Geochemistry of production fluid at Cooper-Basin Enhanced Geothermal System (EGS) field in Australia was analyzed. At production test and circulation test in 2008, Cl concentration was ranged from 7500 to 8900 ppm, Na was from 3800 to 5100 ppm and K was from 560 to 700 ppm. The ratio of Na/K was ranged from 5.9 to 7.3 and this was almost same as the result of water-rock interaction experiment with 250°C and 40 bar circulation system using granite rock at Cooper-Basin.
Geological CO2 storage into deep, saline aquifer becomes important in CCS (Carbon dioxide capture and storage) technology as an effective measure to reduce CO2 emission into atmosphere. The stored CO2 is expected to be fixed by carbonates through reactions between CO2, formation water and reservoir rocks. Because of an environment of saline aquifer in sedimentary strata, dawsonite, or Na-Al hydrous carbonate, is frequently formed in geochemical simulation on geological CO2 storage. However, its stability in a long period over sociological time scale is not understood well at present. We carried out a sensitivity analysis on the formation of dawsonite to parameters used in the geochemical simulation modeling the underground Tokyo Bay area (Todaka et al., 2009). It is concluded that Al-bearing chemical species are important in the formation of dawsonite in the CO2 reservoir, in addition to fco2 pointed out in our previous study.
To reduce greenhouse gas, the carbon storage underground has been tried; however, it is considered to be difficult to precipitate calcite in reasonable timescale. In contrast, calcite veins are very common in the oceanic crusts, metamorphic rocks, and accretionary prisms.
The purpose of this study is to understand the controlling factors on calcite precipitation. As a first step, we conducted hydrothermal flow-through experiments to precipitate calcite at 300 ˚C and 30 MPa by using the temperature dependency of solubility.
After the run of 240 h (10 days), the total increase of weight of calcite substrates was 0.051 g. Observation of the surface reveal that euhedral calcite crystals with size of 0.02-0.03 mm grew from the calcite in the substrates. Our results suggest that calcite veins could be formed around 300 ˚C, if fluids saturated with calcite at lower temperature would be brought accompanying with subduction of slabs.
In considering water-rock interactions, it is fundamental to quantitatively estimate the mass transport and reaction in rock pore spaces. To address material transport, estimation of hydraulic conductivity is essential. On the other hand, to treat reactions (dissolution and precipitation of minerals and adsorption of dissolved matters onto minerals), evaluation of mineral-water reactive surface area is important. In the earth surface, the rock pores are not filled only with water but also with air. In such unsaturated condition, hydraulic conductivity and mineral-water reactive surface area may differ from water-saturated condition. Therefore we performed dissolution experiments using sandstone and evaluated the relationship between "water saturation", "hydraulic conductivity", and "mineral-water reactive surface area". As water saturation decreased, the hydraulic conductivity decreased but the mineral-water reactive surface area almost unchanged. We attribute this result to the existence of water films wetting mineral surfaces.
Silica minerals are good indicator of the terrestrial processes including diagenesis and hydrothermal alteration. Hydrothermal cristobalite and amorphous silica show characteristic morphology and crystallinity depending on their formation processes. In this study, silica minerals produced by acidic hydrothermal alteration and hydrothermal crystallization experiments from diatom are examined.
The hydrothermal flow-through experiments of precipitation of silica minerals were conducted at 430°C and 31MPa. With increasing of the Al concentration in the input solution (0–6.7 ppm), the change of dominant precipitation of silica mineral was revealed such as amorphous silica → cristobalite → quartz, and the logarithmic precipitation rate increased linearly. The precipitation via nucleation is determined the third–order reaction. The rate equations of surface reaction and nucleation suggest that, for example, the dominant reaction is nucleation in the fracture of 0.1 mm width whereas it is surface reaction in the fracture of 0.01 mm width when the precipitation occurs from the solution of Ω = 2 at 200°C. This trend coincides with that the formation of blocky veins occurred in wider fractures comparatively in nature.
Three types of fluid inclusion assemblage (FIA) are recognized in a quartz vein intercalated with a metapelite collected from Besshi area. Garnet of the host metamorphic rock includes chloritoid and talc, which suggests it suffered nearly eclogite facies metamorphism. FIA-I and II are arranged at intragrain planes, suggesting that they are trapped before higher-T conditions. FIA-I consists of aqueous fluid and CH4 gas. Some inclusions of FIA-I show annular shape, suggesting they suffered nearly isothermal compression. FIA-II consitsts of CH4+N2+CO2+H2 gas inclusions. FIA-III, which shows transgrain plane, consists of CH4+N2 gas and aqueous fluid. Those facts suggests that three stage fluid activities (aqueous > anhydrous > aqueous) occurred during the Sambagawa metamorphism.
We observed magma-driven hydraulic fracturing and fluid infiltration in the Sor Rondane Mountains, East Antarctica. We studied homogeneous temperature and salinity of fluid inclusions, hydration reaction process of metamorphic minerals, and mineral assemblages of host and vein rocks. According those observation and measurements formation of microcrack around magmatic vein had dominant role to input geofluids into the host rocks from pegmatitic vein rather than homogeneous diffusion in matrix.
We conducted hydration experiments of peridotites at 580°C,1.3GPa to investigate the hydration rate of peridotite in the mantle wedge. Orthpyroxene(opx) showed serrated texture ,but olivine(ol) did not show any obvious reaction texture. Thus, hydration rate of opx is probably much higher than that of ol at this condition. Avrami equation was fitted into bulk(peridotite) conversion rate data,and we got the reaction front migration velocity G=1 μm/day.Then, the hydration velocity was compared with the fluid advection velocity by using the characteristic time. Consequently, it is suggested that the modes of porous flow and channel flow are equilibrium and disequilibrium respectively. These flow modes is the same as the assumed flow modes in Iwamori(1998).
Groundwater flow is controlled by fracture network in upper crust, of which density and azimuth have been investigated in situ observations of subsurface samples. We executed rock magnetic analysis on oriented core samples of siliceous mudstone of the Wakkanai Formation obtained at Horonobe, north Hokkaido, Japan. Directions of its remanent magnetization imply tectonic rotation, and anisotropy of magnetic susceptibility delineates microscopic fabric governed by tectonic / sedimentary processes.
Deep aqueous fluids derived from subducted plate significantly affect volcanic activity in the subduction zone. It is important to examine the chemical compositions of dehydrated fluids from hydrated minerals to grasp H2O behavior in the subduction zone. In present study, we synthesized aquous inclusion of dehydrated fluids from hydrated minerals by crack healing method.
As crack rates in starting quartz increased, amount of synthetic dehydrated fluids inclusions also increased. As synthesis durations were longer, size of synthetic dehydrated fluids inclusions were larger.
A few post-metamorphic igneous dykes were newly found from Skallevikshalsen, Rundvagshetta, and Niban-Iwa in the Lutzow-Holm Complex. Internal textures are parallel to the trend of the dyke intrusion. Dykes in Rundvagshetta were strongly related for the origin with post-genetic pegmatites, and partly modified to amphibolite with coarse hornblende by the pegmatitic activity.
The dykes are holocrystaline, and consist dominantly of alkali-feldspar and subsequent biotite, augite, hornblende, titanite, apatite and minor amount of plagioclase and quartz:. Minerals, especially biotite flakes are commonly aligned to parallel to boundary between the dykes and the host gneisses. Based on their mineral assemblages, it is expected that the dykes have potassic and intermediate to mafic compositions.
In Rundvagshetta, host metamorphic rocks were partly metasomatized by hydrated reaction and garnet was broken down to biotite in the metasomatized domain. Since the dyke contains abundnat biotite and subsequent apatite as well as alkali feldspar, it is expected that the dyke supplied fluid for the metasomatism during its activity.
The Bt-Grt-Sil gneiss from Balchenfjella, East Antarctica characteristically contains rounded, coarse-grained Zrn in the rim of Grt porphyroblasts and in the matrix locally. Chlorine-rich Bt is also included in the outer side of Grt than Zrn. The presence of Cl-rich Bt, and the abrupt increase of Zrn inclusions in the Grt rim implies the infiltration of Cl-rich fluid and the addition of Zr, respectively. Because Bt inclusion predates Zrn inclusion, theses two might represent different events. The P-T condition for the entrapment of Cl-rich Bt in Grt is estimated to be ca. 800oC, 9kbar. The leucocratic vein consisting of Kfs, myrmekite, Bt-Qtz intergrowth and etc. is present in the matrix, and similar pseudo-inclusion exists in the garnet. From the petrographical and chemical constraints, pseudo-inclusion would be three-dimensionally connected with the matrix.
Hydration of ultramafic rocks (sperpentinization) commonly occurs in mid-ocean ridges, and the extent and distribution of hydrated mantle plays an important role on the global circulation of H2O fluids. In this study, we conducted hydrothermal experiments on serpentinization to clarify the relationship between the temporal evolution of solution chemistry, progress of hydration reaction and textural developments. The starting materials were powders of olivine or orthopyroxene. The powders and the distilled water were set in the batch type vessel. The temperatures were 250 degreeC at the liquid-vapor saturation curve. The duration was up to 1008 hours. We will show these experimental results and olivine-orthopyroxene-water system experimental result in poster.
We propose a broadband seismometer system as a payload instrument of the first Japanese landing mission on the moon SELENE-2. In this presentation, we introduce its scientific significance and current state of the development of the seismometer. In the Apollo projects, a triangular seismometer network provided information on the internal structure shallower than a depth of ~1,000 km. It, however, has slightly insufficient sensitivity to detect often occurred deep moonquakes without PEAKED MODE. Moreover, scattering codas in seismic waveforms are generated in the shallow brecciated layer, and masks reflection and converted waves at a structural interface in the moon. To overcome those issues, we propose a broadband seismometer observation. Due to weak coda in long period components, we can obtain information of the lunar deep interior by detecting reflection and converted waves.
SELENE-2, the next Japanese lunar mission, is being planned by the Japan Aerospace Exploration Agency (JAXA). Our team proposed a hyper-spectral macro camera, the Lunar Macro Imager (LUMI), for the SELENE-2 mission to investigate spectral characteristics and texture of polished rock samples on the Moon.
The objective of our observation is to measure the modal abundance, composition of the lunar highland rocks and to observe mineralogical texture of the rock that reflects their thermal and pressure histories. The mineralogical texture is also enables us to estimate composition (Fe content) of the lunar magma ocean.
To achieve these objectives, we designed our instrument to obtain hyper-spectral images in wavelengths ranging from 750 nm to 1700 nm with the spatial resolutions of 20 micron /pixel.
Laser-induced breakdown spectroscopy (LIBS) is an ideal and useful instrument for chemical compositional analyses of the lunar and planetary surface materials for the future landing missions, with high spatial resolution (< 1mm), short analytical time (~a few seconds), a capability of remote analyses, and a wide variety of detectable elements from major to trace elements.
Since the Apollo feldspathic rocks mainly include plagioclase and low-Ca pyroxenes, it has been suggested that lunar crust is noritic. However, mineralogical studies of feldspathic lunar meteorites show that plagioclase and olivine are primary phases with minor low-Ca pyroxenes as a secondary replacement of the primary olivines. The fact suggests that lunar crust is likely troctolitic and plagioclase and olivine are initial crystallization products of its source magma (possibly a primordial magma ocean). This inference seems consistent with a reflectance spectral observation of the lunar crust exposed at the Copernicus crater by the Kaguya Multiband Imager.
It is important to determine the true chemical and mineralogical compositions of lunar rock samples unaffected by the space weathering effects. However, it would be difficult to measure space weathering effects by the SELENE-2 mission. Therefore, we propose an alternative index based on the major element composition, which allows in-situ quantification of space weathering effects.
The lunar sample collected at clear older-outcrops in terrestrial and extraterrestrial locations can expect the development to obtain significant information to the formation process of the complicated Earth.Clear difference in carbon and rare-earth element (REE) contents are obtained at four kind samples of the lunar basalt (mantle), highlands rocks, breccias and regolith soils.From two peaks of REE contents (including carbon), two types are classified as (1) Y type of basaltic mantle rocks, and (2) C type of surface melting by impact or magma process.Two types of C and Y are obtained at the lunar basalts, breccias and the KREEPy rocks, which are separated at collected sites. The highlands are molten type C, surface soil is type Y. And orange glass and lunar meteorite (Antarctica) are type Y rocks.
Asama-Eboshi volcanoes including an active volcano (Asama volcano) is located in East Japan. We determined the K-Ar ages of 8 volcanic rock samples of the initial-early stage with aim of elucidating temporal and spatial changes in this volcanoes.
The initial-early stage of Asama-Eboshi volcanoes formed a stratovolcano which has fixed eruption area and some volcanic bodies like monogenic volcanoes which have widespread eruption area. Volcanic activity of the latter is limited to short term ca. 0.8 Ma and ca. 0.3 Ma. Volcanic field until ca. 0.3 Ma is also around Eboshidake area, after that volcanic field is widespread from Sampogamine to Asama area. Thus, it is believe that activity field expanded toward east after 0.3 Ma rapidly.
The level of volcanic activity evaluation can be done based on the statistical examination to the scale, generation, frequency of the eruption. The frequency of the eruption at Nantai Volcano which is no eruption in recently 7000 yrs was calculated based on the tephrochronology and the level of volcanic activity was evaluated statistically. As the eruptions occur randomly, the test was performed to determine the probability of not eruptions occurring in the 7,000 yrs recently. Therefore, the volcanic activity of the Nantai Volcano is a volcanic activities dormant period for 7000 yrs recently.
Catastrophic outburst floods by a breach of volcanic dam or caldera rim tend to be hazardous with voluminous impounded water and loose unconsolidated pyroclastic material. Such extreme floods can travel long distance from the source volcano that ultimately affect landform and hydrology of downstream areas and eventually threaten human life and economy. Tohoku area hosting active volcanoes is susceptible for such a catastrophic flood by dam break as shown by two examples from Numazawa and Towada calderas.
Kumanodake agglutinate of the Zao volcano in NE Japan comprises pyroclastic surge layers accumulated during the early newest stage. Rocks are mixed calc-alkaline olv-cpx-opx andesite (55.2-56.2% SiO2). The magma feeding system comprises a shallow felsic magma (63-67% SiO2, 940-970 deg C, cpx-opx-plg) injected from depth by mafic magmas. The main mafic magma was basalt (ca. 50% SiO2, 1110-1150 deg C, olv). The mafic magmas are stored occasionally at 3-6 km depth and are differentiated to basalt (1080-1110 deg C, olv-plg). The forced injection of mafic magmas withdrew felsic magma before their mixing during eruption. Their explosivity decreased over time because the scale of the scoriae decreased and the erupted magma composition became more mafic. These features reflect the increased percentage of mafic magma involved in mixing. At the beginning of activity, the mafic magma also acted as a heat source for activation of the felsic magma chamber, thereby suppressing the volume percentage of mafic magma in the mixing. End-member magmas mixed more easily as the activity proceeded.
The eruptive products from a caldera cluster are exposed around the southern base of Kurikoma volcano. Most of them were regarded as members of the Neogene Onoda Formation. Tsuchiya et al.(1997) reported these pyroclastic deposits are exposed at Modume Osaki, Miyagi and Uguisuzawa Kurihara, Miyagi. We previously reported the stratigraphy and K-Ar ages for these pyroclastic deposits around Modume(Kuzumaki and Ohba, 2010). In this study, the stratigraphy was newly established for Uguisuzawa area and was correlated with that around Modume area with using petrologic data.
Onoda Formation around Uguisuzawa contains five tuff members; Shimatai, Yubama, Chijimisawa, Uguisuzawa, and Aonokisawa Tuffs, in stratigraphic order. Yubama and Chijimisawa tuffs were correlated with those distributed around Modume.
Every 100 years, Chokai erupts explosively, according to our observation on the only outcrop at where the sequence of fallout layers is well preserved. Scoriaceous ash is accompanied by hydrothermally altered lithics in varying degrees, indicating that the eruption type ranges from volcanic-hydrothermal to magmatic (strombolian and vulcanian) eruptions. Chemical variations of altered ash grains imply that the hydrothermal system involves silicic and advanced argillic alteration zones. The hydrothermal system interacts with ascending magma in each eruption.
Iwate volcano is an active volcano at NE Japan. The volcano is composed of two volcanic bodies, Higashi-Iwate and Nishi-Iwate, which have an individual magma plumbing system. In this study, the eruption rate of Iwate volcano is estimated by the field observation and microgravity survey. The result is 2.3 to 3.8 x 10-2 km3; DRE/kyr during the last 70,000 years, that includes 3 volcanic stages. The eruption rate does not show the clearly difference between Higashi-Iwate and Nishi-Iwate. Thus, the supply of magma from the deeper area is considered as a control system that is driven to Higashi-Iwate and Nishi-Iwate.
Using the CL images and Ti concentrations of quartz, we estimate magma temperatures. (1)We compare the Obirakiyama tuff mainly contains two types of quartz bearing pumice clast (Bt-type and Hb-type; Kudo et al.,2007). CL images of Bt-type quartz crystals are almost uniform (710C). In contrast, Hb-type quartz crystals has darker core (750C) with brighter rim(800C). It is concluding that only Hb-type magma has recharged mafic magma its triggered eruption. (2)There is a across arc variation of the caldera forming felsic magma. Chijimisawa tuff (volcanic front region) has higher temperature (40-90C) than Obirakiyama tuff (back arc region).
Our study has revealed two new eruption units beneath 6.8 cal ka ejecta in the northern flank area of Hokkaido-Komagatake Volcano, Northern Japan. A block-and-ash flow deposit composed of agglutinate and its fine particle was newly recognized on the northern slope, the occurrence of which suggests that the deposit is derived from collapse of welded pyroclasts emplaced at the summit part. Another welded pyroclasts was also recognized below the block-and-ash flow deposit, the distribution of which suggests that the deposit is issued from the nroth-northeast parasitic vent. Those two eruptive styles have never reported in this volcano. Our new findings could provide important information for prevention of volcanic disaster of the volcano.
The eruptive history and magma systems of large-scale eruptions (VEI>5) in eastern Hokkaido, Japan was reviewed on the basis of resent studies. Approximately 80 tephra layers were derived from Akan, Kutcharo, Atosanupuri and Mashu volcanoes in the past 1.7 Ma. The latter two are the post caldera, active volcanoes of Kutcharo. Total volume of all tephras is 1000 km3. Their discharge rate is remarkably increased at 0.4~0.2 Ma from 0.2 to 2.0 km3/ky. This rate is not decreased during the last 3.5 ky, post caldera stage of Kutcharo. Although silicic magma systems of Akan, Kutcharo and Mashu were distinct, chemistry of Atosanupuri magma is similar to Kutcharo's one.
The eruption of 0.12Ma at Adatara volcano has been considered as the major turning point of the magma plumbing system during recent 0.25 my. The pyroclastic fall deposits (pfa) at the summit of the Adatarayama, Dake pfa at the eastern foot, Yukawa pyroclastic flow (pfl) of the eastern valley and Motoyama pfl of the western frank, was all presumed to be the products at the 0.12 Ma eruption. These ejecta are examined in terms of their stratigraphy, lithofacies and petrography, to reveal their eruption sequence. The temporal change of eruption styles is elucidated as follows:1)in the early stage, small-scale eruptions from unstable, low eruption column occurred repeatedly, 2) Plinian eruption occurred from a stable column in the middle stage, 3) several pyroclastic flows were generated by collapse of the eruption column in the later stage, 4) the eruption column became stable again, and terminated with Strombolian style at the final phase.
Two major explosive eruptions occurred in Narugo volcano around 40 and 80 ka. Eeruption features of the explosive magmatism must be elucidated by revealing these major pyroclastic flow events in detail.
I subdivided Nizaka Tuff into 5 flow units.Early ejection lacks clinopyroxene phenocryst,and rich in SiO2.Later eruptives contain clinopyroxene phenocryst,and come silica-poor and TiO2, Al2O3, FeO*, MnO, CaO-rich compositions.
Yanagisawa tuff has newly been divided into 4 units.Pyroclastic surge deposit was also recognized in Unit3.Unit1 shows SiO2 rich, mafic mineral poor characteristics.Unit2 and 3 show the largest variation among the 4 units.Unit4 is somewhat similar to the Unit1,although K2O contents are distinctive.
Because of Yanagisawa tuff involves pyroclastic surge deposit along with hornblende phenocryst in the Unit3,H2O contents of the Yanagisawa tuff had possibly been higher than that of the Nizaka tuff.
The purpose of this study is to reveal distribution and stratigraphy of eruptions and to examine the magma plumbing system, the east part of main strato cone, Akita-Komagatake volcano. Eruptions were divided into 20, and erupted from two craters located north and south. In addition, eruptions from the south crater were classified 2 groups and from the north were classified 5 groups by the period of eruption, petrography, and whole rock major-element chemistry. The examination of the magma plumbing system is as follows: First, tholeiite basaltic magma flowed from the south and north craters. Next, Calc-alkari andesitic magma erupted from the north. Then tholeiite basaltic magma flowed once more, after magma that has the feature of between tholeiitic and Calc-alkaric erupted from the north.
Takakura volcanic chain is located in the Sengan geothermal area. Kotakakura(KO), Takakura(TK) and Marumori(MM) volcanic edifices are arranged in a line from the north, southward. Development history of the MM is revealed in this study. Evolutionary processes of the coexisting tholeiitic(TH) and calc-alkaline(CA) magma series are also examined.
Whole rock chemistry of the neighboring TH series of KO, TK and MM are distinctive in terms of their characteristics and compositional trends, indicating that their parental magmas are distinctive. In MM, compositional variation of the TH series may not be explained by a simple crystallization differentiation ; incorporation of mafic magma must have occurred concurrently. The evolution process for the CA series is well-inferable from the heterogeneity recognized within a single lava flow. Mixing of andesitic and felsic magmas must be an essential role in the evolution of the CA magma.
During Pliocene to Pleistocene ages, a caldera swarm was formed by felcic volcanisms at Shimokita Peninsula.We examined stratigraphy of Ohata Formation, which is composed of intra-caldera pyroclastic deposit within the Yagen caldera, one of the calderas.The depositional age was determined by the K-Ar method as 2.6Ma-3.0Ma.The formation was divided by their petrographical features into four members: Yaichirousawa, Ohatagawa, Hairosawa, and Komenasawa Pumice Tuffs. The lithological features of the volcaniclastic deposits imply that they emplaced as subaqueous volcaniclastic flows within the caldera basin that had collapsed prior to the deposition of Ohata Formation.
We examined the sandy deposits distributed around Noboribetsu, southwest Hokkaido, and identified the deposits as the 17th-century tsunami deposits derived from the 1640 Hokkaido Komagatake eruption associated with a large scale debris avalanche.
Rheology profiles created by recent results on rock mechanics and geophysical observations predict the current lithospheric deformation of the NE Japan arc. The lateral variation in the lithospheric strength well explains the current geodetic strain accumulation and shallow seismicity. The various mechanisms likely operated in the lithosphere (e.g. partial melting and grain size reduction) reduce viscosity significantly at deeper parts of the lithosphere. The strain localization along such weak zones may explain the estimates of viscosity by post-seismic creep and cause reactivation of pre-existing faults.
We show that a simple plagioclase flow law can be employed to explain the microstructural evolution of gabbroic mylonites and ultramylonites that occur extensively along the surface of fault-induced asymmetric spreading over the ∼125 km length of the Godzilla megamullion, at a temperature of 650 to 900 degree C and a remarkably higher strain rate of ∼10E-9 s-1 to 10E-10 s-1. Our results indicate that superplastic flow within the lower crust played a significant role in movement along the detachment fault that formed the megamullion during asymmetric back-arc rifting.
Many lakes in Tibet have shorelines developed around them. When water level decreases, a buoyancy force tends to cause uplift. For uplift to occur, flow in the mid crust is required. The time scale for the flow is related to the basin geometry and mid crustal viscosity. The basin shape is known, so the viscosity can be calculated from the amount of uplift and the time taken. Uplift is should be maximum at the lake center and shorelines at different distances from the center along their length will develop a slope as a result of uplift. Heights of shorelines were determined with kinematic GPS around L. Nam Co, one of the largest lakes in Tibet. These were combined with 14C ages of tufa deposits attached to the shorelines to give an estimate of >10^20 Pa s for the viscosity of the mid crust of the area. This value is much higher than that generally considered and suggests that the idea of a weak partially molten mid crust in central Tibet needs revising.
The influence of surface-energy driven grain growth in dynamic recrystallization was evaluated and integrated to the steady-state grain size model (Shimizu, 1998, 2008). The result of the improved model is consistent with the empirical piezometric relation for quartz.
We conducted the albite decomposition experiments at 1.1-4.1 GPa and 673-1073K under differential stresses using multi-anvil type deformation apparatus with synchrotron X-ray. Flow stresses of each phase and transformation rates were observed by time-resolved two-dimensional X-ray diffraction measurements, and axial strains were measured from radiography images of the samples. Based on the results obtained, we will discuss the interaction between the albite decomposition and plastic flow.
It is quite important for considering tectonics of the terrestrial planets to study about rheology of the mineral. Rheological structure of terrestrial planets has been inferred by extrapolating of power-law to temperature and pressure of planet's interior (e.g., Mackwell et al. 1998). However, it is not sure that power-law that was constrained by high temperature experiments can be applied for Moho condition. In our study, strength contrast between plagioclase and olivine was studied utilizing two-phase deformation experiments to directly decide strength contrast between crust and mantle. Our results indicate that olivine can be weaker than plagioclase at relatively low temperature. Moreover, it is considered from our study that the strength contrast between lower crust and upper mantle is large in Venus, and there is possibility that the decoupling occur.
We conducted phase transformation experiments (1) from supinel lherzolite to garnet lherzoltite and (2) from garnet lherzolite to spinel lherzolite in order to study the mechanism and kinetics of these reactions.
Experiments were conducted (1) at 3.2 GPa, 1000-1200 °C and for 0.6-30 hours with a spinel single crystal embedded into powder mixture of orthopyroxene and clinopyroxene and (2) at 1.2 GPa, 1000-1100 °C and for 5-30 hours with a garnet single crystal embedded into powdered olivine.
As results, (1) the garnet reaction rim was formed between single crystalline spinel and polycrystalline pyroxenes. The kinetics of the reaction rim growth was analysed based on the diffusion-controlled growth mechanism. (2) Partial melting occured and the orthopyroxene reaction rim and spinel domain were formed between single crystalline garnet and pollycrystalline olivine.
Deformation experiments on hydrous melt-bearing dunite were conducted under upper mantle conditions, in order to explore the effect of intergranular fluids on the plastic flow of olivine in Earth's upper mantle. The creep strength of hydrous melt-bearing dunite was about 2 times lower than the dislocation creep strength of hydrous olivine under these experimental conditions. The strain rate was proportional to differential stress to the 2.1 power, and the differential stress markedly increased with increase in grain size. These observations show that grain boundary sliding dominated the deformation of olivine (i.e., superplasticity). Superplasticity is the dominant creep mechanism of olivine in fluid-bearing fine-grained peridotites under low-temperature and high-stress conditions
We conducted grain growth and creep experiments on forsterite -enstatite system with varying volumetric fraction of these minerals under 1 atmosphere and temperature of 1260-1360 degree C. Observed grain growth velocity and grain size for primary phase becomes smaller with increasing volume fraction of secondary mineral. Overall, our results can be reproduced by previously proposed grain growth model for two solid phase system. Flow parameters such as grain size and stress exponents, activation energy are determined for a wide range of enstatite fraction. Flow laws with such parameters are well decomposed to two different flow laws for mono-phase systems of forsterite and enstatite with different grain size, respectively. Flow law including a fraction of secondary mineral can be established based on laws of grain growth in two phase system and single phase flow.
In order to clarify the dominant deformation mechanism in the upper mantle, we have conducted deformation experiments at pressure and temperature conditions of 3.0–5.3 GPa and 1473–1573 K, respectively, using fine-grained (grain size of ∼1 um) forsterite aggregate. The analysis of stress-strain rate data taken at dry conditions using a flow law equation yielded the activation volumes of ∼7 and ∼11 cm3/mol for diffusion creep and dislocation creep accommodated grain-boundary sliding, respectively. The present results implies that the diffusion creep is the predominant deformation mechanism at the most conditions of pressure, temperature and strain-rate in the upper mantle.
In situ creep strength measurements on hydrous wadsleyite were conducted at P-T conditions of the mantle transition zone using a deformation-DIA apparatus (D-DIA) and 6-6 type multi-anvil assembly in order to study dynamics at the mantle transition zone. Deformation of wadsleyite was achieved at 15-16 GPa, 1700 K and strain rates of 4-6 x 10^-5 s^-1 to strains of 20-32 %, and our preliminary results suggest that incorporation of water into wadsleyite substantially enhances its plastic deformation.
Deformation experiments of (Mg,Fe)SiO3-perovskite and post-spinel ((Mg,Fe)SiO3-perovskite + ferropericlase) at the lower mantle conditions (25 GPa, 1873 K) were conducted using the Kawai-type apparatus for triaxial deformation (KATD) installed at Magma Factory, Tokyo Institute of Technology. Lattice preferred orientation (LOP) of recovered samples were measured using monochromatic 2D X-ray diffraction pattern. After deformation of ∼25% strain with strain rate of 7 * 10-5 /s, no clear change was observed in LPO of perovskite for both samples.
Halite crystal growth from NaCl solution was conducted within a polydimethylsiloxane (PDMS) microfluidic device to understand the mineral deposition behavior in a confined environment as well as the properties and evolution of the crystallization pressure. Halite crystal growth caused the PDMS to deform when the crystal faces reached the PDMS channel walls, that was evident from the photoelastic effect within the PDMS material. The crystallization pressure during halite growth was quantitatively evaluated, based on the retardance of the PDMS and numerical models of PDMS deformation due to halite crystal growth. The crystallization pressure was inhomogeneously distributed along the interface, with a maximum value of 2.0 MPa at the crystal corner.