The Department has an active weekly seminar program. Find links to this week's seminar and past seminars here.

This week's seminar:

25 September, 2008
PC 310
3:30 to 4:30 pm

Scales of heterogeneity in the Hawaiian plume

Dr. Michael Bizimis,  Research Assistant Professor
Dept of Geological Sciences
University of South Carolina

Abstract

: I will be presenting new high precision isotope (Hf-Nd-Sr-Pb) data on the two isotopically most extreme endmemebers of the Hawaiian plume
volcanism: the Kaula rejuvenated stage lavas and pyroxenites, and the Makapuu stage Koolau lavas. The Kaula lavas and pyroxenites (as well as new data from the Oahu pyroxenites) extend to less radiogenic 206Pb/204-208Pb/204Pb isotope compositions than previously reported in the Hawaiian lavas. Lead isotope compositions show a well defined negative correlation with Nd and Hf isotopes, arguing for a time-integrated depleted (low U-Th/Pb, high Sm/Nd-
Lu/Hf) component. There is isotopic compositional continuity between KEA- type lavas (Mauna Keea, West Maui) and the pyroxenites / rejuvenated lavas, arguing that this depleted component is part of the plume. The presence of the same component both in Kaula and Oahu pyroxenites argues that this depleted has been present in the plume for at least the last 4 million years.

The new Makapuu lavas extend less radiogenic Nd isotope compositions than previously reported in the Hawaiian plume. The Pb isotope data argues for the presence of a depleted component, similar to that identified by the pyroxenites
within these otherwise isotopically enriched lavas. When plotted on any combination of 3-isotope systems (3D plots) the Makapuu and the stratigraphically lower KSDP lavas show well defined but non-intersecting binary arrays. This feature cannot be explained by any two or three- component mixing, and requires that the plume source changed significantly and abruptly during the shield stage volcanism at Koolau. A reexamination of available high precision isotope data from other Hawaiian volcanoes further shows that each shield volcano defines a unique linear array (implying binary
mixing) in all 3D isotope plot combinations that involve Hf-Nd-Sr-Pb isotopes.
Note that, in general, there is very little overlap between the individual arrays.
This requires that only a unique set of two end members, responsible for the isotopic variability of each volcano, is available during the eruption of that particular volcano. This observation is consistent with vertical heterogeneity within the Hawaiian plume, and the implications will be further discussed in the talk.