DETERMINING THE ORIGIN OF OBSIDIAN SAMPLES USING LASER-INDUCED BREAKDOWN SPECTROSCOPY (LIBS)

Archaeological materials can provide important information about the timing, strength, and longevity of prehistoric trading patterns. Multi-element chemical analysis has become a common means for attributing the provenance of different kinds of artifacts (e.g. obsidian tools, pottery, and ornamental materials). The Coso Volcanic Field (CVF) in California contains a large number of high-silica rhyolite domes, many of which contain obsidian glass that was quarried for tools by the indigenous population for more than 12,000 years. Coso-Type obsidian artifacts are found throughout the southwestern United States. Geochemical analysis has found these obsidians to quite similar in major element character, but abundance differences for several trace elements have been used as the basis for establishing a 'geochemical fingerprint' that can be utilized as a means to distinguish obsidian from different local sources. Based upon this success, laser-induced breakdown spectroscopy (LIBS) was applied to characterize and discriminate Coso obsidian samples. LIBS is an atomic emission spectroscopy technique that is simultaneously sensitive to all elements which, with a single laser shot, captures the plasma broadband emission spectrum and provides chemical fingerprint of any material. Sets of broadband LIBS spectra were collected for obsidians from important obsidian sites across the California, with the data analyzed using advanced multivariate statistical signal processing techniques. Although all obsidians exhibited quite similar broadband LIBS spectra, a PLS-DA approach was able to clearly discriminate Coso obsidians from other regional sources. This study demonstrates the potential of LIBS as a viable analytical technique for obsidian provenance determination and, because the technique has an attractive potential for real-time man-portable geochemical analysis in the field and, also the in-situ chemical analysis of obsidian artifacts.