We investigated two CB type carbonaceous chondrites, Gujba and Bencubbin to describe high-pressure polymorphs in their melting textures. Many kinds of high-pressure polymorphs were identified both in their melting textures, implying that the parent-body of CB type carbonaceous chondrite were heavily shocked.
Distorted garnet with a tetragonal symmetry was discovered in fragments of host rock in a melt vein in a shocked chondrite by ATEM. The garnet occurs as aggregates of fine-grained crystals (< 1.5µm in size) with nearly the same chemical composition with the host low-Ca pyroxene. This occurrence indicates the tetragonal garnet has formed a solid-state transformation from the host pyroxene at >1600 °C and 16-22 GPa. Cooling rate of the melt vein was estimated to be larger than 103 °C/sec based on diffraction intensity analysis of the garnet.
We conducted a series of systematic shock recovery experiments on single crystal quartz. We found that the cathodoluminescence (CL) intensity of a blue emission increases with increasing shock pressure. Also, Raman spectra shows that as the pressure increase, the crystallinity decrease, finally transformed to diaplectic glass. A continuous increase in CL intensity of blue emission at higher presures for both quatz and shock induced diaplectic glass indicates a spectral change related to the extent of amorphization.
We observed and analyzed an ungrouped primitive achondrite, NWA 6112. This meteorite shares mineralogical similarity with MIL 090206/090340 and brachinites and its oxygen isotopic is very similar to that of Divnoe which is mineralogically similar to brachinites. Therefore, we suggest that NWA 6112 is key to understand the origin of brachinites and related primitive achondrites.
We performed mineralogical and crystallographic study on silico-phosphates in angrite meteorites. The silico-phosphate is present as up to 30 micrometer euhedral grains and contains 10-15 wt% SiO2. The electron diffraction images by FIB-TEM reveal that it has an apatite structure, which is consistent with earlier works by Raman spectroscopy and SEM-EBSD analyses, and so it is called "silico-apatite". Approximately half of P5+ is replaced with Si4+. Fe3+ and Ti4+ partly replaces Ca2+, and Cl- may be similarly replaced with vacancy in order to maintain charge balance in the apatite structure, and thus the composition is written as Ca9(Fe3+,Ti4+)(PO4)4(SiO4)2(Cl, )2.
Water content of the Moon was thought to be less than 1 ppb, but water-rich apatite and melt inclusion were recently discovered in the lunar samples, speculating water content of 1-100 ppm order in the mantle. Here, we measured infrared spectra of clinopyroxene and olivine in lunar mantle-derived gabbroic/basaltic breccia of NWA 2727 meteorite, with KREEP component and 2.9 Ga crystallization age, to estimate water content in the mantle, directly. Only clinopyroxene and olivine in the gabbroic clasts contain 518 ppm and 484 ppm water, respectively, implying a wet lunar mantle with 494 ppm water, comparable to terrestrial mantle.
It is considered that olivine in Martian meteorites is darkened by strong shock. However, their detailed processes and conditions are not clear. Our previous study implies that they are formed with transformation to high-pressure polymorphs. In this study, our Raman analyses of darkened olivine and lamellar textures observed in slightly darkened olivine in Tissint show that there are extra Raman shift peaks in 650 ~ 680 cm-1. These peaks indicate that they have been high-pressure polymorph. Although Martian meteorites with brown olivine rarely contain high-pressure polymorphs, they have undergone higher temperature and pressure than those the other meteorites done.
The studies on the general method for the classification of stony meteorites by the X-ray diffraction method have not been enough. In the present study, I thus examined it. The method would be applied for (1) the quantitative method of the classification of stony meteorites and (2) the restricted small samples. The distinction of the chemical group of equilibrated ordinary chondrites is possible on the olivine peak useful for the composition. The petrologic types of unequilibrated or equilibrated is possible based on the phase distinction of the low-Ca pyroxenes and the diffraction peak of plagioclase.
The local structures of meteorite fusion crusts were studied by Ca, Ti and Fe K-edge XANES and EXAFS spectroscopy in order to provide qualitative and quntitative data on coordination environments. This study indicated that meteorite fusion crusts gives unique local structures. The Ca, Ti and Fe XANES spectra for fusion crusts have unique and various shapes. The Ca-O distance in meteorite fusion crusts are 2.61-2.66 A and are extremely longer than the other natural glasses. The fusion crusts have unique local structure since it was experienced extremely high temperature and short quenching time.
In the islands of Japan, minor amounts of Paleozoic granites are distributed only in the restricted area. Among them, we discuss the geological significance of the late Carboniferous to Permian granitic rocks based on the zircon U--Pb ages and petrochemical features of these rocks. The results of U-Pb geochronology suggest that the onset of the late Carboniferous and Permian granitic activity may have initiated at ca. 300 Ma and continued to Ca. 280 Ma. From the petrochemical investigations, these granitic rocks are considered to be the product of a series of volcanic arc, which was an oceanic arc with subduction of young oceanic lithosphere.
Petrological studies of the plutonic rocks in the eastern area of the Abukuma Mountains are carried out. Biotite granite and hornblende-bearing granodiorite are widely exposed in the main part of the Abukuma Mountains and of the east of the Hatagawa Fracture Zone. They show typical chemical characteristics of evolved granitic rocks. In contrast, granitic rocks in the east of the Futaba Fracture Zone along the coastal area are mainly tonalitic and show chemical characteristics poor in incompatible elements such as K2O.
One of enigmas of the layered gabbros which IODP Exp.345 drilled at the Hess Deep Rift is the fact that Opx occurs as a cumulus phase. In the Multi-textured layered gabbro which constitutes the upper unit of the Hole U1415P, we can observe the following occurrences of Opx: (1) Opx+Cpx+Pl vein parallel to the layered structure of its surrounding troctolite. (2) Undeformed Opx+Pl veinlets in kinked Ol. (3) Opx in the concave of anhedral Ol. (4) Opx in the surroundings of Cr-spl adjacent to the Ol+Pl domain. The occurrences of Opx suggest the reaction between Ol and SiO2-saturated melt.
Lherzolite, harzburgite and dunite forms layers in the basal part of the mantle section above metamorphic sole in Sumaini window of northern Fizh block of Oman ophiolite. Peridotite with Cr# of spinel between 0.48-0.56 is absent. As a result, peridotites are divided into two group: Cr# higher or lower than this range. Chondrite-normalized REE patterns of clinopyroxene show light REE depleted patterns. The peridotites with high Cr# spinel formed by flux melting of the peridotites with low Cr# spinel after fluid infiltration. The peridotites with high Cr# spinel may have acted as a route for fluid migration within mantle section.
In the northern Oman ophiolile mantle section, an orthopyroxenite veinlet within a komatiitic dunite has been found. It exhibits a relatively high-Mg character. Whether this orthopyroxenite represents the final product of differentiation of the komatiitc melt involved in the dunites genesis, or it is of a boninitic affinity, as those already reported. In this second case, it may implicate that the komatiitic melt activity occurred during the Oman ophiolite obduction in between two boninitic melt episodes; the predating one being responsible for the genesis of the chromitite pod and, the postdating one, being responsible for that of the orthopyroxenite.
It is of prime interest to understand how subducted slab circulates and is assimilated to the convecting asthenospheric mantle. The residual mantle comprising the majority of slab is considered to have been fragmented and dispersed within the depleted MORB mantle (DMM), enhancing the heterogeneity of the upper mantle. These residues are highly refractory and are hence uninvolved in most magmas produced in the convecting mantle. Analyses of the genetic conditions of boninite revealed an essential role of Proterozoic slab as the boninite magma source, providing an insight to the heterogeneity of the upper mantle.
We found rare orthopyroxene veins intruding into an olivine grain in a two-peridotite xenolith from the Shiribeshi Seamount, Japan Sea. The orthopyroxenes in the veins are characterized by low Al2O3, CaO and Cr2O3 contents, which are similar to secondary orthopyroxenes replacing olivines reported in arc-peridotite xenoliths. REE patterns of the melts in equilibrium with the orthopyroxenes imply that the orthopyroxene veins were derived from garnet-bearing source material. These orthopyroxene veins were possibly produced by the addition of Si-rich melt/fluid released from the subducted slab into the back-arc mantle beneath the Japan Sea.
Thick lithosphere beneath continents plays an important role in suppressing heat loss from the earth. Heat flux through lithosphere-asthenosphere boundary (LAB) is critical in this regard and has been estimated from surface heat flow and thermal structure of the lithosphere from mantle xenoliths in alkali basalts and kimberlites by assuming steady heat flow and chemical equilibrium. We have estimated temporal change of thermal structure of the lithosphere near the LAB without such assumptions from mineral chemical study of spinel lherzolite xenoliths in alkali basalt from the Middle Atlas in Morocco and succeeded in detection of asthenospheric thermal event.
Log-linear CSD(Crystal Size Distribution)s which are frequently observed in natural volcanic rocks, has been considered to form under the condition that nucleation rate increases exponentially and growth rate is constant with time. In this study, we propose a new model to form a log-linear CSD where nucleation rate and crystallization rate are constant with time, and discuss the conditions behinds the assumptions, and address how the CSD analysis will be developed in applying the model to natural CSDs.
Zircon growth collected from a granitic pluton shows four (1st – 4th) events with specific mechanisms, crystallization temperatures and U-Pb ages, revealing the sequential formation process from intrusion through emplacement to crystallization / solidification. The events are recognized by: 1) internal structure of zircon based on the cathodoluminescence observation, 2) crystallization temperatures by the Ti-in-zircon thermometer in the internal structure and 3) U-Pb ages in the internal structure.
Salang Massif that is located in the Western Hindu Kush, Afghanistan consists of granitoids and that igneous activity occurred by subduction of the Tethys ocean beneath the north Afghanistan platform. We report here geochemical and Zrn U-Pb age data that we analyzed by XRF and LA-ICP-MS to elucidate igneous activity in detail and the tectonic setting of the area. We concluded that Salang Massif granitic rocks emplaced at 213 to 224 Ma and made from three different parental magma and K rich parent rocks.
Size distributions in thinsections of rocks in the lower marginal zone in the Nosappumisaki doleraite intrusion, Northern Japan, were obtained with using the polarization CCD camera system. Mineral types were identified with using the retardation obtained by the system. Analyses of the retardation and primary-axis direction in groundmass of the rocks revealed systematic evolution of size distribution, that corresponded to solidification progression from the contact with host rock toward the inner region of the magma chamber.
We performed geological and petrological study on Torikabutoyama-Yokokurayama, Old Kumanodake, and Nakamaruyama volcanic edifices of Zao volcano. The former one was formed ca. 500 ka and the latter two were during ca. 350-250ka. These three edifices are composed of thick andesitic to dacitic lava flows, relatively thin basaltic andesite to andesitic lava flows, and thin basaltic andesite lava flows. All products belong to medium-K calk-alkaline series. The compositional trends of these three edifices and eruption units are slightly different each other.
For mixed rocks of Kumanodake pyroclastics, we calculated residence times for the olivine on the assumption that the compositional zoning was produced by diffusion of the elements after the injection. We obtained the residence times of <3.5 years from lower unit, and <130 days from upper unit.
This study develops a heat and mass transfer model to describe the compositional relationships between the bulk crystals, liquid, magma (crystals plus liquid), and crystal rims during open-system magma chamber processes. The model incorporates the effects of concurrent magma recharge (or mixing), assimilation, magma extraction, and fractional crystallization. The isotopic zoning profiles in phenocrysts vary markedly depending on the relative rates of recharge, assimilation, magma extraction, and fractional crystallization.
Assimilation of mantle-derived magma with crustal rocks is one of the important processes of formation of upper continental crust materials. In this study, we tried melting experiments for examining assimilation process of magma with crustal rocks using a piston-cylinder type high-pressure apparatus. We used Setouchi high Mg andesites and Shimanto metasedimentary rocks. Two starting materials are prepared; (1) mixture of powders of both high Mg andesites and metasedimentary rocks, and (2) mixture of andesite powder and fragments (~0.1mm) of metasedimentary rocks. Experiments of starting material (1) produced homogeneous trondhjemitic glasses. In contrast, those of (2) produced granitic glasses.
Two types of Miocene volcanic rocks are distributed in Utsunomiya, central Japan. Andesite and rhyolite are intercalated with Kazamiyamada Formation, in the lower, and Oya Formation, in the upper, respectively. The Kazamiyamada formation derives subaerial volcanism, and in contrasts the Oya formation formed by submarine volcanic eruption. These igneous activities correspond to the opening event of Japan Sea. On the other hand, Miocene volcanic rocks distributed are Kanuma and Motegi areas, around of the Utsunomiya area. This study compared the Kazamiyamada andesites with the Kanuma and Motegi mafic volcanic rocks.
We investigated the origin of lithological variation in the Upper Zone of the Horoman peridotite complex using whole rock major and incompatible element contents. Plagioclase lherzolite adjacent to mafic layer is enriched in basaltic components as a result of refertilization by a melt that formed mafic layer. Plagioclase lherzolite became enriched by a melt that formed mafic layer. Chondrite-normalized REE patterns of whole rocks indicate the reaction with LREE-MREE enriched fluid that infiltrated during partial melting of plagioclase lherzolite when the Horoman complex uplifted from the upper mantle to the crust.
Tsushima granite and the related rocks, southwestern Japan, are known for abundant aqueous polyphase inclusions with large daughter crystals. We non-destructively analyzed the polyphase fluid inclusions in quartz crystals from a miarolitic cavitie at the Tsushima granite with synchrotron radiation XCT and Raman microspectroscopy. The results show presence of daughter crystals of halite, sylvite, saltonseaite siderite, and Fe-OH mineral in the inclusions. Then, after we peeled the surface of mother phase, quartz, polyphase inclusions were directly observed and analyzed with SEM-EDS.
We report hydrothermal chromitites in diopsidites from the Oman ophiolite. They typically occur as thin seams where fine subhedral chromite grains are interstitial to coarse euhedral Cr-bearing diopside grains. They are similar in Ir to Pt contents to some of mantle chromitite, but almost free of both Os and Pd. No PGM have been found, and PGE may be contained in silicate and oxide minerals as trace elements. Chromitites can be formed from hydrothermal fluids if the condition permits.
We report a new occurrence of a polymorph of sapphirine from a kelyphite after garnet in a garnet peridotite, Czech Moldanubian Zone. It has a composition of sapphirine but TEM analysis reveals a tricrinic symmetry.
We have been able to get information of the arc upper mantle (petrographical features and processes) but they are limited to from relatively small (< 1 m) peridotite xenoliths, enclosed by arc magma, and then spatial variations and whole view of the mantle wedge are poorly understood. We examined the petrographical and geochemical features of the ultramafic rocks from the Mersin ophiolite, possible supra-subduction zone origin (e.g., Parlak et al., 1995). The mantle peridotite is highly depleted spinel harzburgite and olivine-replacing orthopyroxene is rarely observed.
Jadeitite veinlets cutting across albitite have been found from the Ohya-district, Hyogo Prefecture. The veinlets are consisted of jadeite crystals elongating parallel to the veinlets, whereas the jadeite crystals in the jadeitite veinlets from the other localities elongate perpendicular to the veinlet-wall boundaries.
Hydrothermal alteration process was examined on the Nabekura ore deposit area of the Iwafune granite, Uetsu region. Biotite, feldspars, apatite, were analyzed by EPMA. The results are: plagioclase is An11-39% in the granite, and An1-4% in the ore host rock. The F content of biotite, 0.4-1.2 wt% in the granite, 0.9-2.2 wt% in the ore host rock. The F content of apatite, 2.5-3.8 wt% in the granite, 2.7-3.8 wt% in the ore host rock. These results indicate that the Nabekura W deposit was formed by fluids rich in fluorine.
As for the building stones used for the stone-wall of the Kami-no-hashi Gateway of Fukuoka Castle, so many granitic rocks and subsequent dioritic to gabbroic plutonic rocks were used. Most of the granitic rocks were mostly hornblende-biotite granodiorite to adamellite, on the other hand, the dioritic to gabbroic plutonic rocks were almost grouped into hornblende quartz diorite. Major element compositions of the plutonic rocks were coincident with those of the Shikanoshima granodiorites and Shikanoshima basic rocks. Since the stone-wall of the Kami-no-hashi Gateway were also built from alkali basalt and serpentinite which were found around the Hakata Bay area as well as the plutonic rocks, the building stones of the wall were probably provided from the Miyanoura on Itoshima Peninsula and Shikanoshima Island, and supplemented by various rocks from neighbor areas at the northern Hakata Bay.
Cathodoluminescence (CL) spectroscopy of quartz grains in eolian sediments reveals an obvious correlation of emission components between Al3+ defect center and the other centers (Fe3+, Ti4+, and NBOHC). CL obtained from the quartz grains can be used as an indicator for their provenance and stratigraphic assignments among the sediments.
In this study, we examined the progressive metamorphic P-T history of UHP eclogite from Yangzhuang in the Sulu belt using distribution of SiO2 phases, residual pressure of quartz and thermodynamic calculation based on inclusions in garnet.
Spinel lherzolite represents the most common lithology among mantle xenoliths, but its common occurrence is not exploited in geotherm estimation since there is no appropriate geobarometer for spinel lherzolites. This study aims to develop geobarometer for spinel lherzolites. Thermal history of mantle xenoliths from the Middle Atlas in Morocco were carefully examined backward starting from the quenching upon eruption without assuming equilibrium for application of thermobarometers. We pinpointed portions of minerals and components representing condition just before xenolith entrapment in magmas, on which appropriate geothermobarometers are applied. We have detected 0.5GPa pressure difference for 100°C variation in temperatures.
Mantle wedge peridotite at South Bohemia of the Bohemian massif (Czech Republic) experienced transformations from earlier garnet peridotite to chlorite peridotite in the early exhumation, followed by subducted to high-pressure garnet peridotite condition at ca. 3 GPa and 850-1050ºC. We report on hydrous minerals and multiphase solid inclusions (MSI) in earlier stage UHP chromite to unravel the nature of melt in the mantle wedge. The UHP chromite includes MSI consisting of 40 % phlogopite, 47 % carbonates, and 3 % apatite. The reconstructed composition is ultrapotassic dolomitic carbonatite. The trace element pattern for the dolomitic carbonatite is enriched in Ba, Sr, LREE, and depleted in U, Th, Pb, HFSE and HREE, and it is quite similar to the carbonatite melt in equilibrium with pyrolite at the asthenosphere depth. Such alkali-rich dolomitic carbonatite in the mantle wedge was sourced either from deeply subducted oceanic crust or asthenospheric mantle.
Armalcolite, found on the Moon in Mare Tranquillitatis at Tranquility Base, on July 20, 1969 by the Apollo 11 mission and named after the Apollo 11 crew (ARMstrong, ALdrin, and COLlins), is stable at low pressure and high temperature in the low oxygen fugacity conditions and breaks down to ilmenite and rutile below 1000 C. Fe3+-rich armalcolite has been found from an ultrahigh-temperature metamorphosed quartzofeldspathic gneiss from Mt. Riiser-Larsen, Napier Complex, East Antarctica (Miyake Hokada 2013). We (2013) reported a possible armalcolite pseudomorph-bearing garnet-sillimanite gneiss from Skallevikshalsen, Lützow-Holm Complex, East Antarctica. These indicate armalcolite can be a new index mineral of the ultrahigh-temperature metamorphism. We present a preliminary report on the stablility of the Fe3+-rich armalcolite at the high-oxygen fugacity.
Preliminary deformation experiments were carried out on sintered polycrystalline diopside. Creep tests were made in a uniaxial compressional apparatus at temperatures T = 1150 to 1200°C. The specimens were deformed such that strain exceed by 30%.
U-Pb zircon dating using LA-ICP-MS was carried out for four granitoid samples in the Goyu area, Aichi Prefecture. The weighted mean 238U-206Pb zircon ages for the Kamihara Tonalite, the Tenryukyo granite and the Busetsu granite are 79.9±0.7 Ma, 77.8±0.8 Ma and 69.3±4.3 Ma, respectively. These are interpreted as the timing of granitoid crystallization. Our results are about 15-10 Ma younger than the previously reported CHIME monazite ages. The reason for this discrepancy will be considered in a future study.
The Raman spectral intensity of CO2 in the cordierite channel varies considerably depending on the crystal orientation of cordierite,because it is orientated linearly along the a-axis in cordierite channel. From the Raman intensity ratio of cordierite peaks obtained from euhedral crystals of cordierite, it is possible to identify crystal orientation of cordierite. In order to check the reliability of this method and its application for the determination of CO2 contents in cordierite channel, we analyzed and compared using cordierite from gneisses in the KKB, southern India.
We investigated the southern end of the Hidaka Metamorphic belt to clarify heat transport mechanisms during metamorphism. We found a high thermal gradient in the metamorphic rocks adjacent to the high-temperature Nikanbetsu peridotite body, suggesting a thermal effect of the mantle material. Garnet grains, the compositions of which were used to detect the thermal gradient, have mineral and fluid inclusions with textural diversities. The size and internal distribution of inclusions in garnet show systematic spatial variations conformable to the thermal gradient. This implies spatial variation of thermal history affecting nucleation and growth of garnet.
Tseel terrane has WPB and MORB-type protoliths. Darvi and Han-Hohey areas have VAB and MORB-derived protoliths.Tsagaan Shuvuut terrane has protolith of IAB. Zavkhan terrane has VAB and MORB-derived protoliths, which is divided into two zones, Urgamal and Zavkhan-Mandal. Geochronology of mafic metamorphic rocks from Zavkhan area shows 903±15 Ma and 830±37Ma. VAB-type rock has age of 904±9.3 Ma.
Three types of garnets have been identified in the pelitic schists surrounding the Sebadani metagabbro mass. Type I garnet is zoned with Fe and Mg increasing and Mn decreasing from core to rim. Type II garnet contains high-Mg garnet in the core, and the rim shows the similar zoning as Type I garnet. Type III garnet is poikiloblastic, and it contains polyphase inclusions probably after lawsonite. Presence of lawsonite pseudomorph in the Type III garnets suggests a higher P/T geothermal gradient for the eclogite metamorphism in the pelitic schists.
The Tonaru metagabbro mass occurs as a large lenticular body in the Sambagawa metamorphic belt in central Shikoku, and it consists of two different lithologies. One is diopside amphibolites, and the other is garnet epidote amphibolite, accompanied by small amounts of eclogites. Garnet epidote amphibolites composed mainly of garnet, epidote, amphibole (tschermakite, pargasite, magnesio-hornblende), plagioclase (An14-20) and quartz. Two types of garnets have been identified, coarse grained garnet up to 7 mm and fine grained garnet up to 2 mm across. The chemical compositions of the coarse grained garnet are similar to the core of the fine grain garnet.
Barroisite eclogites and garnet amphibolite exposed in the Kotsu area, eastern Shikoku, Japan. We have collected several loose block of barroisite eclogites and garnet amphibolites from outcrops. We described zoned amphibole from the garnet amphibolite, with barroisite core, rimmed by glaucophane and again barroisite at the outermost rim. Garnet compositions in the barroisite eclogites and garnet amphibolites show a similar prograde zoning with decreasing Mn and increasing Mg from the core to the rim. This suggests garnet amphibolites in the Kotsu area share the similar eclogitic metamorphism with the barroisite eclogites.