Petrological variation of large-volume felsic magmas from Hakkoda-Towada caldera cluster: Implications for the origin of high-K felsic magmas in the Northeast Japan Arc     

Takashi  Kudo  Minoru  Sasaki  Yoshihiro  Uchiyama  Akifumi  Nozawa  Hisashi  Sasaki  Takeshi  Tokizawa  Shinji  Takarada 《Island Arc》2007,16(1):133-155

Abstract The Hakkoda‐Towada caldera cluster (HTCC) is a typical Late Cenozoic caldera cluster located in the northern part of the Northeast Japan Arc. The HTCC consists of five caldera volcanoes, active between 3.5 Ma and present time. The felsic magmas can be classified into high‐K (HK‐) type and medium‐ to low‐K (MLK‐) type based on their whole‐rock chemistry. The HK‐type magmas are characterized by higher K₂O and Rb contents and higher ⁸⁷Sr/⁸⁶Sr ratios than MLK‐type magmas. Both magmas cannot be derived from fractional crystallization of any basaltic magma in the HTCC. Assimilation‐fractional crystallization model calculations show that crustal assimilation is necessary for producing the felsic magmas, and HK‐type magmas are produced by higher degree of crustal assimilation with fractional crystallization than MLK‐type magmas. Although MLK‐type magmas were erupted throughout HTCC activity, HK‐type magmas were erupted only during the initial stage. The temporal variations of magma types suggest the large contribution of crustal components in the initial stage. A major volcanic hiatus of 3 my before the HTCC activity suggests a relatively cold crust in the initial stage. The cold crust probably promoted crustal assimilation and fractional crystallization, and caused the initial generation of HK‐type magmas. Subsequently, the repeated supply of mantle‐derived magmas raised temperature in the crust and formed relatively stable magma pathways. Such a later system produced MLK‐type magmas with lesser crustal components. The MLK‐type magmas are common and HK‐type magmas are exceptional during the Pliocene–Quaternary volcanism in the Northeast Japan Arc. This fact suggests that exceptional conditions are necessary for the production of HK‐type magmas. A relatively cold crust caused by a long volcanic hiatus (several million years) is considered as one of the probable conditions. Intensive crustal assimilation and fractional crystallization promoted by the cold crust may be necessary for the generation of highly evolved HK‐type felsic magmas.  相似文献   

Hydrothermal Alteration and Mineralization of Middle Jurassic Dexing Porphyry Cu-Mo Deposit, Southeast China   总被引：9，自引：0，他引：9  

Xiaofeng Li  Munetake Sasaki 《Resource Geology》2007,57(4):409-426

The Dexing deposit is located in a NE‐trending magmatic belt along the southeastern margin of the Yangtze Craton. It is the largest porphyry copper deposit in China, consisting of three porphyry copper orebodies of Zhushahong, Tongchang and Fujiawu from northwest to southeast. It contains 1168 Mt of ores with 0.5% Cu and 0.01% Mo. The Dexing deposit is hosted by Middle Jurassic granodiorite porphyries and pelitic schist of Proterozoic age. The Tongchang granodiorite porphyry has a medium K cal‐alkaline series, with medium K₂O content (1.94–2.07 wt%), and low K₂O/(Na₂O + K₂O) (0.33–0.84) ratios. They have high large‐ion lithophile elements, high light rare‐earth elements, and low high‐field‐strength elements. The hydrothermal alteration at Tongchang is divided into four alteration mineral assemblages and related vein systems. They are early K‐feldspar alteration and A vein; transitional (chlorite + illite) alteration and B vein; late phyllic (quartz + muscovite) alteration and D vein; and latest carbonate, sulfate and oxide alteration and hematite veins. Primary fluid inclusions in quartz from phyllic alteration assemblage include liquid‐rich (type 1), vapor‐rich (type 2) and halite‐bearing ones (type 3). These provide trapping pressures of 20–400 ´ 10⁵ Pa of fluids responsible for the formation of D veins. Igneous biotite from least altered granochiorite porphyry and hydrothermal muscovite in mineralized granodiorite porphyry possess δ¹⁸O and δD values of 4.6‰ and ?87‰ for biotite and 7.1–8.9‰, ?71 to ?73‰ for muscovite. Stable isotopic composition of the hydrothermal water suggests a magmatic origin. The carbon and oxygen isotope for hydrothermal calcite are ?4.8 to ?6.2‰ and 6.8–18.8‰, respectively. The δ³⁴S of pyrite in quartz vein ranges from ?0.1 to 3‰, whereas δ³⁴S for chalcopyrite in calcite veins ranges from 4 to 5‰. These are similar to the results of previous studies, and suggest a magmatic origin for sulfur. Results from alteration assemblages and vein system observation, as well as geochemical, fluid inclusion, stable isotope studies indicate that the involvement of hydrothermal fluids exsolved from a crystallizing melt are responsible for the formation of Tongchang porphyry Cu‐Mo orebodies in Dexing porphyry deposit.  相似文献   

Spectral observations of impact dark spots     

B. Suzuki  H. Kurihara  T. Sasaki  J. Watanabe 《Earth, Moon, and Planets》1994,66(1):19-27

We carried out a spectral observation of traces of the comet impacts within the wavelength region between 440 and 830 nm. Three dark spots of fragments K, E, and G impact sites were investigated. The spectrum of these dark spots shows no special emission or absorption lines in this observation. The global spectral feature resembles that of Jovian zone cloud rather than that of the belt. While the continuum reflectivity of the dark spots of K and E sites is less than 0.42 at 600 nm, that of the G site is 0.33. These values should be interpreted as an upper limits because of the influence of atmospheric seeing. The equivalent width of the absorption lines at the K sites is also derived. Both the continuum reflectivity and the equivalent width of the dark spots are smaller than those of any Jovian zonal cloud. This indicates that the dark spots are low-albedo cloud formed at the upper atmosphere.  相似文献   

Determination of Stress State from Focal Mechanisms of Microseismic Events Induced During Hydraulic Injection at the Hijiori Hot Dry Rock Site     

S. Sasaki  H. Kaieda 《Pure and Applied Geophysics》2002,159(1-3):489-516

—?The stress state at the Hijiori hot dry rock site was estimated based on the inversion from focal mechanisms of microseismic events induced during hydraulic injection experiments. The best fit stress model obtained by inverting 58 focal mechanisms of seismic events simultaneously indicates that the maximum principal stress σ₁ is vertical, while the minimum principal stress σ₃ is horizontal and trends north-south. The average misfit between the stress model and all the data is 6.8°. The inversion results show that the average misfit is small enough to satisfy the assumption of homogeneity in the focal mechanism data and that the 95% confidence regions of σ₁ and σ₃ are well constrained, i.e., they do not overlap, suggesting that the inversion results are acceptable. The stress estimates obtained by the focal mechanism inversion essentially agree with other stress estimates previously obtained. It is therefore concluded that the focal mechanism inversion method provides a useful tool for estimating the stress state. The hypocentral distributions of microseismic events associated with the hydraulic fracturing experiments are distributed around the plane that spreads to almost east–west from the injection wells and declines to the north at a high angle. The vertical orientation and east–west strike of the seismic events are essentially coplanar with the caldera ring-fault structure in the southern portion of the Hijiori Caldera. This indicates that tensile fractures of intact rock were not being created, but pre-existing fractures were being re-opened and developed in the direction of the maximum horizontal principal stress, although microseismic events were caused by shear failures.  相似文献   

Plutonium diffusivity in compacted bentonite     

Kazuya Idemitsu  Katsuhiko Ishiguro  Yasuhisa Yusa  Noriaki Sasaki  Naomi Tsunoda 《Engineering Geology》1990,28(3-4):455-462

Measurements on plutonium diffusivity in water-saturated compacted bentonite were carried out. Representative specimens of sodium bentonite were taken from the Tsukinuno and Kuroishi mines situated in northeast Japan. Tsukinuno bentonite was divided into three types: raw type, purified Na-type, and H-type which was prepared by treating Na-type bentonite with hydrochloric acid. Kuroishi bentonite contained chlorite as impurity. H-type bentonite was used as reference for the convenience of profile measurement in bentonite, since plutonium diffusivity in H-type bentonite was considered to be larger than that in Na-type bentonite because of low pH and low swelling pressure of H-type bentonite.

Sampled bentonite was compacted into pellets of 20 mm in diameter and 20 mm in height. Bulk densities of these specimens were 1200–1800 kg/m³ for purified Na-type and H-type bentonite and 1600 kg/m³ for raw type bentonite.

Plutonium profiles obtained in H-type bentonite can be explained by diffusion equation with constant concentration source. Diffusivity ranges from 10^-13 to 10¹² m²/s for H-type and Kuroishi impure sodium bentonite. Diffusivity in both raw type and purified Tsukinuno bentonite was was estimated to less than 10^-14 M²/s. Diffusivity in H-type bentonite showed a tendency to decrease with increasing density. Influence of in bentonite was also studied. Quartz content up to 50% or hematite content up to 1% did not influence diffusivity significantly in H-type bentonite.

The chemical species of plutonium in pore water of Na-type and H-type were estimated Pu(OH)₃^-; and PuO₂^- , respectively.  相似文献   

Physical size of tsunamigenic earthquakes of the northwestern Pacific     

Katsuyuki Abe 《Physics of the Earth and Planetary Interiors》1981,27(3):194-205

The new scale M_t of tsunami magnitude is a reliable measure of the seismic moment of a tsunamigenic earthquake as well as the overall strength of a tsunami source. This M_t scale was originally defined by Abe (1979) in terms of maximum tsunami amplitudes at large distances from the source. A method is developed whereby it is possible to determine M_t at small distances on the basis of the regional tsunami data obtained at 30 tide stations in Japan. The relation between log H, maximum amplitude (m) and log Δ, a distance of not less than 100 km away from the source (km) is found to be linear, with a slope close to 1.0. Using three tsunamigenic earthquakes with known moment magnitudes M_w, for calibration, the relation, M_t = log H + log Δ + D, is obtained, where D is 5.80 for single-amplitude (crest or trough) data and 5.55 for double-amplitude (crest-to-trough) data. Using a number of tsunami amplitude data, M_t is assigned to 80 tsunamigenic earthquakes that occurred in the northwestern Pacific, mostly in Japan, during the period from 1894 to 1981. The M_t values are found to be essentially equivalent to M_w for 25 events with known M_w. The 1952 Kamchatka earthquake has the largest M_t, 9.0. Of all the 80 events listed, at least seven unusual earthquakes which generated disproportionately-large tsunamis for their surface-wave magnitude M_s are identified from the relation. From the viewpoint of tsunami hazard reduction, the present results provide a quantitative basis for predicting maximum tsunami amplitudes at a particular site.  相似文献   

Practical determination of mechanical design parameters of intact rock considering scale effect   总被引：4，自引：0，他引：4  

R. Yoshinaka  M. Osada  H. Park  T. Sasaki  K. Sasaki 《Engineering Geology》2008,96(3-4):173-186

As a rule, the change in mechanical properties of rock by specimen size is regarded as scale effect. A rock mass basically consists of two components: intact rock and discontinuities, each of which has different scale effects. In order to numerically analyze the behavior of discontinuous rock masses, sufficient mechanical properties must be determined not only for discontinuities but also for intact rock taking into consideration the different scale effects. This paper reviews the scale effect on strength and deformation characteristics of intact rock, and also discusses the possibility of using standard specimens to estimate strength and deformation characteristics of actual-scale rock. Finally, we propose an adequate method for the practical determination of mechanical design parameters based on the above discussions.  相似文献   

Immobilization of Se(VI) in mine drainage by permeable reactive barriers: column performance     

K. Sasaki  D.W. Blowes  C.J. Ptacek  W.D. Gould 《Applied Geochemistry》2008

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Hydrocarbons in surface sediments of harbor areas in a tropical region (Ceará state,northeast Brazil)     

Lucas Moreira Buruaem  Satie Taniguchi  Silvio Tarou Sasaki  Márcia Caruso Bícego  Leticia Veras Costa-Lotufo  Denis Moledo Souza Abessa 《Environmental Earth Sciences》2016,75(8):642

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Bio-Optical Properties of Seawater in the Western Subarctic Gyre and Alaskan Gyre in the Subarctic North Pacific and the Southern Bering Sea during the Summer of 1997   总被引：1，自引：0，他引：1  

Hiroaki Sasaki  Sei-Ichi Saitoh  Motoaki Kishino 《Journal of Oceanography》2001,57(3):275-284

Chlorophyll a concentrations (chla) and the absorption coefficients of total particulate matter [a _p()], phytoplankton [a _ph()], detritus [a _d()], and colored dissolved organic matter: CDOM [a _CDOM()] were measured in seawater samples collected in the subarctic North Pacific and the southern Bering Sea during the summer of 1997. We examined the specific spectral properties of absorption for each material, and compared the light fields in the Western subarctic Gyre (area WSG) with those in the Alaskan Gyre (area AG), and the southern Bering Sea (area SB). In the area WSG, the irradiance in the surface layer decreased markedly, indicating high absorption. In the area AG, the radiant energy penetrated deeply, and the chl a and absorption values were low throughout the water column. In the area SB, light absorption was high in the surface layer on the shelf edge and decreased with increasing depth; on the other hand, light absorption was low in the surface layer in the shelf area and increased with increasing depth.  相似文献