ELEMENTAL, ISOTOPIC, AND GEOCHRONOLOGICAL VARIABILITY IN MOGOLLON-DATIL VOLCANIC PROVINCE ARCHAEOLOGICAL OBSIDIAN, SOUTHWESTERN NEW MEXICO: SOLVING ISSUES OF INTER-SOURCE DISCRIMINATION

The Mogollon-Datil Volcanic Province in western New Mexico has been a subject of geological and geoarchaeological research for over three decades. These Neogene magmatic rocks are derived from large-scale crustal melting events occurring over several million years. Obsidian of rhyolite composition produced from these events have similar elemental compositions even though the five major rhyolite exposures are isolated by over 100 km, spanning a number of cultural territorial boundaries in the late prehistoric period. The obsidian sources are archaeologically significant in that they were used from Paleoindian through Historic times (ca. 14,000 ka to ≈A.D. 1600), and transported throughout the North American Southwest. The need to discriminate between obsidian sources is crucial for testing archaeological interpretations regarding 21st century issues of exchange, migration and social networking. The number of cultural territories throughout prehistory is extensive and extreme care in source assignment is required to evaluate the exchange of obsidian and consequent social interaction in the region. Elemental compositions and trace element ratios obtained by x-ray fluorescence spectrometry (XRF) show similarities between various outcrops, particularly when compared to other Southwestern sources. An exploratory isotopic (Sr, Pb, Nd) and ⁴⁰Ar/³⁹Ar dating program was employed to provide discriminating clarity and yielded good results. The isotopic and ⁴⁰Ar/³⁹Ar data indicate these sources are distinguishable, and using these results, a strategy for discriminating sources was devised using laboratory XRF. Furthermore, the symbiotic relationship between geology and archaeology in this study points to the continuing positive relationship between these disciplines offering clarity to both.