HR: 11:45h
AN: V42B-06    [Abstracts]
TI: Geochemical Evolution of the Louisville Seamount Chain
AU: * Vanderkluysen, L
EM: loyc@hawaii.edu
AF: Geology and Geophysics Dept., SOEST, University of Hawaii at Manoa, Honolulu, HI 96822, United States
AU: Mahoney, J J
EM: jmahoney@hawaii.edu
AF: Geology and Geophysics Dept., SOEST, University of Hawaii at Manoa, Honolulu, HI 96822, United States
AU: Koppers, A A
EM: akoppers@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AU: Koppers, A A
EM: akoppers@coas.oregonstate.edu
AF: Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, United States
AU: Lonsdale, P F
EM: plonsdale@ucsd.edu
AF: Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093, United States
AB: The Louisville seamount chain is a 4300 km long chain of submarine volcanoes in the southwestern Pacific that is commonly thought to represent a hotspot track. It spans an ~80 Myr age range, comparable to that of the Hawaiian-Emperor chain (Koppers et al., G-cubed, 5 (6), 2004). The few previously dredged igneous samples are dominantly basaltic and alkalic, and have been inferred to represent post-shield volcanism (Hawkins et al., AGU Monograph, 43, 235, 1987). Their isotope and trace element signatures suggest an unusually homogenous mantle source (Cheng et al., AGU Monograph, 43, 283, 1987). Dredging in 2006, during the AMAT02RR cruise of the R.V. Revelle, was carried out in the hope of recovering both shield and post-shield samples and of exploring the geochemical evolution of the chain. Igneous rocks were recovered from 33 stations on 23 seamounts covering some 47 Myr of the chain's history. Our study, focusing on the major and trace element and Sr, Nd and Pb isotopic characteristics of these samples, shows that all are alkalic basalts, basanites and tephrites containing normative nepheline. Variations in major and trace elements appear to be controlled predominantly by variable extents of melting and fractional crystallization, with little influence from mantle source heterogeneity. Indeed, age-corrected isotopic values define only a narrow range, in agreement with long-term source homogeneity relative to the scale of melting; e.g., ε_Nd varies from +4.1 to +5.7, ²⁰⁶Pb/²⁰⁴Pb from 19.048 to 19.281, and ⁸⁷Sr/⁸⁶Sr from 0.70362 to 0.70398. These values broadly fall within the fields of the proposed "C" or "FOZO" mantle end-members. However, small variations are present, with less radiogenic Nd and Pb isotope ratios at the older, western end of the chain, defining a trend toward a broadly EM2-like composition. Although some workers have postulated that the Louisville hotspot was the source of the ~120 Myr Ontong Java Plateau, our samples are isotopically distinct from any known Ontong Java compositions.
DE: 1025 Composition of the mantle
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting