HR: 11:50h
AN: V22A-07    [Abstracts]
TI: Evolution of Diverse Mantle Sources for the Kilauea Volcano Over 270 Ka
AU: * Shimizu, N
EM: nshimizu@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Kobayashi, K
EM: katsura@pheasant.misasa.okayama-u.ac.jp
AF: ISEI, Okayama University, Misasa, 682-0193 Japan
AU: Sisson, T
EM: tsisson@usgs.gov
AF: US Geological Survey, USGS, Menlo Park, Menlo Park, CA 94250 United States
AU: Layne, G
EM: glayne@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Nakamura, E
EM: eizonak@misasa.okayama-u.ac.jp
AF: ISEI, Okayama University, Misasa, 682-0193 Japan
AU: Kurz, M
EM: mkurz@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AB: Isotopic composition of Pb was determined in-situ in glass shards derived from the pre-shield stage alkaline magmatism (270 Ka), and in olivine-hosted melt inclusions from the 1960 picrite flow (MK91-8), using Cameca IMS 1270 ion microprobes at WHOI and ISEI. Salient features of the results are summarized as follows: (1) the pre-shield stage alkaline glasses (270 Ka) display a range of Pb isotopic composition much greater than the entire Hawaiian array (208Pb/206Pb from 2.004 to 2.099, 207Pb/206Pb from 0.805 to 0.864). The isotopic compositions cluster on three distinct compositions without much mixing among them. Clustering may be interpreted as a result of yet-poorly-developed crustal plumbing. (2) The most radiogenic composition (208Pb/206Pb = 2.004, 207Pb/206Pb = 0.805) is more radiogenic than any known Hawaiian lavas. (3) The least radiogenic composition (208Pb/206Pb = 2.099, 207Pb/206Pb = 0.864) is rather Loa-like (Koolau - Honolulu), suggesting a broader geographic coverage and continued existence of a Loa-like source 2.6 Ma to 270 Ka. (4) Olivine-hosted melt inclusions from the 1960 picrite flow (MK91-8) display a large range of Pb isotopic composition (208Pb/206Pb from 1.951 to 2.102, 207Pb/206Pb from 0.795 to 0.851). In the 208Pb/206Pb - 207Pb/206Pb space, there appear to be three distinct mixing arrays: a high 208/206 (EM2 - EM1) array, a low 208/206 (DMM - HIMU) array, and an intermediate array between the two. (5) The observed isotopic variability reflects the fact that melts delivered to the crust in the tholeiitic stage today are as diverse as those at the nascent alkaline stage of the volcano, and suggests that efficiency of magma mixing in the crustal plumbing system has increased as the volcanic edifice developed. (6) The radiogenic component observed in the 270 Ka glasses is present in the analyzed melt inclusions (208Pb/206Pb = 1.951, 207Pb/206Pb = 0.796), indicating the presence of a source carrying radiogenic Pb with a vertical dimension up to hundreds of kilometers. The results, combined with the presence of Kea and Loa trends for extended periods of time, suggest a structure of the Hawaiian plume in which isotopically distinct sources are vertically continuous and are distributed asymmetrically.
DE: 1025 Composition of the mantle
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005