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.

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