Slab melting versus slab dehydration in subduction-zone magmatism

Mibe, Kenji; Kawamoto, Tatsuhiko; Matsukage, Kyoko N.; Fei, Yingwei; Ono, Shigeaki

doi:10.1073/pnas.1010968108

Cited by 160 publications

(89 citation statements)

References 52 publications

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“…1E). Mibe et al (23,24) reported similar observations in the experimental products of peridotite/ basalt-H 2 O system. We interpret the large glass globules and portions as quench products from hydrous melts, and the void space as a quench product from aqueous fluids.…”

Section: X-ray Radiography Experimentssupporting

confidence: 70%

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Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

Kawamoto

Kanzaki

Mibe

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Subduction-zone magmatism is triggered by the addition of H 2 Orich slab-derived components: aqueous fluid, hydrous partial melts, or supercritical fluids from the subducting slab. Geochemical analyses of island arc basalts suggest two slab-derived signatures of a melt and a fluid. These two liquids unite to a supercritical fluid under pressure and temperature conditions beyond a critical endpoint. We ascertain critical endpoints between aqueous fluids and sediment or high-Mg andesite (HMA) melts located, respectively, at 83-km and 92-km depths by using an in situ observation technique. These depths are within the mantle wedge underlying volcanic fronts, which are formed 90 to 200 km above subducting slabs. These data suggest that sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, react with mantle peridotite to form HMA supercritical fluids. Such HMA supercritical fluids separate into aqueous fluids and HMA melts at 92 km depth during ascent. The aqueous fluids are fluxed into the asthenospheric mantle to form arc basalts, which are locally associated with HMAs in hot subduction zones. The separated HMA melts retain their composition in limited equilibrium with the surrounding mantle. Alternatively, they equilibrate with the surrounding mantle and change the major element chemistry to basaltic composition. However, trace element signatures of sediment-derived supercritical fluids remain more in the melt-derived magma than in the fluid-induced magma, which inherits only fluid-mobile elements from the sedimentderived supercritical fluids. Separation of slab-derived supercritical fluids into melts and aqueous fluids can elucidate the two slab-derived components observed in subduction zone magma chemistry.water | second critical point | synchrotron X-ray | pelite | adakite A ddition of aqueous fluids to the mantle wedge plays an important role in reducing the melting temperature and in producing partial melts (1-4). Alternatively, partial melts of downgoing sediment or oceanic basalt themselves are added to the mantle wedge, resulting in subduction-zone magmatism (5), especially in hot environments occurring with subduction of a young oceanic plate (6, 7). Arc basalts are characterized by their higher concentrations of H 2 O and large ion lithophile elements than those of mid-ocean ridge basalts (3,4,(8)(9)(10)(11)(12). Such subductionzone signatures are attributed to the addition of slab-derived components into a mid-ocean ridge basalt source mantle. Whether the slab-derived component is an aqueous fluid, a partial melt, or a supercritical fluid persists as an open question (13-15). In general, with increasing pressure, aqueous fluids dissolve more silicate components and silicate melts dissolve more H 2 O. Under low-pressure conditions, those aqueous fluids and hydrous silicate melts are divided by an immiscibility gap. Its highest temperature is designated as a critical point. The temperature of the critical point decreases concomitantly with increasing pressure, f...

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Section: X-ray Radiography Experimentssupporting

confidence: 70%

“…P-T diagram shows critical endpoints and an inferred schematic illustration in a mantle wedge with thermal structure suggested by Peacock and Wang (37). (A) P-T diagram shows critical endpoints and critical curves (13,23,24,28). (Ab, albite; Ca-Hgr, CaO bearing haplogranite; Hgr, haplogranite; Jd, jadeite; Ne, nepheline.)…”

Section: Methodsmentioning

confidence: 99%

Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

Kawamoto

Kanzaki

Mibe

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Composition and structure of silicate-saturated aqueous fluids at high temperature and pressure have been determined experimentally for pure SiO 2 -H 2 O systems as well as for some more complex silicate and aluminosilicate compositions (Newton and Manning 2002;Kessel et al 2005;Mibe et al 2008Mibe et al , 2011Mysen 2010). From those experiments, it is evident that silicate solubility in aqueous fluids depends on the presence of other components in addition to SiO 2 .…”

Section: Introductionmentioning

confidence: 83%

Silicate solution, cation properties, and mass transfer by aqueous fluid in the Earth’s interior

Mysen

2018

Prog Earth Planet Sci

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Aqueous fluids in the Earth's interior are multicomponent systems with silicate solubility and solution mechanisms strongly dependent on other dissolved components. Here, solution mechanisms that describe the interaction between dissolved silicate and other solutes were determined experimentally to 825°C and above 1 GPa with in situ vibrational spectroscopy of aqueous fluid while these were at high temperature and pressure. The silicate content in Na-bearing, silicate-saturated aqueous fluid exceeds that in pure SiO 2 at high temperature and pressure. Silicate species were of Q 0 (isolated SiO 4 tetrahedra) and Q 1 (dimers, Si 2 O 7 ) type. The temperature dependence of its equilibrium constant, K = X Q1 /(X Qo ) 2 , yields enthalpies of 22 ± 12 and 51 ± 17 kJ/mol for the SiO 2 -H 2 O and Na-bearing fluids. In contrast, in Ca-bearing fluids, the solubility is more than an order of magnitude lower, and only Q 0 species are present. The present data together with other published experimental information lead to the conclusion that the silicate solubility in aqueous fluids in equilibrium with mafic rocks such as amphibolite and peridotite is an order of magnitude lower than the solubility in fluids in equilibrium with felsic rocks such as andesite and rhyolite compositions (felsic gneiss) under similar temperature and pressure conditions. The silicate speciation also is more polymerized in the felsic systems. This difference is also why second critical end-points in the Earth are at lower temperature and pressure in felsic compared with mafic systems. Alkali-rich fluids formed by dehydration of felsic rocks also show enhanced high field strength element (HFSE) solubility because alkalis in such solution form oxy complexes with the HFSE cations. Fluids formed by dehydration of felsic rocks in the Earth's interior are, therefore, more efficient transport agents of silicate materials than fluids formed by dehydration of mafic and ultramafic rocks, whether for major, minor, or trace elements.

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“…% of dissolved water; and (3) supercritical fluid, which exhibits the complete miscibility between aqueous solution and hydrous melt with variable proportions between the two fluid phases. The aqueous solution and the hydrous melt become progressively miscible with increasing pressure, eventually giving rise to a supercritical fluid above the second critical endpoint at UHP conditions (Manning 2004;Hermann et al 2006a;Mibe et al 2011;Adam et al 2014). In this region, the amount of solutes in the supercritical fluid varies gradually as a function of pressure and temperature (Hack et al 2007), with a variety of compositions between aqueous solution and hydrous melt (Zheng et al 2011a;Hermann and Rubatto 2014).…”

Section: Water In Subduction-zone Rocksmentioning

confidence: 99%

“…Dashed lines denote the geothermal gradients at 5°C/km and 15°C/km, respectively, in subduction zones. Solid dark-red curves denote the wet solidi for basalt (Schmidt and Poli 1998) and granite (Holtz et al, 2001), with circles for the second critical endpoints of the basalt-water system (after Mibe et al 2011) and the granite-water system (after Hermann et al 2006a). Mineral abbreviations: Amp, amphibole; Chl, chlorite; Cld, chloritoid; Law, lawsonite; Zo, zoisite.…”

Section: Water In Subduction-zone Rocksmentioning

confidence: 99%

Geochemistry of continental subduction-zone fluids

2014

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The composition of continental subduction-zone fluids varies dramatically from dilute aqueous solutions at subsolidus conditions to hydrous silicate melts at supersolidus conditions, with variable concentrations of fluid-mobile incompatible trace elements. At ultrahigh-pressure (UHP) metamorphic conditions, supercritical fluids may occur with variable compositions. The water component of these fluids primarily derives from structural hydroxyl and molecular water in hydrous and nominally anhydrous minerals at UHP conditions. While the breakdown of hydrous minerals is the predominant water source for fluid activity in the subduction factory, water released from nominally anhydrous minerals provides an additional water source. These different sources of water may accumulate to induce partial melting of UHP metamorphic rocks on and above their wet solidii. Silica is the dominant solute in the deep fluids, followed by aluminum and alkalis. Trace element abundances are low in metamorphic fluids at subsolidus conditions, but become significantly elevated in anatectic melts at supersolidus conditions. The compositions of dissolved and residual minerals are a function of pressure-temperature and whole-rock composition, which exert a strong control on the trace element signature of liberated fluids. The trace element patterns of migmatic leucosomes in UHP rocks and multiphase solid inclusions in UHP minerals exhibit strong enrichment of large ion lithophile elements (LILE) and moderate enrichment of light rare earth elements (LREE) but depletion of high field strength elements (HFSE) and heavy rare earth elements (HREE), demonstrating their crystallization from anatectic melts of crustal protoliths. Interaction of the anatectic melts with the mantle wedge peridotite leads to modal metasomatism with the generation of new mineral phases as well as cryptic metasomatism that is only manifested by the enrichment of fluid-mobile incompatible trace elements in orogenic peridotites. Partial melting of the metasomatic mantle domains gives rise to a variety of mafic igneous rocks in collisional orogens and their adjacent active continental margins. The study of such metasomatic processes and products is of great importance to understanding of the mass transfer at the slab-mantle interface in subduction channels. Therefore, the property and behavior of subduction-zone fluids are a key for understanding of the crust-mantle interaction at convergent plate margins.

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Slab melting versus slab dehydration in subduction-zone magmatism

Cited by 160 publications

References 52 publications

Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

Separation of supercritical slab-fluids to form aqueous fluid and melt components in subduction zone magmatism

Silicate solution, cation properties, and mass transfer by aqueous fluid in the Earth’s interior

Geochemistry of continental subduction-zone fluids

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