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Department of Solid Earth Geochemistry

Seminar Schedule

[D-SEG seminar]

Date:
2015/12/10(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Alexander Nichols (ODS)
Title:
Origin of xenoliths in basalts from West Zealandia Seamount, Mariana Arc: comparing inferences from mineral chemistry and volatiles in melt inclusions - the significance of vapour bubbles
Abstract:
Basalts recovered from West Zealandia Seamount in the southern Mariana Arc contain dunite and wehrlite xenoliths. Olivines within these xenoliths contain glassy silicate melt inclusions. I will examine the crystal chemistry and also use clinopyroxene-liquid thermobarometry to estimate the depths at which the xenoliths crystallised. These will be compared with equilibration pressures for the olivine-hosted melt inclusions estimated from the volatiles dissolved in the glass of the melt inclusions, inferred to represent the olivine crystallisation depths. I will discuss the large discrepancy between pressures estimated using the two methods and show that if the volatiles that could reside in bubbles, present in many inclusions, are considered there is much closer agreement.

[D-SEG seminar]

Date:
2015/12/4(Friday)15:40−17:00
Place:
Meeting Room at 3F, Marine Research Building YOKOSUKA HQ
Speaker:
Kenta Ueki(DSEG)
Title:
Numerical modeling for the calculations of density, compressibility and seismic velocity of hydrous melts
Abstract:
We present a new model for the calculations of the density of the various hydrous silicate melts as a function of temperature, pressure, H2O concentration and melt composition. We optimize volumetric parameters of H2O end-member component in hydrous silicate melt as well as K’ of anhydrous silicate melt using previously reported experimental results. The model uses the Birch-murnaghan equation for the equation of state and parameter values reported in Lange and Carmichael (1990) for the properties of anhydrous silicate melt. The modeling undertaken during this study reproduces the experimentally determined densities of various hydrous melts including basalt and rhyolite. The model can be used to calculate relationships between pressure, temperature and H2O concentration of various subduction zone hydrous melts up to 5 GPa. We demonstrate the effect of the melt H2O content on the seismic velocity of the silicate melt and the partially molten zone of the subduction zone.

[D-SEG seminar]

Date:
2015/11/19(Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Natsue Abe(ODS)
Title:
1. Bulk-rock major-element chemistry of the Pacific crust subducting into the Izu-Bonin Trench
2. A tour of D/V Chikyu on-board laboratories and daily life (Slide show)
Abstract:
Oceanic crust samples were successfully taken from several dredge stations at the edge of the Mesozoic Pacific Plate subducting along the Izu-Bonin Trench during the RR1412 cruise aboard R/V Roger Revelle in 2014. The main objective of the cruise was to test the hypothesis that the altered oceanic crust (AOC) is a major source for the volcanic rocks erupting along the Izu-Bonin arc. The compositions of volcanic rocks that have formed in the Izu-Bonin arc since about 42 Myr ago are distinctly different from those that formed earlier and this may have been due to compositional change in the subducting AOC along the trench (Straub et al., 2009) . The samples were collected through dredging of the active, vertical fault scarps along the subducting plate from 27.5 N to 34.5 N, roughly between the Ogasawara Plateau in the south and Honshu Island in the north.
The samples were taken along a nearly 700 km trench transect and, thus, are useful for determining any latitudinal compositional variation of the AOC. The major element chemistry of the whole rock basaltic samples varies from tholeiitic to alkaline, with high K2O (up to 4.2 wt%) and TiO2 (up to 2.96 wt%) contents. Significantly, the alkaline basalts are mainly from the northernmost part of the area near the T-T-T triple junction in the mid-Cretaceous Quiet Zone of the Pacific Plate, where a propagating ridge was discovered (Nakanishi 2011).

[D-SEG seminar]

Date:
2015/11/12(Thursday) 16:00-17:00
Place:
Meeting Room at Guest House 2F, YOKOSUKA HQ
Speaker:
Takashi Miyazaki (DSEG)
Title:
Geochemical characteristics of the deeper part of Site U1437, IODP Exp. 350
Abstract:
The Izu-Bonin-Mariana arc (IBM) is an intra-oceanic arc that formed ~50 million years ago (Ma). Previous drilling and dredging at the volcanic front and dredging in the rear-arc of the IBM has provided a record of the magmatic evolution of the volcanic front since the arc’s formation, and revealed a geochemical asymmetry between the volcanic front and rear-arc. One of the scientific objectives of IODP Exp. 350 is to clarify the geochemical characteristics of the Paleogene basement underlying the Izu rear-arc region, which has not be accessed by dredging (Tamura et al., 2013). Determining the causes of this geochemical asymmetry and when it became established is important to understand the magmatic process of the entire IBM arc. Site U1437 is located in the Izu rear-arc, ~330 km west of the axis of the Izu-Bonin Trench and ~90 km of the arc-front volcanoes Myojinsho and Myojin Knoll, at 2117 mbsl. Site U1437 consists of three coherent holes (U1437B, D, and E), reaches 1806.5 mbsf, and is divided into seven lithostratigraphic units (Unit I–VII). Units VI and VII, below 1320 mbsf, are volcaniclastics with coarser material, while Units I to V are tuffaceous mud and mudstone with intercalated volcaniclastic layers. The Unit VI is intruded at ~1390 mbsl by a single rhyolitic intrusion (igneous Unit 1) (Tamura et al., 2015). Initially we have focused on Hole U1437E (Units V to VII) in order to obtain as much information on the older basement as possible. In this seminar, I will talk about our ongoing age, geochemical and Sr-Nd-Pb-Hf isotopic studies with some new interpretations.

[D-SEG seminar]

Date:
2015/10/29(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Satoru Haraguchi(D-SEG)
Title:
Geochemical characteristics of the basement at the site C0012 of IODP EXP333, northern Shikoku Basin
Abstract:
The Shikoku Basin is a back arc basin located Westside of the Izu-Ogasawara (Bonin) arc, spreading was from 25Ma to 15Ma. The drilling of the DSDP, ODP and IODP recovered the backarc basin basalt (BABB) of the Shikoku Basin. Site C0012, south of the Kii Peninsula, was operated during the IODP EXP333. This BABB has different geochemical characteristics, enrichment of alkali elements, from other Shikoku Basin BABBs (e.g. DSDP Leg58). And geochemical regional variations of BABBs are found among sites in the Shikoku Basin. I will discuss the enrichment process of alkali elements based on identification of secondary minerals, and origin of regional variation of the Shikoku Basin BABBs.

[D-SEG seminar]

Date:
2015/10/22(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Ryoko Senda(D-SEG)
Title:
What is the source of difference between Ogasawara boninites and Guam boninites?
Abstract:
Subduction systems are directly related to arc volcanism. The initiation of arc are suggested by many researchers however there are still many unknowns. To know the initiation of arc magma and behavior of Platinum group elements in arc related rocks, trace elements and Os isotope ratios of whole-rock and Cr-spinels from boninites and tholeiites along Izu-Bonin-Mariana arc were analysed. Boninites are related to infant arc settings and the tholeiites are subsequent.
Major and trace element abundances of boninites from Guam are clearlyss different from those from Ogasawara and they are close to fore arc basalts from Mariana fore arc. The Os isotope ratios however are similar range between boninites from Ogasawara and Guam. In the platinum group elements, Ir abundances of Guam boninites are characteristically enriched than Os and other boninites. The enrichment of Ir is not known to other kinds of volcanic rocks. I will discuss about the source of differences between boninites from Ogasawara and Guam.

[D-SEG seminar]

Date:
2015/10/1 (Thursday)16:00-17:00
Place:
Seminar Room at 1F, Marine Ecosystem Research Building YOKOSUKA HQ
Speaker:
Hitomi Nakamura(D-SEG)
Title:
Rare earth elements of the Arima spring waters, Southwest Japan: implications for fluid-crust interaction during ascent of deep brine
Abstract:
Rare earth elements (REEs) of the eight Arima spring waters in southwest Japan, including Arima-type brine that represents a specific type of deep-seated brine of up to 6 wt.% NaCl in the non-volcanic fore-arc region, have been investigated in order to discuss their upwelling processes and origins. We found four distinct patterns of REE composition of the spring waters within the Arima area of ~1 km2, based on which two sources for REEs and two aquifers are inferred in the modification of the original deep-seated brine composition. On the basis of the REEs and isotopic compositions of the original deep brine, one of the two sources is thought to be slab-derived fluid dehydrated from the subducted Philippine Sea slab beneath the Arima area, represented by the ‘Kinsen’ hot spring water (Nakamura et al., 2014). The convex-down REE pattern of most Arima spring waters, except for ‘Kinsen’ and ‘Tansansen’, suggests the presence of an oxidizing aquifer deeper than 160 m that causes co-precipitation of REEs with oxyhydroxides. CO2 and He degassed from this aquifer flux the overlying shallow aquifer less than ~50 m in depth, producing highly carbonated water such as ‘Tansansen’ water that was originally derived from meteoric water. The carbonated water may dissolve a significant amount of REEs to the ‘Tansansen’ spring water from the host rocks, which are possibly silicic igneous rocks with Eu-negative anomalies. The four types of REE patterns with a wide concentration range, therefore, provide invaluable information concerning fluid-crust interaction during ascent of the deep brine.

[D-SEG seminar]

Date:
2015/9/3 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Yoshihiko Tamura(ODS)
Title:
Andesite Magmas are Produced along Oceanic Arcs where the Crust is Thin: Evidence from Nishinoshima Volcano, Ogasawara Arc, Japan
Abstract:
The incentive for this study is the ongoing explosive eruption of Nishinoshima volcano, located about 1,000 km south of Tokyo along the Ogasawara (Bonin) Arc. The straightforward but unexpected relationship presented here relates crustal thickness and magma type in the Izu-Ogasawara Oceanic Arc. Volcanoes along the Ogasawara segment of the arc, which include Nishinoshima, are underlain by thin crust (16-21 km)-in contrast to those along the Izu segment, where the crust is ~35 km thick. Interestingly, andesite magmas are dominant products from the former volcanoes and mostly basaltic lavas erupt from the latter.
Why and how do volcanoes on the thin crust erupt andesite magmas? An introductory petrology textbook might answer this question by suggesting that, under decreasing pressure and hydrous conditions, the liquidus field of forsterite expands relative to that of enstatite, with the result that, at some point, enstatite melts incongruently to produce primary andesite melt. According to the hypothesis presented here, however, rising mantle diapirs stall near the base of the oceanic arc crust at depths controlled by the thickness of the overlying crust. Where the crust is thin, as along the Ogasawara segment of the arc, pressures are relatively low, and magmas produced in the mantle wedge tend to be andesitic. Where the crust is thick, as along the Izu segment, pressures are greater, and only basaltic magmas tend to be produced.
To examine this hypothesis, JAMSTEC cruise NT15-E02 on the R/V Natsushima took place from 11 June to 21 June 2015 to Nishinoshima. It’s present island has an elevation of only ~150 m, but its submarine flanks extend to ocean depths of 2,000-3,000 m, so the great bulk of the volcano is submarine and yet-to-be explored. We present the new hypothesis and its evidence from Nishinoshima based on the primitive lavas collected from the submarine parts of the volcano.

[D-SEG seminar]

Date:
2015/07/23(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Shigeaki Ono(ODS)
Title:
High pressure study of iron and iron alloy
Abstract:
Ab initio molecular dynamics simulations and high-pressure experiments were performed to investigate the physical properties of iron and iron-silicon alloy at core pressure- temperature conditions. The spin transition, which has an affect on the seismic velocities, of the high-pressure Fe phase with the hcp structure from high to low state was confirmed. The P-V-T relationship and seismic velocities of iron-silicon alloy was determined by calculations. The estimated density of FeSi was lower than that of hcp-Fe, whereas the compressional and shear sound wave velocities of FeSi were higher than those of hcp-Fe. The inner core model for a mixture of Fe and FeSi was able to explain the density and seismic wave velocities of PREM. However, the estimated temperature at the top of the inner core was too high. This indicated that silicon is excluded from the candidate light elements in the inner core.

[D-SEG seminar]

Date:
2014/07/02(Thursday)16:00-17:00
Place:
Seminar Room 3 at Marine Ecosystem Research Building 1F, YOKOSUKA HQ
Speaker:
Takeshi Hanyu (DSEG)
Title:
Nuugurigia Atoll; a new type of volcanism on Ontong Java Plateau
Abstract:
Several atolls have been recognized on the Ontong Java Plateau (OJP). These atolls are possibly related to a late-stage volcanism of OJP, but no volcanic rocks were available before. During R/V Mirai cruise in 2012, basalts were sampled for the first time by dredge haul from three small volcanic cones on the northeastern ridge of Nuugurigia (Tau) Atoll on OJP. In this presentation, the geochemical composition and age of basalts from Nuugurigia are reported.
These basalts have more enriched isotopic signature toward EM1 compared to any rocks from OJP (including those from Solomon Islands). Their isotopic signature is close to, but even more enriched than, that of some basement rocks from Manihiki Plateau. This reinforces the presence of EM1 component from OJP that has been recognized as a major source of Manihiki Plateau (Tejada et al., 2013). These basalts show unique trace element characteristics. They show mildly enriched pattern in the spidergram with robust Sr positive spike and Zr-Hf negative spike. We confirmed that this was not caused by alteration by comparing trace element abundance of less-, moderately-, and highly-altered parts of rocks with laser-ablation ICP-MS technique. Sr enrichment and Zr-Hf depletion relative to rare earth elements is a feature shared with quartz-bearing garnet pyroxenite found as xenoliths from Solomon Islands. Moreover, such xenoliths show enriched isotopic characteristics; thereby we intepret that the basalts from Nuugurigia is a melting product of the garnet pyroxenite underplating beneath the OJP lithosphere.
Ishikawa et al. (2007) suggested that the quartz-bearing garnet pyroxenite was delaminated granulitic lower crust from Rodinia supercontinent. Such lower crustal material would have been transported upwards by a mantle plume, stored beneath the OJP lithosphere, and then recently melted to form a late-stage volcano on OJP.

[D-SEG seminar]

Date:
2015/06/18(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Junichi Kimura(DSEG)
Title:
Behavior of water, major and trace elements in subduction zone magmatism
Abstract:
I present a forward model perspective on behavior of water, major and trace elements, and isotopes in subduction slab fluxes and in magmas in subduction zones. Arc Basalt Simulator version 4 (ABS4: Kimura J.-I. et al. [2014]
Diverse magmatic effects 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 mantle wedge peridotite by fluxing of the slab fluid/melt to estimate element abundances in the primary arc magmas, such as arc 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 this numerical model.
Once element mass balance is established between the source materials (e.g., slab sediment, igneous oceanic crust, and mantle wedge peridotite) and a primary arc magma, source conditions including (1) depth and temperature of slab dehydration/melting, (2) contributions of sediment and igneous slab layer fluxes, (3) slab flux fraction in the mantle, (4) depth and temperature of fluxed mantle melting, (5) degree of melting of mantle, and (6) element abundance including water in the primary basalt can be estimated. I will compare the results of ABS4 analyses on SW Japan and the NE Japan subduction zones representing hot/young and old/cold subduction cases, respectively. Analyses of these endmember subduction zones reveal genetic conditions of almost all magma types occurring in subduction zones.
Long-term isotopic growth of the residual subducted sediment and igneous oceanic crust after subduction zones are compared with the recycled oceanic crust components found in ocean island basalts to examine Sr-Nd-Pb-Hf isotopic growth in the Earth’s mantle. The results show that the subduction magmatism is a key to understand evolution of the Earth’s mantle.

[D-SEG seminar]

Date:
2015/06/04(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Kazutaka Yasukawa(The University of Tokyo)
Title:
Decoding geochemical signals: Statistically independent components constituting deep-sea sediments
Abstract:
Independent Component Analysis (ICA) is a relatively new computational statistical technique established in the fields of neuroscience and information science during the past quarter century, which can extract original independent source signals on the basis of intrinsic non- Gaussian data structures. Here I applied ICA to a huge data set composed of chemical compositions of 3,968 bulk sediment samples collected from the Pacific and the Indian Oceans. The result of ICA indicates that the chemical compositions of bulk sediment samples can be successfully expressed by statistically independent components (ICs) including biogenic carbonate and silica components, hydrothermal component, volcaniclastic component, and two components controlling concentrations of rare-earth elements.
In the seminar, I will introduce the mathematical principle of ICA, how to interpret the extracted geochemical ICs, and implications of the ICs for Earth’s surface system.

[D-SEG seminar]

Date:
2014/5/21(Thursday)16:00-17:00
Place:
seminar room at Marine Ecosystem Research Building, YOKOSUKA HQ
Speaker:
Bogdan Stefanov Vaglarov (DSEG)
Title:
Experimental presentation of plate subduction using paraffin wax
Abstract:
Experimental approaches using analogue materials have been widely used to understand kinematic behaviors of tectonic plates. In order to simulate the plate and its motion as a well-developed thermo-mechanical boundary layer on top of vigorously convecting mantle, we have developed a tank apparatus and performed preliminary experiments using paraffin wax.
To control the complex heat and convection processes and for easy observation we used a glass tank with double pane glass walls.The paraffin was melted from bellow by a copper heat-sink containing ceramic heating elements. To reduce heat loss from the back wall the wall was isolated with 8cm thick foam. At the boundary layer where the paraffin wax was sticking as it cooled down we applied NiCr wire heater to the inner walls. All heating sections were controlled by variable controllers. We cooled the top layer of the wax with a cold air flow carefully controlled with thin foam plates from a vat filed with liquid Nitrogen.
We observed continuous subduction and clear “crust” forming with subsequent subduction. We can say that our experiment properly reproduces the general features of plate motion of the earth. Artificially fracturing or weakening the boundary layer and applying a vertical, downward external force were required to initiate subduction in addition to collision of the plates.
Our experiment results suggest that the driving force of subduction and plate motion is slab pull, not the thermal convection of the molten paraffin or ridge push.
I will explain the technical details of the experiments and present visually the observed processes.

[D-SEG seminar]

Date:
2014/05/14 (Thursday)15:40-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Tatsu Kuwatani(DSEG)
Title:
Data-driven analysis for extracting earth processes - Geochemical discrimination of 2011 Tohoku-oki tsunami sediments by using machine-learning techniques -
Abstract:
It is important to extract essential information from high-dimensional data in order to understand the behavior of dynamic earth. Recently, we have launched a big scientific project entitled as “Initiative for high-dimensional data-driven science through deepening sparse modelling” (http://sparse-modeling.jp/index_e.html). The main purpose of this project is to develop the innovative mathematical methodology for understanding the world of nature by tight fusion of information science and natural science. The project includes a wide variety of natural sciences such as biology, medicine, brain science, earth and planetary sciences and astronomy. The project focuses on the innovative multivariate analysis methods called as ‘Sparse Modeling’ that based on fundamental principle of sparseness: most of useful information is embedded in the low-dimensional subspace for high-dimensional observation data in the various fields of natural science. In this presentation, I will share an example of the collaboration work between earth science and information science within the project: Geochemical discrimination of 2011 Tohoku-oki tsunami sediments by using machine-learning techniques. In addition, I will introduce my new research theme in JAMSTEC.

[D-SEG seminar]

Date:
2014/03/12(Thursday)16:30-18:00
Place:
3rd Seminar room at Marine Ecosystem Research Building 1F, YOKOSUKA HQ
Speaker:
CHANG QING(DSEG)
Title:
Determination of rare earth elements at extremely low concentration in saline geothermal water by ICP-MS
Abstract:
Concentration and distribution of rare earth elements (REE) is one of the key factors for characterizing and modeling water transport and cycling processes in subduction zones. Recent studies based on REE and isotopic data argued for slab fluid upwelling in non-volcanic hot springs (Nakamura et al. 2014; Kusuda et al. 2014). However analytical uncertainty of REE caused by extremely low REE content, puzzling spectral interference and high salinity of geothermal water analyzed critically challenge this interpretation. Almost every light REEs (from La to Gd) suffers from strong interference of molecular ions (mostly oxides and hydroxides of barium) while high matrix content of brine load to plasma affects whole analyte signals in ICP-MS analysis (known as “matrix effect”). These problems obviously alter REE distribution pattern, consequently disturb geochemical modeling not only on quantitation but on correctness as well. Standard addition method is generally adopted to overcome matrix effect between sample and calibration standards. A prerequisite for this approach is the elimination of interfering and background signals before it can be used effectively. In the case of applying standard addition for high matrix samples such as geothermal water, a dramatic signal drift within the sample set of standard additions also needs to be compensated. In this seminar, we’ll talk about estimation and correction of all potential interfering species for the analysis of REE in brine geothermal waters.

[D-SEG seminar]

Date:
2014/3/5 (Thursday)16:30-18:30
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Natsue Abe (R&D Ocean Drilling Science)
Title:
Preliminary report of a dredge cruise: Implications for Geochemicalsubducting beneath the Izu-Bonin arc
Abstract:
The bulk of subduction zone magmas are produced by partial melting of the mantle wedge metasomatized by the slab component. The latter is enriched in volatiles and other (fluid-) mobile elements and mainly comes from subducted sediment and altered oceanic crust (AOC). Many studies have shown a strong link between subduction input and arc output, particularly in sedimented arc-trench systems.
In order to investigate the issue, we dredged basaltic samples from the active, vertical fault scarps along a ~700 km long section of the Pacific Plate subducting into the Izu-Bonin Trench during the RR1412 cruise aboard R/V Revelle in late 2014. The samples were collected on the active, vertical fault scarps along the subducting Pacific Plate in the Izu-Bonin Trench from 26.5 N to 34.5 N, roughly between the Ogasawara Plateau in the south and Honshu Island in the north. Our sampling transect encompasses a significant range of crustal ages that includes the purported compositional change of the Mesozoic Pacific crust at ~125 Ma. We plan to analyze these samples in order to perform detailed mass balance calculations of slab input vs. arc output that, in turn, will allow us to better constrain whether the AOC is indeed a significant source of the Izu-Bonin arc magma chemistry. The preliminary results of thesites will be shown in the seminar.
PI: P. R. Castillo, Scripps Institution of Oceanography (SIO), UCSD, USA Investigators:(SIO), Q. Yan (FIO-SOA, China), R. Kaneko (Niigata Univ. & JAMSTEC), Y. Tamura(JAMSTEC)

[D-SEG seminar]

Date:
2015/2/20(Thursday)16:00-18:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Tatsuhiko Kawamoto(Kyoto University)
Title:
Role of saline fluids in sub-arc mantle and subducting slab
Abstract:
Saline fluid inclusions are found from sub-arc mantle peridotite xenoliths: 3.7 wt% NaCl in Ichinomegata lherzolites, Northeast Japan arc [Kumagai et al., 2014] and 5.1 wt% NaCl in Pinatubo harzburgites, Luzon arc [Kawamoto et al., 2013]. These indicate that aqueous fluids in mantle wedge can contain certain amounts of Cl. Such saline fluids are also found in jadeitites of serpentinite mélanges located in Southwest Japan [Mori, Shigeno, Kawamoto, Nishiyama, in progress]. We suggested that separation of slab-derived supercritical fluids into aqueous fluids and melts plays an important role in elemental transfer from subducting slab to the mantle wedge [Kawamoto et al., 2012]. It is, therefore, important to determine the effect of Cl on the trace element partitioning between aqueous fluids and melts. Synchrotron radiation X-ray fluorescence (XRF) analysis is conducted to know Rb, Sr, and Pb partitioning between aqueous fluids and melts simultaneously at high-temperature and high-pressure conditions. There is a positive correlation between partition coefficients and pressure, as well as salinity [Kawamoto et al., 2014]. Two slab-derived components, melt and fluid components, are suggested to explain trace element characteristics of arc-basalts in the Mariana arc [Pearce et al., 2005]. The fluid component is characterized by enrichment of alkali, alkali earth elements, and Pb. Such features can be explained if the fluid component is a saline fluid, because alkali earth elements and Pb are much less mobile with Cl-free fluids than Cl-rich fluids [Kawamoto et al., 2014]. We suggest that slab-derived components have compositional features consistent with a saline fluid and a melt, which can be formed through a separation of a slab-derived supercritical fluid [Kawamoto et al., 2012, 2014]. Slab-derived supercritical fluids contain Cl, and separated aqueous fluids inherit much of the Cl and some of the large-ion lithophile elements.

[D-SEG seminar]

Date:
2014/2/5 (Thursday)16:30-18:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
MORIHISA HAMADA
Title:
Overview of IODP Expedition 351 ~ Izu-Bonin-Mariana Arc Origins ~
Abstract:
IODP Expedition 351 (June-July 2014) was conducted to understand how subduction zones initiate and continental crust forms in intraoceanic arcs. To achieve these purpose, we drilled the Amami Sankaku Basin, west of the Kyushu-Palau Ridge (KPR) as a paleo- Izu-Bonin-Mariana (IBM) arc and recovered cores which record the earliest evolution of the IBM system. In this seminar, I will talk about the overview and preliminary results of this expedition.

[D-SEG seminar]

Date:
2015/1/29(Thursday)16:30-18:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
SHIGEAKI ONO
Title:
Pressure measurements in high-pressure apparatuses
Abstract:
Accurate characterization of the pressure environment in high-pressure apparatuses is of essential importance when we apply laboratory data to the study of the Earth's interior. In this talk, I will introduce the techniques of pressure measurements revised by my recent works. In the first part, I will present the optical methods used in the diamond anvil cell experiments. Second, I will describe the phase transition points used in the multi-anvil high-pressure apparatus.

[D-SEG seminar]

Date:
2015/1/22 (Thursday)16:30-18:00
Place:
Meeting Room at Guest House 2F, YOKOSUKA HQ
Speaker:
Alex Nichols (ODS)
Title:
Volatiles in submarine HIMU basaltic glasses from the Austral Islands, South Pacific
Abstract:
I will present volatile data (H2O, CO2, S, Cl, F) measured in basaltic glasses collected with the Shinkai 6500 from the submarine flanks of the Austral Islands, Rurutu and Tubuai, in the South Pacific during Hanyu-san's cruise YK06-14. These are some of the only submarine samples with HIMU signatures that have been collected to date. Thus they are important in understanding the origin of the HIMU reservoir, particularly as there is chance, due to their eruption underwater at pressure, that the glasses may have retained their pre-eruption volatile contents. Hanyu-san has already published radiogenic isotope and trace element chemistry for bulk rock samples from these dives (Hanyu et al., 2013, CMP, 166, 1285) and explained the data as reflecting variable mixing between HIMU and DM components in the sources of Rurutu and Tubuai. After evaluating the extents to which the volatile concentrations measured in the glass from the same samples may have been affected by degassing, low-temperature hydration, and assimilation of brines and altered crust, I will place constraints on volatiles in the sources of Rurutu and Tubuai. Then, using the mixing scenario outlined by Hanyu-san in his paper, I will examine what this tells us about volatiles in the HIMU component, and whether HIMU has experienced subduction- related volatile-loss and, if so, how efficient and variable this was.