HR: 0800h
AN: V51A-1467    [Abstracts]
TI: The Heterogeneous Hawaiian Lithosphere: New Isotope Data From Kauai and Oahu Peridotites
AU: * Bizimis, M
EM: bizimis@magnet.fsu.edu
AF: NHMFL and Dept of Geological Sci., FSU, 1800 E Paul Dirac Dr, Tallahassee, FL 32306 United States
AU: Salters, V J
EM: salters@magnet.fsu.edu
AF: NHMFL and Dept of Geological Sci., FSU, 1800 E Paul Dirac Dr, Tallahassee, FL 32306 United States
AU: Sen, G
EM: seng@fiu.edu
AF: Department of Earth Sci. FIU, PC 344, University Park, 11200 SW 8th Street, Miami, FL 33199 United States
AU: Keshav, S
EM: s.keshav@gl.ciw.edu
AF: Geoph. Lab, CIW, 5251 Broad Branch Rd., Washington, DC 20015 United States
AU: Ducea, M
EM: ducea@geo.arizona.edu
AF: Dept. of Geosciences, Univ. Arizona, Tuscon, AZ 85721 United States
AB: The Hf-Os isotope systematics of peridotites from Oahu suggest that the Hawaiian lithosphere is highly heterogeneous. We found that many Salt Lake Crater (SLC) peridotites vent are fragments of > 500Ma old recycled depleted lithosphere brought to the surface by the Hawaiian plume. In contrast, peridotites from the Pali vent have Hf-Os compositions appropriate for the 90 Ma old Pacific lithosphere. Here we present additional Sr-Nd isotope, major and trace element data from peridotites from the island of Kauai and from Salt Lake Crater and Pali vents on Oahu, in order to further constrain the extent and origin of the heterogeneity observed in the Hawaiian lithosphere. Two Kauai peridotites overlap the Koloa Volcanics post erosional lava compositions in Sr-Nd isotope space. A third Kauai peridotite has higher ⁸⁷Sr/⁸⁶Sr (0.70422) and lower ¹⁴³Nd/¹⁴⁴Nd (0.51291) than any published Kauai lavas and extends towards more radiogenic Sr (for a given Nd) than the Hawaiian lavas in general. This sample has depleted characteristics with high Mg# (0.925) and Cr# (0.311), and low HREE in cpx. It also has the highest La/Yb ratio and largest Ti depletions we have yet determined in Hawaiian peridotites. In contrast, three peridotites from SLC have less radiogenic ⁸⁷Sr/⁸⁶Sr (0.70316-0.70334), for a given ¹⁴³Nd/¹⁴⁴Nd (0.51285-0.51278) than all other analyzed peridotites and Hawaiian lavas. One peridotite straddles the proposed LoNd array thought to represent mixing between HIMU and EM-I mantle endmember components. In Hf-Nd space, this sample falls below the Hawaiian lava array having lower ¹⁷⁶Hf/¹⁷⁷Hf (0.28287) than even the most isotopically enriched Koolau lavas. Our new peridotite data show a much greater Sr and Nd isotope variability than previously observed, and support our conclusions based on the Hf-Os systematics for a highly heterogeneous lithosphere. The incompatible nature of Sr and Nd in peridotites makes them very susceptible to metasomatic overprint but the observed spectrum of Sr-Nd compositions in these peridotites cannot be reconciled by metasomatism of the Pacific lithosphere from Hawaiian-type melts. We propose that the observed isotope heterogeneity is largely inherited in these samples, as pieces of recycled metasomatized lithosphere that are part of the Hawaiian plume.
DE: 1000 GEOCHEMISTRY
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
DE: 3615 Intra-plate processes (1033, 8415)
DE: 3621 Mantle processes (1038)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005