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   

Late Paleozoic adakites and Nb-enriched basalts from northern Xinjiang, northwest China: Evidence for the southward subduction of the Paleo-Asian Oceanic Plate   总被引：9，自引：0，他引：9  

Haixiang  Zhang  Hecai  Niu  Hiroaki  Sato  Xueyuan  Yu  Qiang  Shan  Boyou  Zhang  Jun'ichi  Ito  Takashi  Nagao 《Island Arc》2005,14(1):55-68

Abstract   Volcanic rocks consisting of adakite and Nb-enriched basalt are found in the early Devonian Tuoranggekuduke Group in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, northwest China. The geochemical characteristics of the andesitic and dacitic rocks in this area resemble that of adakites. The relatively high Al₂O₃, Na₂O and MgO content and Mg^♯ values indicate that the adakites were generated in relation to oceanic slab subduction rather than the partial melting of basaltic crust. A slightly higher SrI and a lower ɛ _Nd( t  = 375 Ma) compared to adakites of mid-oceanic ridge basalt (MORB) imply that slab sediments were incorporated into these adakites during slab melting. The Nb-enriched basalt lavas, which are intercalated in adakite lava suite, are silica saturated and are distinguished from the typical arc basalts by their higher Nb and Ti content (high field strength element enrichment). They are derived from the partial melting of the slab melt-metasomatized mantle wedge peridotite. Apparently, positive Sr anomalies and a slightly higher heavy rare earth element content in these adakites compared to their Cenozoic counterparts indicate that the geothermal gradient in the Paleo-Asian Oceanic subduction zone and the depth of the Paleo-Asian Oceanic slab melting are between those of their Archean and Cenozoic counterparts. The distribution of the adakites and Nb-enriched basalts in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, indicates that the Paleo-Asian Oceanic Plate subducted southward beneath the Kazakhstan-Junggar Plate in the early Devonian period.  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   

Behavior of gases in the Nojima Fault Zone revealed from the chemical composition and carbon isotope ratio of gases extracted from DPRI 1800 m drill core   总被引：2，自引：0，他引：2  

Takashi Arai  Tamotsu Okusawa  Hiroaki Tsukahara 《Island Arc》2001,10(3-4):430-438

  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

  相似文献   

Oscillatory orbits in the planar three‐body problem with equal masses     

Kiyotaka Tanikawa  Hiroaki Umehara 《Celestial Mechanics and Dynamical Astronomy》1998,70(3):167-180

In the free‐fall three‐body problem, distributions of escape, binary, and triple collision orbits are obtained. Interpretation of the results leads us to the existence of oscillatory orbits in the planar three‐body problem with equal masses. A scenario to prove their existence is described. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Responses of diatoms to iron-enrichment (SEEDS) in the western subarctic Pacific, temporal and spatial comparisons     

Atsushi Tsuda  Hiroshi Kiyosawa  Akira Kuwata  Mamiko Mochizuki  Naonobu Shiga  Hiroaki Saito  Sanae Chiba  Keiri Imai  Jun Nishioka  Tsuneo Ono 《Progress in Oceanography》2005,64(2-4):189

Phytoplankton species composition was analyzed inside and outside of the iron-enriched patch during the SEEDS experiment. Before the iron-enrichment, the phytoplankton community consisted of similar proportions of pico-, nano- and micro-sized phytoplankton, and the micro-phytoplankton was dominated by the pennate diatom Pseudo-nitzschia turgidula. Although all the diatoms, except the nano-sized Fragilariopsis sp., increased during the two weeks of the observation period, the flora in the patch dramatically changed with the increase of phytoplankton biomass to a centric diatom-dominated community. Neritic diatoms, especially Chaetoceros debilis, showed higher growth rates than other diatoms, without any delay in the initiation of growth after the enrichment, and accounted for 90% of the micro-phytoplankton after day 9. In contrast, the oceanic diatoms showed distinct delays in the initiation of growth. We conclude that the responses of the diatoms to the manipulation of iron concentration were different by species, and the fast and intensive response of the phytoplankton to iron-enrichment resulted from the presence of a small amount of neritic diatoms at the study site. The important factors that determine the dominant species in the bloom are the potential growth rates under an iron-replete condition and the growth lag. Abundant species in the patch are widely distributed in the North Pacific and their relative contributions in the Oyashio area and at Stn KNOT are high from spring to summer. However, a characteristic difference of species composition between the SEEDS bloom and natural blooms was the lack of Thalassiosira and Coscinodiscus species in the patch, which usually account for a major part of the phytoplankton community under blooming conditions in the western North Pacific.  相似文献   

Three-year investigations into sperm whale-fall ecosystems in Japan   总被引：2，自引：0，他引：2  

Yoshihiro Fujiwara  Masaru Kawato  Tomoko Yamamoto  Toshiro Yamanaka  Waka Sato-Okoshi  Chikayo Noda  Shinji Tsuchida  Tomoyuki Komai  Sherine Sonia Cubelio  Takenori Sasaki  Karen Jacobsen  Kaoru Kubokawa  Katsunori Fujikura  Tadashi Maruyama  Yasuo Furushima  Kenji Okoshi  Hiroshi Miyake  Masayuki Miyazaki  Yuichi Nogi  Akiko Yatabe  & Takashi Okutani 《Marine Ecology》2007,28(1):219-232

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.  相似文献   

Effect of iron enrichment on the dynamics of transparent exopolymer particles in the western subarctic Pacific   总被引：1，自引：0，他引：1  

Neelam Ramaiah  Shigenobu Takeda  Ken Furuya  Takeshi Yoshimura  Jun Nishioka  Tatsuo Aono  Yukihiro Nojiri  Keiri Imai  Isao Kudo  Hiroaki Saito  Atsushi Tsuda 《Progress in Oceanography》2005,64(2-4):253

Dynamics of transparent exopolymer particles (TEP) was studied during the first in situ iron-enrichment experiment conducted in the western subarctic Pacific in July–August 2001, with the goal of evaluating the contribution of TEP to vertical flux as a result of increased primary production following iron enrichment in open ocean ecosystems. Subsequent to the enhancement of phytoplankton production, we observed increase in TEP concentration in the surface layer and sedimentation of organic matter beneath it. Vertical profiles of TEP, chlorophyll a (Chl a) and particulate organic carbon (POC) were obtained from six depths between 5 and 70 m, from a station each located inside and outside the enriched patch. TEP and total mass flux were estimated from the floating sediment traps deployed at 200 m depth. Chl a and TEP concentrations outside the patch varied from 0.2 to 1.9 μg L⁻¹ and 40–60 μg XG equiv. L⁻¹, respectively. Inside the patch, Chl a increased drastically from day 7 reaching the peak of 19.2 μg L⁻¹ on day 13, which coincided with the TEP peak of 189 μg XG equiv. L⁻¹. TEP flux in the sediment trap increased from 41 to 88 mg XG equiv. m⁻² d⁻¹, with 8–14% contribution of TEP to total mass flux. This forms the basic data set on ambient concentrations of TEP in the western subarctic Pacific, and evaluation of the effect of iron enrichment on TEP.  相似文献   

Primary productivity in the offshore Oyashio in the spring and summer 1990     

Akihiro Shiomoto  Katsuyuki Sasaki  Toru Shimoda  Satsuki Matsumura 《Journal of Oceanography》1994,50(2):209-222

Primary productivity was measured byin situ method using¹³C in the offshore Oyashio region in the spring (May) and summer (September) of 1990. Most of the values were within the range of 0.1 to 4 gC 1^–1 h^–1 although a very large value, 7.96 gC l^–1 h^–1, was observed in summer. Most daily primary production fell within the range of 372 to 633 mgC m^–2 d^–1 although a very large value, 2,109 mgC m^–2 d^–1, was observed around the frontal area in summer. Chlorophylla (Chl.a) exceeded 1 g l^–1 in many cases, and the maximum was 4.61 g l^–1 in spring and 7.53 g l^–1 in summer. Most primary productivity per unit Chl.a (photosynthetic assimilation ratio) was within the range of 0.1 to 3 gC gChl.a ^–1 h^–1 although higher values, 3–6 gC gChl.a ^–1 h^–1, were observed where small-size phytoplanktons (<2 m) were dominant. These results were compared with results obtained until now in the Oyashio region. The values beyond the range obtained so far in the offshore region were also observed in this study. Furthermore, it was pointed out that the size composition of phytoplankton community has significant influence on the results of Chl.a and photosynthetic assimilation ratio in the Oyashio region.  相似文献