The Geochemical Characteristics of the Hawaiian Plume: Constraints From Studies of Lavas Forming the Koolau and Kahoolawe Shields

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FreyEAR-0105557Terrestrial volcanoes are associated with three different tectonicsettings. Two are associated with plate boundaries, that is, regions ofplate divergence and convergence, and the third is intraplate volcanism.Magmas erupted in these different environments differ significantly ingeochemical characteristics. In this proposed research the goal is tounderstand the source and processes which determine the geochemicalcharacteristics of Hawaiian lavas. This endmember is of great interestbecause it may in part represent the consequences of subducting oceaniccrust deep into the mantle at subduction zones.The approach will be to determine abundances of major and trace elementsand isotopic ratios of O, Sr, Nd, Pb, Hf and Os in lavas of varyingrelative age from these two shields. For Koolau the samples to be studiedare from a recently drilled core, that penetrates the shield to a greaterdepth and older age than previously studied surficially exposed samples.For Kahoolawe, which has not been intensively studied, the samples will befrom several stratigraphic sections across the shield. The principalobjective is to understand the source components contributing to thesemagmas; hence emphasis will be on evaluating correlations between abundanceratios of highly incompatible elements, e.g., Ba/Th, Ce/Pb and La/Nb, andisotopic ratios. These geochemical characteristics will be determinedusing analytical facilities such as inductively couples plasma massspectrometry and thermal ionization mass spectrometry.Because of their oceanic plate setting, relatively simple mineralogy and awealth complementary studies, Hawaiian volcanoes present the bestopportunity for understanding the role of recycled crustal components inoceanic island volcanism. In particular, this research will aid inconstraining the processes and source components which create a geochemicalendmember of Hawaiian shield lavas.