SCG14-01

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Carbon mobility by hydrous carbonate liquids at subduction zones
POLI, Stefano1∗
1

University of Milan

More than half a gigaton of CO2 per year is recycled in the Earth interior at convergent margins. At least 40% of thisCO2 returns to the atmosphere via igneous activity at subduction zones. Experimental and thermodynamic modelling of phaserelationships at high pressure indicate that decarbonation or carbonate dissolution in fluids account for only a portion of CO2
released, and that dry carbonate melts are feasible only if thermal relaxation occurs in a subduction environment.
The subducted oceanic crust includes a range of gabbroic rocks, altered on rifts and transforms, with large amounts of An-richplagioclase. It has been shown that epidote disappearance with pressure depend on the normative anorthite content of the bulk
composition considered; we therefore expect that altered gabbros might display a much wider pressure range where epidote
persists, potentially affecting the location and the nature of volatiles release.
New experimental data from 3.7 to 4.6 GPa, 750 o C to 1000 o C are intended to unravel the effect of variable bulk and volatilecompositions in model eclogites, enriched in the normative anorthite component (An37 and An45 ). Experiments are performedin piston cylinder apparatus and multianvil machine, using both single and, buffered, double capsule techniques.
Garnet, clinopyroxene and coesite form in all syntheses. Lawsonite was found to persist at 3.7 GPa, 750 o C, with both dolomite
and magnesite; at 3.8 GPa, 775-800 o C, fluid saturated conditions, epidote coexists with kyanite, dolomite and magnesite. The
anhydrous assemblage garnet, omphacite, aragonite, kyanite is found at 4.2 GPa, 850 o C. At 900 o C, fluid-rich conditions, asilicate fluid/melt of granitoid composition, a carbonatitic melt and Na-carbonate are observed upon quenching. Close to fluidsaturation, 3.8-4.2 GPa, 870 - 900 o C, garnet and Na-rich clinopyroxene coexist with a carbonatitic liquid, Mg-calcite/dolomite
and aragonite. The carbonatitic melt is enriched in Ca compared to liquids previously obtained in dry carbonated experiments.
Sandwich experiments, at variable volatile content and variable CO2 :H2 O ratio, have been designed to demonstrate attainmentof equilibrium and to challenge the suggested supercritical nature of the carbonate liquid produced. H2 O strongly depresses
liquidus surface for Ca-rich carbonates allowing the generation of liquids efficiently scavenging volatiles, Ca and Si from theslab.
Hydrous silicate carbonate liquids are therefore feasible if a H2 O source is provided along a relatively warm subducting path.
Such source may correspond to fluids flushed from the dehydrating serpentinized lithosphere or to an internal source, i.e. epidote.
In warm subduction zones, the possibility of extracting hydrous carbonatitic liquids from a variety of gabbroic rocks offers new
scenarios on the metasomatic processes in the lithospheric wedge of subduction zones and a new mechanism for recycling carbon.
Such liquids are expected to be extremely reactive in a percolated mantle wedge, where they generate carbonate pyroxenites, afertile CO2 source for magmatism at subduction zones.

Keywords: carbonate, subduction, carbon, water

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SCG14-02

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H/D isotope salt effects in electrolyte-bearing aqueous solutions: In situ experiments at
supercritical conditions
FOUSTOUKOS, Dionysis1∗ ; MYSEN, Bjorn1
1

Geophysical Laboratory, Carnegie Institution of Washington

Equilibrium involving two-phase fluid flow (vapor and brine) describes the evolution of halogen-enriched magmatic systems
and defines the relative distribution and chemical composition of the immiscible ionic vapor and brine endmembers. The stablehydrogen and oxygen isotope composition of these phases is often used to describe evolution pathways and to determine thesource of hydrothermal crustal fluids and volatile emissions from arc volcanoes. For example, the exchange and fractionationof hydrogen isotopes between H-bearing volatiles (e.g. H2 , CH4 , hydrocarbons, H2 O) in open-system Rayleigh distillation processes associated with magmatic degassing in subduction zones is critical to understanding the isotopic composition of evolved
magmatic fluids, and the overall mantle-crust cycling of water and reduced C-O-H volatiles.
Experiments have shown that the presence of water affects the distribution of H- and D-bearing C-O-H species, inducing
substantial changes in the isotope composition of C-O-H volatiles even at lower crust/mantle conditions (>600 ℃) (1,2). Thus,
isotope fractionation effects in magmatic fluids depart significantly from the traditional statistical mechanics models that calculate isotope fractionations assuming ideal-gas conditions. Such effects have also been shown to be prominent in the presence ofdissolved ions that control the dielectric properties of the supercritical fluids and the structure of water (3,4). Key hypothesisis that the solvation mechanisms and the solubility of neutral species (e.g. H2 , CH4 ) are greatly affected under conditions ofelevated ionic strength in electrolyte-concentrated aqueous solutions (’salting-out’). For the H2 O-NaCl system, in particular,
experimental studies have shown that low-salinity vapors are D-enriched relative to brines, with the extent of D/H fractionation
being dependent of the density of the vapor phase (Fig. 1a) (review in (5)).
Here, we present a series of hydrothermal diamond anvil cell experiments that assess the partitioning of D and H between coexisting magmatic vapors and brine in-situ and in real-time by Raman vibrational spectroscopy (Fig. 1b). These HDAC experiments
have been conducted in Na-bearing and Mg-bearing H2 O and D2 O solutions that reached the supercritical phase (homogeneous
fluid) at temperatures and pressures exceeding 900 ℃ and 2 GPa, respectively. However, when lower temperatures were approached (e.g. 600-450 ℃), phase separation effects were induced allowing for the formation of a volumetrically abundant vapor
phase coexisting with a conjugated brine endmember. The effect of Na+ on the speciation and structure of the H2 O and D2 O wasmonitored in-situ and in real time. Our data suggest for the dominant presence of NaOD(aq) (and MgOD2(aq) ) neutral aqueous
species in the vapor, consistent with the ’salting out’ effects imposed by highly ionic brine (liquid) phase. Enhanced stabilityof Na-OD relative to Na-OH neutral species can explain the D/H enrichment of low-salinity vapors sampled from low-pressurehydrothermal experiments (Fig. 1a).
(1) Foustoukos, D. I.; Mysen, B. O. Geochimica et Cosmochimica Acta 2012, 86, 88.
(2) Foustoukos, D. I.; Mysen, B. O. Amer. Mineral. 2013, 98, 946.
(3) Horita, J. Geochemical Journal 2005, 39, 481.
(4) O’Neil, H.; Truesdell, A. H. In Stable Isotope Geochemistry: A Tribute to Samuel Epstein; The Geochemical Society 1991;
3, 17.
(5) Foustoukos, D. I.; Seyfried, W. E. Rev. Mineral. Geochem. 2007, 65, 213.

Keywords: subduction zone, supercritical fluids, hydrogen isotope systematics, vapor, brine, hydrothermal diamond anvil cell

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SCG14-02

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SCG14-03

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Time:May 25 14:15-14:45

IMAGING FLUIDS AND FLUID REACTIONS IN SUBDUCTION ZONESREYNARD, Bruno1∗
1

CNRS, ENS Lyon, France

Water is recycled to the Earth’s interior at subduction zones, and a large portion of the subducting fluid is mobilised at depths
shallower than 150 km. Seimological and magneto-telluric methods are potential tools for imaging fluid circulation when combined with petrophysical models. Measurements of the physical properties of hydrous phases allow refining fluid circulation in
the mantle wedge from geophysical data.
In the cold (<700 degree C) melt-free fore-arc mantle wedge above the subducting slab, serpentinisation is caused by therelease of large amounts of hydrous fluids in the cold mantle above the dehydrating subducting plate. Low seismic velocities in
the wedge give a time-integrated image of extensive hydration and serpentinisation within the stability of serpentine below 700
degree C. Using elastic properties, the amount of serpentinization is calculated to reach 50-100% in hot subductions, while it isbelow 10% in cold subduction. This amount corresponds to a time-integrated reaction of water-rich fluids originated from thedehydrating slab with the overlying mantle wedge.
Electromagnetic profiles of the mantle wedge reveal high electrical-conductivity bodies. In hot areas of the mantle wedge(>700 degree C), water released by dehydration of the slab induces melting of the mantle under volcanic arcs, explaining theobserved high conductivities. In the cold wedge (<700 degree C), high conductivities in electromagnetic profiles provide ”instantaneous” images of fluid circulation.
Small fractions (ca. 1% in volume) of connective high-salinity fluids account for the highest observed conductivities. Modelling shows that low-salinity fluids (<0.1 m) released by slab dehydration can evolve towards high-salinity (>1 m) fluids during
progressive serpentinisation in the wedge. These fluids can mix with arc magmas at depths to produce high-chlorine melt inclusions in arc lavas.
Electrical conductivities up to 1 S.m−1 are observed in the hydrated wedge of the hot subductions (Ryukyu, Kyushu, Cascadia), while moderate conductivities are observed in the cold subductions (N-E Japan, Bolivia), reflecting low fluid flow in thecold wedge of the latter. This is consistent with the seismic observations of extensive shallow serpentinisation in hot subduction
zones, while serpentinisation is sluggish in cold subduction zones.

Keywords: Fluids, Subduction

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SCG14-04

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Time:May 25 14:45-15:00

Intergranular fluid compositions in mantle xenoliths inferred from direct observation of
crystal surfaces
OHTANI, Mari1∗ ; NAKAMURA, Michihiko1 ; YOSHIDA, Takeyoshi1 ; TAKAHASHI, Eiichi2
1

Tohoku University, 2 Tokyo Institute of Technology

Recent geophysical observations of the Earth’s interior indicate the presence of aqueous fluids in the uppermost mantle. However, direct observations of these fluids, apart from fluid inclusions observed in xenoliths and the phenocrysts of volcanic rocks,
are rare; hence, the characteristics of intergranular fluids, such as volume fraction, chemical composition, and connectivity, arepoorly understood. To calculate these parameters, we investigated the geometry of ”dimples” (Watson and Brenan, 1987[1]) on
the grain boundaries of mantle xenoliths. The dimples can be used to interpret the fossil pore fluid parameters since they retain
the shape of the intergranular fluids. We estimated the compositions of intergranular fluids by analyzing the pore dihedral angles
and combining them with the pressure (P) and temperature (T) conditions of the xenoliths.
We collected spinel peridotite xenolith samples from San Carlos (AZ, USA), Bullen-merri (Victoria, AU), Girona (Spain),
Lanzarote Island (Canary Islands), and Ichinomegata (NE Japan) localities. Based on the relationship between the forsterite content of olivine and the chromium number of spinel, the samples from San Carlos, Bullen-merri, and Ichinomegata were classified
as fertile peridotites, while the samples from Girona and Lanzarote were classified as depleted peridotites.
We observed dimples on the olivine surfaces of all the samples, and measured their three-dimensional shapes using a multiangle SEM (Keyence VHX-1000). The lherzolite xenoliths from Bullen-merri, Lanzarote Island, and Ichinomegata containedplenty of dimples, while dimples were rare in the samples from San Carlos. The average dihedral angles of the intergranular
fluids were 89o , 68o , and 82o for the Bullen-merri, Lanzarote island, Ichinomegata samples, respectively. The equilibrium P-T
conditions obtained on the basis of two-pyroxene thermobarometry (Putirka, 2008[2]) or two-pyroxene geothermometry (Wells,
1977[3]) were 12.3 kbar/1130o C, 10.4 kbar/1020o C, 7.6 kbar/1100o C, 6-10 kbar/1113o C, and 6.5 kbar/861o C for the San Carlos,
Bullen-merri, Girona, Lanzarote Island, and Ichinomegata samples, respectively. The obtained CO2 mole fraction of the fluids
was nearly zero (pure H2 O) for the Lanzarote and Ichinomegata samples, and 0.9 for the Bullen-merri sample.
The obtained P-T conditions of the lherzolite samples were hotter than the geothermal gradients of their respective areas andwere located just below the solidus (Green et al., 2010[4]) in saturation with each fluid composition estimated from the dimple
geometry. This suggests that these mantle xenoliths should not be sampled randomly from the conduit wall of the magma halfway
between the mantle and surface, but from just above the partially molten region, which possibly has some genetic relation withthe host basaltic magmas.
References[1] Watson and Brenan, Earth Planet. Sci. Lett. 85.4 (1987): 497-515.
[2] Putirka, Keith D., Rev. Mineral. Geochem. 69.1 (2008): 61-120.
[3] Wells, Contr. Mineral. Petrol. 62 (1977): 129-139[4] Green, David H., et al., Nature 467.7314 (2010): 448-451.
Keywords: mantle xenolith, pore fluid, dihedral angle, 3D measurement

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SCG14-05

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Time:May 25 15:00-15:15

Dehydration of chlorite and formation of a new hydrous phase
CAI, Nao1∗ ; INOUE, Toru1 ; FUJINO, Kiyoshi11

Geodynamics Research Center, Ehime university

Subducting slabs are supplying water into the deep mantle, so the stabilities of hydrous minerals under high pressure andhigh temperature are important issue to clarify the water transportation mechanism into deeper part of the Earth’s mantle. Dense
hydrous magnesium silicates (DHMS) have been well constrained in the MgO-SiO2 -H2 O system, while few researches have been
done in the MgO-SiO2 -H2 O-Al2 O3 system under relatively high pressure (i.e. higher than 6 GPa). Previously we have reported
the existence of a new aluminum-bearing hydrous phase named 23A phase, which shows a quite unique structure among the
mantle minerals in having an extraordinarily long c axis (˜23A). This new hydrous phase can be stable as deep as the lower partof upper mantle. Here we conducted high pressure and high temperature experiments on the decomposition of natural chlorite. At
6 GPa 700oC, we found the coexistence of chlorite, pyrope and Mg-surssasite, while at 7 GPa and 800oC the chlorite decomposes
into 23A phase plus pyrope, chondrodite and fluid. The discovery of 23A phase in the chlorite composition extends the stability
region of hydrous phases in the subducting slabs, and may also open a new field on studying the structure of hydrous phases
under high pressure. This 23A phase may play an important role in transporting water into the deep Earth along the subducting
slabs.
Keywords: chlorite, new hydrous phase, subduction, high pressure and high temperature

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SCG14-06

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Time:May 25 15:15-15:30

Concentration dependence of water diffusion in silica glass at water pressure of 50 bar
KURODA, Minami1∗ ; TACHIBANA, Shogo1 ; OKUMURA, Satoshi2 ; NAKAMURA, Michihiko2 ; SAKAMOTO, Naoya1 ;YURIMOTO, Hisayoshi1
1

Hokkaido University, 2 Tohoku University

Water is the most abundant component in volcanic gas in subduction zones, and its bubble nucleation and growth have strong
influences on magmatisms, such as silicate melt properties and a volcanic eruption style. Diffusion of water in silicate melts is
one of the controlling factors of the bubble growth in magma, and it is thus important to be clarified to understand the mechanismof volcanisms in subduction zones.
Water diffusivity in silicate melt is known to depend on its own concentration (e.g., Wakabayashi and Tomozawa, 1989; Doremus, 2000; Zhang and Behrens, 2000; Okumura and Nakashima, 2004). However, the diffusion mechanism that is responsible
for the observed water concentration dependence has not yet be fully understood. In this study, we carried out diffusion experiments of water in SiO2 glass at 650-850 degree C and water vapor pressure of 50 bar in order to understand the mechanisms ofwater diffusion in silicate melt. We used SiO2 glass because it allows us to consider only the water concentration dependence ofwater diffusion without any other compositional effects (e.g., NBO/T).
A SiO2 glass chip was enclosed in a silica glass tube with pure water corresponding to a water vapor pressure of 50 bar at
experimental temperatures. The sealed glass tube was heated in a box furnace over the range from 650 to 850 degree C for 25
and 40 hours. Diffusion profiles of 1 H and 30 Si were measured on the cross section of a run product with the ion microprobe(Cameca ims-6f at Hokkaido University) using a Cs+ primary beam (20 nA and 20 micron in diameter). Negatively charged ionsof 1 H and 30 Si were counted for 2 sec. and 1 sec. respectively, with a 5-micron step. An electron gun was used for electrostatic
charge compensation. Glasses with known water contents were used for conversion of secondary ion counts (1 H/30 Si) to thewater content in the samples.
The surface concentration of water in run products ranged from 0.25 to 0.35 wt%. The concentration profiles of water from thesurface, especially at the low concentration region, cannot be simply explained by previously proposed diffusion models, where
the diffusion coefficient of water is proportional simply to the water concentration or to a relative abundance of molecular water
to the total dissolved water and an empirical exponential function of total water content. The concentration profiles obtained inthis study show much stronger water-concentration dependence compared with previous studies.
We explain this stronger water concentration dependence of water diffusion in SiO2 glass as follows: (1) The main diffusion
species is molecular H2 O, and its relative abundance to OH groups decreases with lowering the water content in the glass; (2)The number of pathways available for diffusion is controlled by the number of non-bridging oxygen that is determined by theconcentration of OH groups. Because the diffusion coefficient of water is proportional to the above factors (the relative abundance of molecular water and the number of pathways for diffusion) and both depend on the total water content in the glass, thewater-concentration dependence of water diffusion is larger than the previous models proposed for rhyolite glasses.
The smaller water-concentration dependence observed for water diffusion in other silicate glasses can be attributed to the little
dependence of non-bridging oxygen concentration on water contents because it is controlled extrinsically by other network modifier cations.
Keywords: water, diffusion, silica glass, diffusion model

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SCG14-07

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Behavior of water, major and trace elements in subduction zone magmatism
KIMURA, Jun-ichi1∗
1

JAMSTECI present a forward model perspective on the behavior of water mixed with major and trace elements in the slab fluxes andin the magmas from subduction zones. Arc Basalt Simulator version 4 (ABS4: Kimura J.-I. et al. (2014) Diverse magmaticeffects of subducting a hot slab in SW Japan: results from forward modeling. G3, doi:10.1002/2013GC005132) is a forward
model calculating element mass balance in the slab dehydration/melting and melting of the wedge mantle peridotite by fluxingof the slab fluid/melt to estimate element abundances in the primary arc magmas, such as basalt, high-Mg andesite, and adakite.
Mass balance of water is considered together with major and trace elements, and Sr-Nd-Hf-Pb isotopes in the numerical model.
Once element mass balance between the source materials (slab sediment, altered oceanic crust, and peridotite, and mantle wedge
peridotite) and a primary arc magma is established, source conditions including (1) depth of the slab dehydration/melting, (2)contributions of slab fluxes, (3) slab flux fraction in the mantle, (4) depth and temperature of mantle melting, and (5) degree ofmelting of mantle, and (6) element abundance including water in the primary basalt can be estimated. I will present the resultsof ABS4 analyses on the SW Japan and the NE Japan subduction zone magmas representing hot-young and old-cold subduction
cases, respectively, with the special emphasis in water contents in the primary magmas.
Keywords: subduction zone, magma, water, major element, trace element, numerical model

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SCG14-08

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Time:May 25 15:45-16:00

Phase diagrams for CaCO3 + H2 O and their bearing on the genesis of carbonate melts
POLI, Stefano1∗
1

University of Milan

Phase transformations in the system CaCO3 and CaCO3 + H2 O have been of primary concern for Earth scientists since early
XIX century. Sir J. Hall performed the first investigations in this system in 1798 and pursued various attempts at defining decarbonation reactions and melting of calcite with water in externally heated gun barrels, successfully performing the first highpressure experiments in geoscience.
Despite two centuries passed, experimental results on phase transformations in CaCO3 are still contradictory. Discrepancy
between ex-situ and in-situ determination of the reaction calcite = aragonite is in the order of 3 GPa at 1200 o C. Experimental
data on melting of calcite with an aqueous fluid differ by 300 o C. Uncertainties on the phase diagram for CaCO3 and CaCO3 +H2 O have profound consequences in predicting the fate of altered oceanic crust and of metasedimentary materials re-introducedin the mantle at subduction zones.
Multianvil experiments were performed at 4.2 GPa on model bulk compositions in the system CaO-Al2 O3 -SiO2 -H2 O-CO2 ,obtained from natural calcite, Al(OH)3 and silica. Stoichiometric proportions are intended to produce at run conditions kyanite +CaCO3 + a fluid or/and a melt. Al2 SiO5 saturation prevents the formation of portlandite and offers a basis for modelling meltingof impure marbles. Furthermore the usage of Al(OH)3 in the starting material allows an accurate control of H2 O added, fixedat 10 wt% in the present study. This amount is expected to produce H2 O-undersaturated melts, on the basis of solubility data
determined at low pressure.
Aragonite + kyanite + fluid, and minor lawsonite form at 700 o C, replaced by zoisite at 800 o . At 850 o and 900 o a complex
sequence of quenching textural features is observed; ”chains” and dendrites of CaCO3 grow nucleating from liquid-solid interface; they are followed by growth of Si-Al-bearing fibres; finally spheres of silica precipitate from the residual fluid exsolved
from the liquid carbonate phase. Excess silica is required to prevent the formation of corundum.
Estimates of liquid ? solid proportions, retrieved by image analysis, at known bulk H2 O content, along with the solid ? porevolume proportions in the liquid region of the run charge provide constraints for H2 O solubility in CaCO3 liquid. Chemographic
analysis support the occurrence of a single hydrous silicate carbonate liquid at large CaCO3 :H2 O ratios.
The model system investigated here, and the minimum temperatures of melting found, represent the upper bound of the formation of hydrous Ca-carbonate melts able to metasomatise the mantle at subduction zone environments. Alkali may further
promote the generation of Ca-carbonate liquids at lower temperatures.

Keywords: calcite, mixed fluids, carbonate liquids, subduction

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SCG14-09

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Time:May 25 16:15-16:30

C-O-H volatiles, redox variation and hydrogen isotope fractionation in silicate-COH systems in subduction zones
MYSEN, Bjorn1∗
1Geophysical Laboratory, CIW

The structural behavior of volatiles in silicate-C-O-H melts and fluids aids in characterization of element partitioning and as
well as isotope fractionation (e. g., D/H recycling) in subduction zones. In order to characterize this behavior, experiments
were conducted in-situ to 900 ℃ and 1.6 GPa under reducing and oxidizing conditions. Vibrational spectroscopy (infrared andRaman) was employed for structural characterization and for determination of hydrogen isotope partitioning within and between
haploandesitic melts and fluids in alkali aluminosilicate-COH systems.
Under oxidizing conditions, melt and fluid comprise CO2 , CO3 -groups, HCO3 -groups, H2 O, and silicate components. The
abundance ratios, CO3 /CO2 and CO3 /HCO3 , decreases with increasing temperature and pressure with 4H-values for the exchange equilibria between -15 and -25 kJ/mol. The abundance ratio, CO3 /silicate, also decreases with increasing temperatureand pressure. Hydrogen isotope exchange within coexisting fluids and melts yields 4H-values near 14 and 34 kJ/mol, respectively, which results in 4H=-25 kJ/mol for D/H exchange between coexisting fluid and melt. Lack of spectroscopic resolution
precluded determination of D/H behavior in the bicarbonate (HCO3 ) species.
Under reducing conditions (near that to the iron-wustite oxygen fugacity buffer), melt and fluid comprise molecular CH4 ,CH3 -groups, H2 , OH-groups, and H2 O. Hydrogen isotope exchange within fluids and melts yields 4H near -5 and -1 kJ/mol,
respectively with a 4H-value for D/H exchange between coexisting fluid and melt of -4kJ/mol. The D/H exchange between
CH4 and CD4 species results in 4H near 40 kJ/mol, whereas the 4H-value is near -4 kJ/mol under oxidizing conditions where?H-values average near -6 kJ/mol for D/H exchange between hydrous melt and silicate-saturated aqueous fluid.
The redox-dependent D/H-behavior reflects species-dependent bond strengths. Therefore, D/H fractionation between C-O-H
volatiles, released during subduction, and both residual subducting materials, and overlying mantle wedge likely will vary withdepth. Somewhat analogous pressure-dependence can be seen in olivine/melt transition metal partition coefficients, which mayvary by as much as 100% simply by transforming carbon-speciation from methane-rich to carbon dioxide-rich and, thereforelikely depend on depth in subduction zones. This variation depth dependence partly is because subduction zone redox conditions
vary with depth and partly because the solubility of C-O-H volatiles in silicate melts and of silicate in coexisting fluid arepressure-dependent.
Keywords: melt structure, COH volatiles, spectroscopy, isotope fractionation, high-pressure experiments

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SCG14-10

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Time:May 25 16:30-16:45

Deep slab structure, dehydration and the Changbai intraplate volcanism
CHEN, Chuanxu1 ; ZHAO, Dapeng1∗ ; TIAN, You2 ; LEI, Jianshe3 ; HASEGAWA, Akira1 ; WU, Shiguo4 ;PARK, Jung-ho5 ; KANG, Ik-bum5
1

Tohoku University, Department of Geophysics, 2 Jilin University, 3 China Earthquake Administration, 4 Chinese Academy of
Sciences, 5 Korea Institute of Geoscience and Mineral Resources
We obtained a new 3-D P-wave tomography model down to 800 km depth beneath NE Asia by assembling a large number ofarrival-time data of local, regional and teleseismic events recorded by ˜2500 seismic stations in Japan, China and South Korea.
The data from a portable seismic network (NECESSArray) in NE China are also collected and used. Our updated model showsa sharper image of the volcanism-related asthenospheric upwelling and the stagnant Pacific slab in the mantle transition zone
(MTZ) beneath the Changbai intraplate volcano. The main findings are summarized as follow.
(1) Relative travel-time residuals of teleseismic events alone are not able to recover the flat stagnant slab in the MTZ, and aslab gap in the MTZ beneath the Changbai volcano imaged by relative travel-time tomography is an artifact.
(2) The low-velocity anomaly in the big mantle wedge (BMW) becomes the most prominent near the hinge of the stagnant
slab, which is located slightly east of the Changbai volcano and may reflect focused hot upwelling in the BMW. This low-velocity
feature coincides with the depression of both 410-km and 660-km discontinuities and a cluster of very deep earthquakes (>500
km depth) in the Pacific slab.
(3) Besides the deep dehydration of hydrous minerals within the stagnant slab, additional fluids released through deepearthquake faulting and a stronger mantle flow circulation near the hinge of the Pacific slab have made Changbai the largest
and most active intraplate volcano in NE Asia.
(4) The BMW origin of the Changbai volcanism agrees well with other geophysical, geochemical and numerical-modelingstudies.
Keywords: Northeast Asia, Changbai volcano, Pacific plate, slab dehydration, deep earthquakes

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SCG14-11

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Time:May 25 16:45-17:00

Hydrogen isotope fractionation between melts and aqueous fluid: Implications for magmatic processes
DALOU, Celia1∗ ; LE LOSQ, Charles2 ; MYSEN, Bjorn2
1

University of Minnesota, USA, 2 Geophysical Laboratory, CIW, USA, 3 Geophysical Laboratory, CIW, USA

The δD of silicate glass inclusions trapped in minerals is an important tool in geochemistry because it provides informationon the δD of deep fluids, and, therefore, on the water cycle between the atmosphere, the hydrosphere and the lithosphere. Suchunderstanding relies on the knowledge of the D/H isotopic fractionation values between aqueous fluids, melts, and minerals at
temperature and pressure conditions relevant to the interior of the Earth. Significant D/H isotopic fractionation between silicate
melts and aqueous fluids were reported at hundreds of MPa and ℃ by using in situ measurements in hydrothermal diamond anvil
cell (HDAC)[1] However, available datasets are focused on fluids and melts with D/H ratios close to unity. The relevance of suchdata for natural processes D/H ratios in the ‰ range may not always be clear because the a role of bulk D/H ratio of the system
was not assessed. To address such concerns, the effect of the bulk D/H ratio on hydrogen isotopes partitioning between watersaturated silicate melts and coexisting silicate-saturated aqueous fluids has been determined in the Na2 O?Al2 O3 ?SiO2 ?H2 O
system. To this end, in situ Raman spectroscopy measurements were performed on fluids and melts with D/H ratios from 0.05 up
to 2.67 at equilibrium in a HDAC, in the 300 - 800?C and 200 - 1500 MPa temperature (T) and pressure (P) range, respectively.
In the P-T range studied, the D/H ratios of fluids barely change with temperature (in average ∆Hf luid = 0.47±1.15 kJ/mol). In
contrast, the D/H ratios of coexisting melts display strong dependence on temperature (in average ∆Hmelt = 7.18±1.27 kJ/mol).
The temperature-dependence of the D/H fractionation factor between melt and fluid (αmelt−f luid = D/Hmelt / D/Hf luid ) is similar in all the experiments and can be written:
ln(αmelt−f luid ) = -747 (±75).T-1 + 0.65 (±0.10) .
The αmelt−f luid is independent of the bulk D/H ratio of the melt + fluid system.
Therefore, experimental determination of αmelt−f luid using D-enriched fluids can be applied to natural systems. As a result,hydrogen isotope fractionation between silicate melts and aqueous fluids probably affect the δD values recorded in the geochemical observables such as the melt inclusions (MIs). Such knowledge alters the present understanding of the water cycle insubduction zones. Indeed, it has been assumed that the δD composition of MIs trapped in crystals in back-arc basalts represents
the δD composition of the slab fluids present in the mantle wedge. This interpretation was based on the hypothesis that no fractionation occurs between the slab fluids and the deep magma. However, the present data leave this hypothesis open to question,and indicate that D and H likely fractionated between the slab fluids and the back-arc magma. Although these data do not allow
a definitive quantification of the effect because of the simple chemical composition we used, they demonstrate the necessity of amore complete understanding of H and D fractionation processes between silicate melts and aqueous fluids. Such processes may
have a direct impact on δD of the various isotopic reservoirs in subduction zones, and therefore influence our understanding of
the water cycle in such a geological context.
[1] Mysen, B. O. American Mineralogist 98, 1754-1764 (2013)
Keywords: Experiment, vibrational spectroscopy, hydrogen isotope fractionation, melt-fluid equilibria

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SCG14-12

Room:303

Time:May 25 17:00-17:15

Experimental study on the origin of the D/H fractionation between silicate melts andaqueous fluids at HT/HP conditions
LE LOSQ, Charles1∗ ; CODY, George D.1 ; DALOU, Celia2 ; MYSEN, Bjorn O.1
1

GL, Carnegie Institution for Science, 2 University of Minnesota

Subduction zones are open paths for the exchange of volatile elements between the geosphere and the atmo-, hydro- andbiospheres on Earth. Water is present in the subducting slab as hydrated minerals and is released at high pressure (P) andtemperature (T) during the subduction. This results in a hydrated mantle wedge, and eventually promotes volcanism in thefore-arc and back-arc regions. The water cycle can be tracked by measuring the δD of various geochemical observables. In
particular, δD measured in melt inclusions trapped in crystals in back-arc magmas may reflect the δD of the slab fluids. From
those values, it may be possible to assess the amount of water released from the slab to the mantle wedge by using mass balance
models. However, this relies on knowledge of how D and H fractionate between silicate melts and aqueous fluids at high P and
T. Results from in situ experiments of silicate-H2 O systems in a Hydrothermal Diamond Anvil Cell (HDAC) show that 1000ln (αmelt−f luid = [D/H]melt /[D/H]f luid ) values can reach -100 ‰ at 1073 K and ∼1 GPa, conditions similar to those at theonset of fluid-saturated melting in subduction settings. Such values are high, particularly when compared to those observed inminerals: for instance, the 1000 ln (αphlogopite−f luid ) is about 7 ‰ at 1073 K. Considering that, the origin of such fractionation
appears surprising. One explanation may be that, in addition to the zero-point energy contribution that usually drive equilibrium
isotopic fractionation, D/H intramolecular fractionation within silicate melts may promote D/H exchange between coexisting
aqueous fluids and silicate melts. Such effect is suggested by recent results from 2 H and 1 H MAS NMR of Na2 Si4 O9 quenchedmelts equilibrated with various amounts of (Dx H(1−x) )2 O (x = D/[D+H]) at 1673 K and 1.5 GPa, which show differences in thepartitioning of D and H in the structure of the melts at their glass transition temperature.
To address this problem, we studied how the O-H and O-D bond strengths change with temperature and pressure in aqueous
fluids and silicate melts for a series of HDAC experiments performed with aluminosilicate melts coexisting with fluids withvarious H2 O-D2 O mixtures. We also examined the local environments of H and D with 2 H and 1 H Magic Angle Spinning
Nuclear Magnetic Resonance (MAS NMR) spectroscopy in M2 Si4 O9 glasses (M = Li, Na or K) with 1, 3 and 6 wt% of pure
H2 O or pure D2 O, and with 3 wt% of a H2 O-D2 O mixture.
Comparison of the in situ Raman spectroscopic signals assigned to O-H and O-D stretching vibrations in fluids and melts atgiven P-T shows significant differences in the distribution of O-H and O-D bond distances and thus strengths between melts andfluids. These differences are correlated with the observed fractionation. They may be related to the fact that water can reside as
molecules (H2 Omol ) or as OH groups bonded to the ionic structure of the melt, the two species presenting differences in O-Hbond strength. Such effect might be enhanced by an intramolecular fractionation of D and H that occurs in the melt. Indeed,
comparison of 2 H and 1 H MAS NMR spectra of the M2 Si4 O9 glasses shows that D and H populate the same environments, but
H is more concentrated in an environment with an oxygen-oxygen distance around 295 pm. Therefore, D and H do not have thesame distribution within the structure of melts at their glass transition temperature. This may arise from a volume effect and/orfrom an isotopic effect on the equilibrium H2 Omol + OD *) D2 Omol + OH. In any case, this effect, in turn, can explain thelarge fractionation factors observed in the HDAC experiments. They may also lead to large δD variations in subduction zone
processes, which makes use of δD to trace water cycling more complex.

Keywords: hydrogen isotopes, silicate melt, silicate glass, NMR spectroscopy, Raman spectroscopy, HDAC in situ experiments

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SCG14-P01

Room:Convention Hall

Time:May 25 18:15-19:30

GHz P wave buffer rod-transducer and its application to DAC experiments
YONEDA, Akira1∗
1

ISEI, Okayama Univ.

GHz ultrasonic velocity measurements was developed for future diamond anvil cell experiments. First of all, ZnO transducer
was coated on the bottom surface of diamond anvil by a sputtering machine. Simulation tests were conducted by using a single
diamond anvil; expected accuracy of ˜0.1 % was confirmed for ˜50 ns travel time of ˜160 micron meter thickness glass plate.
However it was turned out that the direct diamond ZnO transducer technique has potential difficulty for actual DAC experiments.
i.e., durability of ZnO layer. In order to solve the problem, P wave buffer rod made of sapphire single crystal was developed
newly. The usage of the P wave buffer rod is now under examining.
Keywords: GHz ultrasonic technique, diamond anvil cell, P wave buffer rod

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