Experimentally Determined Phase Relations in Hydrous Peridotites to 6{middle dot}5 GPa and their Consequences on the Dynamics of Subduction Zones

Fumagalli, P.; Poli, Stefano

doi:10.1093/petrology/egh088

Cited by 200 publications

(172 citation statements)

References 59 publications

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“…The amounts of each component and degree of melting from the model is given in insets temperatures for different age groups. If confirmed, these high temperatures would place the mantle source at the uppermost limit of amphibole stability in the mantle wedge (Foley 1991;Fumagalli and Poli 2005;Niida and Green 1999;Schmidt and Poli 1998;Wallace and Green 1991). Our interpretation supports an OIB-type mantle component (Volynets 1994;Churikova et al , 2007Münker et al 2004); however, different mantle sources are evident in slightly variable isotopic compositions for only a few samples (Fig.…”

Section: Mantle Source Compositionssupporting

confidence: 59%

Mafic Late Miocene–Quaternary volcanic rocks in the Kamchatka back arc region: implications for subduction geometry and slab history at the Pacific–Aleutian junction

Volynets

Churikova

Wörner

et al. 2009

Contrib Mineral Petrol

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New 40 Ar/ 39 Ar and published 14 C ages constrain voluminous mafic volcanism of the Kamchatka backarc to Miocene (3-6 Ma) and Late Pleistocene to Holocene (\1 Ma) times. Trace elements and isotopic compositions show that older rocks derived from a depleted mantle through subduction fluid-flux melting ([20%). Younger rocks form in a back arc by lower melting degrees involving enriched mantle components. The arc front and Central Kamchatka Depression are also underlain by plateau lavas and shield volcanoes of Late Pleistocene age. The focus of these voluminous eruptions thus migrated in time and may be the result of a high fluid flux in a setting where the Emperor seamount subducts and the slab steepens during rollback during terrain accretions. The northern termination of Holocene volcanism locates the edge of the subducting Pacific plate below Kamchatka, a ''slab-edge-effect'' is not observed in the back arc region.

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Section: Mantle Source Compositionssupporting

confidence: 59%

Mafic Late Miocene–Quaternary volcanic rocks in the Kamchatka back arc region: implications for subduction geometry and slab history at the Pacific–Aleutian junction

Volynets

Churikova

Wörner

et al. 2009

Contrib Mineral Petrol

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“…Removal of H 2 O from the fluid forces the fluid to evolve along the graphite/diamond saturation surface continuously precipitating graphite/diamond concomitantly with the formation of hydrous magnesium silicates. Note that step 2 requires temperatures within the stability fields of these phases, which, in equilibrium with olivine, for the most part do not exceed 700-800°C (Fumagalli and Poli, 2005).…”

Section: A Model For Sic Formation In Naturementioning

confidence: 99%

Natural moissanite (SiC) – a low temperature mineral formed from highly fractionated ultra-reducing COH-fluids

Schmidt

Gao

Golubkova

et al. 2014

Prog. in Earth and Planet. Sci.

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Natural moissanite (SiC) is reported from dozens of localities, most commonly from ultramafic rocks where it may be associated with diamond and iron silicides. Yet, formation conditions of moissanite remain in the realm of speculation. The key property of SiC is its extremely reduced nature. We have experimentally equilibrated SiC with olivine and orthopyroxene at 1300-1700°C, 2 and 10 GPa, to determine the oxygen fugacity of the C + orthopyroxene = SiC + olivine + O 2 buffer (MOOC) and the equilibrium X Mg of coexisting mantle silicates. The experiments resulted in olivine and orthopyroxene with X Mg of 0.993-0.998 in equilibrium with SiC and iron silicides. Calculated oxygen fugacities are 5-6.5 log units below the iron-wustite (IW) buffer at 2-10 GPa. The experimental results concur with calculated phase relations for harzburgitic mantle under reducing conditions that include metal alloys, carbides and silicides. The extremely reducing character of SiC precludes coexistence with silicates with appreciable Fe 2+ , and hence excludes equilibrium with mantle phases with typical X Mg 's of~0.9. Calculated Fe-Mg diffusion lengths reveal that SiC grains of 1 mm would react with the Fe-component of olivine to iron carbide or metal and orthopyroxene within <1 Ma at temperatures above 800°C. We thus conclude that SiC forms through a low-temperature process (<700-800°C) where equilibrium is only reached at the grain scale. The most plausible formation mechanism is a strong fractionation of a C-O-H fluid from metamorphosed sediments originally rich in organic material. Such a fluid is initially saturated with graphite or diamond and is slightly more reduced than the H 2 O-C join. Fluid percolation in the mantle leads to H 2 O-sequestration by crystallizing hydrous phases (most likely serpentine, brucite or phase A), and hence O 2 -removal from the fluid causing its reduction and continuous graphite or diamond precipitation. A small, highly fractionated fluid fraction may then reach CH 4 and H 2 concentrations that allow SiC formation on grain boundaries without equilibration with the bulk rock on a larger scale. Such a mechanism is corroborated by the strongly negative δ 13 C of moissanites (-20 to -37), consistent with reduced fluids originating from metamorphosed organic carbon.

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“…3). Mé dard and Grove (2006) used results from Fumagalli and Poli (2005) and Schmidt and Poli (1998) to infer hydrous mineral phase relations at P43 GPa (Fig. 3B).…”

Section: Deep Water Storage and Melting Path: Comparison With Previoumentioning

confidence: 99%

“…which is closer to our composition (Mg#¼75). The compositions used by Fumagalli and Poli (2005) has Mg# ¼83-91. Therefore, it seems that the humite minerals and phase E are favored in ironrich peridotites compared to the one of phase A and 10Å phase, stable in compositions with higher Mg#.…”

Section: Deep Water Storage and Melting Path: Comparison With Previoumentioning

confidence: 99%

Water storage and early hydrous melting of the Martian mantle

Pommier¹,

Grove²,

Charlier³

2012

Earth and Planetary Science Letters

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a b s t r a c tWe report an experimental investigation of the near-solidus phase equilibria of a water-saturated analog of the Martian mantle. Experiments were performed at low temperatures (700-920 1C) and high pressure (4-7 GPa) using multi-anvil apparatus and piston cylinder device (4 GPa). The results of this study are used to explore the role of water during early melting and chemical differentiation of Mars, and to further our understanding of the near-solidus behavior in planetary mantle compositions at high pressure. Water has a significant effect on the temperature of melting and, therefore, on accretion and subsequent differentiation processes. Experiments locate the wet solidus at $ 800 1C, and is isothermal between 4 GPa and 7 GPa. The Martian primitive mantle can store significant amounts of water in hydrous minerals stable near the solidus. Humite-group minerals and phase E represent the most abundant hydrous minerals stable in the 4-7 GPa pressure range. The amount of water that can be stored in the mantle and mobilized during melting ranges from 1 to up to 4 wt% near the wet solidus. We discuss thermal models of Mars accretion where the planet formed very rapidly and early on in solar system history. We incorporate the time constraint of Dauphas and Pourmand (2011) that Mars had accreted to 50% of its present mass in 1.8 Myr and include the effects of 26 Al radioactive decay and heat supplied by rapid accretion. When accretion has reached 30% of Mars current mass ( $ 70% of its present size), melting starts, and extends from 100 to 720 km depth. Below this melt layer, water can still be bound in crystalline solids. The critical stage is at 50% accretion ( $ 80% of its size), where Mars is above the wet and dry solidi with most of its interior melted. This is earlier in the accretion process than what would be predicted from dry melting. We suggest that water may have promoted early core formation on Mars and rapidly extended melting over a large portion of Mars interior.

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Experimentally Determined Phase Relations in Hydrous Peridotites to 6{middle dot}5 GPa and their Consequences on the Dynamics of Subduction Zones

Cited by 200 publications

References 59 publications

Mafic Late Miocene–Quaternary volcanic rocks in the Kamchatka back arc region: implications for subduction geometry and slab history at the Pacific–Aleutian junction

Mafic Late Miocene–Quaternary volcanic rocks in the Kamchatka back arc region: implications for subduction geometry and slab history at the Pacific–Aleutian junction

Natural moissanite (SiC) – a low temperature mineral formed from highly fractionated ultra-reducing COH-fluids

Water storage and early hydrous melting of the Martian mantle

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