SPATIAL TRACE ELEMENTAL COMPOSITION MAPPING OF SAMOA VOLCANICS BY LA-ICP-MS

The Samoa Island volcanic chain is a significant area of mantle geochemistry research because of the complex interaction of potentially multiple mantle sources. At first glance, Samoa appears to represent a typical hotspot mantle plume with progressively younger volcanics towards the E-SE, which is similarly parallel to other Pacific Plate Island Chains. Recently, this model has been questioned because of evidence for youthful volcanism on Savai’i (west) and Ta’u (east) Islands with composition differing from other Pacific Plate island chains. To evaluate these processes, we will present trace element results in various samples taken from the Samoa Island Chain. We present cryogenic laser ablation (CLA)-ICP-MS results of the elemental composition (Majors, transition metals, alkaline earths (Sr, Ba), REEs, actinides, HFSEs) of the mineralized grain boundaries of Samoan xenoliths and groundmass that we previously analyzed for noble gas and stable isotopic composition. We chose appropriate mineral grain boundaries by first performing traditional thin section optical microscopy petrographic analysis. Through LA-ICP-MS we were able to create a raster-type plot of the elemental composition of Samoan volcanics thin sections after optical petrographic analysis to create elemental geospatial “maps” of the Samoan volcanics. This spatial geochemical elemental analysis was used to differentiate trace elements present within mineral crystals from fluids migrating in the Earth’s mantle (i.e. along grain boundaries). This analysis will enable us to determine trace element migration processes that occur during mantle metasomatic processes, which may alter the chemistry of mantle source rocks and influence melt composition. These results will provide insights into the unique lava composition at Samoa, and will provide a better understanding of the fluid migration from the Earth’s mantle.