P-wave velocity (Vp) and S-wave velocity (Vs) of Ichino-megata mafic xenoliths, northeast (NE) Japan, were measured simultaneously under the subsolidus conditions. We obtain non-linea r velocity-temperature correlation for all rock studied. Significant Vp and Vs decreases at higher temperatures are probably attributed to thermal cracking and/or phase transition of plagioclas e and/or amphibole.
Hydrogen diffusivity in synthesized polycrystalline wadsleyite and ringwoodite, the major constituent minerals in the mantle transition zone, was measured by Fourier Transform Infra-Red (FTIR) Spectroscopy. Hydrogen diffusion rate in wadsleyite is roughly comparable to the average diffusion rate of hydrogen in olivine. The hydrogen diffusivity in ringwoodite is also measured and found that it is comparable to that of wadsleyite.
Water transported to the transition zone by hydrous phases is dehydrated at the top of the lower mantle. The dehydrated water moves upwards and is reacted and absorved by the overlying ringwoodite phase in the slab of the transition zone depth. Superhydrous phase B can be formed as the reaction product. This mechanism is effective to concentrate water in the slab at the transition zone depths; even if the amount of water transported by the slab (with the subducting speed of 10 cm /year) is very small around 0.05 wt.%, absorption of the dehydrated water by overlying ringwoodite crystals can build the hydrous zone containing 1 wt.% water with a thickness of 250 km in the slab at the transition zone depths by continuous subduction during 50 Ma. The transition zone surrounding the slab may also be hydrated but the region may be limited to less than 1 km in width due to a relatively slow diffusion of hydrogen in wadsleyite and ringwoodite.
An internally-consistent thermodynamic data set for phase A, clinohumite, and chondrodite has been derived by mathematical programming analysis of phase equilibrium and thermophysical data. The derived thermodynamic data are in excellent agreement with measured volumes and most experimental phase equilibrium data. Calculated phase diagram suggests that, at pressures higher than ca. 8 GPa, clinohumite and/or chondrodite are stable in the average mantle composition. This suggests that, at the conditions, these phases may play an important role for hydration of mantle wedge peridotite.
In this study, we compare the P-wave velocity (Vp) and S-wave velocity (Vs) crustal model of the NE Honshu arc by Nakajima (unpublished) with the laboratory measurements of Vp and Vs values by Nishimoto et al. (this meeting), and interprete petrological/ seismic crustal structure. The Vp and Vs of lower crustal layer beneath the back-arc side are comparable to the measured Vp and Vs values of Ichino-megata mafic xenoliths (hb. (px.) gabbro and/or
amphibolite) at solidus conditions (600-700 deg.C).
部分溶融マントルにおいて、パーコレーション閾値がどこにあるかということは、初生マグマの組成を考える上で重要な問題である。マグマ発生のモデルとして、分別融解モデルとバッチ融解モデルが両端成分モデルとして重要である。これまで閾値は限りなく低いという見解と有意に高いという見解が対立してきた。いずれにしてもこれまでの閾値のコンセプトでは、ある値を越えると、それを超えた分だけのメルトが流出するという、いわば静的なものであった。これだとバッチ融解は発生しない。Obata and Takazawa (2004）はメルトと結晶固体の境界の界面エネルギーを考慮した組織平衡の問題と重力場における固体、液体の密度差から発生するメルト圧と固体圧の差を考えあわせて、上昇による圧力低下で部分融解が進行しつつあるマントルでパーコレーション閾値がダイナミックに変化し、その結果バッチ融解が実現する可能性を指摘した。
文献：Obata, M. and Takazawa, E. (2004)
Anomalously young volcanoes, of approximately 6, 4 and 1 Ma in age, for the 130-135 Ma Pacific Plate were discovered form the toe of the oceanward slope of the northern Japan Trench  and the abyssal plain on the Northwestern Pacific Basin. The new bathymetric, geological and petrological data indicate two types of eruptive style, different in the degree of vesicularity and major element composition; one is very vesicular lava forming knolls, another is dense lava forming sheet flows. The distributions of these volcanoes clearly have the trend of WNW to ESE, which are perpendicular to the hinge line of the flexural lithosphere (outer-rise) due to plate-subduction.
The lavas are trapped some xenoliths of basalts, gabbros and peridotites, which are likely oceanic crust and lithospheric mantle in origin. Two types of olivine are also present in these lavas, xenocrysts with reaction rims and magmatic. The forsterite (Fo) (#91-92) values and NiO contents (0.3-0.5 wt%) of the xenocrysts are similar in composition to those of the depleted mantle peridotite. Chromian spinel inclusions in the xenocrysts also show the depleted composition in the range of abyssal peridotite. These data indicate that the xenocrysts originate from MORB-depleted mantle . The calculated primitive magma, on the other hand, follows a low degree of partial melting along the 2.5 to 3 GPa cotectic lines, which would corresponds the depth of asthenosphere.
The ascending magma from asthenosphere, therefore, would trap some xenoliths and xenocrysts originating in the conduit wall, possibly when brittle fractures occurs in the upper lithosphere due to the concave flexure of the plate in front of the convex bowing of outer-rise. The eruption occurred along some fissures being bent before subduction, in parallel to the maximum horizontal compression due to the down-warping of the Pacific plate motion for sub-crustal magma injection.
The upper Paleozoic Yakuno ophiolite in the Asago body, southwest Japan exposes a 3.0 km-thick middle to lower crustal section of intra-oceanic island arc, which is composed of metabasites (metagabbro and schistose amphibolite) of MORB-like affinity and granitoid intrusives of island arc affinity (Hayasaka, 1990; Suda, 2004). Mafic migmatite develops in the lower crustal section, whereas the granitoid intrusives forming plutons and dykes develop in the middle crustal section. Mmorphological change of the migmatite with increasing structural level suggests the melt segregation process. Small-scale primary melt formed at the lowermost horizon (metatexite migmatite), which moved upward, accompanied by increasing degree of melt segregation (melt-enriched migmatite), and finally led to the formation of plutons.
背弧拡大時に伴って噴出した未分化玄武岩マグマの化学組成を求めることは，背弧拡大時からその後のマントル内部における熱的進化に対してモデル化を行うのに有益である．本論では，South China basinの北側に位置する海南島玄武岩について岩石記載を行い，比較的未分化な玄武岩の特徴を有する試料を用いて，マントルと平衡である未分化マグマの全岩化学組成とカンラン石の鉱物組成を求め，それを基にして平衡温度を推定した．鉱物の化学組成を検討した結果，マントルポテンシャル温度は約1380℃∼1530℃と推定される．以上の結果は，背弧拡大時あるいはその後の海南島直下のマントル内部の温度はMORBのポテンシャル温度（Niu et al., 2001；1350℃）より高いばかりでなく背弧拡大に伴う玄武岩の生成温度が高温であることを示唆する．
The mechanism of development of shallow magma chambers and their relationships with caldera collapse are poorly known. Here we review the studies of pluton emplacement and caldera collapse, proposing a model linking the two processes. Magma ascending through diapirs or dikes is mostly halted at middle crustal levels. In the upper crust, the further rise of magma occurs by diking and the emplacement occurs along major anisotropies. Many plutons are emplaced at subhorizontal discontinuities, consisting of tabular, sill-like intrusions. Their growth will eventually induce doming of the overburden, forming laccoliths. Various evidence for shallow felsic and mafic laccoliths have been provided, suggesting that laccoliths are the most common mechanism to store magma in the upper crust, especially when the magmatic rates exceed the tectonic ones.
Sulaibikhat bay is a subsystem of Kuwait bay where intertidal mudflats are extended. It receives variety of discharges from land use activities. Significant changes in the sediment characteristics of the northern territorial waters of Kuwait exist; the construction of the Third River and the effect of draining of the Iraqi marshes. the scope of this study is to evaluate the effects of the previous incidents and investigate the secular variation of the heavy metals in the intertidal sediments of Sulibikhat bay. Geochemical characteristics of these sediments provide us last 50 years environmental change in northern parts of Kuwait. Eight cores were collected from intertidal zone sediments and geochemical analyses were carried out. XRF and ICP-MASS were used to measure the major and the trace elements of the sediments. Initially the longest core was analyzed by XRF and XRD, and the data with depth shows clear secular chemical variation.
超苦鉄質岩の一種である斜方輝岩は造山帯かんらん岩中にしばしば産し，SiO2に乏しい通常のマントルかんらん岩と比べてシリカ成分に富む．このような斜方輝岩を形成する一つの可能性として，かんらん岩へのSiO2の付加が考えられる．北海道，日高変成帯南西端に位置する幌満かんらん岩体には斜方輝岩が少量存在する．本地域の斜方輝岩はかんらん岩と，斜長石・単斜輝石を主とする塩基性岩に密接に伴って産する．この関係は，Yaxley and Green (1998)の実験で見られた関係とよく似ている．これらのことから，幌満かんらん岩中の斜方輝岩が，マントル内における塩基性岩の部分融解メルトとかんらん岩との反応によって形成された可能性が考えられる．そこで，本研究では幌満かんらん岩中の斜方輝岩の産状・鉱物組織・化学組成を報告し，斜方輝岩の成因と，不均質マントル融解の可能性を議論する．
Chromian diopside with high K content up to 0.56 wt% was discovered from the Osayama serpentinite melange, SW Japan (Tsujimori and Liou, 2005). K-bearing clinopyroxene (K-Cpx) fills hydrothermal micro-veins together with uvarovite within albite vein of a tremolite rock. K-Cpx consists mainly of kosmochlor + augite (92-98%; Ko19-38Aug56-76) components and minor amounts of jadeite (0-6%), aegirine (0-5%), Ca-Tschermak (0-3%), and K-kosmochlor (0-2%). K correlates with Na and Cr, indicating a simultaneous enrichment of K for Na and Cr during pyroxene growth. The incorporation of K into the kosmochlor_-_diopside series solid solution with at least 0.2 Cr cation p.f.u. is possible even at low P conditions.
Mechanism of Ni incorporation into dunite has been studied in order to simulate the compatible elements behavior in fluid-bearing rocks. Fe-free dunites were synthesized from gel powders using a piston cylinder apparatus. The gel powders were put into Pt-lined Ni capsules with water. As the run proceeded, Ni penetrated Pt liner all the way through and infiltrated into dunite in which forsterite grains were continuously growing. The sweeping of the grain boundaries that are enriched in Ni by grain boundary diffusion and surface equilibration should be responsible for more effective Ni - Mg exchange flux between fluid and olivine than by inter-diffusion from the stationary grain boundaries.
The Kodaikanal region of Madurai Block in southern India exposes a vast segment of high-grade metamorphic rocks dominated by Al-rich migmatite suite, designated herein as the Kodaikanal Metapelite Belt (KMB). The peak metamorphic assemblage is considered to be garnet-spinel-cordierite-quartz, which indicates possible pressure-temperature conditions of 900 °C at 7-8 kbar based on petrogenetic grid considerations. We show that the evidence for extreme crustal metamorphism at ultrahigh-temperature (UHT) conditions in granulite facies rocks can be extracted even if they lack typical UHT mineral assemblages due to bulk chemical constraints.
To reveal exhumation history of UHPM rocks, isochron ages in K-Ar system are examined with phengite and paragonite in the eclogitic rocks from the Tso Morari complex (TMC), western Himalaya, India. TMC is composed of pelitic gneisses and schists including mafic rock lenses (eclogites and basic schists). Eclogite has coesite pseudomorph in garnet and/or quartz rods in omphacite, suggesting UHPM. Pelitic schist gives an isochron age of 91±13 Ma using K-Ar analyses of paragonite and phengite. Phengite and paragonite in eclogite were analyzed by Ar/Ar method. Step-heating analyses using single phengite crystal showed 132 Ma plateau ages. The inverse isochron age by spot analyses of paragonite and phengite is 130±39 Ma.
The Lesser Himalaya in central Nepal exposes an inverted metamorphic sequence. The metabasites in the sequence occur as sheet-like bodies of a meter to tens of meters thickness. All the samples studied have the mineral assemblage Amp+Ab+Ep+Qtz+Titanite±Magnetite. Amphiboles occur as (1) sheared and elongated porphyroclasts with asymmetric pressure shadows and overgrown rims, (2) acicular and bladed aggregates parallel to the foliation and (3) inclusions in plagioclase. Amphibole chemistry suggests that (i) the peak metamorphism was attained during shearing related to the MCT movement and (ii) the peak thermal structure is inverted in the MCT shear zone.
Schirmacher Hillsは東南極の中央ドロンイングモードランドのPrincess Astrid 海岸（東経11°30'∼11°50' ，南緯70°45'）に位置する東西20km, 南北3kmの露岩である．その海岸線から約100∼150kmの内陸には，内陸山地群（CDMLN）（標高2500∼3000m) が東西約400kmに渡って分布している．Baba et al.(2003, in press)はSchirmacher Hillsより，含サフィリン斜方輝石-ザクロ石グラニュライトを見出し，その鉱物組み合わせ，斜方輝石のAl203含有量から変成ピーク時の条件として950°C以上, 約8kbarを見積もり超高温変成作用の存在をはじめて報告した．CDMLNは角閃岩相∼グラニュライト相の変成作用を被っているが，Schirmacher Hillsに見られる変成作用と一連かつ同時期のものであるかについては不明である．そこで，今回は含サフィリン斜方輝石-ザクロ石グラニュライト中のジルコンについて，U-Pb年代を国立極地研究所のSHRIMP IIを用いて測定した結果を報告し，CDMLNにおける変成作用との関係について議論する．
We examined petrological characteristics of the metapelites from the Androyen system, which occupies the eastern part of the terrain. It is composed of charnockite, leptynites, pyroxenite, granite and metapelites. This terrain is bounded by two major shear zones: to the north by the SW-SE trending Bongolava-Ranotsara shear zone and to the west by NS Betroka shear zone.
In this study we mapped Spl-Qtz occurrences in the metapelites in strikingly wide areas extending over ∼200km. Spl-Qtz rocks are distributed along the two shear zones (Bongolava Ranotsara shear zone and Betroka shear zone). The Spl-Qtz metapelites probably represent the roots of the continental crust uplifted during the Pan African collision event.
The Ntem Complex is situated at the north-western border of the Congo Craton in the south of Cameroon. It makes up the Archean basement and extends over its contact with the North Equatorial Mobile Belt represented by the Yaounde group. This group overthrusted the Ntem Complex during the Pan-African orogeny (650-500 Ma) and is affected by high pressure syn-tectonic metamorphism.
The Sangmelima region belongs to the Ntem Complex made up of three main lithologic groups: the intrusive complex (TTG, Granodiorites and Granites), the banded series and greenstone belts or iron trenches, so has undergone several magmatic episodes. The first is linked with the beginning of the major deformation phase (D1) faced by the region, associated with a granulite facies metamorphism. It corresponds to the successive diapiric emplacement of charnockitic rocks (TTG suite) during Meso to Neoarchean (2.9-2.8 Ga). The intense migmatization of TTG and the emplacement of Potassic Granitoids which marked the second magmatic episode, correspond to the period between 2.6-2.5 Ga.
TTG and Orthogneisses are of Trondhjemitic affinity whereas Potassic Granitoids are high-K acid rocks of typical Calc-alkaline differentiation series. This Archean-Proterozoic transition granitic magmatism (2.6-2.5 Ga) is one of the important stages in the evolution of the Ntem Complex (Congo Craton) since it marks a crustal reworking event.