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

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Frey EAR-0105557 Terrestrial volcanoes are associated with three different tectonic settings. Two are associated with plate boundaries, that is, regions of plate divergence and convergence, and the third is intraplate volcanism. Magmas erupted in these different environments differ significantly in geochemical characteristics. In this proposed research the goal is to understand the source and processes which determine the geochemical characteristics of Hawaiian lavas. This endmember is of great interest because it may in part represent the consequences of subducting oceanic crust deep into the mantle at subduction zones. The approach will be to determine abundances of major and trace elements and isotopic ratios of O, Sr, Nd, Pb, Hf and Os in lavas of varying relative age from these two shields. For Koolau the samples to be studied are from a recently drilled core, that penetrates the shield to a greater depth and older age than previously studied surficially exposed samples. For Kahoolawe, which has not been intensively studied, the samples will be from several stratigraphic sections across the shield. The principal objective is to understand the source components contributing to these magmas; hence emphasis will be on evaluating correlations between abundance ratios of highly incompatible elements, e.g., Ba/Th, Ce/Pb and La/Nb, and isotopic ratios. These geochemical characteristics will be determined using analytical facilities such as inductively couples plasma mass spectrometry and thermal ionization mass spectrometry. Because of their oceanic plate setting, relatively simple mineralogy and a wealth complementary studies, Hawaiian volcanoes present the best opportunity for understanding the role of recycled crustal components in oceanic island volcanism. In particular, this research will aid in constraining the processes and source components which create a geochemical endmember of Hawaiian shield lavas.