2012
● IFREE MC seminar
Place: Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 10th, May (Thursday)
Speaker: Takashi Nakagawa（IFREE 2C）
Title: Influence of magmatism on mantle-core cooling, surface heat flow, Urey ratio and material circulation in Earth's mantle
Abstract:
Here we present the state-of-the-art numerical modeling on thermo-chemical evolution in Earth's mantle and core, focusing in particular on matching the present-day surface heat flow and 'Urey ratio'. Most of numerical mantle convection models have ignored magmatic heat transport to argue their estimates on heat budget across the Earth's mantle. Regarding with the surface heat flow, the magmatic heat transport could contribute an upper bound of 9% to Earth's present heat flow. The magmatic heat transport may be dominated in first 2.0 billion years for surface heat flow. The mantle cooling has the similar phase to the magmatic heat transport. Since the heat production rate in the mantle inferred from geochemical and geoneutrino analyses has a great uncertainty, the Urey ratio should also have a huge uncertainty. This means that the Urey ratio is a poor constraint for thermal evolution of Earth's mantle.
New synthesized image of mantle dynamics from early to present Earth ('BAM': Basal Melange of both primordial and recycled origins of dense material in the deep mantle at the present day) has been proposed [Tackley, 2012], which has two different compositionally-distinct material coming from early Earth differentiation such as basal magma ocean [Labrosse et al., 2007] and upside-down differentiation [Lee et al., 2010] related to the magmatism in the deep mantle.
Here we present the possibility on new synthesized image of mantle dynamics with multi-component and phase system of numerical mantle convection simulations including magmatism and core cooling. As a consequence of numerical simulations, two styles of BAM-like structure are found at the present age of the Earth. 1. The primordial material is stably existed beneath the recycled basaltic material. 2. Both primordial and recycled materials are completely mixed. They are dependent on the relationship of density contrasts between recycled basalt and primordial material.
In addition, we show global-scale numerical mantle convection simulations with a continental lithosphere that allows to generate the ultra mafic residual beneath edges of continental lithosphere. Incorporating experimental data on the ultra mafic residue as phase change parameters into numerical mantle convection simulations, such a residual material can be transported by cold subjecting slabs with forming compositionally-dense piles above the core-mantle boundary. This behavior of ultra mafic residue from continental lithosphere might be important for explaining large-scale heterogeneous structure in the deep mantle.
● IFREE MC seminar
Place: Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 26th, April (Thursday)
Speaker: Junichi Kimura（IFREE 4B）
Title: Origin of matrix effect in determination of major and trace elements using laser ablation inductively coupled plasma mass spectrometry: 27 years after the first LA-ICPMS
Abstract:
An ultraviolet (200-nm) femtosecond laser ablation (200FsLA) sector-field inductively coupled plasma mass spectrometry (SF-ICPMS) system has been installed, tested, and developed at IFREE for major and trace element analyses in anhydrous silicate glasses and minerals. Use of 200FsLA minimized the matrix effect by 50% compared to that by a 193-nm nanosecond excimer LA. The origin of this improvement was identified as the suppression of 'melting point (MP)-induced' element fractionation at the laser ablation site due to a decreased thermal effect by 200FsLA. Sensitivity enhancement in elements with high first ionization energy still remained in the basalt aerosols relative to silica-rich aerosols. This was interpreted to be due to the higher thermal conductivity of the basalt aerosols in the inductively coupled plasma enhancing ionization controlled basically by first ionization energy of an element. We successfully confirmed this by a simulation using Saha's plasma state equation with the analytical data after reduction of the MP-induced fractionation at the laser ablation site. Accurate determination of trace elements (within 5% relative difference from the accepted values in 71% of the data obtained) was achieved for glasses ranging from MPI-DING komatiite to rhyolite, using single basalt glass BHVO-2G as the calibration standard. This seminar lecture also includes an overall review on the instrumentation and the mechanisms of element fractionation in LA-ICPMS for users/consumers of the relevant facilities/data.
● IFREE MC＆HQ seminar
Place: International Exchanging Room at 5th Floor, YOKOSUKA HQ
Time: 16:30-18:00 on 12th, April (Thursday)
Speaker: Yuka Masaki（IFREE3C)
Title: Hydrothermal activity in the mid-Okinawa trough and experiment of hydrothermal alteration of dacite
Abstract:
I will talk about two aspects of my research on hydrothermal activity in the mid-Okinawa Trough: 1) heat flow observations within the Iheya-North Hydrothermal Field; and 2) ongoing experimental work that I am conducting to constrain the rates of hydrothermal alteration of dacite in the Okinawa trough.
The Okinawa Trough is an active back-arc basin, located between the Ryukyu Arc-Trench system and the Asian continent. It is considered be forming as a result of rifting of continental lithosphere. The trough is covered with both hemipelagic and volcanic sediments, and a number of hydrothermal sites have been found.
My study area, the Iheya-North Hydrothermal Field is, in the mid-Okinawa Trough and is surrounded by the Iheya-North Knoll. Between 2002 and 2008 we obtained 78 heat flow data from 2002 to 2008 in and around the knolls to clarify the spatial scale of the hydrothermal circulation system. In 2010, IODP Expedition 331 "Deep Hot Biosphere", to the region obtained new subseafloor temperature data around the hydrothermal field. I will show the evidence that these data provide for the recharge of the Iheya-North hydrothermal circulation system and the pattern of this recharge.
Now I am working on dacite samples, representative of the mid-Okinawa Trough, to experimentally constrain how the dacite is hydrothermally altered and the rate at which it is altered at 325 °C and 310 bars. I will outline the experimental set up and present the initial results.
● IFREE MC seminar
Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 5th, April (Thursday)
Speaker: Heye Freymuth（Bristol Univ.)
Title: Molybdenum isotopes as a novel tracer for fluids in arc magmas
Abstract:
At least two different slab-derived components have been proposed to be present in arc volcanoes: a sediment component and a fluid component derived from the dehydration of altered oceanic crust and/or underlying serpentinites.
Despite a widely held belief of the involvement of these components in the genesis of arc volcanoes [e.g. 1,2], unambiguously attributing geochemical signatures to either component and discriminating them from residual phase mineralogy in the subducting slab remains difficult. I will show stable Mo isotope data for samples from the Mariana arc which are suggested as a novel tracer for the fluid component in arc magmas.
Molybdenum isotopes were measured on basalts from the Mariana arc as well as representative samples of subducting sediments from ODP sites 800, 801 and 802 using a double-spike technique [3]. The sediments are dominantly light in their isotopic composition with δ98/95Mosediments < 0 ‰, consistent with the incorporation of Mo into the sediment under oxic conditions [4,5]. The arc basalts are isotopically heavy and their δ98/95Mo exceeds the range of compositions found for ocean island basalts. They are also enriched in Mo relative to Pr, an element with similar degree of incompatibility during mantle melting. The Mo isotopes in the arc basalts correlate well with Pr/Mo and tracers for fluid addition with fluid-dominated samples having the highest δ98/95Mo, suggesting that not sediments but Mo bearing fluids are the dominant source of Mo in arc magmas and that Mo isotopes can be used as a tracer for their fluid component.
[1] Plank & Langmuir (1998) Chem. Geol. 145, 325–394. [2] Elliott et al. (1997) JGR, 102, 14,991-15,019. [3] Archer et al. (2008) Nature Geosc., 1, 597-600. [4] Anbar & Rouxel (2007), Ann. Rev. Earth Planet. Sci., 35, 717–746. [5] Siebert et al. (2003) EPSL 211, 159–171.
● IFREE MC seminar
Place: Seminar Room, Administration Bldg. 1F, Yokosuka HQ
Time: 16:30-18:00 on 29th, March (Thursday)
Speaker: Haruka Ozawa（IFREE 4C）
Title: Chemical analysis on recovered sample from Earth's core pressure in a laser-heated diamond-anvil cell
Abstract:
In 1952, Birch first proposed that the Earth's core contains light element(s) such as S, O, Si, C, or H in addition to iron and nickel evident from the density difference between the preliminary reference Earth model (PREM) and pure iron at the relevant conditions. Although considerable research attention has been paid to thermodynamic and physical properties of iron-light element alloys at high pressures to understand the composition of the Earth's core, the identification of light element(s) in the core still remains uncertain.
The solid inner core has grown by crystallization of the liquid core, and thus the solid and liquid should be thermodynamically equilibrated at the inner core boundary (ICB). Because the fraction of light elements between solid and liquid iron must be consistent with the seismologically determined density jump at the ICB, the melting phase relations in iron-light element systems at the relevant pressure can provide essential information to identify light elements and constrain their amounts.
I would like to examine the melting phase relations in iron-light element alloys at the ICB pressure (329GPa) by combining high-pressure and -temperature experiment with chemical analysis on the recovered sample by transmission electron microscope (TEM). The material synthesized at ICB pressure in a laser-heated diamond-anvil cell is extremely small (20 μm in diameter and <1μm in thickness), and therefore chemical analysis by TEM is necessary. Focused ion beam technique will be used for thin foil preparation for TEM observation. I will talk about these experimental techniques and the actual status.
● IFREE HQ＆MC seminar
Place: Conference Room, Administration Bldg. 1F, Yokosuka HQ
Time: 15:30-17:30 on 22nd, March (Thursday)
Speaker: Dr. Sebastien Pilet (University of Lausanne, Switzerland)
Title: Which Source(s) for Intraplate Basalts?
Abstract:
Intraplate lavas from oceanic and continental settings range from highly nepheline (ne)-normative alkaline rock types such as nephelinites and basanites to hypersthene (hy)-normative tholeiites and are characterized by fractionated incompatible trace-element contents that are higher than those found in mid-ocean ridge basalts (MORB). Although aspects of the high trace element contents of intraplate basalts can be explained by low degrees of partial melting of a garnet-peridotite source, the TiO2 contents of OIBs suggest that the sources of these lavas have TiO2 concentrations higher than those estimated for primitive mantle [1], which in turn suggests that other incompatible minor and trace elements may also be enriched in these sources. Such inferences for magma sources with traceelement enrichments relative to the primitive mantle are consistent with the need for trace-element enriched components in the sources of OIB to explain the range of their radiogenic isotopic compositions.
The question that I will discuss in this seminar is how the sources of alkaline rocks acquire these enrichments. Recycled oceanic crust, with or without sediment, is often invoked as a source component of alkaline magmas to account for their trace-element and isotopic characteristics.
Nevertheless, melting behaviour predicted for such material embedded in an upwelling plume suggests that recycled oceanic crust is not sufficiently enriched in trace element to explain by melting the composition observed in alkaline rocks [2, 3].
Alternatively, the source enrichment can be attributed to metasomatic process in the lithospheric mantle. Melting experiments on natural amphibole-rich veins [4] demonstrate that moderate to high degrees of partial melting of metasomatic veins can reproduce key major- and trace-element features of alkaline magmas.
These results are consistent with
metasomatized lithosphere as a viable source for alkaline basalts, and, emphasize the need to understand how such veins form.
Amphibole-rich veins have been interpreted as cumulates formed by crystallization of low-degree melts of the underlying asthenosphere as they ascend through the lithosphere [5]. To constrain this mechanism and clarify the nature and origin of the initial metasomatic agent, we performed a series of high-P experiments simulating differentiation of such low-degree melts within continental or mature oceanic lithosphere to determine whether the evolution of such melts would produce cumulates similar to the assemblages of metasomatic veins [6]. We also conducted Monte Carlo simulations of vein formation to evaluate the trace-element budgets of these cumulates [7]. These complementary studies show that, in terms of both major- and trace-elements, hydrous cumulates formed in this way are suitable source regions of alkaline magmas and that such cumulates can be produced by high-P fractional crystallisation of low-degree melts from "normal"
mantle (i.e., the formation of such veins does not require that the initial near-solidus melt have unusual compositional characteristics).
Given these results, we propose the following model for the generation of alkaline magmas: (1) low-degree melts from the convecting mantle percolate and differentiate within the lithospheric mantle, producing metasomatic veins plus cryptic enrichments in the surrounding peridotite; (2) subsequent melting of these hydrous cumulates characterized by low solidus temperatures generates ne-normative alkaline liquids (e.g., nephelinites, basanites); the interaction of these alkaline melts with lithospheric peridotite causes them to evolve toward less ne-normative compositions (e.g., alkali olivine basalts) thus explaining the compositional range of alkaline rocks observed in intraplate volcanoes worldwide.
[1] Prytulak and Elliott (2007) Earth Planet. Sci. Lett.
263, 388-403.
[2] Ito and Mahoney (2005) Earth Planet. Sci. Lett. 230, 29-46.
[3] Stracke et al. (2003) G3 doi:10.1029/2001GC000223.
[4] Pilet et al. (2008) Science 320, 916-919.
[5] Harte et al. (1993). Phil. Trans. Royal Soc. London, A 342, 1-21.
[6] Pilet et al. (2010) Contrib. Mineral. Petrol. 159, 621-643.
[7] Pilet et al. (2011) J. of Petrol. 52, 1415-1442.
● IFREE MC seminar
Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 8th, March (Thursday)
Speaker: Toshiro Takahashi（IFREE 4B)
Title: Petrological study of Quaternary Chokai volcano - generation and evolution process of TH and CA suites
Abstract:
Tholeiitic (TH) and Calc-alkaline (CA) series lavas is coexisting at Quaternary volcanos in NE Japan arc.
Generally, CA lavas have evidence of magma mixing, e.g.
diseqilibrium phenocrystic assemblage such as olivine and quartz. Therefore, many previous works discussed that the former is evolved from mantle-derived basalt magma by fractional crystallization, and the latter is generated by magma mixing between basic and acidic magmas, both derived from the common TH basalt through fractionation. However, based on Sr isotope micro-analysis of plagioclase phenocrysts in lavas from Zao and Azuma volcanos at central area of NE Japan arc, Tatsumi et al. (2008) and Takahashi et al. (submitted) argued that isotopically radiogenic TH basalt was formed by melting of the lower-crustal amphibolite and CA was formed by magma mixing of the unradiogenic mantle-derived basalt, the radiogenic crust-derived basalt and the differentiated magma which relates to basalt magmas. Additionally, although estimated primary CA basaltic melt composition at Zao and Azuma volcanos is in frontal-arc, it is medium-K basalt and closely similar in composition to back-arc side basalt at Chokai volcano. This result is not in agreement with traditional across-arc variation model for mantle-derived basalt magma in island-arc magmatism (e.g. Kuno, 1966), and need reconsideration of the mechanism for geochemical across-arc variation in island-arc volcanic lavas.
The Quaternary Chokai volcano is located at the rear-arc side of NE Japan arc, and this is typical of stratovolcano in Chokai volcanic zone. Chokai volcano activity is divided into Stage1 to Stage3 (Hayashi, 1984: Ban et al., 2001).
Stage 1 lavas has not disequilibrium texture or rarely has plagioclase phenocryst which has dimly dusty zone. Stage 2 is composed largely of olivine two-pyroxene andesite with a small amount of olivine two-pyroxene basalt. Most of them contain hornblende as phenocryst. Stage 3 is olivine two-pyroxene andesite and two-pyroxene andesite. The almost plagioclase phenocryst in Stage 2 and 3 lavas has dusty zone and sieve texture. An% of plagioclase phenocrysts core in Stage 1 lavas generally shows monomordal distribution
(basalt: An80-90, andesite: 50-60), whereas these in Stage 2 lavas have wide range or bimordal distribution (An50-80).
Chokai lavas are plotted on boundary of high-K and medium-K on the SiO2 vs. K2O diagram. On the FeO*/MgO vs. SiO2 diagram, trend of Stage 1 and Stage 2 & 3 lavas show the TH and CA, respectively. Additionally, some Stage 1 lavas are plotted in Basaltic trachyandesite to trachyandesite area on the SiO2 vs. total alkali diagram (High alkali TH). The range of bulk Sr isotope ratio of TH and High alkali TH (Stage 1), CA (Stage 2 and 3) are very similar (TH: 0.70303 to 0.70341, CA: 0.70297 to 0.70342). Sr isotope ratio of TH and High alkali TH are constant, whereas CA is ascent with increasing SiO2. Pb isotope ratio of TH is also constant, but TH and High alkali TH trends are parallel to each other(e.g. TH: 208Pb/204Pb=38.33, High alkali TH: 38.37).
Whereas, Pb isotope ratio of CA is distinctly ascent with increasing SiO2 (38.26 to 38.33).
Petrographical and petrological feature of Chokai volcanic lavas indicate that TH and High alkali TH are produced by fractional crystallization from basic magma, but Pb isotope ratio of the High alkali TH primary basic magma is higher than TH primary magma. On the other hand, CA is formed by magma mixing between basic (unradiogenic Sr and Pb) and felsic magma (radiogenic Sr and Pb). Sr and Pb isotopic features indicate that CA primary basic magma is mantle-derived basaltic magma, whereas it is surmised that primary basic magma of TH and High alkali TH are subject to the contribution of crustal melt. High alkali TH have most enriched Pb isotopic feature and relatively high Zr/Hf, and this has a possibility that primary basic magma of High alkali TH strongly shows the geochemical feature of crust-derived magma by melting of lower crustal amphibolite.
Next we need to study the matter further by Sr isotope miro-analysis of plagioclase phenocryst and groundmass in Chokai lavas.
● IFREE MC seminar
Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 9th, February (Thursday)
Speaker: Yuka Masaki（IFREE3C)
Title: Hydrothermal activity in the mid-Okinawa trough and experiment of hydrothermal alteration of dacite
Abstract:
I will talk about two aspects of my research on hydrothermal activity in the mid-Okinawa Trough: 1) heat flow observations within the Iheya-North Hydrothermal Field; and 2) ongoing experimental work that I am conducting to constrain the rates of hydrothermal alteration of dacite in the Okinawa trough.
The Okinawa Trough is an active back-arc basin, located between the Ryukyu Arc-Trench system and the Asian continent. It is considered be forming as a result of rifting of continental lithosphere. The trough is covered with both hemipelagic and volcanic sediments, and a number of hydrothermal sites have been found. My study area, the Iheya-North Hydrothermal Field is, in the mid-Okinawa Trough and is surrounded by the Iheya-North Knoll. Between 2002 and 2008 we obtained 78 heat flow data from 2002 to 2008 in and around the knolls to clarify the spatial scale of the hydrothermal circulation system. In 2010, IODP Expedition 331 "Deep Hot Biosphere", to the region obtained new subseafloor temperature data around the hydrothermal field. I will show the evidence that these data provide for the recharge of the Iheya-North hydrothermal circulation system and the pattern of this recharge.
Now I am working on dacite samples, representative of the mid-Okinawa Trough, to experimentally constrain how the dacite is hydrothermally altered and the rate at which it is altered at 325 °C and 310 bars. I will outline the experimental set up and present the initial results.
● IFREE MC seminar
Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 26th, January(Thursday)
Speaker: Ryoko Senda（IFREE 4B)
Title: How to determine trace elements in bulk rocks~ Acid digestion vs. Alkali fusion
Abstract:
To understand geological environments and systems, we use a lot of information from elements and isotopes. In these days, chemical analysis methods are developed and it becomes rapidly with high sensitivity. However, to select suitable analytical method which includes dissolution, extraction and measurement of the elements is important to get highly reliable data for each samples and for your purpose.
There are mainly two options for dissolving bulk rock samples for trace element analysis in IFREE4. One is acid digestion and another is fusion with flux. Acid digestion method is dissolved the powdered rock samples using HF with other acids, such as HClO4, HNO3, HCl, etc. HF cuts the bond of Si-O of silicate minerals most of which compose rocks so it is efficient to dissolve many kinds of rocks. On the other hand, alkali fusion method is the method of melting the sample powder with alkaline reagent like Na2CO3 and B4Li2O7 at around 1000℃. This method is a valuable method for rocks with hardly acid-soluble minerals like Zirconium, Monazite, Chromite and so on. I will show the detailed methods of them and compare them from the data of the reference rocks.
● IFREE MC seminar
Place: Meeting Room at 3F, YOKOSUKA HQ
Time: 16:30-18:00 on 12nd, January(Thursday)
Speaker: Yuka Hirahara（IFREE 4B)
Title: Ce isotopic compositions from Quaternary volcanic rocks in northeastern Japan arc: Determination of Ce isotope ratio using the three-step chemical separation procedure and thermal ionization mass spectrometry (TIMS)
Abstract:
The Rare earth elements (REE) have similar chemical, physical properties and exhibit a gradual change in the ionic radius therefore they are the most useful tool for the studies of geological process. The REE have two long-lived decay systems, the 147Sm-143Nd and 138La-138Ce decay systems. A combination of Ce and Nd isotope (143Nd/144Nd) ratios has provide us information on ages, initial ratios, and enable estimation of the time-integrated LREE evolution of complex geological reservoirs in the mantle or crust.
However, the variation of Ce isotopic ratio due to secular radiogenic decay to 138Ce is small because of the low abundance of 138La and its long half-life. For example, the total variation in reported global oceanic samples show less variation than 3 units of epsilon Ce. Therefore, highly precise determination of Ce isotopic ratios is necessary to obtain valuable data for application of geochemical studies.
We have reported a price determination method of Ce isotope using the three-step chemical separation procedure and TIMS (TRITON TI®, Thermo Fisher Scientific Co., Germany) equipped with nine Faraday cups at IFREE, JAMSTEC. The analytical result of Ce isotopic ratio in JMC 304, were obtained
0.0225733 ± 2 (2σ, N=67). The Ce isotope measurements with normalization to JMC 304 in BCR-1 were 0.0225644 ± 4 (2σ, N=7), the results agree well with reported values (0.0225652 ± 4 (N=7), Makishima & Nakamura, 1991).
In northeastern Japan, there are numerous Quaternary volcanoes are distributed. The volcanic rocks have a spatial
variation of Sr-Nd-Pb-Hf isotopic compositions (e.g. the
rocks form volcanic front have a more enriched isotopic compositions than those of the rear arc side), and a wide range of isotopic compositions could be explained by contamination of heterogeneous crust materials. However, the geochemical information of crustal materials is poor. We estimated the contaminated crustal materials using Ce isotopic ratios in NEJ volcanic rocks.
