THE TAOS PLATEAU VOLCANIC FIELD AND NO AGUA PEAK OBSIDIAN

The No Agua obsidian source has been reported variously times in the geological and archaeological literature (Baugh and Nelson 1987; Glascock et al. 1999; Lipman and Mehnert 1979; Stevenson and McCurry 1990; Whitson 1982; Figure 3.19 here). The archaeologists have been generally copying each other’s data and source samples. Lipman and Mehnert (1979) describe the No Agua Peak source as part of the multi-modal Taos Plateau Volcanic Field providing field descriptions, major and elemental chemistry and K-Ar dates for the obsidian proper. The No Agua source has been extensively disturbed by current and past perlite mining; currently the El Grande Perlite Mine. This is what Lipman and Mehnert describe in the 1970s:
A cluster of four steep-sided lava domes of silicic alkalic rhyolite occurs at No Agua Peaks (North, South, East, and West domes) near the center of the volcanic field. These domes, which have average slopes of 25-30º and stand 200-500 m above the surrounding younger flows of Sevilleta Basalt and xenocrystic basaltic andesite, define and elliptical ring structure about 2 km in diameter. The rhyolite consists of tan, frothy, hydrated, perlitic glass at its margins, locally studded with black “apache tears” of nonhydrated obsidian a few centimeters in diameter. A new K-Ar age of 3.9 m.y. on nonhydrated obsidian is in reasonable agreement with a previously determined fission-track age. 
The rhyolite of No Agua contains 76-77 percent SiO2 [similar the analysis here]—among the most silicic volcanic rock compositions known from the southern Rocky Mountains (Lipman and Mehnert 1979:306).

In 2000 when No Agua Peaks was revisited, only a remnant of the eastern dome remained, but abundant obsidian nodules are still present in the mined perlite. We sampled in the area that would have been the western dome and the eastern dome, the data from which is presented in the Appendix. As in Lipman and Mehnert’s description, the No Agua obsidian has about “1 percent phenocrysts of plagioclase, sanidine, and quartz” (1979:300), and as such is barely a tolerable media for tool production---certainly why it has not been seen in the archaeological record to my knowledge anywhere in northern New Mexico or southern Colorado, although Glascock et al. note that “prehistoric inhabitants of the San Luis Valley made frequent use of the raw material” (1999:864).




The Taos Plateau Volcanic Field. No Agua Peaks Rhyolite (Trh) is near center of sheet with the Rio Grande approximately 20 km east (adapted from Lipman and Mehnert 1979:291, legend in original).

Baugh and Nelson (1987), Glascock et al. (1999), and Stevenson and McCurry (1990) all report chemical differentiation between the North and West domes. Our sampling of nodules from what should have been the west dome and the east dome derived a composition similar to the west dome data as reported by Baugh and Nelson (1987) and Glascock et al. (1999), and did not detect the composition from the North domes in their reports. The data reported in the Appendix included nodules supplied by Chris Stevenson in the 1980s. Since the raw material quality from nodules from the No Agua Peaks is very low and it has not been recovered in archaeological contexts outside the immediate area, these issues are probably not important. However, an examination of the east dome by Bruce Huckell and me in 2000 did indicate the presence of abundant lithic reduction at the dome. The field description of the 2000 survey is a follows:
UTM 13S 0413358/4066453, Tres Piedras 7.5’ USGS Quadrangle 1995, Collection locality 081000-1&2. Nodules all with abundant phenocrysts of sanidine up to 10 cm in diameter (most <5 cm). Density of nodules on undisturbed portion of the east dome (UTM 13S 0413955/4066865) 15/m2 at the highest density. Obsidian occurs interbedded with perlite as observable in the mined areas.

 

No Agua West

Element N Minimum Maximum Mean Std. Deviation
Ti 5 721 1114 838.9 158.5
Mn 5 738 1450 981.2 272.6
Fe 5 7420 8932 8048.0 554.4
Zn 4 72 85 79.1 5.3
Rb 5 272 321 302.8 19.2
Sr 5 8 15 11.4 2.6
Y 5 50 60 54.9 4.5
Zr 5 91 96 93.1 1.8
Nb 5 87 90 88.8 1.4
Ba 5 0 21 7.9 10.0
Ce 4 8 49 25.9 19.0
Pb 4 37 45 41.2 3.4
Th 4 23 27 24.9 2.0

No Agua North

Element N Minimum Maximum Mean Std. Deviation
Ti 14 820 1002 901.5 57.5
Mn 14 429 623 503.4 56.3
Fe 14 7937 9522 8422.3 486.1
Zn 14 49 66 55.6 4.8
Rb 14 127 166 139.9 9.3
Sr 14 39 56 44.9 4.3
Y 14 21 27 24.6 1.8
Zr 14 76 88 81.7 3.4
Nb 14 33 43 38.1 3.2
Ba 14 113 175 150.9 17.0
Ce 14 19 63 40.7 13.0
Pb 14 21 29 23.8 2.2
Th 14 5 21 13.8 5.0

Raw Elemental Data for the No Agua Peak domes

Sample Locality Ti Mn Fe Zn Rb Sr Y Zr Nb Ba Ce Pb Th
081000-1-1 West Dome 721 888 7850 78 309 11 52 92 89 1 8 43 26
081000-1-2 West Dome 779 897 7937 85 321 15 60 93 88 1 49 41 23
081000-1-3 West Dome 1114 1450 8932   298 8 54 96 90 16      
081000-1-4 West Dome 754 738 7420 72 272 12 58 91 87 0 13 37 23
081000-1-5 West Dome 826 934 8100 81 314 11 50 93 90 21 33 45 27
NAN-2 North Dome 966 607 9083 64 133 43 23 77 34 113 62 24 21
NAN-3 North Dome 868 472 8202 56 144 46 27 76 42 173 40 26 19
NAN-4 North Dome 830 473 8028 51 146 44 22 83 33 175 42 22 21
NAN-5 North Dome 995 560 8920 59 147 47 26 82 40 148 32 24 11
NAN-6 North Dome 872 477 8085 53 136 44 23 83 42 143 63 22 14
NAN-7 North Dome 928 469 8493 49 135 49 26 80 36 146 42 26 9
NAN-8 North Dome 843 496 8102 53 138 41 24 80 37 156 46 21 5
NAN-9 North Dome 1002 623 9522 66 166 56 25 85 40 164 57 29 15
NAN-10 North Dome 890 495 8258 59 142 45 26 79 40 157 36 23 12
NAN-11 North Dome 863 483 8230 54 135 40 26 88 39 161 19 24 17
NAN-12 North Dome 914 467 8150 52 138 39 27 86 43 127 23 24 16
NAN-13 North Dome 820 468 8016 56 134 43 21 82 35 138 30 23 11
NAN-14 North Dome 921 429 7937 52 127 46 26 83 39 156 39 23 15
NAN-15 North Dome 909 529 8886 55 138 46 24 79 36 155 39 21 7
RGM1-S4 USGS Standard 1523 295 13168 48 146 109 29 224 15 779 41 21 6

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Revised: 18 April 2020