Petrology and Geochemistry of Volcanic Rocks from the South Kauaʻi Swell Volcano, Hawaiʻi: Implications for the Lithology and Composition of the Hawaiian Mantle Plume

The South Kauaʻi Swell (SKS) volcano was sampled during four JASON dives and three dredge hauls recovering rocks that range from fresh pillow lavas to altered volcanic breccias. Two geochemical groups were identified: shield-stage tholeiites (5·4–3·9 Ma) and rejuvenation-stage alkalic lavas (1·9–0·1 Ma). The young SKS ages and the coeval rejuvenated volcanism along a 400km segment of the Hawaiian Islands (Maui to Niʻihau) are inconsistent with the timing and duration predictions by the flexure and secondary plume melting models for renewed volcanism. The SKS tholeiites are geochemically heterogeneous but similar to lavas from nearby Kauaʻi, Niʻihau and Waiʻanae volcanoes, indicating that their source regions within the Hawaiian mantle plume sampled a well-mixed zone. Most SKS tholeiitic lavas exhibit radiogenic Pb isotope ratios (208Pb*/206Pb*) that are characteristic of Loa compositions (>0·9475), consistent with the volcano’s location on the west side of the Hawaiian Islands. These results document the existence of the Loa component within the Hawaiian mantle plume prior to 5 Ma. Loa trend volcanoes are thought to have a major pyroxenite component in their source. Calculations of the pyroxenitic component in the parental melts for SKS tholeiites using high-precision olivine analyses and modeling of trace element ratios indicate a large pyroxenite proportion (≥50%), which was predicted by recent numerical models. Rejuvenation-stage lavas were also found to have a significant pyroxenite component based on olivine analyses (40–60%). The abundance of pyroxenite in the source for SKS lavas may be the cause of this volcano’s extended period of magmatism (>5 Myr). The broad distribution of the Loa component in the northern Hawaiian Island lavas coincides with the start of a dramatic magma flux increase (300%) along the Hawaiian Chain, which may reflect a major structural change in the source of the Hawaiian mantle plume

Temporal geochemical variations in lavas from Kīlauea's Pu‘u ‘Ō‘ō eruption (1983–2010): Cyclic variations from melting of source heterogeneities

[1] Geochemical time series analysis of lavas from Kīlauea's ongoing Pu‘u ‘Ō‘ō eruption chronicle mantle and crustal processes during a single, prolonged (1983 to present) magmatic event, which has shown nearly two-fold variation in lava effusion rates. Here we present an update of our ongoing monitoring of the geochemical variations of Pu‘u ‘Ō‘ō lavas for the entire eruption through 2010. Oxygen isotope measurements on Pu‘u ‘Ō‘ō lavas show a remarkable range (δ^(18)O values of 4.6–5.6‰), which are interpreted to reflect moderate levels of oxygen isotope exchange with or crustal contamination by hydrothermally altered Kīlauea lavas, probably in the shallow reservoir under the Pu‘u ‘Ō‘ō vent. This process has not measurably affected ratios of radiogenic isotope or incompatible trace elements, which are thought to vary due to mantle-derived changes in the composition of the parental magma delivered to the volcano. High-precision Pb and Sr isotopic measurements were performed on lavas erupted at ∼6 month intervals since 1983 to provide insights about melting dynamics and the compositional structure of the Hawaiian plume. The new results show systematic variations of Pb and Sr isotope ratios that continued the long-term compositional trend for Kīlauea until ∼1990. Afterward, Pb isotope ratios show two cycles with ∼10 year periods, whereas the Sr isotope ratios continued to increase until ∼2003 and then shifted toward slightly less radiogenic values. The short-term periodicity of Pb isotope ratios may reflect melt extraction from mantle with a fine-scale pattern of repeating source heterogeneities or strands, which are about 1–3 km in diameter. Over the last 30 years, Pu‘u ‘Ō‘ō lavas show 15% and 25% of the known isotopic variation for Kīlauea and Mauna Kea, respectively. This observation illustrates that the dominant time scale of mantle-derived compositional variation for Hawaiian lavas is years to decades

Trace-element distribution coefficients for pyroxenes, plagioclase, and olivine in evolved tholeiites from the 1955 eruption of Kilauea Volcano, Hawaii, and petrogenesis of differentiated rift-zone lavas

Reliable values for mineral-melt trace-element distribution coefficients (D) are essential for constructing realistic models of magma evolution based on trace elements. We have determined D-values for an extensive set of compatible and incompatible trac

Crustal Contamination of Kilauea Volcano Magmas Revealed by Oxygen Isotope Analyses of Glass and Olivine from Puu Oo Eruption Lavas

Oceanic island basalts have a large range in δ^(18)O values (4.5−7.5‰) compared with the assumed primordial mantle values (5.5–6.0‰) and with mid-ocean ridge basalts (5.7 ± 0.2‰). Some Hawaiian tholeiitic basalts have low ^(18)O values (4.6–5.2‰), which have been interpreted to be either a primary source feature or caused by crustal contamination. This study was undertaken to evaluate the cause of low δ^(18)O values in Hawaiian tholeiitic basalts. We determined the δ^(18)O values of glassy matrix material and coexisting olivines from pristine basalts produced during the current, 14-year-old Puu Oo eruption of Kilauea Volcano. Our results show that the Puu Oo eruption lavas have significant ranges in matrix (0.7‰) and olivine δ18O values (0.5‰) which do not correlate consistently with other geochemical parameters and that many of the lavas are out of oxygen isotopic equilibrium. These features probably reflect partial assimilation of and oxygen exchange with metamophosed Kilauea rocks during the magma's 19 km transit through the volcano's east rift zone. The parental magmas for Puu Oo lavas had a δ^(18)O value of at least 5.2‰ and perhaps as high as 5.6‰. Thus, Puu Oo lavas do not give a clear indication of the δ18O value of Kilauea's mantle source but they do indicate that the oxygen in these otherwise pristine basalts has undergone significant modification by interaction with crustal rocks

Geochemical variations during Kilauea's Pu'u 'O'o Eruption reveal a fine-scale mixture of mantle heterogeneities within the Hawaiian Plume

Long-term geochemical monitoring of lavas from the continuing 25-year-old Pu'u 'Ōō eruption allows us to probe the crustal and mantle magmatic processes beneath Kīlauea volcano in unparalleled detail. Here we present new Pb, Sr, and Nd isotope ratios

Chemical heterogeneity in the Hawaiian mantle plume from the alteration and dehydration of recycled oceanic crust

Inter-shield differences in the composition of lavas from Hawaiian volcanoes are generally thought to result from the melting of a heterogeneous mantle source containing variable amounts or types of oceanic crust (sediment, basalt, and/or gabbro) that was recycled into the mantle at an ancient subduction zone. Here we investigate the origin of chemical heterogeneity in the Hawaiian mantle plume by comparing the incompatible trace element abundances of tholeiitic basalts from (1) the three active Hawaiian volcanoes (Kilauea, Mauna Loa, and Loihi) and (2) the extinct Koolau shield (a compositional end member for Hawaiian volcanoes). New model calculations suggest that the mantle sources of Hawaiian volcanoes contain a significant amount of recycled oceanic crust with a factor of ~2 increase from ~8-16% at Loihi and Kilauea to ~15-21% at Mauna Loa and Koolau. We propose that the Hawaiian plume contains a package of recycled oceanic crust (basalt and gabbro, with little or no marine sediment) that was altered by interaction with seawater or hydrothermal fluids prior to being variably dehydrated during subduction. The recycled oceanic crust in the mantle source of Loihi and Kilauea lavas is dominated by the uppermost portion of the residual slab (gabbro-free and strongly dehydrated), whereas the recycled oceanic crust in the mantle source of Mauna Loa and Koolau lavas is dominated by the lowermost portion of the residual slab (gabbro-rich and weakly dehydrated). The present-day distribution of compositional heterogeneities in the Hawaiian plume cannot be described by either a large-scale bilateral asymmetry or radial zonation. Instead, the mantle source of the active Hawaiian volcanoes is probably heterogeneous on a small scale with a NW-SE oriented spatial gradient in the amount, type (i.e., basalt vs. gabbro), and extent of dehydration of the ancient recycled oceanic crust

Rapid passage of a small-scale mantle heterogeneity through the melting regions of Kilauea and Mauna Loa Volcanoes

Recent Kilauea and Mauna Loa lavas provide a snapshot of the size, shape, and distribution of compositional heterogeneities within the Hawaiian mantle plume. Here we present a study of the Pb, Sr, and Nd isotope ratios of two suites of young prehistoric lavas from these volcanoes: (1) Kilauea summit lavas erupted from AD 900 to 1400, and (2) 14C-dated Mauna Loa flows erupted from ∼ 2580-140 yr before present (relative to AD 1950). These lavas display systematic isotopic fluctuations, and the Kilauea lavas span the Pb isotopic divide that was previously thought to exist between these two volcanoes. For a brief period from AD 250 to 1400, the 206Pb/204Pb and 87Sr/86Sr isotope ratios and εNd values of Kilauea and Mauna Loa lavas departed from values typical for each volcano (based on historical and other young prehistoric lavas), moved towards an intermediate composition, and subsequently returned to typical values. This is the only known period in the eruptive history of these volcanoes when such a simultaneous convergence of Pb, Sr, and Nd isotope ratios has occurred. The common isotopic composition of lavas erupted from both Kilauea and Mauna Loa during this transient magmatic event was probably caused by the rapid passage of a small-scale compositional heterogeneity through the melting regions of both volcanoes. This heterogeneity is thought to have been either a single body (∼ 35 km long based on the distance between the summits of these volcanoes) or the plume matrix itself (which would be expected to be present beneath both volcanoes). The time scale of this event (centuries) is much shorter than previously noted for variations in the isotopic composition of Hawaiian lavas due to the upwelling of heterogeneities within the plume (thousands to tens of thousands of years). Calculations based on the timing of the isotopic convergence suggest a maximum thickness for the melting region (and thus, the heterogeneity) of ∼ 5-10 km. The small size of the heterogeneity indicates that melt can be extracted from small regions within the Hawaiian plume with minimal subsequent chemical modification (beyond the effects of crystal fractionation). This would be most effective if melt transport in the mantle beneath Hawaiian shield volcanoes occurs mostly in chemically isolated channels. © 2007 Elsevier B.V. All rights reserved.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Time scales of formation of zoned magma chambers: U-series disequilibria in the Fogo A and 1563 A.D. trachyte deposits, São Miguel, Azores

High precision measurements of 226Ra–230Th–238U disequilibria and Ba concentrations are reported for samples from two chemically zoned trachyte deposits from Fogo volcano, São Miguel, Azores. High-precision U-series disequilibria measurements by plasma ionization multicollector mass spectrometry were performed on pumice lapilli and volcanic glass separates from Fogo 1563 A.D. (∼ 0.14 km3) and the ∼ 4.7 ka Fogo A (∼ 0.7 km3) deposits in order to quantify the time scales of magmatic processes. Observed (226Ra)/Ba–(230Th)/Ba relationships in Fogo 1563 are compatible with a conventional instantaneous fractional crystallization model and a pre-eruptive magma residence time of ∼ 50 y. However, the Fogo A data cannot be explained by instantaneous fractional crystallization, and require a prolonged crystallization history. Continuous differentiation models better explain the observed 226Ra–230Th variations within the Fogo deposits and may be more realistic in general. Such models suggest magma residence times prior to eruption of ∼ 50–80 years for Fogo 1563, and ∼ 4.7 ka for the larger volume Fogo A eruption. These time scales represent liquid residence ages rather than the crystallization ages documented in most previous magmatic time scale studies, and allow constraints to be placed on the time scales necessary for the development of chemical zonation within the Fogo magma chamber. Our results indicate that calculated time scales are relatively insensitive to the precise nature of the continuous differentiation models, and further indicate that meaningful magma differentiation time scales can be obtained despite open system behavior, because the Ra–Th disequilibria are overwhelmingly controlled by feldspar fractionation. Calculated time scales are, however, extremely sensitive to DRa/DBa ratios. We therefore emphasize the crucial importance to better constrain the relative partitioning of Ra and Ba when employing Ra–Th disequilibrium data to constrain the rates and time scales of igneous processes