GEOCHEMICAL AND PETROLOGIC CHARACTERIZATION OF PUMICE ARTIFACTS FROM THE MIAMI CIRCLE-BRICKELL POINT ARCHAEOLOGICAL SITE, MIAMI, FLORIDA – RELATIONSHIP TO OTHER PUMICE ARTIFACTS IN FLORIDA AND POTENTIAL PROVENANCE LOCATIONS
Most pumice samples are small (4 cm), white or very light gray in color, and have a low percentage of phenocrysts (biotite+magnetite+plagioclase±amphibole±quartz). All samples have bulk densities less than 1.0. A majority of the pumice is characterized by high silica (74-76 wt. %) and high K2 O contents (3.5-4.5 wt. %). The high-silica pumice has strong light REE enrichment, La 50-70 times chondritic abundance, LaN/SmN (~10) and GdN /YbN (~1.0). Most of these samples also exhibit moderate to strong (0.5-0.25) negative Eu anomalies. A limited number of pumice artifacts have medium-K rhyolitic to medium-K andesitic compositions, characterized by moderate light REE enrichment and no significant Eu anomalies. All rhyolitic samples have Rb versus (Y + Nb) contents that are characteristic of a calc-alkaline, volcanic-arc setting. Rare mafic pumice and scoria artifacts have an alkaline composition, which is characterized by elevated concentrations of K, Ti, and Nb, relative to cal-alkaline basalts.
The felsic, calc-alkaline composition of most of the pumice artifacts is compatible with derivation from two potential, nearby sources - stratovolcanoes of the Lesser Antilles of the southern Caribbean and volcanoes of the easternmost portion of the Trans Mexico Volcanic Belt (TMVB), located 100 km west of Vera Cruz, Mexico. However, the overall high silica and high-K composition of the Florida pumice artifacts has not been observed in volcanics of the Lesser Antilles, but is common in the TMVB. Medium-K rhyolitic to andesitic pumice artifacts are similar to volcanics of the central Lesser Antilles. Mafic pumice artifacts have chemical compositions similar to the volcanics of the Azores and Cape Verde Islands.