Tatsuhiko Kawamoto - Profile on Academia.edu (original) (raw)
Papers by Tatsuhiko Kawamoto
Bulletin of Volcanology, 2010
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H 2 O were carried ... more Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H 2 O were carried out at a pressure range from 250 MPa to 30-75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10-90 MPa/s) produced huge BNDs (≈ 2×10 14 m −3 at 10 MPa/s ; ≈ 2× 10 15 m −3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (10 15 -10 16 m −3 ). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×10 12 m −3 ) close to those observed at 800°C and 1 MPa/s (≈ 6×10 12 m −3 ), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).
Journal of Petrology, 2012
Carbonates carried by oceanic platesçin the form of sediment or alteration products of basaltsçar... more Carbonates carried by oceanic platesçin the form of sediment or alteration products of basaltsçare introduced into the mantle by subduction. The high-pressure^high-temperature stability of carbonates in a closed system has been constrained by a number of studies, but the effects of the interactions between subducted carbonates and the surrounding mantle on carbonate stability are poorly known. These interactions may, however, influence the stability depth of the subducted material, the composition of the interaction zone, and the rate of carbon transfer from the slab to the mantle. To determine the exchange mechanisms at the interface between a subducted dolomite þ coesite assemblage and the overlying mantle, we performed experiments at 6 GPa and 9008C and 11008C in a multi-anvil apparatus. In a first series of experiments, we studied the reaction and migration processes operating along the interface between a cylinder of dolomite þ coesite and a cylinder of garnet peridotite. In a second series of experiments, homogeneous mixtures of dolomite þ coesite and garnet peridotite were equilibrated at high pressure and high temperature to characterize the phase relations as a function of the (dolomite þ coesite)/peridotite ratio. We show that the destabilization temperature of a subducted dolomite þ coesite assemblage is less than 9008C at 6 GPa when in contact with a garnet lherzolite or a harzburgite. A reaction zone composed mainly of clinopyroxene þ magnesite is produced at the interface between dolomite þ coesite and peridotite. Carbonçin the form of a fluid or in a carbonatitic meltçalso infiltrates the garnet peridotite to form magnesite and clinopyroxene. Moreover, graphite was observed in two experiments. We believe that it was produced by a redox reaction at the interface between dolomite þ coesite and iron-bearing silicates in the peridotite. As our experimental conditions are in the stability field of diamond, this suggests a potential mechanism for diamond crystallization from subducted dolomite þ coesite in contact with the mantle wedge.
Agu Fall Meeting Abstracts, Dec 1, 2009
Bubble number density (BND; the number of bubbles produced per unit volume of liquid) is strongly... more Bubble number density (BND; the number of bubbles produced per unit volume of liquid) is strongly controlled by decompression rate of ascending magmas (Toramaru 1995, 2006; Mourtada-Bonnefoi and Laporte, 2004). Previous decompression experiments of hydrous and crystal-free rhyolitic magmas have produced BNDs up to 1013 m-3 at the highest decompression rate (8.5 MPa/s; Mangan and Sisson, 2000), while observed BNDs in natural silicic pumices commonly exhibit much higher BNDs: up to 1016 m-3. To reproduce such huge BNDs and to characterize effects of magma ascent rate on bubble nucleation kinetics, we carried out decompression experiments of crystal-free rhyolitic liquid with 6.6 wt.% H2O at a pressure range from 250 MPa to 30-75 MPa, at decompression rates of 10 MPa/s and 90 MPa/s. A first series of experiments at 800 °C and fast decompression rates (10-90 MPa/s) produced huge BNDs (2×1014 m-3 at 10 MPa/s; 2×1015 m-3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015-1016 m-3). A second series of experiments at 700 °C and 1 MPa/s produced BNDs (9×1012 m-3) close to those observed at 800 °C and 1 MPa/s (6×1012 m-3; Mourtada-Bonnefoi and Laporte, 2004). These experimental results confirm that BNDs are strongly depending on decompression rate and that temperature has an insignificant effect on BNDs at a given decompression rate. Therefore, BNDs are good markers of the decompression rate of magmas in volcanic conduits irrespective of temperature. Observed BNDs in natural silicic pumices from Plinian eruptions are as high as 1016 m-3. In addition, bubbles commonly show a bimodal size distribution with a numerically minor population of large bubbles (about 109 m-3), and a major population of smaller bubbles, typically from a few μm to a few tens of μm in diameter. Such huge number densities of bubbles may be attributed to two successive nucleation events in ascending magmas. The large bubbles are presumably related to a first nucleation event that happens relatively deep in the conduit at low decompression rate (about 0.01 MPa/s). The huge popolation of small bubbles implies that a second nucleation event occurs in the upper volcanic conduit at much faster decompression rate(≥ 1 MPa/s). Literature Toramaru A. (1995). Jour. Geophys. Res. 100: 1913-1931. Toramaru A. (2006). Jour. Volcanol. Geotherm. Res. 154: 303-316. Mourtada-Bonnefoi C. C., Laporte D. (2004). Earth Planet. Sci. Lett. 218: 521-537. Mangan M. T., Sisson T. (2000). Earth Planet. Sci. Lett. 183: 441-455.
Physics and Chemistry of Minerals, 2005
Wadsleyite II is a variably hydrous magnesiumiron silicate phase similar to spinelloid IV and a p... more Wadsleyite II is a variably hydrous magnesiumiron silicate phase similar to spinelloid IV and a potential host for H in the Transition Zone of the Earth's mantle. Two separate samples of wadsleyite II synthesized at 17.5 GPa and 1400°C and at 18 GPa and 1350°C have been characterized by electron microprobe, single-crystal X-ray diffraction, visible, IR, Raman, and Mo¨ssbauer spectroscopies, and transmission electron microscopy including electron energy-loss spectroscopy. The two samples have the following chemical formulae: Mg 1.71 Fe 0.18 Al 0.01 H 0.33 Si 0.96 O 4 and Mg 1.60 Fe 0.22 Al 0.01 H 0.44 Si 0.97 O 4 . Mö ssbauer spectroscopy and electron energy loss spectroscopy (EELS) indicate that about half of the iron present is ferric. Refinement of the structures shows them to be essentially the same as spinelloid IV. Calculated X-ray powder diffraction patterns show only subtle differences between wadsleyite and wadsleyite II.
Proceedings of the National Academy of Sciences, 2013
Slab-derived fluids play an important role in heat and material transfer in subduction zones. Deh... more Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressuretemperature conditions of fluids are few. This report describes CO 2 -bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaClequivalent magnesite crystals, CO 2 -bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830°C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO 2bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H 2 O and affect the chemical evolution of the mantle wedge.
Aqueous fluids and sedimentary melts as agents for mantle wedge metasomatism, as inferred from peridotite xenoliths at Pinatubo and Iraya volcanoes, Luzon arc, Philippines
Mantle xenoliths entrained in subduction-zone magmas often record metasomatic signature of the ma... more Mantle xenoliths entrained in subduction-zone magmas often record metasomatic signature of the mantle
wedge. Such xenoliths occur in magmas from Iraya and Pinatubo volcanoes, located at the volcanic front of the
Luzon arc in the Philippines. In this study, we present the major element compositions of the main minerals,
trace element abundances in pyroxenes and amphiboles, and Nd–Sr isotopic compositions of amphiboles in
the peridotite xenoliths from Pinatubo volcano. The data indicate enrichment in fluid-mobile elements, such as
Rb, Ba, U, Pb, and Sr, and Nd–Sr isotopic ratios relative to those of mantle. The results are considered in terms
of mixing of asthenospheric mantle and subducting oceanic crustal components. The enrichments observed in
the Pinatubo mantle xenoliths are much less pronounced than those reported for the Iraya mantle xenoliths.
This disparity suggests differences in the metasomatic agents contributing to the two suites; i.e., aqueous fluids
infiltrated the mantle wedge beneath the Pinatubo volcano, whereas aqueous fluids and sediment-derived
melts infiltrated the mantle wedge beneath the Iraya volcano.
PDF file will be sent for a request. kawamoto@bep.vgs.kyoto-u.ac.jp
Geiger, C. A., Kawamoto, T., Experimental Mineralogy and Petrology, in: White, W.M. (Ed.), Encycl... more Geiger, C. A., Kawamoto, T., Experimental Mineralogy and Petrology, in: White, W.M. (Ed.), Encyclopedia of Geochemistry: A Comprehensive Reference Source on the Chemistry of the Earth. Springer International Publishing, pp. 1-6. in press
Halogen and noble gas systematics are powerful tracers of volatile recycling in subduction zones.... more Halogen and noble gas systematics are powerful tracers of volatile recycling in subduction zones. We present halogen and noble gas compositions of mantle peridotites containing H 2 O-rich fluid inclusions collected at volcanic fronts from two contrasting subduction zones (the Avacha volcano of Kamchatka arc and the Pinatubo volcano of Luzon arcs) and orogenic peridotites from a peridotite massif (the Horoman massif, Hokkaido, Japan) which represents an exhumed portion of the mantle wedge. The aims are to determine how volatiles are carried into the mantle wedge and how the subducted fluids modify halogen and noble gas compositions in the mantle. The halogen and noble gas signatures in the H 2 O-rich fluids are similar to those of marine sedimentary pore fluids and forearc and seafloor serpentinites. This suggests that marine pore fluids in deep-sea sediments are carried by serpentine and supplied to the mantle wedge, preserving their original halogen and noble gas compositions. We suggest that the sedimentary pore fluid-derived water is incorporated into serpentine through hydration in a closed system along faults at the outer rise of the oceanic, preserving Cl/H 2 O and 36 Ar/H 2 O values of sedimentary pore fluids. Dehydration–hydration process within the oceanic lithospheric mantle maintains the closed system until the final stage of serpentine dehydration. The sedimentary pore fluid-like halogen and noble gas signatures in fluids released at the final stage of serpentine dehydration are preserved due to highly channelized flow, whereas the original Cl/H 2 O and 36 Ar/H 2 O ratios are fractionated by the higher incompatibility of halogens and noble gases in hydrous minerals.
Direct observation of coexisting aqueous fluid and silicate melt using x-ray radiography
ABSTRACT
It is now widely accepted that Earth’s transition zone, located at depth between 410 km to 670 km... more It is now widely accepted that Earth’s transition zone, located at depth between 410 km to 670 km is most likely hydrated. However, a definite conclusion has yet to be reached regarding the nature of the hydrous phase or phases that have the capacity to efficiently transport water down to such depths. In their study, Nishihara and Matsukage ( Am Mineral, 2016, April issue) show that (FeH)1-xTixO2 can be stable in wet basalts and sediments in high pressure and high temperature conditions. These phases allow the subducting lithosphere to transport far more water to the mantle transition zone than previously thought possible.
Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived flux: aqueous flu... more Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived flux: aqueous fluids, hydrous partial melts or supercritical fluids from the subducting slab through reactions. Whether the slab-derived flux is an aqueous fluid, a partial melt, or a supercritical fluid remains an open question. In general, with increasing pressure, aqueous fluids dissolve more silicate components and silicate melts dissolve more H2O. Under low-pressure conditions, those aqueous fluids and hydrous silicate melts remain isolated phases due to the miscibility gap. As pressure increases, the miscibility gap disappears and the two liquid phases becomes one phase. This vanishing point is regarded as critical end point or second critical end point. X-ray radiography experiments locate the pressure of the second critical end point at 2.5 GPa（ 83 km depth）and 700 °C for sediment-H2O, and at 2.8 GPa （92 km depth） and 750 °C for high-Mg andesite（HMA）-H2O. These depths correspond to the depth range of a subducted oceanic plate beneath volcanic arcs. Sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, may react with the mantle peridotite to form HMA supercritical fluids due to peritectic reaction between silica-rich fluids and olivine-rich mantle peridotite. Such HMA supercritical fluids may separate into aqueous fluids and HMA melts at 92 km depth during ascent. HMA magmas can be erupted as they are, if the HMA melts segregate without reacting to the overriding peridotite. Partitioning behaviors between aqueous fluids and melts are determined with and without（Na, K）Cl using synchrotron X-ray fluorescence. The data indicate that highly saline fluids effectively transfer large-ion lithophile elements. If the slab-derived supercritical fluids contain Cl and subsequently separate into aqueous fluids and melts in the mantle wedge, then such aqueous fluids inherit much more Cl and also more or less amounts of large ion lithophile elements than the coexisting melts. In contrast, Cl-free aqueous fluids cannot effectively transfer Pb and alkali earth elements to the magma source. Enrichment of some large-ion lithophile elements in arc basalts relative to mid-oceanic ridge basalts has been attributed to mantle source fertilization by such aqueous fluids from a dehydrating oceanic plate. Such aqueous fluids are likely to contain Cl, although the amount remains to be quantified. If such silica-rich magmas survive as andesitic melts under a limited reaction with mantle minerals, they may erupt as HMA magmas having slab-derived signatures.
Almost all physico-chemical characteristics of earthforming materials are influenced by the prese... more Almost all physico-chemical characteristics of earthforming
materials are influenced by the presence of
H2O. As N. L. Bowen stated in 1928, H2O plays the role
of Maxwell’s demon - it does just what a petrologist may
wish it to do [p. 282, The evolution of the igneous rocks
(Bowen 1928)]. In the following decades, this has been
proven to be the case not only in petrology but in every
field of solid Earth science.
Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/... more Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/or supercritical
fluids from the subducting slab to the sub-arc mantle. Partitioning of large-ion lithophile elements between
aqueous fluids and melts is crucial as these two liquid phases are present in the sub-arc pressure-temperature
conditions. Using a micro-focused synchrotron X-ray beam, in situ X-ray fluorescence (XRF) spectra were obtained
from aqueous fluids and haplogranite or jadeite melts at 0.3 to 1.3 GPa and 730°C to 830°C under varied concentrations
of (Na, K)Cl (0 to 25 wt.%). Partition coefficients between the aqueous fluids and melts were calculated for Pb, Rb, and
Sr (D fluid/melt
Pb; Rb; Sr). There was a positive correlation between D fluid/melt
Pb; Rb; Sr values and pressure, as well as D fluid/melt
Pb; Rb; Sr values and
salinity. As compared to the saline fluids with 25 wt.% (Na, K)Cl, the Cl-free aqueous fluids can only dissolve one tenth
(Pb, Rb) to one fifth (Sr) of the amount of large-ion lithophile elements when they coexist with the melts. In the
systems with 13 to 25 wt.% (Na, K)Cl, D fluid/melt
Pb; Rb values were greater than unity, which is indicative of the capacity of
such highly saline fluids to effectively transfer Pb and Rb. Enrichment of large-ion lithophile elements such as Pb and
Rb in arc basalts relative to mid-oceanic ridge basalts (MORB) has been attributed to mantle source fertilization by
aqueous fluids from dehydrating oceanic plates. Such aqueous fluids are likely to contain Cl, although the amount
remains to be quantified.
Lherzolite xenoliths containing fluid inclusions from the Ichinomegata volcano, located on the r... more Lherzolite xenoliths containing fluid inclusions
from the Ichinomegata volcano, located on the rear-arc side
of the Northeast Japan arc, may be considered as samples
of the uppermost mantle above the melting region in the
mantle wedge. Thus, these fluid inclusions provide valuable
information on the nature of fluids present in the subarc
mantle. The inclusions in the Ichinomegata amphibolebearing
spinel–plagioclase lherzolite xenoliths were found
to be composed mainly of CO2–H2O–Cl–S fluids. At equilibrium
temperature of 920 °C, the fluid inclusions preserve
pressures of 0.66–0.78 GPa, which correspond to depths
of 23–28 km. The molar fraction of H2O and the salinity
of fluid inclusions are 0.18–0.35 and 3.71 ± 0.78 wt%
NaCl equivalent, respectively. These fluid inclusions are
not believed to be fluids derived directly from the subducting
slab, but rather fluids exsolved from sub-arc basaltic magmas that are formed through partial melting of mantle
wedge triggered by slab-derived fluids.
Kawamoto, T., Yoshikawa, M., Kumagai, Y., Mirabueno, M. H. T., Okuno, M., Kobayashi, T.
Slab-derived fluids play an important role in heat and material transfer in subduction zones. Deh... more Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressuretemperature conditions of fluids are few. This report describes CO 2 -bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaClequivalent magnesite crystals, CO 2 -bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830°C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO 2bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H 2 O and affect the chemical evolution of the mantle wedge.
Subduction-zone magmatism is triggered by the addition of H 2 Orich slab-derived components: aque... more 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.
A new hydrous silicate phase with formula , 0 has been synthesized at 1400°C and 17.5 4 GPa from ... more A new hydrous silicate phase with formula , 0 has been synthesized at 1400°C and 17.5 4 GPa from a hydrous iron-rich mantle peridotite composition.
At the BL43IR of SPring-8, infrared microanalysis on various kinds of solid specimens under multi... more At the BL43IR of SPring-8, infrared microanalysis on various kinds of solid specimens under multiple environments with a spatial resolution smaller than 10 mm in diameter is planned in the infrared region. In order to perform such analysis, two different stations, a multipurpose spectromicroscopy apparatus and a magneto-optical imaging one have been constructed. Measurements on the spatial two-dimensional cross-section of the infrared beam at the spectromicroscopy station have proven that the stations have a good prospective feature in the performance. #
In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of ... more In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of Ca 5 (PO 4 ) 3 F 0.94 Cl 0.06 were carried out using a diamond anvil cell and angle-dispersive technique at Photon Factory (PF), Japan. Pressure-volume data were collected up to 7.12 GPa at 300K. The pressures were determined from the ruby fluorescence spectra shift. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus and its pressure deviative were obtained in this study. The third order Birch-Murnaghan equation of state yielded the isothermal bulk modulus of K T = 91.5(38) GPa, its pressure derivative K T ' = 4.0(11), and the zero-pressure volume V 0 = 524.2(3) Å 3 .
Samples of olivine, wadsleyite, ringwoodite and majorite with Mg/(Mg + Fe) = 0.85-0.90 were synth... more Samples of olivine, wadsleyite, ringwoodite and majorite with Mg/(Mg + Fe) = 0.85-0.90 were synthesised at high pressure and temperature using a multianvil press under nominally anhydrous conditions as well as hydrous conditions with varying conditions of oxygen fugacity, and examined ex situ using Mössbauer spectroscopy to determine Fe 3+ / Fe, and either Fourier Transform Infrared Spectroscopy or Secondary Ion Mass Spectrometry to determine H concentration. Under oxidising conditions, the relative concentration of Fe 3+ increases with water content in olivine, wadselyite and ringwoodite. Majorite does not incorporate significant water, but shows high Fe 3+ / Fe values when synthesised under oxidising conditions in the presence of water. Fe 3+ / Fe is strongly influenced by oxygen fugacity for all phases studied, and the mechanism of hydration is likely coupled to Fe 3+ incorporation in the crystal structure. Enhanced Fe 3+ / Fe in mantle-derived olivine and orthopyroxene has a negligible effect on oxygen fugacities estimated using olivine-orthopyroxene-garnet oxybarometers, while increased Fe 3+ / Fe in garnet due to dehydrogenation could lead to an overestimation of oxygen fugacity in exhumed samples. Subduction zones are likely oxidised relative to the rest of the mantle, and hence represent regions where not only water is concentrated, but also Fe 3+ .
Bulletin of Volcanology, 2010
Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H 2 O were carried ... more Decompression experiments of a crystal-free rhyolitic liquid with ≈ 6.6 wt. % H 2 O were carried out at a pressure range from 250 MPa to 30-75 MPa in order to characterize effects of magma ascent rate and temperature on bubble nucleation kinetics, especially on the bubble number density (BND, the number of bubbles produced per unit volume of liquid). A first series of experiments at 800°C and fast decompression rates (10-90 MPa/s) produced huge BNDs (≈ 2×10 14 m −3 at 10 MPa/s ; ≈ 2× 10 15 m −3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (10 15 -10 16 m −3 ). A second series of experiments at 700°C and 1 MPa/s produced BNDs (≈ 9×10 12 m −3 ) close to those observed at 800°C and 1 MPa/s (≈ 6×10 12 m −3 ), showing that temperature has an insignificant effect on BNDs at a given decompression rate. Our study strengthens the theory that the BNDs are good markers of the decompression rate of magmas in volcanic conduits, irrespective of temperature. Huge number densities of small bubbles in natural silicic pumices from Plinian eruptions imply that a major nucleation event occurs just below the fragmentation level, at which the decompression rate of ascending magmas is a maximum (≥ 1 MPa/s).
Journal of Petrology, 2012
Carbonates carried by oceanic platesçin the form of sediment or alteration products of basaltsçar... more Carbonates carried by oceanic platesçin the form of sediment or alteration products of basaltsçare introduced into the mantle by subduction. The high-pressure^high-temperature stability of carbonates in a closed system has been constrained by a number of studies, but the effects of the interactions between subducted carbonates and the surrounding mantle on carbonate stability are poorly known. These interactions may, however, influence the stability depth of the subducted material, the composition of the interaction zone, and the rate of carbon transfer from the slab to the mantle. To determine the exchange mechanisms at the interface between a subducted dolomite þ coesite assemblage and the overlying mantle, we performed experiments at 6 GPa and 9008C and 11008C in a multi-anvil apparatus. In a first series of experiments, we studied the reaction and migration processes operating along the interface between a cylinder of dolomite þ coesite and a cylinder of garnet peridotite. In a second series of experiments, homogeneous mixtures of dolomite þ coesite and garnet peridotite were equilibrated at high pressure and high temperature to characterize the phase relations as a function of the (dolomite þ coesite)/peridotite ratio. We show that the destabilization temperature of a subducted dolomite þ coesite assemblage is less than 9008C at 6 GPa when in contact with a garnet lherzolite or a harzburgite. A reaction zone composed mainly of clinopyroxene þ magnesite is produced at the interface between dolomite þ coesite and peridotite. Carbonçin the form of a fluid or in a carbonatitic meltçalso infiltrates the garnet peridotite to form magnesite and clinopyroxene. Moreover, graphite was observed in two experiments. We believe that it was produced by a redox reaction at the interface between dolomite þ coesite and iron-bearing silicates in the peridotite. As our experimental conditions are in the stability field of diamond, this suggests a potential mechanism for diamond crystallization from subducted dolomite þ coesite in contact with the mantle wedge.
Agu Fall Meeting Abstracts, Dec 1, 2009
Bubble number density (BND; the number of bubbles produced per unit volume of liquid) is strongly... more Bubble number density (BND; the number of bubbles produced per unit volume of liquid) is strongly controlled by decompression rate of ascending magmas (Toramaru 1995, 2006; Mourtada-Bonnefoi and Laporte, 2004). Previous decompression experiments of hydrous and crystal-free rhyolitic magmas have produced BNDs up to 1013 m-3 at the highest decompression rate (8.5 MPa/s; Mangan and Sisson, 2000), while observed BNDs in natural silicic pumices commonly exhibit much higher BNDs: up to 1016 m-3. To reproduce such huge BNDs and to characterize effects of magma ascent rate on bubble nucleation kinetics, we carried out decompression experiments of crystal-free rhyolitic liquid with 6.6 wt.% H2O at a pressure range from 250 MPa to 30-75 MPa, at decompression rates of 10 MPa/s and 90 MPa/s. A first series of experiments at 800 °C and fast decompression rates (10-90 MPa/s) produced huge BNDs (2×1014 m-3 at 10 MPa/s; 2×1015 m-3 at 90 MPa/s), comparable to those in natural silicic pumices from Plinian eruptions (1015-1016 m-3). A second series of experiments at 700 °C and 1 MPa/s produced BNDs (9×1012 m-3) close to those observed at 800 °C and 1 MPa/s (6×1012 m-3; Mourtada-Bonnefoi and Laporte, 2004). These experimental results confirm that BNDs are strongly depending on decompression rate and that temperature has an insignificant effect on BNDs at a given decompression rate. Therefore, BNDs are good markers of the decompression rate of magmas in volcanic conduits irrespective of temperature. Observed BNDs in natural silicic pumices from Plinian eruptions are as high as 1016 m-3. In addition, bubbles commonly show a bimodal size distribution with a numerically minor population of large bubbles (about 109 m-3), and a major population of smaller bubbles, typically from a few μm to a few tens of μm in diameter. Such huge number densities of bubbles may be attributed to two successive nucleation events in ascending magmas. The large bubbles are presumably related to a first nucleation event that happens relatively deep in the conduit at low decompression rate (about 0.01 MPa/s). The huge popolation of small bubbles implies that a second nucleation event occurs in the upper volcanic conduit at much faster decompression rate(≥ 1 MPa/s). Literature Toramaru A. (1995). Jour. Geophys. Res. 100: 1913-1931. Toramaru A. (2006). Jour. Volcanol. Geotherm. Res. 154: 303-316. Mourtada-Bonnefoi C. C., Laporte D. (2004). Earth Planet. Sci. Lett. 218: 521-537. Mangan M. T., Sisson T. (2000). Earth Planet. Sci. Lett. 183: 441-455.
Physics and Chemistry of Minerals, 2005
Wadsleyite II is a variably hydrous magnesiumiron silicate phase similar to spinelloid IV and a p... more Wadsleyite II is a variably hydrous magnesiumiron silicate phase similar to spinelloid IV and a potential host for H in the Transition Zone of the Earth's mantle. Two separate samples of wadsleyite II synthesized at 17.5 GPa and 1400°C and at 18 GPa and 1350°C have been characterized by electron microprobe, single-crystal X-ray diffraction, visible, IR, Raman, and Mo¨ssbauer spectroscopies, and transmission electron microscopy including electron energy-loss spectroscopy. The two samples have the following chemical formulae: Mg 1.71 Fe 0.18 Al 0.01 H 0.33 Si 0.96 O 4 and Mg 1.60 Fe 0.22 Al 0.01 H 0.44 Si 0.97 O 4 . Mö ssbauer spectroscopy and electron energy loss spectroscopy (EELS) indicate that about half of the iron present is ferric. Refinement of the structures shows them to be essentially the same as spinelloid IV. Calculated X-ray powder diffraction patterns show only subtle differences between wadsleyite and wadsleyite II.
Proceedings of the National Academy of Sciences, 2013
Slab-derived fluids play an important role in heat and material transfer in subduction zones. Deh... more Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressuretemperature conditions of fluids are few. This report describes CO 2 -bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaClequivalent magnesite crystals, CO 2 -bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830°C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO 2bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H 2 O and affect the chemical evolution of the mantle wedge.
Aqueous fluids and sedimentary melts as agents for mantle wedge metasomatism, as inferred from peridotite xenoliths at Pinatubo and Iraya volcanoes, Luzon arc, Philippines
Mantle xenoliths entrained in subduction-zone magmas often record metasomatic signature of the ma... more Mantle xenoliths entrained in subduction-zone magmas often record metasomatic signature of the mantle
wedge. Such xenoliths occur in magmas from Iraya and Pinatubo volcanoes, located at the volcanic front of the
Luzon arc in the Philippines. In this study, we present the major element compositions of the main minerals,
trace element abundances in pyroxenes and amphiboles, and Nd–Sr isotopic compositions of amphiboles in
the peridotite xenoliths from Pinatubo volcano. The data indicate enrichment in fluid-mobile elements, such as
Rb, Ba, U, Pb, and Sr, and Nd–Sr isotopic ratios relative to those of mantle. The results are considered in terms
of mixing of asthenospheric mantle and subducting oceanic crustal components. The enrichments observed in
the Pinatubo mantle xenoliths are much less pronounced than those reported for the Iraya mantle xenoliths.
This disparity suggests differences in the metasomatic agents contributing to the two suites; i.e., aqueous fluids
infiltrated the mantle wedge beneath the Pinatubo volcano, whereas aqueous fluids and sediment-derived
melts infiltrated the mantle wedge beneath the Iraya volcano.
PDF file will be sent for a request. kawamoto@bep.vgs.kyoto-u.ac.jp
Geiger, C. A., Kawamoto, T., Experimental Mineralogy and Petrology, in: White, W.M. (Ed.), Encycl... more Geiger, C. A., Kawamoto, T., Experimental Mineralogy and Petrology, in: White, W.M. (Ed.), Encyclopedia of Geochemistry: A Comprehensive Reference Source on the Chemistry of the Earth. Springer International Publishing, pp. 1-6. in press
Halogen and noble gas systematics are powerful tracers of volatile recycling in subduction zones.... more Halogen and noble gas systematics are powerful tracers of volatile recycling in subduction zones. We present halogen and noble gas compositions of mantle peridotites containing H 2 O-rich fluid inclusions collected at volcanic fronts from two contrasting subduction zones (the Avacha volcano of Kamchatka arc and the Pinatubo volcano of Luzon arcs) and orogenic peridotites from a peridotite massif (the Horoman massif, Hokkaido, Japan) which represents an exhumed portion of the mantle wedge. The aims are to determine how volatiles are carried into the mantle wedge and how the subducted fluids modify halogen and noble gas compositions in the mantle. The halogen and noble gas signatures in the H 2 O-rich fluids are similar to those of marine sedimentary pore fluids and forearc and seafloor serpentinites. This suggests that marine pore fluids in deep-sea sediments are carried by serpentine and supplied to the mantle wedge, preserving their original halogen and noble gas compositions. We suggest that the sedimentary pore fluid-derived water is incorporated into serpentine through hydration in a closed system along faults at the outer rise of the oceanic, preserving Cl/H 2 O and 36 Ar/H 2 O values of sedimentary pore fluids. Dehydration–hydration process within the oceanic lithospheric mantle maintains the closed system until the final stage of serpentine dehydration. The sedimentary pore fluid-like halogen and noble gas signatures in fluids released at the final stage of serpentine dehydration are preserved due to highly channelized flow, whereas the original Cl/H 2 O and 36 Ar/H 2 O ratios are fractionated by the higher incompatibility of halogens and noble gases in hydrous minerals.
Direct observation of coexisting aqueous fluid and silicate melt using x-ray radiography
ABSTRACT
It is now widely accepted that Earth’s transition zone, located at depth between 410 km to 670 km... more It is now widely accepted that Earth’s transition zone, located at depth between 410 km to 670 km is most likely hydrated. However, a definite conclusion has yet to be reached regarding the nature of the hydrous phase or phases that have the capacity to efficiently transport water down to such depths. In their study, Nishihara and Matsukage ( Am Mineral, 2016, April issue) show that (FeH)1-xTixO2 can be stable in wet basalts and sediments in high pressure and high temperature conditions. These phases allow the subducting lithosphere to transport far more water to the mantle transition zone than previously thought possible.
Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived flux: aqueous flu... more Subduction-zone magmatism is triggered by the addition of H2O-rich slab-derived flux: aqueous fluids, hydrous partial melts or supercritical fluids from the subducting slab through reactions. Whether the slab-derived flux is an aqueous fluid, a partial melt, or a supercritical fluid remains an open question. In general, with increasing pressure, aqueous fluids dissolve more silicate components and silicate melts dissolve more H2O. Under low-pressure conditions, those aqueous fluids and hydrous silicate melts remain isolated phases due to the miscibility gap. As pressure increases, the miscibility gap disappears and the two liquid phases becomes one phase. This vanishing point is regarded as critical end point or second critical end point. X-ray radiography experiments locate the pressure of the second critical end point at 2.5 GPa（ 83 km depth）and 700 °C for sediment-H2O, and at 2.8 GPa （92 km depth） and 750 °C for high-Mg andesite（HMA）-H2O. These depths correspond to the depth range of a subducted oceanic plate beneath volcanic arcs. Sediment-derived supercritical fluids, which are fed to the mantle wedge from the subducting slab, may react with the mantle peridotite to form HMA supercritical fluids due to peritectic reaction between silica-rich fluids and olivine-rich mantle peridotite. Such HMA supercritical fluids may separate into aqueous fluids and HMA melts at 92 km depth during ascent. HMA magmas can be erupted as they are, if the HMA melts segregate without reacting to the overriding peridotite. Partitioning behaviors between aqueous fluids and melts are determined with and without（Na, K）Cl using synchrotron X-ray fluorescence. The data indicate that highly saline fluids effectively transfer large-ion lithophile elements. If the slab-derived supercritical fluids contain Cl and subsequently separate into aqueous fluids and melts in the mantle wedge, then such aqueous fluids inherit much more Cl and also more or less amounts of large ion lithophile elements than the coexisting melts. In contrast, Cl-free aqueous fluids cannot effectively transfer Pb and alkali earth elements to the magma source. Enrichment of some large-ion lithophile elements in arc basalts relative to mid-oceanic ridge basalts has been attributed to mantle source fertilization by such aqueous fluids from a dehydrating oceanic plate. Such aqueous fluids are likely to contain Cl, although the amount remains to be quantified. If such silica-rich magmas survive as andesitic melts under a limited reaction with mantle minerals, they may erupt as HMA magmas having slab-derived signatures.
Almost all physico-chemical characteristics of earthforming materials are influenced by the prese... more Almost all physico-chemical characteristics of earthforming
materials are influenced by the presence of
H2O. As N. L. Bowen stated in 1928, H2O plays the role
of Maxwell’s demon - it does just what a petrologist may
wish it to do [p. 282, The evolution of the igneous rocks
(Bowen 1928)]. In the following decades, this has been
proven to be the case not only in petrology but in every
field of solid Earth science.
Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/... more Geochemical signatures of arc basalts can be explained by addition of aqueous fluids, melts, and/or supercritical
fluids from the subducting slab to the sub-arc mantle. Partitioning of large-ion lithophile elements between
aqueous fluids and melts is crucial as these two liquid phases are present in the sub-arc pressure-temperature
conditions. Using a micro-focused synchrotron X-ray beam, in situ X-ray fluorescence (XRF) spectra were obtained
from aqueous fluids and haplogranite or jadeite melts at 0.3 to 1.3 GPa and 730°C to 830°C under varied concentrations
of (Na, K)Cl (0 to 25 wt.%). Partition coefficients between the aqueous fluids and melts were calculated for Pb, Rb, and
Sr (D fluid/melt
Pb; Rb; Sr). There was a positive correlation between D fluid/melt
Pb; Rb; Sr values and pressure, as well as D fluid/melt
Pb; Rb; Sr values and
salinity. As compared to the saline fluids with 25 wt.% (Na, K)Cl, the Cl-free aqueous fluids can only dissolve one tenth
(Pb, Rb) to one fifth (Sr) of the amount of large-ion lithophile elements when they coexist with the melts. In the
systems with 13 to 25 wt.% (Na, K)Cl, D fluid/melt
Pb; Rb values were greater than unity, which is indicative of the capacity of
such highly saline fluids to effectively transfer Pb and Rb. Enrichment of large-ion lithophile elements such as Pb and
Rb in arc basalts relative to mid-oceanic ridge basalts (MORB) has been attributed to mantle source fertilization by
aqueous fluids from dehydrating oceanic plates. Such aqueous fluids are likely to contain Cl, although the amount
remains to be quantified.
Lherzolite xenoliths containing fluid inclusions from the Ichinomegata volcano, located on the r... more Lherzolite xenoliths containing fluid inclusions
from the Ichinomegata volcano, located on the rear-arc side
of the Northeast Japan arc, may be considered as samples
of the uppermost mantle above the melting region in the
mantle wedge. Thus, these fluid inclusions provide valuable
information on the nature of fluids present in the subarc
mantle. The inclusions in the Ichinomegata amphibolebearing
spinel–plagioclase lherzolite xenoliths were found
to be composed mainly of CO2–H2O–Cl–S fluids. At equilibrium
temperature of 920 °C, the fluid inclusions preserve
pressures of 0.66–0.78 GPa, which correspond to depths
of 23–28 km. The molar fraction of H2O and the salinity
of fluid inclusions are 0.18–0.35 and 3.71 ± 0.78 wt%
NaCl equivalent, respectively. These fluid inclusions are
not believed to be fluids derived directly from the subducting
slab, but rather fluids exsolved from sub-arc basaltic magmas that are formed through partial melting of mantle
wedge triggered by slab-derived fluids.
Kawamoto, T., Yoshikawa, M., Kumagai, Y., Mirabueno, M. H. T., Okuno, M., Kobayashi, T.
Slab-derived fluids play an important role in heat and material transfer in subduction zones. Deh... more Slab-derived fluids play an important role in heat and material transfer in subduction zones. Dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow. Nevertheless, direct observations of the fluid chemistry and pressuretemperature conditions of fluids are few. This report describes CO 2 -bearing saline fluid inclusions in spinel-harzburgite xenoliths collected from the 1991 Pinatubo pumice deposits. The fluid inclusions are filled with saline solutions with 5.1 ± 1.0% (wt) NaClequivalent magnesite crystals, CO 2 -bearing vapor bubbles, and a talc and/or chrysotile layer on the walls. The xenoliths contain tremolite amphibole, which is stable in temperatures lower than 830°C at the uppermost mantle. The Pinatubo volcano is located at the volcanic front of the Luzon arc associated with subduction of warm oceanic plate. The present observation suggests hydration of forearc mantle and the uppermost mantle by slab-derived CO 2bearing saline fluids. Dehydration and decarbonation take place, and seawater-like saline fluids migrate from the subducting slab to the mantle wedge. The presence of saline fluids is important because they can dissolve more metals than pure H 2 O and affect the chemical evolution of the mantle wedge.
Subduction-zone magmatism is triggered by the addition of H 2 Orich slab-derived components: aque... more 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.
A new hydrous silicate phase with formula , 0 has been synthesized at 1400°C and 17.5 4 GPa from ... more A new hydrous silicate phase with formula , 0 has been synthesized at 1400°C and 17.5 4 GPa from a hydrous iron-rich mantle peridotite composition.
At the BL43IR of SPring-8, infrared microanalysis on various kinds of solid specimens under multi... more At the BL43IR of SPring-8, infrared microanalysis on various kinds of solid specimens under multiple environments with a spatial resolution smaller than 10 mm in diameter is planned in the infrared region. In order to perform such analysis, two different stations, a multipurpose spectromicroscopy apparatus and a magneto-optical imaging one have been constructed. Measurements on the spatial two-dimensional cross-section of the infrared beam at the spectromicroscopy station have proven that the stations have a good prospective feature in the performance. #
In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of ... more In-situ synchrotron X-ray diffraction (XRD) experiments of a natural apatite with the formula of Ca 5 (PO 4 ) 3 F 0.94 Cl 0.06 were carried out using a diamond anvil cell and angle-dispersive technique at Photon Factory (PF), Japan. Pressure-volume data were collected up to 7.12 GPa at 300K. The pressures were determined from the ruby fluorescence spectra shift. The unit-cell parameters and volume decreased systematically with increasing pressure, and a reliable isothermal bulk modulus and its pressure deviative were obtained in this study. The third order Birch-Murnaghan equation of state yielded the isothermal bulk modulus of K T = 91.5(38) GPa, its pressure derivative K T ' = 4.0(11), and the zero-pressure volume V 0 = 524.2(3) Å 3 .
Samples of olivine, wadsleyite, ringwoodite and majorite with Mg/(Mg + Fe) = 0.85-0.90 were synth... more Samples of olivine, wadsleyite, ringwoodite and majorite with Mg/(Mg + Fe) = 0.85-0.90 were synthesised at high pressure and temperature using a multianvil press under nominally anhydrous conditions as well as hydrous conditions with varying conditions of oxygen fugacity, and examined ex situ using Mössbauer spectroscopy to determine Fe 3+ / Fe, and either Fourier Transform Infrared Spectroscopy or Secondary Ion Mass Spectrometry to determine H concentration. Under oxidising conditions, the relative concentration of Fe 3+ increases with water content in olivine, wadselyite and ringwoodite. Majorite does not incorporate significant water, but shows high Fe 3+ / Fe values when synthesised under oxidising conditions in the presence of water. Fe 3+ / Fe is strongly influenced by oxygen fugacity for all phases studied, and the mechanism of hydration is likely coupled to Fe 3+ incorporation in the crystal structure. Enhanced Fe 3+ / Fe in mantle-derived olivine and orthopyroxene has a negligible effect on oxygen fugacities estimated using olivine-orthopyroxene-garnet oxybarometers, while increased Fe 3+ / Fe in garnet due to dehydrogenation could lead to an overestimation of oxygen fugacity in exhumed samples. Subduction zones are likely oxidised relative to the rest of the mantle, and hence represent regions where not only water is concentrated, but also Fe 3+ .