Erratum to Edward A. Boyle, Bridget A. Bergquist, Richard A. Kayser and Natalie Mahowald (2005) “Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA: Temporal variability and an intermediate water hydrothermal plume”, Geochimica et Cosmochimica Acta 69, 933–952 (original) (raw)

Geochemical Evidence for Excess Iron in the Mantle Beneath Hawaii

Science, 2004

zircon into baddelyite and silica. Comparison of U-Xe and U-Pb ages (24) suggests that Xe is at least as strongly retained as Pb. Nevertheless, Pb loss associated with metamictization is commonly observed in zircons (25), and, given the antiquity and complex history of the ancient detrital zircons, it is likely that loss of Xe will also have occurred in a portion of our samples.

An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific

Earth and Planetary Science Letters, 2020

We observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount. The 3 He/ 4 He of the added helium was 27.3 times the atmospheric ratio, clearly marking its origin to a primitive mantle plume. The dissolved iron to 3 He ratio (dFe: 3 He) exported to surrounding waters was 9.3 ± 0.3 × 10 6. We observed the Loihi 3 He and dFe "signal" at a depth of 1100 m at several stations within ∼100-1000 km of Loihi, which exhibited a distal dFe: 3 He ratio of ∼4 × 10 6 , about half the proximal ratio. These ratios were remarkably similar to those observed over and near the Southern East Pacific Rise (SEPR) despite greatly contrasting geochemical and volcanictectonic origins. In contrast, the proximal and distal dMn: 3 He ratios were both ∼ 1 × 10 6 , less than half of that observed at the SEPR. Dissolved methane was minimally enriched in waters above Loihi Seamount and was distally absent. Using an idealized regional-scale model we replicated the historically observed regional 3 He distribution, requiring a hydrothermal 3 He source from Loihi of 10.4 ± 4.2 mol a −1 , ∼2% of the global abyssal hydrothermal 3 He flux. From this we compute a corresponding dFe flux of ∼40 Mmol a −1. Global circulation model simulations suggest that the Loihi-influenced waters eventually upwell along the west coast of North America, also extending into the shallow northwest Pacific, making it a possibly important determinant of marine primary production in the subpolar North Pacific.

The age of subducted component in the source of Hawaiian plume

Recycling of oceanic crust through subduction, mantle upwelling, and remelting in mantle plumes is a widely accepted mechanism to explain ocean island volcanism 1 . The timescale of this recycling is important to our understanding of mantle circulation rates. Correlations of uranogenic lead isotopes in lavas from ocean islands such as Hawaii or Iceland, when interpreted as model isochrons, have yielded source differentiation ages between 1 and 2.5 billion years (Gyr) 2-5 . However, if such correlations are produced by mixing of unrelated mantle components 6 they will have no direct age significance. Re-Os decay model ages take into account the mixing of sources with different histories 7,8 , but they depend on the assumed initial Re/Os ratio of the subducted crust, which is poorly constrained because of the high mobility of rhenium during subduction 9 . Here we report the first data on 87 Sr/ 86 Sr ratios for 138 melt inclusions in olivine phenocrysts from lavas of Mauna Loa shield volcano, Hawaii, indicating enormous mantle source heterogeneity. We show that highly radiogenic strontium in severely rubidium-depleted melt inclusions matches the isotopic composition of 200-650-Myr-old sea water. We infer that such sea water must have contaminated the Mauna Loa source rock, before subduction, imparting a unique 'time stamp' on this source. Small amounts of seawater-derived strontium in plume sources may be common but can be identified clearly only in ultra-depleted melts originating from generally highly (incompatible-element) depleted source components. The presence of 200-650-Myr-old oceanic crust in the source of Hawaiian lavas implies a timescale of general mantle circulation with an average rate of about 2 (61) cm yr 21 , much faster than previously thought.

Manganese and methane in hydrothermal plumes along the East Pacific Rise, 8°40′ to 11°50′N

Geochimica et Cosmochimica Acta, 1995

In November, 1991, we surveyed the water column for hydrothermal plumes along 350 km of the East Pacific Rise axis from 8'40 ' to 1 lo50 ' N, using a combination of physical and chemical measurements. Our survey included the two major ridge segments north and south of the Clipperton Transform Fault at about lO"lO'N, both limbs of the overlapping spreading centers (OSC's) at 9"03 'N and 1 lo45 'N, and a 30&m section of the next ridge segment to the south. We found vigorous plumes along most of this ridge axis, in keeping with its magmatically robust cross-section, axial summit caldera, and shallow, magma-related seismic reflector. These plumes were detectable by both physical (temperature and light attenuation) and chemical (dissolved Mn and CR) measurements, although the chemical measurements were more sensitive. The least active sections were the southern third of the northern segment from lo"20 to 52'N and the OSCs, especially the OSC at ll"45'N. Plumes there had weak Mn and CH4 signals and were barely detectable by physical methods. These axial sections were the only ones surveyed that lie deeper than 2600 m and appear to be magma starved. The most active sections on the northern segment gave stronger signals for Mn and temperature than for CH, and light attenuation, whereas the opposite was true on the southern segment, which was the site of a volcanic eruption at 9"45-52'N only seven months prior to our cruise. On the northern segment the four physical and chemical plume tracers correlated positively and linearly with one another, suggesting that the segment was fed by relatively uniform endmember fluids with a mean C&Nn molar ratio of 0.075. The southernmost section surveyed, from 8"42' to 9'08 'N, closely resembled the northern segment. The rest of the southern segment fell into three sections with different CHJMn ratios: 9"39 to 53'N with CHJMn as high as 10, 9'08 to 39'N with CHJMn of 0.51, and 9"53 ' to lO"07'N with CH,/Mn of 0.85. The section with the highest CHJMn was the site of the volcanic eruption, which produced high-temperature, low-salinity, gas-rich vent fluids carrying abundant bacterial Darticles. The high CH, concentradons are clearly associated with the volcanic eruption, but the origin of the CH, is uncle&.

Evidence for hydrothermal venting in Fe isotope compositions of the deep Pacific Ocean through time

Earth and Planetary Science Letters, 2006

Temporal variations in Fe isotope compositions at three locations in the Pacific Ocean over the last 10 Ma are inferred from high-resolution analyses of three hydrogenetic ferromanganese crusts. Iron pathways to the central deep Pacific Ocean appear to have remained constant over the past 10 Ma, reflected by a remarkably constant Fe isotope composition, despite large changes in the Fe delivery rates to the surface ocean via dust. These results suggest that the Fe cycle in the deep ocean is decoupled from that in surface waters. By contrast, one ferromanganese crust from the Izu-Bonin (IB) back-arc/marginal basin of the W. Pacific exhibits large δ 56 Fe variations. In that crust, decreases in δ 56 Fe values correlate with increases in Mn, Mg, Ni, Cu, Zn, Mo, and V contents, and consistent with periods of intense hydrothermal input and increased growth rates. A second crust located within 100 km of the first IB sample does not record any of these periods of enhanced hydrothermal input. This probably reflects the isolated pathways by which hydrothermally sourced Fe may have migrated in the back arc, highlighting the high degree of provinciality that Fe isotopes may have in the modern (oxic) oceans. Our results demonstrate that despite efficient removal at the source, hydrothermal Fe injected into the deep ocean could account for a significant fraction of the dissolved Fe pool in the deep ocean, and that hydrothermally sourced Fe fluxes to the open ocean may have lower δ 56 Fe values than those measured so far in situ at hydrothermal vents. Correlation between δ 56 Fe values and elements enriched in hydrothermal fluids may provide a means for distinguishing hydrothermal Fe from other low-δ 56 Fe sources to the oceans such as dissolved riverine Fe or porewaters in continental shelf sediments.

A young source for the Hawaiian plume

Nature, 2011

OXYGEN ISOTOPE CONSTRAINTS ON THE STRUCTURE AND EVOLUTION OF THE HAWAIIAN PLUME

American Journal of Science, 2010

The oxygen isotope stratigraphy of Ko'olau volcano, Hawaii, is constructed by analyzing olivine phenocrysts from the KSDP drill core and submarine land-slide deposits. Along with those of subaerial (Makapu'u) Ko'olau olivines (Eiler and others, 1996a), they span the full range of the ␦ 18 O VSMOW variation previously observed in "Loa-trend" Hawaiian volcanoes (Lō'ihi, Mauna Loa, Hualalai, and Ko'olau), vary systematically with the stratigraphic position, and correlate with other geochemical properties of their host lavas (Tanaka and others, 2002; Haskins and Garcia, 2004; Huang and Frey, 2005; Salters and others, 2006; Fekiacova and others, 2007). These observations can be explained if the "Loa-trend" volcanoes (including Ko'olau) are constructed of magmas made by mixing peridotite melt with variable proportions of eclogite melt derived from a mafic constituent of the Hawaiian plume having a composition resembling recent mid-ocean-ridge basalts.

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