 54 19 239 7 3.404 0.642 12.054 74.738 0 5.096 1.798 0.227 0.058 1.864 rhyolite 1171-2 16 12151 44 142 62 30 164 11 2.125 0.757 7.394 49.793 1.199 8.031 15.337 1.445 0.191 13.203 phonotephrite 1605-1 16 13678 37 147 106 24 216 8 3.014 0.421 11.917 75.218 0 7.164 0.259 0.239 0.054 1.553 rhyolite 1605-2 16 13683 33 146 106 25 215 5 3.807 0 12.047 74.061 0 5.325 1.884 0.31 0.109 2.276 rhyolite 1664-1 16 13466 29 185 165 30 118 15 3.125 0.739 12.253 73.033 0 4.747 1.704 0.22 0.052 3.991 rhyolite 1664-2 16 19417 101 239 445 28 209 13 3.276 1.037 7.916 62.557 0.926 9.412 9.122 0.617 0.129 4.578 trachydacite 1154 16 13039 21 200 52 22 151 7 2.065 1.854 13.037 68.829 0 4.847 3.56 0.537 0.12 4.749 dacite 2659-1 16 27309 113 120 1039 27 196 13 1.138 1.122 9.47 76.16 0 7.092 2.896 0.061 0.151 1.754 rhyolite 2659-2 16 14458 50 256 83 27 166 12 2.947 1.35 9.272 57.691 0.274 9.009 2.592 1.444 0.149 14.637 trachyandesite 1197 16 13914 20 181 181 33 121 15 1.369 0.467 8.346 78.471 0 6.368 2.071 0.202 0.186 2.376 rhyolite 1196-1 16 11197 39 7 129 16 103 13 2.763 0.557 7.937 69.861 0 11.448 2.914 0.416 0.087 3.746 rhyolite 1196-2 16 12421 25 104 79 28 224 13 2.302 1.721 12.162 73.501 0 7.331 0.966 0.23 0.042 1.579 rhyolite 1196-3 16 12776 22 182 212 30 112 11 5.383 0.893 6.855 56.013 2.363 8.718 12.081 0.98 0.079 6.047 phonolite 1196-4 16 12922 46 164 168 25 111 13 2.391 2.738 13.57 67.542 0 5.213 5.676 0.427 0.097 2.097 dacite 1151 16 14460 22 194 181 31 123 16 2.761 2.417 13.999 66.646 0 3.789 3.889 0.472 0.073 5.486 dacite 2412-1 16 8723 10 0 540 1 19 0 2.757 1.579 12.608 71.769 0 5.056 3.845 0.253 0.046 1.963 rhyolite 2412-2 16 16142 48 148 175 24 204 7 3.967 1.201 8.492 55.969 1.5 10.172 7.283 1.745 0.08 8.742 phonolite 1663 16 10901 17 4 102 18 117 11 2.677 0.08 7.589 69.259 0.293 9.418 5.364 0.447 0.105 4.326 rhyolite 3005-1 85 27092 63 152 823 35 248 11 3.025 1.145 12.748 73.396 0 5.1 2.091 0.278 0.05 2.005 rhyolite 3005-2 85 12584 25 249 44 42 210 14 3.636 0.416 7.563 67.117 0.441 10.007 4.701 0.63 0.117 4.926 trachyte 3062-1 85 12457 36 296 48 38 198 13 2.639 1.438 11.237 75.302 0 4.256 3.119 0.238 0.102 1.498 rhyolite 3062-2 85 14822 65 100 65 20 329 10 2.801 1.77 12.966 70.858 0 3.204 2.68 0.732 0.091 4.565 dacite 3062-3 85 14435 87 110 199 20 217 7 2.472 1.823 9.43 80.842 0 2.361 1.347 0.189 0.026 1.385 silicified rhyolite 2998 85 49144 245 7 37 7 24 2 2.68 0.434 7.988 67.446 0.156 9.525 5.284 0.602 0.123 5.406 trachydacite 2999-1 85 10259 25 329 20 39 77 38 1.181 2.505 4.76 78.3 0 0.701 0.993 0 0.35 10.965 rhyolite 2999-2 85 11457 46 259 120 45 144 28 3.122 2.044 12.853 75.566 0 3.468 1.424 0.185 0.093 1.105 rhyolite 3000-1 85 14808 100 183 177 29 112 14 4.247 1.012 6.779 44.17 3.177 11.647 19.479 1.147 0.253 7.524 foidite 3000-2 85 12371 15 439 58 45 203 17 2.652 0.518 7.925 57.934 0.609 5.473 8.766 1.227 0.253 13.607 trachyandesite 3000-3 85 13487 20 198 177 29 116 14 2.872 0.957 8.391 62.568 0 14.052 3.587 0.683 0.132 6.159 phonolite 3043-1 85 27075 143 178 693 39 186 4 2.807 1.262 12.121 73.205 0 6.425 1.897 0.194 0.071 1.782 rhyolite Sample Site (AZAA:12) Fe Zn Rb Sr Y Zr Nb Na2O MgO Al2O3 SiO2 P2O5 K2O CaO TiO2 MnO Fe2O3 Rock Type ppm ppm ppm ppm ppm ppm ppm % % % % % % % % % %

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736 90> 25742 35 190 135 32 230 17 3.075 1.224 12.91 74.135 0 4.978 1.337 0.207 0.055 1.939 rhyolite 1379 90> 13403 17 203 198 30 114 15 2.843 0.912 12.307 74.339 0 4.77 2.827 0.222 0.068 1.583 rhyolite 1699-1 90> 11672 22 183 196 26 113 14 3.392 0.841 12.657 75.355 0 4.91 0.916 0.208 0.057 1.552 rhyolite 1699-2 90> 11051 67 218 100 40 125 23 3.206 1.139 13.172 74.312 0 5.014 0.73 0.268 0.082 1.864 rhyolite 1699-3 90> 18157 22 189 192 31 113 13 3.657 0.636 11.932 75.196 0 5.217 1.235 0.195 0.076 1.677 rhyolite 1989 90> 18765 47 68 116 28 297 25 3.475 0.015 10.258 79.122 0 5.086 0.52 0.107 0.073 1.127 silicified rhyolite 2166 90> 23899 57 148 660 23 206 9 2.861 0.826 10.294 79.639 0 4.86 0.521 0.086 0.067 0.72 silicified rhyolite 791-1 90> 11101 24 67 112 9 73 8 3.05 1.098 12.474 74.862 0 4.828 1.646 0.203 0.044 1.648 rhyolite 791-2 90> 15526 136 249 61 41 256 20 3.529 0.398 7.607 70.339 0.095 9.22 3.319 0.432 0.087 4.526 rhyolite 1977 90> 12929 40 156 168 29 106 12 2.949 1.015 12.408 74.476 0 5.669 1.523 0.241 0.048 1.553 rhyolite 1105 90> 12445 28 176 157 25 98 13 2.924 0.46 12.31 76.269 0 5.066 0.844 0.247 0.081 1.648 rhyolite 923 90> 12538 25 185 160 24 112 13 2.557 1.614 10.872 72.833 0 6.857 3.64 0.155 0.052 1.24 rhyolite 1382 90> 12599 61 181 156 24 108 11 2.765 1.836 13.423 72.911 0 5.053 1.65 0.221 0.074 1.911 rhyolite 1083 90> 11176 39 262 44 45 140 34 3.294 0.56 12.957 74.263 0 5.072 1.153 0.229 0.051 2.235 rhyolite 827 90> 14314 29 178 177 32 120 13 4.278 0.183 7.515 62.297 0.621 11.838 5.397 0.677 0.142 6.603 phonolite 2510 90> 11810 510 83 149 40 176 19 2.125 0 11.494 75.565 0 9.171 0.103 0.108 0.007 1.313 rhyolite 2162 90> 31806 103 120 813 40 184 10 3.061 0.286 11.951 76.066 0 4.967 1.443 0.168 0.044 1.887 rhyolite 1983 90> 34342 90 117 655 45 223 9 2.355 0.707 8.525 58.356 0.332 5.471 9.645 1.207 0.252 12.255 trachyandesite 2324 735 12915 23 171 75 36 200 17 3.041 0.99 9.095 56.729 1.047 7.736 9.908 1.776 0.233 8.448 trachyandesite 1938-1 735 12385 24 156 194 30 111 11 4.902 0 9.972 82.292 0 0.299 1.268 0.113 0.057 0.976 silicified rhyolite 1938-2 735 12653 52 195 199 35 115 15 3.094 0.711 12.826 74.625 0 4.895 1.417 0.209 0.052 2.018 rhyolite 2869-1 735 22797 73 187 444 40 212 8 1.149 0.453 1.019 92.724 0 0.215 0.262 0 3.374 0.129 chert 2869-2 735 13536 55 319 132 44 101 10 2.279 3.096 13.793 66.374 0 5.258 5.115 0.421 0.088 3.328 dacite 1934 735 12081 22 48 110 28 230 11 3.996 0.273 10.22 80.073 0 2.771 0.7 0.168 0.053 1.451 silicified rhyolite 1935-1 735 13970 39 161 206 32 122 14 2.24 3.997 14.688 63.625 0 3.235 4.924 1.007 0.268 5.556 dacite 1935-2 735 13337 60 187 205 29 120 15 2.564 0.841 9.001 59.031 0.449 5.526 6.089 1.131 0.157 14.307 trachyandesite 1935-3 735 14057 41 182 176 28 115 13 2.322 1.333 12.616 72.121 0 6.67 3.11 0.111 0.093 1.466 rhyolite 1935-4 735 12138 26 185 53 42 199 16 1.913 1.633 14.982 64.445 0 6.277 6.533 0.75 0.063 3.075 trachydacite 2325-1 735 12314 24 186 148 32 120 20 4.925 0.382 12.176 73.252 0 3.62 3.574 0.199 0.069 1.585 rhyolite 2325-2 735 13536 77 184 216 32 114 18 2.155 1.814 13.712 67.003 0 3.433 3.58 0.777 0.101 7.131 dacite 1929 735 13359 63 182 139 26 109 14 2.199 2.262 14.911 66.017 0 4.648 4.351 0.543 0.113 4.512 dacite 2867 735 17103 40 170 278 43 200 14 2.464 4.443 15.189 59.644 0 5.162 4.873 0.864 0.193 6.785 trachyandesite 1939 735 31148 193 172 514 22 241 14 4.458 0.732 6.841 80.325 0.404 1.089 2.724 0.202 0.147 2.612 silicified rhyolite RGM1-S4 13678 39 144 106 24 217 11 3.768 0 12.031 74.658 0 5.199 1.513 0.271 0.052 2.298 standard RGM1-S4 13723 39 149 102 26 219 7 4 0 11.94 74.528 0 5.211 1.499 0.264 0.052 2.29 standard RGM1-S4 13678 37 147 106 24 216 8 4 0 11.886 74.706 0 5.225 1.51 0.305 0.043 2.305 standard

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Table 2. Crosstabulation of site by rock type based on alkali/silica content (see Table 1, Figure 1).

Site (AZAA:12) Rock Type Total

chert dacite foidite phonolite phonotephrite rhyolite silicified trachyandesite trachydacite trachyte rhyolite Site Count 0 3 0 2 2 11 1 1 1 0 21 (AZAA:12) % within Site 0.0% 14.3% 0.0% 9.5% 9.5% 52.4% 4.8% 4.8% 4.8% 0.0% 100.0% (AZAA:12) 16 % within Rock 0.0% 37.5% 0.0% 50.0% 100.0% 31.4% 14.3% 16.7% 33.3% 0.0% 30.9% Type % of Total 0.0% 4.4% 0.0% 2.9% 2.9% 16.2% 1.5% 1.5% 1.5% 0.0% 30.9% Count 1 4 0 0 0 3 3 3 1 0 15 % within Site 6.7% 26.7% 0.0% 0.0% 0.0% 20.0% 20.0% 20.0% 6.7% 0.0% 100.0% (AZAA:12) 735 % within Rock 100.0% 50.0% 0.0% 0.0% 0.0% 8.6% 42.9% 50.0% 33.3% 0.0% 22.1% Type % of Total 1.5% 5.9% 0.0% 0.0% 0.0% 4.4% 4.4% 4.4% 1.5% 0.0% 22.1% 85 Count 0 1 1 1 0 7 1 1 1 1 14 % within Site 0.0% 7.1% 7.1% 7.1% 0.0% 50.0% 7.1% 7.1% 7.1% 7.1% 100.0% (AZAA:12)

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% within Rock 0.0% 12.5% 100.0% 25.0% 0.0% 20.0% 14.3% 16.7% 33.3% 100.0% 20.6% Type % of Total 0.0% 1.5% 1.5% 1.5% 0.0% 10.3% 1.5% 1.5% 1.5% 1.5% 20.6% Count 0 0 0 1 0 14 2 1 0 0 18 % within Site 0.0% 0.0% 0.0% 5.6% 0.0% 77.8% 11.1% 5.6% 0.0% 0.0% 100.0% (AZAA:12) 90> % within Rock 0.0% 0.0% 0.0% 25.0% 0.0% 40.0% 28.6% 16.7% 0.0% 0.0% 26.5% Type % of Total 0.0% 0.0% 0.0% 1.5% 0.0% 20.6% 2.9% 1.5% 0.0% 0.0% 26.5% Count 1 8 1 4 2 35 7 6 3 1 68

% within Site 1.5% 11.8% 1.5% 5.9% 2.9% 51.5% 10.3% 8.8% 4.4% 1.5% 100.0% (AZAA:12) Total % within Rock 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% Type

% of Total 1.5% 11.8% 1.5% 5.9% 2.9% 51.5% 10.3% 8.8% 4.4% 1.5% 100.0%

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Figure 1. TAS plot used to determine rock type. (from LeBas et al. 1986).

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Figure 2. Ward's method hierarchical cluster dendrogram of oxide data by sample number.

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