Petrogenesis of Hawaiian postshield lavas: Evidence from Nintoku Seamount, Emperor Seamount Chain

Abstract

[1] We report major and trace element and Sr and Nd isotope data for a 283 m thick sequence of postshield lavas drilled during Ocean Drilling Project Leg 197 from Site 1205, Nintoku Seamount, an approximately 56 m.y. old volcano from the Emperor Seamount Chain. At least 25 subaerially erupted lava flow units were sampled, of which all but one are alkali basalts. Clasts of hawaiite and mugearite are present in a conglomerate overlying the basement sequence. Similar rock types characterize the postshield stage of many young Hawaiian volcanoes. Major and trace element, and age-corrected Sr and Nd isotope compositions of the Nintoku lavas are similar to those of young postshield lavas from the Hawaiian Islands. Concentrations of highly incompatible elements tend to increase, La/Yb and Nb/Zr ratios increase, and 87 Sr/ 86 Sr decreases with decreasing depth in the drill core. The more evolved rock types can be related to the underlying alkali basalts by fractional crystallization of olivine, clinopyroxene, plagioclase, and FeTi oxides, all of which occur as phenocryst or significant groundmass phases in these lavas. However, variations in the trace element and isotopic compositions of the Nintoku lavas indicate derivation from a heterogeneous mantle source. The isotopic and trace element compositions of the lavas can be modeled using a modified version of the Chen and Frey (1985) mixing model for Hawaiian lavas, in which smalldegree melts of the $60 m.y. old oceanic lithosphere beneath Nintoku, previously fertilized by smalldegree melts soon after its formation at a ridge axis, are mixed with melts from the Hawaiian plume. The contribution from the oceanic lithosphere became more important with time as Nintoku Seamount moved away from the Hawaiian plume axis. Together with other data from Leg 197, our results show that the 87 Sr/ 86 Sr ratios of not only shield but also postshield lavas from the Emperor Seamounts increased with decreasing age between $80 and 50 m.y. ago. For alkalic postshield lavas, this could result from either increased melting of the oceanic lithosphere beneath volcanoes situated on younger oceanic crust or lower degrees of incompatible trace element enrichment in the lowermost portions of younger oceanic lithosphere.

Lithospheric control on geochemical composition along the Louisville Seamount Chain

“…(b) Zr/Nb versus La/Yb for the LSC lavas and Hawaiian shield, post‐shield and post‐erosional lavas (note that the LSC lavas display some similarity to the Hawaiian post‐shield lavas). Data for Hawaii are from Huang et al [2005], Shafer et al [2005], Yang et al [2003] and Pietruszka and Garcia [1999].…”

“…Intraplate volcanoes built on young, thin oceanic lithosphere close to spreading centers appear to erupt lavas with relatively depleted compositions. For example, the oldest Emperor seamounts were constructed on thin oceanic lithosphere close to a spreading center, and their comparatively depleted incompatible element compositions have been ascribed to either ‘plume‐ridge interaction’ [ Keller et al , 2000] or a ‘lithospheric lid’ effect [ Frey et al , 2005; Huang et al , 2005; Regelous et al , 2003; Shafer et al , 2005]. Osbourn Guyot was built closest to the fossil Osbourn Trough spreading center, and by analogy with the Emperor seamounts, an effect on the composition of lavas of the oldest Louisville seamounts could be expected.…”

“…This scenario would explain both the lack of a ‘thin lithosphere effect’ for the oldest Louisville seamounts as well as the normal MORB compositions of the youngest Osbourn Trough lavas. On the Emperor Seamount Chain, the effect of variable lithospheric thickness is observed only in lavas from seamounts built on crust younger than about 30 Myr [ Regelous et al , 2003; Shafer et al , 2005].…”

Horizontal and vertical zoning of heterogeneities in the Hawaiian mantle plume from the geochemistry of consecutive postshield volcano pairs: Kohala‐Mahukona and Mauna Kea–Hualalai

“…In particular, the combination of low 87 Sr/ 86 Sr and high 143 Nd/ 144 Nd with high Rb/Sr and low Sm/Nd is a paradox that has been known for some time [e.g., Chen and Frey , 1983], but that remains largely unresolved. To explain the enrichment in trace elements, assimilation models must invoke a source recently enriched (metasomatized) in incompatible trace elements [e.g., Yang et al , 2003; Shafer et al , 2005] or very small degree melts (0.1%–1%) of a depleted source [e.g., Chen and Frey , 1985]. In contrast, other studies attempt to overcome the paradox by arguing that the depleted isotopic signatures are derived from within the plume itself or from entrained deep mantle material [e.g., Frey et al , 2005; Fekiacova et al , 2007].…”

Constraints on past plate and mantle motion from new ages for the Hawaiian‐Emperor Seamount Chain

“…Variation of Zr/Nb with primitive mantle‐normalized Nb (for ease of comparison with Figure ) for SO141 samples, and lavas from different eruptive stages of Hawaiian volcanoes, showing that younger, more alkalic lavas have lower Zr/Nb ratios and higher Nb concentrations. Data for Hawaiian shield tholeiites from Koolau [ Huang and Frey , ] and Kilauea [ Pietruszka and Garcia , ], postshield alkalic lavas from Nintoku Seamount [ Shafer et al ., ], and rejuvenated volcanics from Koolau [ Yang et al ., ] shown for comparison. On the basis of this diagram, we have classified basaltic SO141 samples with Zr/Nb > 9 as shield stage lavas, and samples with Zr/Nb < 5 as rejuvenated lavas.…”