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 North

 

N

Minimum

Maximum

Mean

S.D.

Std. Error

Ti

5

406

692

578

49

111

Mn

5

436

646

513

38

84

Fe

5

6095

7686

6962

270

605

Rb

5

120

147

131

5

11

Sr

5

34

39

36

1

2

Y

5

23

26

24

1

1

Zr

5

69

80

74

2

4

Nb

5

33

40

36

1

3

 

No Agua West

 

N

Minimum

Maximum

Mean

S.D.

Std. Error

Rb

5

292

300

297

1

3

Sr

5

8

9

9

0

1

Y

5

53

55

54

0

1

Zr

5

93

96

94

1

1

Nb

5

88

91

90

1

1

Ba

5

11

24

16

2

5

 

 

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Revised: 21 March 2015