Secular variations of carbon and helium isotopes at Izu-Oshima Volcano, Japan   总被引：1，自引：0，他引：1  

Yuji Sano  Toshitaka Gamo  Kenji Notsu  Hiroshi Wakita 《Journal of Volcanology and Geothermal Research》1995,64(1-2)

Secular variations in ¹³C/¹²C ratios and chemical compositions of gas samples from October 1986 to July 1992 are reported from a 92–95 °C steam well located about 3 km north of Mt. Mihara, an active volcano on Izu-Oshima Island, Japan. The δ¹³C value steeply increased from −2.97‰ (relative to PDB carbonate) in December 1986 to −1.15‰ in March 1988 and then gradually decreased to −1.75‰ in July 1992. Over the same period, the CO₂ content changed similarly with time, even though the experimental error is relatively large. These variations are consistent with helium isotope changes. Initially rapid and then slow enhancements of ³He/⁴He ratio, δ¹³C value and CO₂ content are invoked by violent eruptions of Izu-Oshima volcano from 15 November to 18 December 1986. After the eruptive activity, depletion of magmatic gas emission and subsequent mixing with crustal fluids in the hydrothermal system may produce the gradual decreases of ³He/⁴He ratio, δ¹³C value and CO₂ content. Taking into account the rates of these decreases, we suggest that helium and carbon isotope ratios will return to the situation of before the magmatic eruption within 15 years.  相似文献   

Helium isotopic ratio in Vulcano island fumaroles: temporal variations in shallow level mixing and deep magmatic supply     

Dario Tedesco  Gerarda Miele  Yuji Sano  Jean Paul Toutain 《Journal of Volcanology and Geothermal Research》1995,64(1-2)

Intensive gas emanations occur throughout the island of Vulcano, Italy. Sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source, “crustal” waters. This mixing differs between the beach and crater fumaroles. Gas samples from three crater fumaroles with temperatures ranging from 200 to 550 ° C were sampled repeatedly over a one year period. During the same interval of time, six samples from submarine and subaerial beach fumaroles and water well gases were also sampled. Gases from one crater fumarole (F5) showed variations of (³He/⁴He)_fumarole to (³He/⁴He)_air between 5 and 6 correlated with variations of several chemical species. High ³He/⁴He ratios for the beach fluids, similar to those of crater fluids, suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs. However, temporal changes clearly indicate variable degrees of fluids mixing, and the geographic distribution of the ³He/⁴He ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs, independently related to crater and to beach fumaroles.  相似文献   

Production de²⁶Al dans Fe et Si par protons de 0.6 et 24 GeV     

S. Regnier  M. Lagarde  G.N. Simonoff  Y. Yokoyama 《Earth and Planetary Science Letters》1973,18(1):9-12

A total of 139 breccia and crystalline rock fragments in the size range 2–4 mm from four Apollo 15 soil samples have been examined. Two of the sample stations are on the mare surface (4 and 9A) and two are on the Apennine Front (2 and 6). Approximately 90% of the fragments from the Apennine Front are brown-glass “soil” breccias, but those from the mare surface are 60%–70% basalt. Several textural varieties of mare basalt have been recognized, but within experimental error there is no difference in their⁴⁰Ar-³⁹Ar ages. The major non-mare (Pre-Imbrian) crystalline rock types in the Apennine Front regolith are KREEP basalt, anorthositic rocks, recrystallized norite (including anorthositic norite) and recrystallized polymict breccias; however, such crystalline rocks are rare in the samples examined. Apparently, the near surface Imbrium ejecta below the regolith has not been thermally recrystallized, and probably there are no outcrops of crystalline rocks upslope from the sample stations.  相似文献   

Space—time correlations between inland earthquakes in central Japan and great offshore earthquakes along the Nankai trough: Implication for destructive earthquake prediction     

Yuji Kanaori  Shin-ichi Kawakami  Kenji Yairi 《Engineering Geology》1993,33(4):289-303

Based on the tectonic framework of central Japan, including the surrounding submarine areas, the space-time relationship between destructive inland earthquakes of magnitudesM 6.4 or greater and great offshore earthquakes along the Nankai trough was examined. From east to west, four tectonic lines are defined as lines linking active faults: the Itoigawa-Shizuoka tectonic line (ISTL), the Tsurugawan-Isewan tectonic line (TITL), the Hanaore-Kongo fault line (HKFL), and the Arima-Takatsuki tectonic line (ATTL). The TITL divides central Japan into the Chubu and Kinki districts, and probably extends southward to the Nankai trough. The Chubu district is subdivided into four blocks by boundary lines linking NW-SE trending active faults having left-lateral strike slip. In the Kinki district, N-S trending, active reverse, steep-dip faults are dominant in the triangular region north of the Median Tectonic line, between the TITL and HKFL, forming a basin-and-range province.

Starting from 1586 A.D., a seismic space-time sequence of high seismic activity in the Chubu district in which earthquake occurrence migrates from the eastern to western tectonic lines of central Japan was identified. The sequence also revealed that inland earthquakes preceded great offshore earthquakes which occurred along the Nankai trough. It was also found that a destructive earthquake tends to occur on the HKFL within 30 years after the occurrence on the TITL, and that the western Nankai trough generated great earthquakes ofM≥7.0 at intervals ranging from 8 to 49 years after the HKFL earthquakes. If the eastern Nankai trough is coupled with the western Nankai trough, a forthcoming greater earthquake measuringM 8.5 may be expected. Since such great earthquakes are always accompanied by large tsunamis, much attention should be focussed on possible tsunami disasters along the Pacific coast of central Japan.

Based on its tectonic structure, a tectonic model of central Japan is proposed. The seismic space-time sequence, which attempts to explain the cause of the sequential earthquake generation, is also discussed.  相似文献   

Nikubuchi peridotite body in the sanbagawa metamorphic belt; thermal history of the ‘Al-pyroxene-rich suite’ peridotite body in high pressure metamorphic terrain     

Kazumi Yokoyama 《Contributions to Mineralogy and Petrology》1980,75(1):1-13

Oceanic tholeiite glass has been reacted with natural seawater at 25°–500° C, 1 kbar, with both low (5) and high (50) water/rock mass ratios. Initial experiments were conducted at constant temperatures between 100° C and 500° C (100° intervals) in order to characterize the mineralogy and chemical exchange trends for both water/rock ratios. However, the primary purpose of this investigation was to study the chemical and mineralogical changes that may take place as reacted seawater cools as it traverses a temperature gradient before exiting onto the seafloor, as may happen in some submarine hydrothermal systems. Consequently, a series of cooling or temperature gradient experiments were performed in which seawater that had reacted with basalt at 500° C was cooled to 25° C in a step-wise fashion; mineralogy and fluid chemistry were determined at 100 degree intervals during cooling.For all of the experiments, the elemental exchange trends were the same. With respect to the initial sea-water, Fe, Mn, Ca, Si and H⁺ increased while Na and Mg decreased. However, the extent of the exchange depended heavily on the temperature and water/rock ratio. During cooling, fluid compositions in the temperature gradient runs generally approached those of the constant temperature experiments. Even though fluid compositions were very similar at 500° C for both water/rock ratios, the high water/rock ratio systems were more efficient in leaching transition metals from the rock and maintained substantial concentrations in solution during cooling, even to temperatures as low as 25° C. The Fe/Mn ratio in the fluid, however, was quite different for the two water/rock ratios; consequently, the effective water/rock ratio appears to be one parameter that can control the Fe/Mn ratio in exiting hydrothermal fluids and may influence the Fe/Mn ratio in metal-rich sediments.Alteration minerals produced in these seawater/ basalt experiments are very similar to those found at submarine springs on the East Pacific Rise, 21° N. Iron sulfides, pyrite and pyrrhotite, precipitated during cooling for both water/rock ratios, demonstrating the ore-forming potential of submarine hydrothermal systems.  相似文献   

Paleomagnetic stratigraphy and biostratigraphy of the Plio-Pleistocene in the Kinki district, Japan     

Kazuaki Maenaka  Takuo Yokoyama  Shiro Ishida 《Quaternary Research》1977,7(3):341-362

The magnetostratigraphic subdivision of the Plio-Pleistocene series in the Kinki district around Osaka in southwest Japan, based on NRM measurements of volcanic ash beds, is correlated with biostratigraphic and paleoclimatic marker beds as well as past sea level oscillations. At least 10 high sea level stands occurred in the study area between about 1.5 and 0.27 million years ago, all associated with relative warming. A significant change in the composition of flora, from Metasequoia to Fagus dominated assemblages, was observed around the Jaramillo event.  相似文献   

Determination of210Pb in volcanic gases and210Pb,226Ra,238U in lavas by non-destructive gamma-ray spectrometry     

Y. Yokoyama  H. Van Nguyen  G. Lambert 《Bulletin of Volcanology》1982,45(3):265-266

  相似文献   

Terrestrial heat flow around the aseismic front of the Japanese Island Arc     

Yuji Nakamura  Hiroshi Wakita 《Tectonophysics》1982,81(1-2)

Very few data on heat flow are available in the area around the aseismic front of the Japanese Islands. In order to remedy this situation, measurements of the terrestrial heat flow were made at three locations in the eastern part of Fukushima Prefecture, northeastern Honshu, Japan. The observed values of heat flow were 37 mW/m² (0.88 μcal/cm²·s) at Soma, 52 mW/m² (1.25 μcal/cm²·s) at Kashima and 19 mW/m² (0.46 μcal/cm²·s) at Naraha, respectively. These data partially fill the gaps in the terrestrial heat flow data on land in northeastern Honshu, Japan. These values are considerably lower than the average heat flow over the world, but agree well with the previous estimation for the area.  相似文献   

A gravity survey on Volcano Huzi,Japan by means of a Worden gravimeter     

Yokoyama  Izumi  Tajima  Hirokazu 《Pure and Applied Geophysics》1960,45(1):1-12

Summary Observations and reductions of the gravimeter survey on Volcano Huzi are fully described. The survey was accompanied by various inevitable difficulties but the accuracy of calculating the Bouguer anomalies is kept high enough to bear volcanological discussion. The results are rather suggestive to the theory of caldera-formation. Comparison with the gravity anomaly on the volcanic islands in the middle of the ocean is also made.  相似文献   

Crustal structures that produce eruptions of welded tuff and formation of calderas     

I. Yokoyama 《Bulletin of Volcanology》1966,29(1):51-60

Accumulation of a huge amount of welded tuff and subsequent formation of calderas are typical examples of volcanisms on a large scale. Crustal structures which are related to the phenomena may be a key for the study of volcanisms on the earth. In Japan there are some 10 calderas of low gravity anomaly type, large and small in diameter, and accordingly in volume of their ejecta, welded tuff. The low gravity anomalies are very characteristic inside the calderas and just concentric with their rims, and are due to mass deficiency caused by eruptions of a huge amount of ejecta. The author (1957), hitherto, has clarified the subterranean structures resulting from the caldera formations by a gravimetric method. In this paper, the author describes the crustal structures beneath Sikotu Caldera in Hokkaido, Japan, deduced from the gravimetric, geomagnetic, seismic and geologic surveys. And referring several examples of the subterranean structures of the other calderas in Japan, the author wishes to discuss the crustal structures that would produce the caldera formations.  相似文献