記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Elsevier BV  

DOI： 10.1016/j.earscirev.2022.104122

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：American Chemical Society (ACS)  

DOI： 10.1021/acsearthspacechem.0c00206

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担当区分：責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Tohoku University  

We performed laboratory measurements of the electrical conductivity of a gabbro sample of the Oman ophiolite under high-pressures (0.6 and 0.8 GPa), high-temperatures (250-908 °C), and dry conditions using a piston- cylinder type high-pressure apparatus. The studied gabbro can be regarded as a representative sample of the lower oceanic crustal rocks based on its previously reported elastic wave velocities. The gabbro sample was powdered and hot pressed, and then sintered prior to the electrical conductivity measurements. The measured electrical conductivity of the sample decreased with decreasing temperature, which is consistent with the Arrhenius relationship. Compared with the electrical conductivity values of lower oceanic crust derived from a recent electromagnetic survey in offshore Nicaragua, the measured electrical conductivity of the sample was considerably lower in the temperature ranges expected for lower oceanic crust. The discrepancy can be explained by the presence of conductive pore-fluids in the lower oceanic crust.

DOI： 10.2465/jmps.171110

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記述言語：日本語   掲載種別：研究論文（大学，研究機関等紀要）  

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本地質学会  

<p>瀬戸内火山岩類は九州東部の大野地域から愛知県東部の設楽地域にかけて，中央構造線沿いにおよそ600 kmにわたり分布する．瀬戸内火山岩類を特徴付ける岩石種のひとつである高Mg安山岩は大野地域から紀伊半島中部の範囲で見られ，松山周辺では高縄半島から防予諸島にかけて広く分布する．本巡検対象の松山周辺では，安山岩類の多くは小規模な岩頸あるいは岩脈として産するため，貫入様式の観察には好適である．さらに瀬戸内火山岩類にはピッチストーンなどを含む珪長質火山岩類も広くみられる．この珪長質火山岩類は，松山周辺では砕屑岩および火砕岩からなる高浜層群，興居島層群中に含まれる．分布は極めて狭いが多様な岩相をもつこれらの地層群についても興居島南東海岸の露頭で観察を行う．</p>

DOI： 10.5575/geosoc.2017.0048

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1016/j.lithos.2016.07.035

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

This paper reviews the sedimentological, geochemical and stratigraphic characteristics of the Paleoproterozoic Chaibasa and Dhalbhum Formations (the Singhbhum Group) of eastern India and presents a comparative study with other Paleoproterozoic lithostratigraphic units of India. Both the formations are entirely siliciclastic and deformed and metamorphosed, generally at greenschist to upper amphibolite facies. The older Chaibasa Formation consists of sandstone, shale and sandstone-shale interbanded (heterolithic) facies. It conformably over-lies the Late Archean-Paleoproterozoic Dhanjori Formation of terrestrial (alluvial fan-fluvial) origin. The Lower Chaibasa Member formed in a marine setting; the shale and heterolithic facies formed in a continental shelf setting below and above the storm wave base, respectively. The sandstone fades formed in a subtidal setting during sea level fall. In contrast, the Upper Chaibasa Member formed in a shallow-marine setting; both the shale and heterolithic facies formed above the storm wave base.
In significant contrast, the overlying Dhalbhum Formation is dominated by finer clastics with much lower proportion of sandstones. The base of the terrestrial Dhalbhum Formation is a sequence boundary (unconformity). Sedimentary facies analysis clearly shows two broad facies association of terrestrial origin (fluvial and aeolian). The aeolian facies association overlies the fluvial facies association. The Dhalbhum sandstones show typical REE pattern of quartz dilution with lower concentrations compared to the mudstones. The Dhalbhum finer clastics mimic typical REE patterns resembling abundances in the continental crust. Rare earth element plots display a good match with Post-Archean Australian Shales (PAAS) including similar concentrations, steep negative slope for LREEs, negative Eu anomaly, and nearly flat HREES. The Singhbhum Paleoproterozoic succession is devoid of both chemical sediments and Paleoproterozoic glacial deposits in contrast to neighboring cratons. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.earscirev.2016.10.001

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

In order to evaluate the influence of porosity on the elastic properties of crustal rocks at deep crustal pressures, we performed laboratory measurements of compressional-wave (Vp) and shear-wave (Vs) velocities in a porosity-developed gabbro sample up to 1.0 GPa at room temperature. Based on the measured Vp and Vs data, we evaluated the changes in velocities, Vp/Vs, Poisson's ratio (sigma), and total porosity of the rock as a function of pressure. Compared with the 'porosity-free' intrinsic elastic values of the gabbro sample, our results suggest that the development of porosity in crustal rocks lowers their Vp, Vs, Vp/Vs, and Poisson's ratio. Deviations (Delta Vp, Delta Vs, Delta Vp/Vs, and Delta sigma) of the measured values from the intrinsic values are enhanced with increasing porosity. We evaluated the AVp from previous experimental study on the rocks of Tanzawa plutonic complex providing constraints on interpretation of the seismic velocity profiles of the Izu-Bonin-Mariana (IBM) arc and found a large negative Delta Vp (up to - 22.7%) at lower pressures. The intrinsic velocity combined with the measured velocity data at in situ pressure conditions suggest that the ranges of Vp (6.0-6.5 km/s) in the middle crust of the IBM arc reflect the presence of considerable porosity and its closure in intermediate rocks and/or the change of composition from felsic to intermediate in mid-crustal rocks. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.tecto.2016.03.044

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：WILEY  

In order to determine porosity-free' intrinsic ultrasonic compressional (Vp) and shear wave (Vs) velocities and Vp/Vs of an olivine gabbro from the Oman ophiolite, we developed a new experimental system using a piston-cylinder type high-pressure apparatus. The new system allowed us to measure velocities at pressures ranging from 0.20 to 1.00GPa and at temperatures up to 300 degrees C for Vp and 400 degrees C for Vs. At room temperature, the Vp and Vp/Vs increase rapidly with pressure up to 0.40GPa, while between 0.45 and 1.00GPa the increase is more gradual. The change in increasing rate is attributed to closure of porosity at pressures above 0.45GPa. Based on the linear regression of data obtained at higher pressures (0.45-1.00GPa) and extrapolation to the lower pressures, combined with temperature derivatives of velocities of the sample measured at 1.00GPa, we determined the intrinsic Vp and Vs of the sample as a function of pressure (P, in GPa) and temperature (T, in degrees C). The intrinsic velocities can be expressed as Vp (km/s)=7.004+0.096xP-0.00015xT, and Vs (km/s)=3.827+0.007xP-0.00008xT. We evaluated the intrinsic Vp and Vs of the olivine gabbro at oceanic crustal conditions and compared them with a velocity depth-profile of the borehole seismic observatory WP-2 area in the northwestern Pacific Basin. Although the intrinsic Vp (approximate to 7.0km/s) and Vs (approximate to 3.8km/s) for the olivine gabbro studied are comparable to those of seismic layer 3 in the WP-2 area, the estimated vertical gradients of intrinsic velocities are significantly smaller than those reported from layer 3. These results suggest that velocity profiles of layer 3 in the WP-2 area may reflect the presence of a minor porosity in lower oceanic crust, which closes with increasing depth and/or continuous changes in mineralogy of layer 3 rocks.

DOI： 10.1111/iar.12092

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：TAYLOR & FRANCIS LTD  

This study proposes a measurement and evaluation approach for community resilience to flood disasters using a set of biophysical and socioeconomic indices. It identifies geographic and thematic areas where policy interventions are most critical. The study applies this approach in selected barangays (the smallest administrative units) in the Santa Rosa-Silang subwatershed in the Laguna Lake region of the Philippines. Results suggest that in order to enhance resilience, it is necessary to strengthen the institutional capacity of barangays to formulate and implement disaster risk reduction initiatives as a legitimate part of their overall land-use-based development plans. Disaster risk reduction initiatives should place equal attention on both ex ante and ex post measures. Ex ante measures include putting in place regular community disaster awareness and preparedness programs that would emphasize the cost of a disaster, the value of participation and volunteerism, as well as livelihood and savings formation. Ex post measures include enhancing the capabilities of emergency facilities and services by providing permanent and volunteer personnel with regular training and equipment. Resource constraints could be addressed by maximizing strong linkages between local government units, academics and non-governmental organizations to enable financial, material, and knowledge transfer. Bridging institutional relationships with nearby barangays and strengthening their bonds with local networks of residents, leaders, and organizations may also help to spread the cost of reducing disaster risk and to promote resilience.

DOI： 10.1080/17477891.2014.981497

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2465/gkk.130902

Scopus

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2465/gkk.141215c

Scopus

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

A diorite pluton and widely distributed mafic dykes occur in the Fosdick migmatite-granite complex, which is interpreted to represent middle-to-lower crustal rocks of the paleo-Pacific active continental margin of Gondwana. The mafic dykes exhibit a variety of relationships with host rocks in the field ranging from undeformed dykes with sharp contacts with host gneisses to dismembered dykes with commingled textures and numerous back-veins of leucosome intruded from host migmatitic gneisses suggestive of significant interaction with crustal rocks. New U-Pb ages for magmatic zircon in these rocks yield Cretaceous crystallization ages ranging from ca 113 Ma to ca 98 Ma for the mafic dykes and ca 100 Ma for the diorite pluton. These mafic intrusive rocks, which contain abundant hydrous minerals, are medium- to high-K-series calc-alkaline rocks with basic-intermediate compositions (47-59 wt.% SiO2 for the mafic dykes and 52-56 wt.% SiO2 for the diorite pluton). They have trace element patterns characterized by LILE enrichments and negative Nb anomalies indicating an origin from a hydrous mantle source metasomatized by slab-derived components. The samples without evidence of interaction with crustal rocks (11 of 14 samples), which are likely to better reflect the mantle source composition, have positive epsilon Sr-(100 (Ma)) values (+8.1 to +14.5) and negative to slightly positive epsilon Nd-(100 (Ma)) values (-1.6 to +2.5) consistent with derivation from an enriched mantle source. These eleven samples may be divided into two groups either characterized by higher LILE/HFSE ratios, less radiogenic epsilon Sr-(100 (Ma)) values and more radiogenic epsilon Nd-(100 (Ma)) values, or characterized by relatively lower LILE/HFSE ratios, more radiogenic epsilon Sr-(100 (Ma)) values and less radiogenic epsilon Nd-(100 (Ma)) values suggesting differences in the mantle source. The results of this study are consistent with the melting of a variably metasomatized sub-arc mantle source during a transition from a wrench to a transtensional tectonic setting, but are inconsistent with a mantle plume origin. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

DOI： 10.1016/j.gr.2012.08.002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：SPRINGER  

The Miocene Kaikomagatake pluton is one of the Neogene granitoid plutons exposed in the Izu Collision Zone, which is where the juvenile Izu-Bonin oceanic arc is colliding against the mature Honshu arc. The pluton intrudes into the Cretaceous to Paleogene Shimanto accretionary complex of the Honshu arc along the Itoigawa-Shizuoka Tectonic Line, which is the collisional boundary between the two arcs. The pluton consists of hornblende-biotite granodiorite and biotite monzogranite, and has SiO2 contents of 68-75 wt%. It has high-K series compositions, and its incompatible element abundances are comparable to the average upper continental crust. Major and trace element compositions of the pluton show well-defined chemical trends. The trends can be interpreted with a crystal fractionation model involving the removal of plagioclase, biotite, hornblende, quartz, apatite, and zircon from a potential parent magma with a composition of similar to 68 wt% SiO2. The Sr isotopic compositions, together with the partial melting modeling results, suggest that the parent magma is derived by similar to 53% melting of a hybrid lower crustal source comprising similar to 30% Shimanto metasedimentary rocks of the Honshu arc and similar to 70% K-enriched basaltic rocks of the Izu-Bonin rear-arc region. Together with previous studies on the Izu Collision Zone granitoid plutons, the results of this study suggest that the chemical diversity within the parental magmas of the granitoid plutons reflects the chemical variation of basaltic sources (i.e., across-arc chemical variation in the Izu-Bonin arc), as well as a variable contribution of the metasedimentary component in the lower crustal source regions. In addition, the petrogenetic models of the Izu Collision Zone granitoid plutons collectively suggest that the contribution of the metasedimentary component is required to produce granitoid magma with compositions comparable to the average upper continental crust. The Izu Collision Zone plutons provide an exceptional example of the transformation of a juvenile oceanic arc into mature continental crust.

DOI： 10.1007/s00410-011-0689-1

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：ELSEVIER SCIENCE BV  

The Fosdick migmatite-granite complex in West Antarctica records evidence for crustal melting during two periods of tectonism along the East Gondwana margin. Initial high-temperature metamorphism in the Devonian-Carboniferous (M-1) was broadly contemporaneous with emplacement of calc-alkaline arc magmas during Pacific-style accretionary margin convergence. This event involved metamorphism of arc plutonic rocks soon after their emplacement and partial melting and migmatization of host metasedimentary rocks. Preservation of M-1 garnet-bearing assemblages and mineral equilibria modeling of the metasedimentary rock and calc-alkaline plutonic rock protolith compositions regionally exposed constrain conditions of M-1 metamorphism to 820-870 degrees C and 7.5-11.5 kbar. A second anatectic event during the Cretaceous (M-2) resulted in metamorphism of plutonic rocks and partial melting of fertile metasedimentary rocks that had remained at a high enough structural level to have been subsolidus during the first anatectic event, and a metamorphic overprint on now residual paragneisses characterized by the growth of M-2 cordierite after garnet, and after biotite + sillimanite. Mineral equilibria modeling of para- and orthogneiss compositions in the Fosdick migmatite-granite complex constrain conditions of M-2 metamorphism to 830-870 degrees C and 6-7.5 kbar.
We use the results of mineral equilibria modeling to assess the constituents of the Fosdick migmatite-granite complex as melt sources and as domains of melt transfer and melt accumulation during the two anatectic events. Modeling the range of metasedimentary rock protolith compositions shows that similar to 4-25 vol.% melt was produced at the conditions of M-1 metamorphism, although most compositions would have been fertile enough to reach the melt connectivity transition (similar to 7 vol.%) leading to the development of a melt extraction pathway and subsequent melt loss. The preservation of peak-M-1 assemblages in the paragneiss is consistent with melt loss, and modeling based on a representative protolith composition indicates that a minimum of 70% of the total melt produced must have been extracted from the metasedimentary rock source. The intrusive plutonic rocks produce similar to 2-3 vol.% melt during the M-1 event. Although the plutonic rocks were not a significant melt source at the level exposed, granites derived from these rocks but sourced at a deeper crustal level accumulated within the Fosdick migmatite-granite complex during the M-1 event.
The elevated geotherms in a magmatic arc environment allow the possibility that higher crustal levels in the Fosdick migmatite-granite complex remained subsolid us during the M-1 event, and could be fertile sources during the M-2 event. At peak M-2 conditions, these fertile metasedimentary rocks would produce similar to 5-30 vol.% melt, whereas the plutonic rocks were not likely a significant source of melt at this crustal depth. The residual paragneisses that underwent melting and melt loss during the M-1 event are estimated to produce similar to 12 vol.% additional melt during M-2. The mechanical anisotropy created by the residual gneisses likely produced a gradient in melt pressure. This gradient, together with shallow fabrics in the hosting gneisses, could have acted to focus M-2 melts derived from the fertile metasedimentary rocks into a horizontally-sheeted leucogranite complex. The accumulation of these melts would have lead to pronounced weakening of the crust, facilitating the exhumation of the Fosdick migmatite-granite complex during the transition from regional shortening during M-2 to regional extension at ca. 100 Ma. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.lithos.2009.09.004

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

The similar to 50 Myr old Izu-Bonin-Mariana (IBM) arc consists mostly of Oligocene middle and lower crust that underlies the upper crust; these units are in turn covered by Quaternary volcanic rocks. Seismic imaging, forearc geology, Ocean Drilling Program drilling and magnetic anomalies suggest that most IBM arc crust was created in Eocene-Oligocene times. However, remnants of this old crust have never been found at the northern end of the arc, where it is colliding with the Honshu arc (Izu collision zone). Two batholiths in this collision zone (the Tanzawa tonalites and the Kofu Granitic Complex) were emplaced during the Miocene (4-17 Ma). Major elements, Zr/Y, rare earth element ratios and normalized abundance patterns, and Sr-Nd isotopic data indicate that these plutonic bodies are compositionally similar to the Oligocene IBM volcanic rocks, and that they are dissimilar to the Miocene, Pliocene and Quaternary IBM lavas and volcaniclastic rocks. We suggest that the Miocene plutonic rocks in the Izu collision zone were derived from partially melted Oligocene middle crust. A model is proposed in which IBM arc middle crust in the collision zone was partially melted during the collision and then intruded into the overlying upper crust of the Honshu and IBM arcs. This resulted in the complete loss of chronological information related to their original source.

DOI： 10.1093/petrology/egq002

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

Production of granite in the middle to lower crust and emplacement into the middle to upper crust at convergent plate margins is the dominant mechanism of crustal differentiation. The Fosdick Mountains of West Antarctica host migmatitic paragneisses and orthogneisses corresponding to the middle to lower crust and granites emplaced as dikes, sills and small plutons, which record processes of intracrustal differentiation along the East Gondwana margin. U-Pb chronology on magmatic zircon from granites reveals emplacement at c. 358-336 Ma and c. 115-98 Ma, consistent with a polyphase tectonic evolution of the region during Devonian-Carboniferous continental arc activity and Cretaceous continental rifting. The gneisses and granites exposed in the Fosdick migmatite-granite complex were derived from Early Paleozoic quartzose turbidites of the Swanson Formation and Ford Granodiorite suite calc-alkaline plutonic rocks, both of which are widely distributed outside the Fosdick Mountains and have affinity with rock elsewhere in East Gondwana. Granites of both Carboniferous and Cretaceous age have distinct chemical signatures that reflect different melting reactions and accessory phase behavior in contrasting sources. Based on whole-rock major and trace element geochemistry and Sr-Nd isotope compositions, Carboniferous granites with low Rb/Sr are interpreted to be products of melting of the Ford Granodiorite suite. Extant mineral equilibria modeling indicates that the Ford Granodiorite suite compositions produce melt volumes &gt; 10 vol. % at temperatures above biotite stability, involving the breakdown of hornblende + plagioclase, consistent with the high CaO and Na2O contents in the low Rb/Sr granites. The Carboniferous low Rb/Sr granites show a sequence from near-melt compositions to compositions with increasing amounts of early crystallized biotite and plagioclase and evidence for apatite dissolution in the source. Carboniferous granites derived from the Swanson Formation are scarce, suggesting that the significant quantities of melt produced from the now residual paragneisses were emplaced at shallower crustal levels than are now exposed. The Cretaceous granites are divided into two distinct groups. An older group of granites (c. 115-110 Ma) has compositions consistent with a dominant Ford Granodiorite source, and characteristics that indicate that they may be less evolved equivalents of the regionally exposed Byrd Coast Granite suite at higher crustal levels. The younger group of granites (c. 109-102 Ma) has distinct light rare earth element depleted signatures. The chemical and isotopic data suggest that these granites were derived from partial melting of both fertile and residual Swanson Formation and had low water contents, indicating that the source rocks may have been dehydrated prior to anatexis as the Byrd Coast Granite suite magmas were transferring through and accumulating at higher crustal levels. The Cretaceous granites derived from the Swanson Formation make up a prominent horizontally sheeted leucogranite complex. The accumulation of these melts probably facilitated melt-induced weakening of the crust during a well-documented transition from regional shortening to regional extension, the formation of a detachment structure, and rapid exhumation of the Fosdick migmatite-granite complex. These multiple episodes of melting along the East Gondwana margin resulted in initial stabilization of the continental crust in the Carboniferous and further intracrustal differentiation in the Cretaceous.

DOI： 10.1093/petrology/egp093

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：OXFORD UNIV PRESS  

The Miocene Kofu Granitic Complex (KGC) occurs in the Izu Collision Zone where the Izu-Bonin-Mariana (IBM) arc has been colliding with the Honshu arc since the middle Miocene. The KGC includes rocks ranging in compositions from biotite- bearing granite (the Shosenkyo and Mizugaki plutons), and hornblende-biotite-bearing granodiorite, tonalite, quartz-diorite, and granite ( the Shiodaira, Sanpo, Hirose and Sasago plutons), to hornblende-bearing tonalite and trondhjemite ( the Ashigawa-Tonogi pluton), indicating that it was constructed from multiple intrusions of magma with different bulk chemistry. The Sr-isotopic compositions corrected to sensitive high-resolution ion microprobe ( SHRIMP) zircon ages (SrI) suggest that the primary magmas of each pluton were formed by anatexis of mixed lower crustal sources involving both juvenile basalt of the IBM arc and Shimanto sedimentary rocks of the Honshu arc. After the primary magmas had formed, the individual plutons evolved by crystal fractionation processes without significant crustal assimilation or additional mantle contribution. SHRIMP zircon U-Pb ages in the KGC range from 16.8 to 10.6Ma and overlap the resumption of magmatic activity in the IBM and Honshu arcs at c. 17 Ma and the onset of IBM arc-Honshu arc collision at c. 15 Ma. The age of the granite plutons is closely related to the episodic activity of arc magmatism and distinct granitic magma batches could be formed by lower crustal anatexis induced by intrusion of under-plated mantle-derived arc magmas. Based on pressures determined with the Al-in-hornblende geobarometer, the KGC magmas intruded into the middle crust. Thus, the KGC could represent an example of the middle-crust layer indicated throughout the IBM arc by 6.0-6.5 km/s seismic velocities. This granitic middle-crust layer acted buoyantly during the IBM arc-Honshu arc collision, leading to accretion of buoyant IBM arc middle crust to the Honshu arc.

DOI： 10.1093/petrology/egm037

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.1093/petrology/egl055

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本古生物学会  

DOI： 10.14825/kaseki.78.0_59

CiNii Books

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記述言語：日本語   掲載種別：研究論文（学術雑誌）   出版者・発行元：日本古生物学会  

DOI： 10.14825/kaseki.78.0_1

CiNii Books

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：JAPAN ASSOC MINERALOGICAL SCIENCES  

The Ashigawa and the Tonogi intrusions comprise the southern part of the Miocene Kofu Granitic Complex (KGC), which is the largest pluton exposed in the Izu collision zone. The Ashigawa intrusion mainly consists of tonalite and subordinate amounts of trondhjemite, and the Tonogi intrusion is predominantly composed of tonalite. The rocks in both intrusions are classified as M-type granite. These are characterized by relatively low K2O (&lt;1.9 wt.%) and Rb (&lt;48 ppm) and LREE enriched chondrite normalized REE patterns with a marked negative Eu anomaly. Compared to the Tanzawa tonalites distributed in the south of the KGC, the Ashigawa and Tonogi granitic rocks have higher LILE, REE and Sr-isotope compositions at a given whole rock SiO2 content. Although the Ashigawa intrusion has distinctly different petrographical and geochemical characteristics from the Tonogi intrusion, both intrusions exhibit nearly identical Sr-isotopic composition (0.7037-0.7043 at 13Ma) and well-defined variation in whole rock compositions, suggesting that they are comagmatic. The crystal fractionation modeling involving removals of amphibole, plagioclase and magnetite from a tonalitic parental magma composition well represents the major and trace element variation of the Ashigawa and Tonogi granitic rocks. The Rayleigh fractionation modeling for whole rock REE abundance is also in a good agreement with the observed whole rock data. Mass balance modeling suggests that the proposed tonalitic parental magma can be derived by similar to 40 % melting of hydrous basalt compositionally similar to the basalt occurring in the rift basin of northern Izu-Bonin arc. Anatexis of hydrous basaltic lower crust of the northern Izu-Bonin arc is a likely process for the formation of Ashigawa-Tonogi parental magma.

DOI： 10.2465/jmps.99.104

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記述言語：英語   掲載種別：研究論文（大学，研究機関等紀要）  

Preliminary petrological study was carried out for the Rustenburg Layered Suite in the eastern Bushveld Complex. The Rustenburg Layered Suite consists of the Marginal Zone, Lower Zone, Critical Zone, Main Zone and Upper Zone. The mineral texture and chemical compositional variations were examined from the Lower to the Upper Zone. Although the number of sample is small, the crystallization sequence and presence of two types of magma can be recognized from the following mineral textures and compositions : (1) Plagioclase occurs as a post-cumulus phase in rocks from the Lower Zone to lower subzone in the Critical Zone, whereas it occurs as a cumulus phase in rocks from the upper subzone in the Critical Zone, Main Zone and Upper Zone. (2) A distinctive compositional difference of plagioclase and orthopyroxene can be seen between the lower subzone and upper subzone in the Critical Zone. In the lower subzone in the Critical Zone, post-cumulus plagioclase has low An within the range of 74-50,whereas the upper subzone has An=83-63. This result is consistent with previous work. In addition, Norite in the upper subzone in the Critical Zone has orthopyroxene-developed (Opx-rich) and clinopyroxene-developed (Cpx-rich) domains. In the Opx-rich domain, high-X_<Mg> orthopyroxene and low-An plagioclase inclusions can be seen. On the other hand, both low-X_<Mg> orthopyroxene inclusions and high-An plagioclase inclusions are observed in the Cpx-rich domain. These textural and compositional relationships suggest possible magma mixing on the thin section scale.

CiNii Books

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