HR: 1330h
AN: V32A-0997    [PDF]
TI: Isotopic Study of the Mauna Loa Southwest Rift Mile High Section: Hawaiian Mantle Plume Components
AU: * Weis, D
EM: dweis@eos.ubc.ca
AF: Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, BC V6T 1Z4 Canada
AU: Rhodes, J M
EM: jmrhodes@geo.umass.edu
AF: Dept. of Geosciences, University of Massachusetts, Amherst, MA 01003 United States
AU: Garcia, M O
EM: garcia@soest.hawaii.edu
AF: Dept. of Geology-Geophysics, University of Hawaii, Honolulu, HI 96822 United States
AB: The new JASON2 ROV was employed to collect 51 samples from a 1.8 km thick submarine landslide scarp along the crest of the southwest rift zone of the Mauna Loa volcano to investigate the nature and history of Hawaiian mantle plume components. The rift zone section records about 400,000 years of eruptive activity, 50% of the volcano's total lifetime, which is comparable to the time-period sampled by the Hawaiian Scientific Drilling Project (HSPD2). Sr, Nd, Pb and Hf isotopes have been analyzed on 14 samples from the "Mile High" section. The range of variation observed falls typically within literature data for the Mauna Loa volcano with $^{87}$Sr/$^{86}$Sr from 0.70368 to 0.70378 and $^{206}$Pb/$^{204}$Pb from 18.16 to 18.26, and is somewhat more radiogenic than most Mauna Loa prehistoric ($<$31 ka) lavas. In the section, there is a distinct increase in Pb and Sr isotopes, which is also recorded by major and trace element data, at a depth of 1353 m. Isotope ratios continue to increase to the bottom of the section at 2290 m. High precision Pb-Pb isotopic systematics for Mauna Loa lavas do not show the binary mixing trends as also observed in the upper part of the HSDPI pilot hole and contrary to Mauna Kea lavas (Abouchami et al., Chemical Geology 2000). This might imply that the Mauna Loa plume source is more thoroughly mixed than the Mauna Kea source. Most of Mauna Loa isotopic compositions cluster at 18.15-18.20 for $^{206}$Pb/$^{204}$Pb and $\sim$0.70370 for $^{87}$Sr/$^{86}$Sr, which could be a ubiquitous refractory component in the Hawaiian mantle plume (Rhodes and Weis, Fall AGU 2001). Nevertheless, a more radiogenic plume component with higher $^{208}$Pb/$^{204}$Pb and $^{208}$Pb*/$^{206}$Pb* is clearly present in the lower part of the Mile High section and might be comparable to the Kilauea-like component observed in Mauna Kea lavas in HSDP2 (Blichert-Toft et al., G3 2003). Team members also include: D. Wanless and K. Kolysko, University of Hawaii; H. Guillou, CEA/CNRS, France; M. Kurz and D. Fornari, WHOI; M. Norman and V. Bennett, ANU, Australia; F. Trusdell and S. Schilling, USGS; M. Chapman, Morehead State University; M. Vollinger, University of Massachusetts.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1010 Chemical evolution
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting