Extraction of mid-ocean-ridge basalt from the upwelling mantle by focused flow of melt in dunite channels

Kelemen, P. B.; Shimizu, Nobumichi; Salters, Vincent J. M.

doi:10.1038/375747a0

Cited by 741 publications

(485 citation statements)

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“…Trace element disequilibrium between residual peridotites and MORB provides a similar constraint [Johnson et al, 1990;Spiegelman and Kenyon, 1992]. These constraints can be satisfied by (1) very rapid transport, for example in melt-filled fractures [Nicolas, 1986] (so that the diffusion time is short) or (2) by slower, porous flow in wide, dunite conduits, in which the distance between migrating melt and opx in residual peridotite is longer than the diffusion distance [Kelemen et al, , 1995a[Kelemen et al, , 1995b. For melt transport times through the upper 30 km of the upper mantle of 3000 to 30,000 years and effective diffusivity $5Â 10 À12 m 2 /s (melt diffusivity $10 À10 , porosity $0.05), this requires dunite widths greater than 0.7 to 2 m.…”

Section: Introductionmentioning

confidence: 99%

“…In contrast, surrounding, residual peridotites preserve mineral compositions far from equilibrium with MORB [Kelemen et al, 1995a]. Thus dunites in the Oman mantle section mark conduits for focused flow of melt through the uppermost mantle in a process that preserved disequilibrium between migrating liquid and surrounding peridotite.…”

Section: Introductionmentioning

confidence: 99%

“…If so, this process may be important in producing coalescence from the $100 km wide region of partial melting in the mantle to the $5 km wide zone of igneous crustal formation beneath oceanic spreading ridges. Kelemen et al [1995a] showing general contact relationships of large dunites in the mantle section of the Oman ophiolite and inferred coalescing network of porous dunite channels in the adiabatically upwelling mantle beneath a fast-spreading mid-ocean ridge. Note that the network shown here resembles a bush, with many branches coalescing at the base of the lithosphere beneath the ridge, whereas that published previously [Kelemen et al, 1995a] was a tree-like structure with branches entering a single, central conduit.…”

Section: Geochemistry Geophysicsmentioning

confidence: 99%

“…[6] In general, field evidence from ophiolites demonstrates that most or all dunites formed via in situ replacement due to opx dissolution and concomitant olivine precipitation during porous flow of olivine-saturated melt through opx-bearing peridotite [Kelemen et al, 1995a]. Therefore some dunites may form purely as a result of reactive porous flow processes, and the presence of melt filled cracks is not required to explain them.…”

Section: Introductionmentioning

confidence: 99%

“…[5] Minerals in dunites in the mantle section of the Oman ophiolite have compositions that are close to chemical equilibrium with MORB and with similar basalts from other submarine spreading centers (e.g., ophiolites, back arc basins) [Kelemen et al, 1995a]. In contrast, surrounding, residual peridotites preserve mineral compositions far from equilibrium with MORB [Kelemen et al, 1995a].…”

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Kelemen

Braun

Hirth

2000

Geochem Geophys Geosyst

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[1] Ophiolites are on-land exposures of igneous crust and residual upper mantle formed beneath submarine spreading ridges. Upper mantle outcrops in ophiolites provide insight into focusing of melt transport from a $100 km wide region of partial melting into an $5 km wide zone of igneous crustal accretion beneath the ridges. Dunite veins, composed of the minerals olivine and spinel, mark conduits for melt transport through at least the uppermost 30 km of the mantle. New data in this paper, on dunite veins in the Ingalls ophiolite, central Washington Cascades, show a power law relationship between frequency and width, in which frequency/m %0.02 width À3 over a size interval from $0.1 to 2 m. There may be several ways to generate this relationship, but we favor the hypothesis that the dunites represent a coalescing melt transport network. This conclusion is broadly consistent with the related hypothesis that mantle melt extraction occurs in a fractal, branching network, and with recent results on formation of a coalescing network of dissolution channels via flow of a solvent through a partially soluble, compacting porous medium.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Geochemistry Geophysicsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Kelemen

Braun

Hirth

2000

Geochem Geophys Geosyst

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Pyroxenes as tracers of mantle water variations

2014

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The concentration and distribution of volatiles in the Earth's mantle influence properties such as melting temperature, conductivity, and viscosity. To constrain upper mantle water content, concentrations of H 2 O, P, and F were measured in olivine, orthopyroxene, and clinopyroxene in mantle peridotites by secondary ion mass spectrometry. Analyzed peridotites are xenoliths (Pali Aike, Spitsbergen, Samoa), orogenic peridotites (Josephine Peridotite), and abyssal peridotites (Gakkel Ridge, Southwest Indian Ridge, Tonga Trench). The comparison of fresh and altered peridotites demonstrates that low to moderate levels of alteration do not affect H 2 O concentrations, in agreement with mineral diffusion data. Olivines have diffusively lost water during emplacement, as demonstrated by disequilibrium between olivine and coexisting pyroxenes. In contrast, clinopyroxene and orthopyroxene preserve their high-temperature water contents, and their partitioning agrees with published experiments and other xenoliths. Hence, olivine water concentrations can be determined from pyroxene concentrations using mineral-mineral partition coefficients. Clinopyroxenes have 60-670 ppm H 2 O, while orthopyroxenes have 10-300 ppm, which gives calculated olivine concentrations of 8-34 ppm. The highest olivine water concentration translates to an effective viscosity of 6 × 1019 Pa s at 1250°C and~15 km depth, compared to a dry effective viscosity of 2.5 × 10 21 Pa s. Bulk rock water concentrations, calculated using mineral modes, are 20-220 ppm and correlate with peridotite indices of melt depletion. However, trace element melt modeling indicates that peridotites have too much water relative to their rare earth element concentrations, which may be explained by late-stage melt addition, during which only hydrogen diffuses fast enough for reequilibration.

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Magmatic plumbing at Lucky Strike volcano based on olivine‐hosted melt inclusion compositions

Wanless

Shaw²,

Behn

et al. 2015

Geochem Geophys Geosyst

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Here we present volatile, major, and trace element concentrations of 64 olivine-hosted melt inclusions from the Lucky Strike segment on the mid-Atlantic ridge. Lucky Strike is one of two locations where a crustal melt lens has been seismically imaged on a slow-spreading ridge. Vapor-saturation pressures, calculated from CO 2 and H 2 O contents of Lucky Strike melt inclusions, range from approximately 300-3000 bars, corresponding to depths of 0.5-9.9 km below the seafloor. Approximately 50% of the melt inclusions record crystallization depths of 3-4 km, corresponding to the seismically imaged melt lens depth, while an additional 35% crystallize at depths > 4 km. This indicates that while crystallization is focused within the melt lens, significant crystallization also occurs in the lower crust and/or upper mantle. The melt inclusions span a range of major and trace element concentrations from normal to enriched basalts. Trace element ratios at all depths are heterogeneous, suggesting that melts are not efficiently homogenized in the mantle or crust, despite the presence of a melt lens. This is consistent with the transient nature of magma chambers proposed for slower-spreading ridges. To investigate the petrogenesis of the melt inclusion compositions, we compare the measured trace element compositions to theoretical melting calculations that consider variations in the melting geometry and heterogeneities in the mantle source. The full range of compositions can be produced by slight variations in the proportion of an Azores plume and depleted upper mantle components and changes in the total extent of melting.

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Extraction of mid-ocean-ridge basalt from the upwelling mantle by focused flow of melt in dunite channels

Cited by 741 publications

References 48 publications

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Spatial distribution of melt conduits in the mantle beneath oceanic spreading ridges: Observations from the Ingalls and Oman ophiolites

Pyroxenes as tracers of mantle water variations

Magmatic plumbing at Lucky Strike volcano based on olivine‐hosted melt inclusion compositions

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