Sources of archaeological dacite in northern New Mexico

For years archaeologists in New Mexico, particularly in the northern Rio Grande region have noticed a very fine-grained what appeared to be mafic or basalt raw material source in late Paleoindian and Archaic contexts in northern New Mexico and southern Colorado. Indeed, a number of Folsom, Cody, Plainview, and Archaic bifaces are produced from this material. It appeared that there were at least two possible very fine-grained volcanics that could be the sources for these raw materials – San Antonio Mountain in far northern New Mexico, in the Taos Plateau Volcanic Field, and Cerros del Rio, on the east side of Bandelier National Monument right above the Rio Grande. After reconnaissance collections at the two probable sources, the short story is that the vast majority of “basalt” artifacts were indeed produced from one of these sources, but they are petrologically dacite and silicic volcanic rocks. An additional dacite source, called here the “Newman Dome”, also in the Taos Plateau Volcanic Field was discovered in the 1980s, but remained mainly discussed in the gray literature by CRM archaeologists. Examination of various Paleoindian and Archaic collections from the northern and middle Rio Grande indicates a strong preference for this silicic rock for the production of chipped stone tools, and in concert with obsidian source provenance studies has increased our ability to reconstruct procurement and range in these preceramic periods. These high-alkali dacite sources are easily discriminated with their trace element compositions, and based on this study, procurement seems to be dominantly restricted to these three sources in the region. Here I discuss the petrology, geochemistry, and some of the archaeological issues of these sources and their utility in the Southwest archaeological endeavor in an effort to bring these important prehistoric raw materials into the published realm.

Research highlights► The geology, and geochemistry of sources of archaeological dacite in northern New Mexico are explored in this study. ► Dacite was used in all periods in northern and central New Mexico, particularly in the Paleoindian and Archaic periods. ► This glassy, very fine-grained homogeneous stone raw material is an excellent rock for provenance studies.