Mukhopadhyay, S. and Lassiter, J. C. and Farley, K. A. and Bogue, S. W. (2003) Geochemistry of Kauai shield-stage lavas: Implications for the chemical evolution of the Hawaiian plume. Geochemistry, Geophysics, Geosystems, 4 (1). 2002GC000342. ISSN 1525-2027 http://resolver.caltech.edu/CaltechAUTHORS:MUKggg03
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We measured He, Sr, Nd, Pb, and Os isotope ratios and major and trace element concentrations in stratigraphically and paleomagnetically controlled shield-stage lavas from Kauai, Hawaii. The range of 3He/4He ratios (17–28 RA) from Kauai is similar to that reported from Loihi and thus challenges the prevailing notion that high 3He/4He ratios are restricted to the preshield stage of Hawaiian magmatism. 3He/4He ratios vary erratically with stratigraphic position, and chronostratigraphic control from paleomagnetic data indicates very rapid changes in the 3He/4He ratios (up to 8 RA in ~102 years). These variations in helium isotopic ratios are correlated with variations in radiogenic isotope ratios, suggesting rapid changes in melt composition supplying the magma reservoir. A three-component mixing model, previously proposed for Hawaiian shield lavas, does not adequately explain the isotopic data in Kauai shield lavas. The addition of a depleted-mantle (DM) component with the isotopic characteristics similar to posterosional basalts explains the isotopic variability in Kauai shield lavas. The DM component is most apparent in lavas from the Kauai shield and is present in varying proportion in other Hawaiian shield volcanoes. Shield lavas from Kauai sample a high 3He/4He end-member (Loihi component), but while lavas from western Kauai have a larger contribution from the Kea component (high 206Pb/204Pb, anomalously low 207Pb/204Pb relative to 206Pb/204Pb), lavas from eastern Kauai have a larger proportion of an enriched (Koolau) component. The systematic isotopic differences between eastern and western Kauai reflect a gradual migration of the locus of volcanism from west to east, or alternatively east and west Kauai are two distinct shield volcanoes. In the latter case, the two shield volcanoes have maintained distinct magma supply sources and plumbing systems. Our new geochemical data from Kauai are consistent with the existence of a single high 3He/4He reservoir in the Hawaiian plume and suggest that the proportion of the different mantle components in the plume have changed significantly in the past 5 Myr. The long-term evolution of the Hawaiian plume and the temporal variability recorded in Kauai lavas require more complex geochemical heterogeneities than suggested by radially zoned plume models. These complexities may arise from heterogeneities in the thermal boundary layer and through variable entrainment of ambient mantle by the upwelling plume.
|Additional Information:||Copyright 2003 by the American Geophysical Union. Received: 7 March 2002; Revised: 14 August 2002; Accepted: 30 August 2002; Published: 24 January 2003. We thank John Eiler, Mike Baker, Pete Burnard, and Pete Reiners for stimulating discussions on Hawaiian magmatism. We thank John Eiler and Pete Burnard for making valuable suggestions on an earlier version of this manuscript. Don DePaolo, Mike Garcia, and Mark Kurz are thanked for their thoughtful reviews. This work was funded by the David and Lucille Packard fellowship to KAF, the NSF grant EAR-9725351 to John Lassiter, and the Max-Plank Institut.|
|Subject Keywords:||Helium; mantle plumes; Hawaii; isotope ratios; mixing; 1010 Geochemistry: Chemical evolution; 1025 Geochemistry: Composition of the mantle; 1040 Geochemistry: Isotopic composition/chemistry; 8121 Tectonophysics: Dynamics, convection currents and mantle plumes|
|Official Citation:||Mukhopadhyay, S., J. C. Lassiter, K. A. Farley, and S. W. Bogue, Geochemistry of Kauai shield-stage lavas: Implications for the chemical evolution of the Hawaiian plume, Geochem. Geophys. Geosyst., 4(1), 1009, doi:10.1029/2002GC000342, 2003.|
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|Deposited On:||21 Dec 2005|
|Last Modified:||26 Dec 2012 08:42|
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