Sources of Archaeological Obsidian in the Southwest: An Archaeological, Petrological, and Geochemical Study

Comprehensive geochemical studies of archaeological obsidian sources in the Southwest typically have lagged behind other regions of North American and Mesoamerica. Current archaeological and petrological research indicates four previously unreported sources in Arizona, Sonora, and western New Mexico. This initial semiquantitative X-ray fluorescence (XRF) examination of archaeological silicic-glass sources in this region focuses on current technical problems in southwestern obsidian studies. The chemical variability within some regional obsidian sources appears to be relatively extensive and new data from the San Francisco volcanic field in northern Arizona modifies the results of earlier researchers.

Discrete single-domain and pseudo-single-domain titanomagnetite particles in silicic glass of an ash-flow tuff

Single-domain and pseudo-single-domain titanium-poor magnetite grains are present in silicic vitrophyre glass of an ash-flow tuff from western Nevada. Conventional transmission electron microscopy and analytical electron microscopy corroborate inferences, made solely from rock magnetic and remanence data, that the thermoremanent magnetization in the vitrophyre is carried by such grains. The magnetite grains vary in size, shape, and distribution throughout the glass. They probably crystal lized during violent eruption and welding of the ash flow, at temperatures well in excess of 600 °C.