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Department of Solid Earth Geochemistry

Seminar Schedule

[D-SEG seminar]

Date:
2017/12/21 (Thursday) 16:00-17:00
Place:
Meeting Room on 3F, YOKOSUKA HQ
Speaker1:
Jan Bryan O. Navarro (Visitors of JST Sakura science program) (16:00-16:30)
Title:
MULTIBEAM and SIDESCAN DATA PROCESSING for the SEA BOTTOM CLASSIFICATION of the BENHAM RISE REGION
Abstract:
The Benham Rise is a 13 million hectare undersea region East of Luzon. It lies across a seismically active part of the Eastern Philippines and connected by a trail of seamounts to the Central Basin Fault (CBF) in the West Philippine Basin. The National Mapping and Resource Information Authority (NAMRIA) conducted bathymetric surveys in the area of Benham Rise and in the year 2012 the UN duly recognized it as part of the Philippine territory. The multibeam data from the survey of NAMRIA along with other data from International Agencies were processed using MB System as part of the Sakura Science Program. MBSystem is a free software program used for processing bathymetric data for scientific and research purposes. Using MBSystem, the multibeam data was processed, corrected for tide effects on depth, and edited to clean up the noises. Then the processed data were plotted and gridded to produce the bathymetry. The output from the MBSystem may be used for interpreting seamounts, abyssal hills, topographic configurations and sea bottom classification using the sidescan sonar analysis.
The seamounts and sea bottom topography plays a major role in the ocean circulation, along with the distribution of planktons and development of marine ecosystems. These seamounts act as stirring rods, or sites where some of the lunar and solar tides are converted into internal tides (e.g., Garrett, 2003). The surface tide energy is transferred to seamounts and mid ocean ridges where it begins to cascade the energy toward small scales of turbulence and the mixing intensity of this influences the large-scale ocean and local circulation patterns.
The Benham Rise has a magnificent marine biodiversity and very high potential for resources. Further studies are needed to analyze the ocean circulation pattern, sea bottom characteristics and collect samples and photos to identify the resources that lies beneath the Benham Rise Region. Suggestions for oceanographic survey (ADCP and CTD) and deep bathymetric and gravity survey for high resolutionseafloor topography, dredging, deep tow and ROV for collecting samples and identification of sites for ocean bottom observations and seismic surveys for locating possible energy and mineral resources are needed to fully understand the area. While the rise poses important scientific problems waiting to be resolved, it is also very important to map the diverse marine ecosystems to serve as the basis for a possible marine sanctuary that can be preserved for the future generations.
Speaker2:
John Agustin P. Escudero (Visitors of JST Sakura science program) (16:30-17:00)
Title:
Benham Rise region bathymetry data review: Seafloor fabrics, tectonic and geohazard implications, and mineral resources potential
Abstract:
The Benham Rise is an extinct underwater volcanic plateau located at the northeasternportion of the Philippine Archipelago, connected to the eastern continental shelf of Luzon,and is now part of the country’s extended continental shelf and Exclusive Economic Zone(EEZ). In order to evaluate the area’s geologic nature in terms of tectonics, geohazards andmineral resources potential, baseline data in the form of high-resolution multibeambathymetry obtained from the Philippines’ National Mapping Resource and InformationAuthority (NAMRIA) were reviewed. The seafloor fabric of the Benham Rise and itssurrounding areas was interpreted, and strategic targets for future geophysical surveys werealso pinpointed. Lineaments such as spreading-related ridges and faults, as well as erosion channels ofvarying trends, were recognized in and around the region. Smaller seamounts exhibiting aNE-SW trend, possibly related to hotspot magmatism, protrude the more gently sloping,wider expanse of the main rise which is thought to be a Large Igneous Province (LIP)produced via flood magmatism. In addition, the western margin of the region around theseismogenic East Luzon Trough (ELT) was also detailed. This trough is a particular area ofinterest because its tectonic relationship with the Benham Rise (either as a nascentsubduction zone of a shallowly subducting Philippine Sea Plate underneath the PhilippineMobile Belt or a collision zone of an accreted Benham Rise to the eastern portion of LuzonIsland) is still debated. The continental slope, with its high gradient, shows submarinechannels that could be sources of potential tsunamigenic submarine landslides. Theaccretionary prism just below the break in continental slope shows several bathymetrichighs, one of which seems to indent and control the concavity of the shape of the easterncoast of Luzon. It is also important to note that the supposedly E-W trending left-lateraltransform fault connecting the ELT with the Philippine Trench cannot be discerned byexisting bathymetry, and, together with the ELT, could be the target of future geophysicalsurveys.
Suggested offshore surveys include multibeam bathymetric mapping of areas not covered byprevious cruises, gravity and magnetics, multi-channel seismic reflection/refraction, andocean bottom seismometer/electromagnetometer surveys to reveal the deeper crustalstructure of the area, especially around the ELT. Deep-tow cable, dredging, and deploymentof submersibles can also be conducted to reveal deep seabed mineral resources specificallyaround the smaller seamounts (for possible cobalt-rich ferromanganic crust around theirflanks) and the spreading ridges (for possible polymetalic sulfides on extinct black smokers).A revised five-year plan of scientific exploration in the area is herein proposed.

[D-SEG seminar]

Date:
2017/10/12 (Thursday) 16:00-17:00
Place:
Meeting Room on 2F, Marine Research Building
Speaker:
Hitomi Nakamura
Title:
Distribution of slab-derived fluids around the edge of the Philippine Sea Plate from Central to Northeast Japan
Abstract:
Marginal parts of a plate and subducting slab can play important roles in geodynamics. This is because in areas where a plate interacts with other plates or with the mantle thermal, geochemical, and mechanical interactions are expected. The Philippine Sea (PHS) slab that subducts beneath the Japan arcs has such an edge. To examine the relationship between arc magmatism and the slab edge in the transition zone from Northeast Japan to Central Japan, we investigated isotopic systematics of the regional volcanic rocks, incorporating data from literature and new data for five isotopic ratios of Sr, Nd, and Pb. The new data included major element compositions of 22 samples from the back-arc area, and 5 isotopic ratios for 6 samples selected from Pleistocene to early Quaternary epochs. Consequently, the detailed spatial variation of the isotopic ratios for Northeast to Central Japan was established. Several findings were determined based on the spatial variation of the isotopic ratios and the estimated amount of slab-derived fluid: (1) the amount of fluid derived from the two subducting slabs (i.e., the Pacific slab and the PHS slab) decreases northward from a significantly high value (~5 wt.% fluid added to the source mantle), away from the seismically determined edge of the PHS slab; (2) the proportion of the PHS component in the total slab-derived fluid also decays northward; and (3) the PHS component spreads to the north beyond the seismically determined edge of the PHS slab. These observations strongly suggest that the existence of an aseismic PHS slab beneath southernmost parts of Northeast Japan delivers the PHS component to the arc magmatism. In addition, the dual subduction of the two slabs generates enhanced suction at the corner region near the edge of the PHS slab, which might account for the concentration of fluid described in (1) above.

[D-SEG seminar]

Date:
2017/09/28 (Thursday) 16:00-17:00
Place:
Meeting Room on 3F, YOKOSUKA HQ
Speaker:
Morihisa Hamada
Title:
Evolution of the proto-Izu-Bonin-Mariana arc volcanism: Constraints from statistical analysis on geochemical data of melt inclusions
Abstract:
IODP Exp. 351 (May 2014−July 2014) recovered a unique volcaniclastic sediments deposited immediately after Izu-Bonin-Mariana (IBM) arc initiation at ~52 Ma. In order to unveil the magmatic evolution of the proto-IBM arc, we have analysed major and volatile trace elements (S and Cl) in 236 melt inclusions (MIs) from Unit III of Site U1438 in Amami Sankaku Basin, which record the magmatic evolution of the IBM arc from 40 Ma to 30 Ma. Clinopyroxene- and plagioclase-hosted MIs are diverse in composition and range from low- to high-K basalts through rhyolites. MIs contain up to 3,000 ppm S and up to 12,000 ppm Cl. The MIs were recovered from volcaniclastic sedimentary cores and can be sourced from multiple volcanic centres. In order to better link the MIs with the magmatic evolution of the proto-IBM arc, we performed statistical analyses on MI geochemical data, following to the procedure of Iwamori et al. (2017). MI data were separated into 7 clusters. We recognize volcanism of calc-alkaline high-Mg andesites (Cluster 5) at 40 Ma, which disapeared at 35 Ma. Volcanism of low-K tholeiite magmas (Clsuter 4) and calc-alkaline magmas (Clsuter 2) ocuured from 38 Ma to 30 Ma, and Cluster 4 seems to be replaced by Cluster 2. These observatin suggest that (i) the volcaniclastics that accumulated at Site U1438 originate from both frontal-arc volcanism (low-K series rocks) and rear-arc volcanism (medium-K seris), and that (ii) volcanism around Site U1438 shiufted from frontal-arc to rear-arc volcanism with time. Such identificatin become possible by statistical analysis of multivariable geochemical dataset.

We analyzed concentration of volatiles (H2O, F, Cl and S) of representative 55 melt inclusions by using SIMS at Kochi Institute for Core Sample Research. Characteristics of each clusters will be discussed in terms of volatiles.

[ODS&D-SEG seminar]

Date:
2017/07/27 (Thursday) 16:00-17:00
Place:
3rd Seminar Room on 1F, Marine Ecosystem Research Building, Yokosuka HQ
Speaker:
Shigeaki Ono
Title:
MgSiO3 minerals in the upper mantle
Abstract:
It is known that pyroxene is one of major minerals in the upper mantle. Pyroxene can be observed in not only peridotite but also the subducted oceanic crusts and the subducted sediments under the upper mantle conditions. MgSiO3 is an endmember of pyroxene composition. Therefore, knowledge of MgSiO3 is critical for understanding the dynamics and evolution of the upper mantle. The phase relation in MgSiO3 has been repeatedly investigated by previous studies. However, this phase relation is still an open question especially at low temperatures corresponding to the pressure-temperature path of the subducted slab. We discuss the disputed issue of a couple of phase boundaries in MgSiO3, and a revised phase diagram in MgSiO3 based on our data will be suggested.

[ODS&D-SEG seminar]

Date:
2017/07/13 (Thursday) 16:00-17:00
Place:
Seminar Room at 2nd Floor, Marine Research Building, Yokosuka HQ
Speaker:
Kenta Yoshida
Title:
Direct chemical analysis of individual fluid inclusion by cryo-FIB-SEM-EDS: an application to the UHP Tlc-Grt-Cld schist from the Makbal Complex, Kyrgyz
Abstract:
Direct chemical analysis of a fluid inclusion was carried out by micro-excavation under cryo-temperatures. A scanning electron microscope (SEM) equipped with a focused ion beam (FIB), energy dispersive X-ray spectrometer (EDS), and a cold stage, can be a powerful tool to describe the chemical composition of small fluid inclusions in metamorphic rocks. Studied inclusions are found in the ultrahigh pressure (UHP) talc-garnet-chloritoid schist from the Makbal metamorphic Complex, Kyrgyz (Orozbaev et al., 2015). Conventional techniques such as microthermometry and cryo- and room temperature (RT)-Raman detected NaCl and CaCl2 as solute species in the fluid inclusions, where high salinity of 20.5 mass% CaCl2 and 1.7 mass% NaCl were calculated assuming a NaCl-CaCl2-H2O ternary system. Additional chemical analysis using cryo-FIB-SEM-EDS analysis revealed the existence of KCl as a solute species, which is hardly identified by conventional techniques.
Petrographic description of the fluid inclusions indicated that the studied inclusions have been trapped during the exhumation of the UHP talc-garnet-chloritoid schist, and furthermore, these fluid inclusions are possibly originated from the decompression-breakdown of lawsonite. Reports on CaCl2-bearing aqueous fluid have been known from the HP and UHP metamorphic terranes in the eastern Asia (e.g., Gao and Klemd, 2001). Our data may question the existence of complex chemical system of the aqueous fluids reported in such low-temperature type metamorphic rocks. Misidentification of solute species essentially brings errors in salinity estimates that will propagate inaccuracy in other quantitative analytical methods such as LA-ICP-MS.
Further detailed fluid inclusion petrography requires accurate quantitative analysis combining FIB-based sample-preparation and SEM-EDS analysis. We are now trying to establish a new analytical scheme for the quantitative chemical analysis of fluid inclusions, using a cryo-FIB-SEM-EDS system which is very recently installed in our institute. Current trial involves how to making a standard ice with a variety of compositions. Problems to be solved for a quantitative EDS analysis are also shown in the seminar.

[D-SEG seminar]

Date:
2017/06/29 (Thursday) 16:00-17:00
Place:
701 Boardroom, 7th floor, Administration Building, Yokosuka HQ
Speaker:
Jun-Ichi Kimura (D-SEG)
Co-workers:
Tetsuya Sakuyama, Takashi Miyazaki, Bogdan S. Vaglarov, Yoshio Fukao, and Robert J. Stern
Title:
Plume-stagnant slab-lithosphere interactions: Origin of the late Cenozoic intra-plate basalts on the East Eurasia margin
Abstract:
Intra-plate basalts of ~35-0 Ma in East Eurasia formed in a broad backarc region above the stagnant Pacific Plate slab in the mantle transition zone (mantle transition zone). These basalts have regional-scale variation in Nd-Hf isotopes, showing a quasi-concentric structure with a radius of ~1400 km. The basalts with the most radiogenic Nd-Hf center on the Shandong Peninsula with intermediate Nd-Hf at Hainan and Datong. Unradiogenic basalts occur in the perimeters with thick continental lithosphere. The Shandong basalts possess strong isotopic signatures of young (<80 Ma) igneous oceanic crust of the Pacific Plate. The Hainan and Datong basalts have isotopic signatures of recycled subduction materials with billions of year’s storage in the lower mantle. The perimeter basalts have isotopic signatures similar to the pyroxenite xenoliths from subcontinental lithospheric mantle beneath East Eurasia. The Hainan basalts have the highest mantle potential temperature (Tp), whereas the Shandong basalts the lowest-Tp. The deep high-Tp plume would have interacted with the Pacific Plate slab in the mantle transition zone to form a local low-Tp plume by entrainment of the colder igneous oceanic crust. Regional tectonics shows that Izanagi Plate slab, once a part of the plate in the Pacific, subducted at ~60 Ma and broke off from the Pacific Plate slab at ~35 Ma and sank into the lower mantle. This would have triggered the plume, it interacted with the stagnant Pacific slab, and caused subcontinental lithosphere melting. This coincided with formation of the broad backarc marginal basins due to Pacific Plate slab rollback and stagnation.

[ODS&D-SEG seminar]

Date:
2017/06/22 (Thursday) 16:00-17:00
Place:
Seminar Room #3 on 1st Floor, Marine Ecosystem Research Building, Yokosuka HQ
Speaker:
Yoshihiko Tamura, IODP Expedition 350 scientists
Title:
Volcanic ash interval recovered by IODP expedition 350: a prologue of submarine caldera formation?
Abstract:
IODP Site U1436 lies 1,776 m below sea level and about 60 km east of the arc front volcano Aogashima. Coring at Site U1436 recovered a 132 m record of Quaternary explosive volcanism in the Izu arc. Site U1436 is bathymetrically isolated from all Quaternary volcanic front volcanoes through submarine canyons and edifices except for Higashi Aogashima caldera. One distinctive interval of black ash (~55 meters below seafloor, 0.75 Ma) is comprised of glassy shards of basaltic andesite that comprise an extension of the dominantly basaltic compositional array of Aogashima volcano. Facies analysis and water content of the ash suggest that it was deposited from a submarine, eruption-fed density current derived from a submarine eruption at a water depth >720 m. Based on the geochemistry and age of the black glassy ash, and its inferred submarine Higashi Aogashima caldera origin, we suggest that the ash is an hypothesized, but never before observed, prologue of submarine caldera formation in the Izu arc.

[D-SEG seminar]

Date:
2017/06/01 (Thursday) 16:00-17:00
Place:
3rd Seminar Room on 1F, Marine Ecosystem Research Building, Yokosuka HQ
Speaker:
Hikaru Iwamori (DSEG)
Title:
A new statistical method to identify multivariate data structure
Abstract:
Recent rapid increases in both number and dimension of geological and geophysical data require efficient and accurate methods to capture and describe the data structure. For example, the two databases of GEOROC and PetDB contain ~382,000 sets of data in total. Jenner and O’Neil [2012] provided analysis of 60 elements in 616 ocean floor basaltic glasses. The structure including trends and groups of these data cannot be identified by graphical methods (e.g., Harker diagrams and identifying trends/groups based on them). As will be demonstrated, even 2-dimensional data may be misinterpreted by graphical methods. Here we propose a new multivariate statistical method that combines three conventional but powerful methods to capture the true structure of any multivariate data, including those from natural and social sciences; they are k-means cluster analysis (KCA), principal component analysis (PCA), and independent component analysis (ICA). The reasons for selecting the three methods are (i) KCA and PCA are probably the most fundamental yet powerful tools for multivariate analyses; (ii) ICA is not as common as PCA but is a unique tool for identifying hidden independent structures; and (iii) the three methods are newly found to be closely related and can be integrated to analyze the data effectively. In this study, we first describe the relationship of these three methods to elucidate the entire data structure based mainly on synthetic data. We apply this to a natural data set of isotopic compositions of basalts for which ICA has been performed. On the basis of the results, an effective combination of the methods is clarified, for which we provide an Excel program “KCA” at http://dsap.jamstec.go.jp/ (Iwamori et al., 2017, doi:10.1002/2016gc006663).

[ODS&D-SEG seminar]

Date:
2017/05/18 (Thursday) 16:00-17:00
Place:
3rd Seminar Room on 1F, Marine Ecosystem Research Building, Yokosuka HQ
Speaker:
Katy J. Chamberlain (ODS)
Title:
Magmatic evolution in ocean island volcanoes: Perspectives from Ascension Island and Oki-Dozen.
Abstract:
Ocean island volcanoes, built on thin oceanic crust, are able to produce a range of magmatic compositions and eruptive styles, yet relatively little is understood about the mode of magma evolution in these settings. This seminar will include consideration of detailed volcanological fieldwork, whole rock XRF data, and major and trace element analyses of crystals phases from Ascension Island in the south Atlantic, and the extinct Oki-Dozen complex in the Japan Sea to investigate the processes through which magma evolution occurs in ocean island volcanoes, the origins of these magmatic processes, and the possible implications for future activity at Ascension Island.

[D-SEG seminar]

Date:
2017/04/27 (Thursday) 16:00-17:00
Place:
Meeting Room at 1F, Marine Ecosystem Research Building,YOKOSUKA HQ
Speaker:
Suguru Yabe (DSEG)
Title:
Study on Slow Earthquake
Abstract:
In this seminar, I introduce seismic phenomena called “Slow Earthquake”. Slow earthquake, often observed in subduction zones, is caused by slip on the plate interface. However, its seismic-moment growth is much different from that of regular earthquake. Slow earthquakes are usually detected beneath or above seismogenic zone along the plate interface. Therefore, slow earthquakes are regarded as the phenomena reflecting brittle-ductile transition on the plate interface. Slow earthquakes also show very different characteristics from regular earthquakes. One of the most interesting phenomena is high sensitivity to small stress perturbations. Tidal sensitivity of regular earthquake has been discussed for long time, and it is very weak at most. However, slow earthquake is very sensitive to tidal stress. Slow earthquakes can be triggered by passing surface wave from distant earthquakes as well. These characteristics suggest that high-pressured pore fluid plays an important role in slow earthquake. The existence of such pore fluid is sometimes imaged by seismic analysis. For example, seismic velocity tomography images high Vp/Vs region around the slow earthquake source (Shelly et al., 2007). Receiver function analysis also suggests the existence of such high Vp/Vs oceanic crust (Audet et al., 2009). However, other tomographic studies do not detect such high Vp/Vs area around the slow earthquake source (Kato et al., 2012; Akuhara et al., 2013, 2015). In Yabe et al. (2014, BSSA), we have tried to estimate seismic attenuation of oceanic crust by comparing seismic waves from slow earthquakes with those from intra-slab earthquake just below the slow earthquake. This comparison will reveal the seismic structure of subducting oceanic crust more clearly.

[D-SEG seminar]

Date:
2017/03/16 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
BOGDAN STEFANOV VAGLAROV (DSEG)
Title:
Origin of unusual fractionation of Pb isotope ratios with calcium in Tl-spike-MC-ICPMS
Abstract:
Pb isotope ratio determination using solution-based multiple collector-inductively coupled plasma mass spectrometry (MC-ICPMS) has been applied to various samples, including rocks and minerals. Pb has a single stable isotope, 204Pb, and three radiogenic isotopes, 206Pb, 207Pb, and 208Pb. Therefore, the large mass fractionation that occurs in MC-ICPMS has been corrected using various spiking methods, such as Tl-spike and Pb double-spike (DS). Unlike DS with Pb spikes, different isotopic fractionation, between Tl and Pb isotope ratios have been discussed as the source of inaccurate corrections in instrumental mass fractionation. More recently, Barling and Weis (2008) carried out a systematic examination based on the intentional doping of major element rock matrices, such as Mg, Al, Ca, and Fe, into the (NIST) SRM 981 Pb standard solution, using the Tl-spike method in Nu Plasma MC-ICP-MS. To cope with the matrix effect, the authors proposed intentional doping with any major element into both unknown and bracketing standards for Tl-spike-MC-ICPMS, which proved effective in eliminating the matrix effect (Barling and Weis, 2008). However, the origin of the unusual fractionation resulting from Ca doping was not addressed and remains undetermined. In this study, we examine the discrepant fractionation of Pb isotope ratios by Ca doping using Tl-spike-MC-ICPMS and propose that precipitation of Pb with Ca in dilute HNO3 may cause this unusual isotopic fractionation. We also report the effects of strong acid attack, typically used in rock sample analyses, on Pb isotopic fractionation in a high-Ca matrix.

[D-SEG seminar]

Date:
2017/03/09 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Iona McIntosh (DSEG)
Title:
Investigating silicic submarine volcanism in the Izu-Bonin Arc through FTIR analysis of H2O in volcanic glasses
Abstract:
H2O degassing during magma ascent plays a fundamental role in determining eruption style and deposit characteristics because H2O is a key control on various silicate melt properties, including viscosity, glass transition temperature, diffusivities of mobile species, and crystallization kinetics. Volcanic glasses, which include ash, matrix glasses, and melt inclusions, form a record of magmatic H2O contents throughout the volcanic system; however, silicic glasses are unfortunately particularly susceptible to secondary hydration, i.e. the addition of H2O from the surrounding environment at ambient temperature in the time following eruption and deposition. A method to distinguish between magmatic H2O and H2O added during hydration has been developed using Fourier Transform Infrared (FTIR) spectroscopy, which can measure both total H2O content and H2O speciation i. e. how much H2O is present as molecular H2O (H2Om) versus hydroxyl groups (OH). Application of these H2O speciation data to hydrated glasses from the Izu-Bonin Arc enables investigation of the quench depths and cooling rates of different volcanic deposits, from pumice to lava domes, with implications for their associated hazards.

[D-SEG seminar]

Date:
2017/03/02 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Takeshi Hanyu (DSEG)
Title:
Chemical variation in olivine-hosted melt inclusions in HIMU basalts from Raivavae, South Pacific
Abstract:
Volatile cycle in the mantle has been poorly constrained because of limited number of studies thus far on volatile compositions in the mantle-derived ocean island basalts. We performed in-situ geochemical analyses on the olivine-hosted melt inclusions (MI) from Raivavae Island in the South Pacific to explore geochemical feature of both solid elements and volatiles in the HIMU basalts. Compositions of major elements, trace elements, volatile elements, and Pb isotopes were determined by the combination of analytical methods using EPMA, LA-ICP-MS, SIMS, micro Raman spectrometry, and micro X-ray CT technique. Melt inclusions show larger Pb isotopic variation than the host basalts, suggesting mingling of radiogenic melts and less radiogenic melts during olivine crystallization. Despite some exceptions, Pb isotope ratios in MI are correlated with compositions of some major, trace, and volatile elements. In particular, MI with the most radiogenic Pb are characterized by low SiO2, high CaO, La/Yb, Nd/Hf, Cl/Nb, and F/Nd. All these features could be best explained by the model that the radiogenic-Pb (HIMU) melts were formed by low-degree partial melting of carbonated source possibly derived from recycled altered oceanic crust.

[D-SEG seminar]

Date:
2017/02/23 (Thursday) 16:00-17:00
Place:
Meeting Room, Guest House 2F, YOKOSUKA HQ
Speaker:
QING CHANG (DSEG)
Title:
Laser ablation ICP-MS analysis of major, minor, and trace elements of an olivine reference material
Abstract:
Olivine is the earliest mineral phase crystallizing from mantle-derived melts and is the most ubiquitous mineral in ultramafic rocks. Trace element geochemistry of olivine offers important implications to the origin of these rocks including pressure, temperature and other crystallization conditions (i.e., oxygen fugacity). Due to the unique crystallographic structure, olivine usually hosts only few transition metals which have similar ionic radii and charge with the divalent magnesium and iron. With the advance of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), simultaneous determination of the major, minor and trace element compositions of olivine become available. However, high precision analysis is limited by lack of matrix-matched reference materials even by using the state-of-the-art femtosecond laser ablation technique. Predominant Mg and Fe matrices in olivine largely differ from that of the reference standard materials commonly used in microanalyses (e.g., NIST soda glass and USGS basalt glass standards). To overcome this problem, an olivine sample (MongOl sh11-2) is being proposed for reference standard for various microanalyses, such as EPMA, LA-ICP-MS and SIMS. MonOl sh11-2 is separated from a mantle peridotite xenolith in a basaltic breccia at Shavaryn-Tsaram volcano (48.046N, 99.994E) in the north-central Mongolia. Five leading geoscience laboratories, including JAMSTEC, are now working together to determine reference values of minor to trace element compositions of this olivine using EPMA, XRF, SIMS, LA-ICP-MS and ICP-AES. In this talk I will report analytical results of our femtosecond LA-ICP-MS and inter-laboratory and inter-method comparisons.

[ODS&D-SEG seminar]

Date:
2017/02/16(Thursday)16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Chris Conway (JSPS Postdoctoral Research Fellow, Department of Geology and Paleontology, National Museum of Nature and Science.)
Title:
Studies on the glaciovolcanic and magmatic evolution of Ruapehu volcano, New Zealand
Abstract:
Located at the southern end of the Taupo Volcanic Zone, Ruapehu is New Zealand's largest active andesite-dacite volcano and an iconic example of the lofty composite cone volcanoes that define Earth’s continental volcanic arcs. Constraining the timing and types of eruptive behaviour is critical for reconstructing the growth history of such volcanoes. These constraints are often limited, however, by a complex interplay between erosion and volcanic growth where glaciation has occurred. Geological, geochemical and geochronological data collected from Ruapehu lava flows during this research research have provided new insights into the 200 kyr evolution of the exposed volcanic edifice. This talk will outline three primary outcomes from this research:
1. Identification of glaciovolcanic products formed by lava-ice interaction at Ruapehu and their relevance for studies of volcanic stratigraphies and paleoclimate.
2. Definition of a high-resolution lava flow chronology that underpins new perspectives on the edifice growth history of Ruapehu.
3. Documentation of compositional changes in lava flows with time and their significance for understanding the evolution of subsurface magma systems at Ruapehu.

[ODS&D-SEG seminar]

Date:
2017/02/09 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Thomas Jones (Department of Earth Sciences, Durham University, UK.)
Title:
Magma transport within dykes: from basalts to kimberlites
Abstract:
Magma transport within dykes is a fundamental process that operates during the ascent of most low viscosity magmas. Firstly, we will consider the shallow fluid dynamics that operate during basaltic fissure eruptions (the surface expression of a dyke). It is well known from SO2 measurements during these basaltic eruptions that much more magma degasses within the subsurface than the volume of magma that is erupted. Therefore, subsurface exchange flow is forced between an upwelling, volatile rich magma and a relatively degassed descending magma. These conditions correspond to an upwelling magma that is of low viscosity and density and descending magma of high viscosity and density. In this talk analogue experiments will be presented that aid our understanding of the sub-surface timescales, volume fluxes and flow patterns that operate during basaltic fissure eruptions. Secondly, we will consider deeper processes that operate within the mantle lithosphere during the turbulent transport of kimberlitic magmas. Again a series of analogue experiments will be presented with a comparison to natural eruptive products from the youngest known kimberlite volcano on Earth: the 10Ka Igwisi Hills volcano, Tanzania. Our results show pervasive mechanical milling of the xenocryst cargo within a turbulent particle-laden gas suspension upon transport.

[D-SEG seminar]

Date:
2017/01/12 (Thursday) 16:00-17:00
Place:
Meeting Room at 3F, YOKOSUKA HQ
Speaker:
Satoru Haraguchi(DSEG)
Title:
Parent material of the acidic volcanism in the Izu intra-arc rift zone
Abstract:
The southern Izu arc, from the Aogashima to the Torishima islands is characterized by submarine calderas and bimodal, basaltic and acidic volcanisms. The intra-arc rifting, characterized by back-arc depressions, small volcanic knolls and ridges, is active in this region. Basalts show prominent across-arc geochemical variations depleted to enriched in volcanic front to rear arc side. Rhyolites also show across-arc geochemical variations. However, some parameters show different characteristics to those of basalts. Acidic volcanism in the Izu arc is considered to partial melting of arc middle to lower crust (e.g. Tamura and Tatsumi, 2003) because rhyolite exhibits similar composition to melting experimental results of basaltic or andesitic parental material under anhydrous, low pressure and low temperature (e.g. Shukuno et al., 2006). I will be presenting to geochemical difference between basalt and rhyolite, and considering magma genesis of acidic volcanism based on these hypothesis and geological history of Izu arc.