Rb-Sr Systematics of Basalts from the Hawaiian-Emperor Volcanic Chain

[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.

Section: Discussionmentioning

confidence: 99%

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

Shafer

Neal

Regelous³

2005

“…All samples analyzed for Hf isotope ratios (Tables 1a and 1b) have been previously analyzed for Sr, Nd and Pb isotope ratios. They include 4 samples from Meiji Seamount obtained during DSDP Leg 19 [ Regelous et al , 2003], 28 samples recovered from Detroit Seamount on ODP Legs 145 and 197 [ Regelous et al , 2003; Huang et al , 2005], 4 samples from Suiko Seamount obtained during DSDP Leg 55 [ Lanphere et al , 1980], 16 samples from rejuvenated‐stage lavas, 9 from the Honolulu Volcanics, 7 from the Koloa Volcanics [ Reiners and Nelson , 1998; Lassiter et al , 2000], and 4 samples from the North Arch volcanic field which are geochemically similar to rejuvenated‐stage lavas [ Frey et al , 2000; Yang et al , 2003]. In addition, garnet and clinopyroxene separates from three garnet pyroxenite xenoliths from Salt Lake Crater, Oahu were analyzed for Hf and Nd isotopic ratios.…”

Section: Samplesmentioning

confidence: 99%

“…Our results show that even with consideration of uncertainties arising from age corrections, the sources of Detroit Seamount lavas had lower 87 Sr/ 86 Sr than the sources of Hawaiian lavas. Data sources: Modern Hawaiian shields from GEOROC database; Emperor Seamounts from Lanphere et al [1980], Basu and Faggart [1996], Keller et al [2000], Regelous et al [2003], and Huang et al [2005]. (b) For 176 Hf/ 177 Hf the minimal estimates (data points) of present‐day source ratios are measured 176 Hf/ 177 Hf.…”

Section: Temporal Evolution Of Sr Nd and Hf Isotope Ratios Along Thmentioning

confidence: 99%

Origin of depleted components in basalt related to the Hawaiian hot spot: Evidence from isotopic and incompatible element ratios

Frey

Huang

Blichert‐Toft

et al. 2005

[1] The radiogenic isotopic ratios of Sr, Nd, Hf, and Pb in basaltic lavas associated with major hot spots, such as Hawaii, document the geochemical heterogeneity of their mantle source. What processes created such heterogeneity? For Hawaiian lavas there has been extensive discussion of geochemically enriched source components, but relatively little attention has been given to the origin of depleted source components, that is, components with the lowest 87 Sr/ 86 Sr and highest 143 Nd/ 144 Nd and 176 Hf/ 177 Hf. The surprisingly important role of a depleted component in the source of the incompatible element-enriched, rejuvenated-stage Hawaiian lavas is well known. A depleted component also contributed significantly to the 76-81 Ma lavas erupted at Detroit Seamount in the Emperor Seamount Chain. In both cases, major involvement of MORB-related depleted asthenosphere or lithosphere has been proposed. Detroit Seamount and rejuvenated-stage lavas, however, have important isotopic differences from most Pacific MORB. Specifically, they define trends to relatively unradiogenic Pb isotope ratios, and most Emperor Seamount lavas define a steep trend of 176 Hf/ 177 Hf versus 143 Nd/ 144 Nd. In addition, lavas from Detroit Seamount and recent rejuvenatedstage lavas have relatively high Ba/Th, a characteristic of lavas associated with the Hawaiian hot spot. It is possible that a depleted component, intrinsic to the hot spot, has contributed to these young and old lavas related to the Hawaiian hot spot. The persistence of such a component over 80 Myr is consistent with a long-lived source, i.e., a plume. (2005), Origin of depleted components in basalt related to the Hawaiian hot spot: Evidence from isotopic and incompatible element ratios, Geochem. Geophys. Geosyst., 6, Q02L07,

“… Dalrymple et al [1980] and Sharp and Clague [2002] reported ages of 64.7 ± 1.1 Ma and 61.3 ± 0.5 Ma, respectively, for Suiko Seamount lavas. Important results are that: (1) like Hawaiian volcanoes, Suiko Seamount has shield stage lavas of tholeiitic basalt overlain by alkalic basalt [ Kirkpatrick et al , 1980]; (2) Initial 87 Sr/ 86 Sr ratios of tholeiitic basalt decrease from Daikakuji Seamount at the Hawaiian‐Emperor bend to Suiko Seamount, which represent over 20 Myr of hot spot activity (∼42–61 Ma, Figure 1a) [ Lanphere et al , 1980].…”

Section: Introductionmentioning

confidence: 99%

Petrogenesis of lavas from Detroit Seamount: Geochemical differences between Emperor Chain and Hawaiian volcanoes

Huang

Regelous

Thordarson

et al. 2005

[1] The Hawaiian Ridge and Emperor Seamount Chain define a hot spot track that provides an 80 Myr record of Hawaiian magmatism. Detroit Seamount ($76 to 81 Ma) is one of the oldest Emperor Seamounts. Volcanic rocks forming this seamount have been cored by the Ocean Drilling Program at six locations. Only tholeiitic basalt occurs at Site 884 on the eastern flank and only alkalic basalt, probably postshield lavas, occurs at Sites 883 and 1204 on the summit plateau. However, at Site 1203 the basement core (453 m penetration) includes four thick flows of pahoehoe alkalic basalt underlying $300 m of volcaniclastic rocks interbedded with submarine erupted tholeiitic basalt. The geochemical characteristics of these alkalic lavas indicate that phlogopite was important in their petrogenesis; they may represent preshield stage volcanism. The surprising upward transition from subaerial to submarine eruptives implies rapid subsidence of the volcano, which can be explained by the inferred near-ridge axis setting of the seamount at $80 Ma. A near-ridge axis setting with thin lithosphere is also consistent with a shallow depth of melt segregation for Detroit Seamount magmas relative to Hawaiian magmas, and the significant role for plagioclase fractionation as the Detroit Seamount magmas evolved in the crust. An important long-term trend along the hot spot track is that 87 Pb. We speculate that rejuvenated stage lavas and Detroit Seamount lavas sample a depleted mantle component, intrinsic to the plume, over the past 80 Myr.