PETROGRAPHIC AND GEOCHEMICAL ANALYSIS OF RECENT LAVA FLOWS IN HAWAII: EFFECTS OF INITIAL WEATHERING ON REE CONTENT

Considerable research has been done establishing rare earth element (REE) concentrations in tholeiitic and alkaline basalts, and how these trace elements behave during chemical weathering. In general, REEs appear to be immobile during chemical weathering and tend to concentrate within soils after intense leeching that occurs in wet tropical areas like those on the Hawaiian Islands. Our study focuses on the potential geochemical changes that occur to basalts during the very initial leeching phase of the weathering process, prior to soil formation. We collected samples of basalt from recent lava flows on the “wet” side (Hilo coast) and “dry” side (Kona coast) of Hawaii during the summer of 2013. A total of 35 specimens were collected during the field session. Thin-sections were made from the surface “weathered” side and core of each basalt sample and then petrographically examined to identify microscopic changes in mineralogy. Little change was found in samples from either the dry or wet side of Hawaii. The next portion of the study will be to determine major, trace, and REE concentrations of the samples using electron microprobe/ XRF/ICP whole rock and mineral analysis. We anticipate that the more volatile elements such as alkalis will display mobility in weathered samples versus the more immobile REE.