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1.
Noble gas concentrations and isotopic compositions have been measured in eight samples of pillow basalt glasses collected from seven different localities along 250 km of the Mariana Trough spreading and rifting axis. The samples have uniform and mid-ocean ridge basalt (MORB)-like 3 He/4 He values of 9–12 × 10–6 (6.4–8.6 times atmospheric) despite large variations in 4 He. Concentrations of the noble gases Ne, Ar, Kr, and Xe show much smaller variations between samples, but larger variations in isotopic compositions of Ne, Ar, and Xe. Excess radiogenic 21 Ne is observed in some samples. 40 Ar/36 Ar varies widely (atmospheric to 1880). Kr is atmospheric in composition for all samples. Some samples show a clear excess 129 Xe, which is a well-known MORB signature. Isotopic compositions of the heavier noble gases (Ar, Kr, and Xe) in some samples, however, show more atmospheric components. These data reflect the interaction of a MORB-like magma with an atmospheric component such as seawater or of a depleted mantle source with a water-rich component that was probably derived from the subducting slab. 相似文献
2.
Keika Horiguchi Sadato Ueki Yuji Sano Naoto Takahata Akira Hasegawa George Igarashi 《Island Arc》2010,19(1):60-70
In order to study the precise geographical distribution of helium isotope ratios in northeastern Japan and compare it with geophysical data, we collected 43 gas and water samples from hot and mineral springs in the region where the ratio had never been reported, and measured the 3 He/4 He and 4 He/20 Ne ratios of these samples. It was found that the 3 He/4 He ratios show clear contrasts between the forearc and the back-arc regions in the Tohoku district in northeastern Japan. In the forearc region, the ratios are smaller than 1 RA (1 RA = 1.4 × 10−6 ; RA means the 3 He/4 He ratio of the atmosphere). On the other hand, those along the volcanic front and in the back-arc region are apparently higher. Moreover, we found a variation in the 3 He/4 He ratios along the volcanic front. In Miyagi Prefecture (38–39°N), the ratios range from 2 to 5 RA . On the other hand, the ratios are less than 1 RA in and around the southern border between Iwate and Akita Prefectures (39–39.5°N). Comparing the distribution of helium isotope ratios to results of recent geophysical studies, we found that the features in geographical distribution of helium isotope ratios are similar to those of seismic low-velocity zone distributions and high Qp−1 distributions in the uppermost mantle. These observations strongly suggest that the helium isotope ratios reflect the distribution of melts in the uppermost mantle and are a useful tool for investigating the origin, behavior, and distribution of deep fluids and melts. 相似文献
3.
Abstract Isotopic compositions of He, Ne and Ar were measured on Plio–Quaternary alkaline basalts of Marib–Sirwah and Shuqra volcanic fields in Yemen, south-western Arabian Peninsula. Very high 3 He/4 He isotope ratios were found in olivine phenocrysts of some Quaternary alkaline basalts in both volcanic fields, located on the margin of the dispersed Afar mantle plume, compared with the Afar–Ethiopian province in the center of the mantle plume. This suggests that the Afar mantle plume source may consist of common component (C or focal zone (FOZO)) with variable primordial 3 He/4 He ratio rather than high μ mantle (HIMU) component. The three component mixing C as the Afar mantle plume, depleted mantle (DM) as upper mantle and lithospheric mantle with a hybrid enriched mantle I–II (EM I–EM II) characteristics may be adequate to explain He–Sr–Nd–Pb isotope variation for the Afar–Arabian Cenozoic volcanics. The occurrence of high 3 He/4 He ratios in the Marib–Sirwah volcanic field appears to show that the primitive basaltic magma, derived from the margin of the dispersed trous-like Afar mantle plume during 15–0 Ma, was not by contamination of lithospheric and upper mantle materials in comparison with that from the center of the Afar mantle plume as a result of relatively low thermal anomaly. 相似文献
4.
The large differences in He and Ar diffusivities in silicate minerals could result in fractionation of the He/Ar ratio during melting of the mantle, producing He/Ar ratios in the primary mantle melts that are higher than those of the bulk mantle. Modeling noble gas diffusion out of the bulk mantle into fast diffusion pathways (such as fractures or melt channels) suggests that significant (order of magnitude) He/Ar fractionation will occur if the fast diffusion channels are spaced several meters apart and the noble gas residence in these diffusion channels is of the order days to weeks. In addition, the 15% difference in 3He and 4He diffusivities could also produce isotopic fractionation between the melt and its solid source. Modeling the behavior of He and Ar during melting shows that small increases (few %) in 3He/4He should be correlated with larger variations (factor of 5) in 4He/40Ar. However, in order to test this hypothesis the effects of subsequent He–Ar fractionation that occur during degassing have to be corrected. I describe a scheme that can separate He/Ar variations in the primary melt from overprinted fractionation during magmatic degassing. Using the degassing-corrected data, there is a correlation between the primary melt’s 4He/40Ar and 3He/4He in mid-ocean ridge basalts (MORBs). The slope of the correlation is consistent with the models of preferential diffusion of 3He relative to 4He and of 4He relative to 40Ar from the solid mantle into the melt. Diffusive fractionation of noble gases during melting of the mantle can also account for low 4He/40Ar ratios commonly found in residual mantle xenoliths: preferential diffusion of He relative to Ar will produce some regions of the mantle with low 4He/40Ar, the complement of the high 4He/40Ar ratios in basalts. Diffusive fractionation cannot, however, account for differences between the He and Ne isotopic compositions of MORBs compared with ocean island basalts (OIBs); not only are the extremely high 3He/4He ratios of OIBs (up to 50 Ra) difficult to produce at reasonable mantle time and lengthscales, but also the Ne isotopic compositions of MORBs and OIBs do not lie on a single mass fractionation line, therefore cannot result from diffusive fractionation of a single mantle Ne source. If preferential diffusion of He from the solid mantle into primary melts is a significant process during generation of MORBs, then it is difficult to constrain the He concentration of the mantle: He concentrations in basalts and the He flux to the ocean essentially result from extraction of He from a larger (and unknown) volume of mantle than that that produced the basalts themselves. The He concentration of the mantle cannot be constrained until more accurate estimates of the diffusion contribution are available. 相似文献
5.
Electrokinetic phenomena associated with a water injection experiment at the Nojima fault on Awaji Island, Japan 总被引：2，自引：0，他引：2
Hideki Murakami Takeshi Hashimoto Naoto Oshiman Satoru Yamaguchi Yoshimori Honkura Norihiko Sumitomo 《Island Arc》2001,10(3-4):244-251
Abstract Self-potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self-potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320–450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/ζ (permeability/zeta potential) is in the range 1.6 × 10−13 − 5.4 × 10−13 m2 /V. Permeability of the Nojima fault zone can be estimated as approximately 10−16 –10−15 m2 on the assumption that the zeta potential is in the range –0.01 to –0.001 V. 相似文献
6.
Abstract 40 Ar–39 Ar analysis of phlogopite separated from a plagioclase lherzolite of the Horoman Peridotite Complex, Hokkaido, Japan, has yielded a plateau age of 20.6 ± 0.5 Ma in an environment where the metamorphic fluid was characterized by an almost atmospheric Ar isotopic ratio. The age spectrum is slightly saddle-shaped, implying some incorporation of excess 40 Ar during the formation of the phlogopite at a depth. As the phlogopite has been inferred to have formed in veins and/or interstitials during exhumation of the peridotite body, metasomatic fluids, to which ground- and sea water might have contributed, were probably involved in the formation of phlogopite in the crustal environment. A total 40 Ar–39 Ar age of 129 Ma of a whole rock sample of the plagioclase lherzolite, from which the phlogopite was separated and is representative of the main lithology of the Horoman Peridotite Complex, indicates the occurrence of excess 40 Ar. Hence, the age has no geological meaning. 相似文献
7.
Abstract Chemical data on hydrothermally altered volcanic rocks from a green tuff belt in Japan indicate that the average rate of Mg removal from seawater due to seawater cycling through back-arc basins in the circum-Pacific region during the early to middle Miocene (25–15 Ma) is estimated to be 2.6±1 × 1013 g/year. This is similar to that through present-day mid-ocean ridges (2.4 × 1013 g/year). Hydrothermal fluxes of K, Ca and Si are calculated to be 4.2±1.6 × 1013 g/year, 4.3±1.7×1013 g/year and 1.0±0.4 × 1014 g/year, respectively. These calculated results indicate that the seawater/volcanic rocks interaction at subduction-related tectonic settings have to be taken into account in considering the geochemical mass balance of seawater over geologic time. 相似文献
8.
We report isotope analyses of helium, neon, argon, and xenon using different extraction techniques such as stepwise dynamic and static crushing, and high-resolution stepwise heating of three mantle xenoliths from Réunion Island. He and Ne isotopic compositions were similar to previously reported Réunion data, yielding a more radiogenic composition when compared to the Hawaiian or Icelandic mantle plume sources. We furthermore observed correlated 129Xe/130Xe and 136Xe/130Xe ratios following the mantle trend with maximum values of 6.93 ± 0.14 and 2.36 ± 0.06, respectively. High-resolution argon analyses resulted in maximum 40Ar/36Ar ratios of 9000–11,000, in agreement with maximum values obtained in previous studies. We observed a well-defined hyperbolic mixing curve between an atmospheric and a mantle component in a diagram of 40Ar/36Ar vs. 20Ne/22Ne. Using a mantle 20Ne/22Ne of 12.5 (Ne–B) a consistent 40Ar/36Ar value of 11,053 ± 220 in sample ILR 84-4 was obtained, whereas extrapolations to a higher mantle 20Ne/22Ne ratio of 13.8 (solar wind) would lead to a much higher 40Ar/36Ar ratio of 75,000, far above observed maximum values. This favours a mantle 20Ne/22Ne of about 12.5 considered to be equivalent to Ne–B. Extrapolated and estimated 40Ar/36Ar ratios of the Réunion, Iceland, Loihi, and MORB mantle sources, respectively, tend to be linearly correlated with air corrected 21Ne/22Ne and show the same systematic sequence of increasing relative contributions in radiogenic isotopes (Iceland–Loihi–Réunion–MORB) as observed for 4He/3He. In general, He–Ne–Ar isotope systematics of the oceanic mantle can be explained by following processes: (i) different degree of mixing between pure radiogenic and pure primordial isotopes generating the MORB and primitive plume (Loihi-type) endmembers; (ii) relatively recent fractionation of He relative to Ne and Ar, in one or both endmembers; (iii) after the primary fractionation event, different degrees of mixing between melts or fluids of MORB and primitive plume affinity generate the variety of observed OIB data, also on a local scale; (iv) very late-stage secondary fractionation during magma ascent and magma degassing leads to further strong variation in He/Ne and He/Ar ratios. 相似文献
9.
W. Cie&#x;kowski M. Grning P.M. Le niak S.M. Weise A. Zuber 《Journal of Hydrology》1992,140(1-4):89-117
Isotope and hydrochemical data of the thermal water system in Cieplice
laskie Zdrój (Spa) indicate the existence of two subsystems that greatly differ in volume and which meet at the fault zones of a granitic horst, where they discharge at an altitude of about 340m. One of the subsystems is very small (about 4 × 103 m3) as indicated by the tritium age of the order of 10 years and a low outflow rate. Its recharge area found from the δ18O and δD values, is about 200m above the springs, most probably on the slopes of the foothills of the Karkonosze Mountains south-southwest of the spa. The large subsystem contains water which is free of tritium and whose 14C content is from 1 to 8 pmc with δ13C = −8.0 to −9.2‰. The isotopic composition of this water reflects either the climatic effect (low-altitude recharge during a cooler pre-Holocene climate) or the altitude effect (recharge in the early Holocene period at about 1000m at the heights of the Karkonosze assuming that the 14C concentration is strongly reduced by exchange with calcite in veins). For the former hypothesis, the recharge area of this water is probably either at the foot of the southeastern slopes of the Kaczawa Mountains or/and at the foot of the Rudawy Janowickie Mountains, to the east of Cieplice. The noble gas temperatures are more consistent with the pre-Holocene recharge. Similarly, the 4He excess and 40Ar/36Ar ratio support the hypothesis of a pre-Holecene age. The constant 3He/4He ratio of 26 × 10−8 for highly different helium contents indicates crustal origin of helium. For the pre-Holocene age of water its volume is calculated at >- 109m3 (stagnant water in micropores and mobile water in fractures) and the hydraulic conductivity of the host granite massif is estimated at about 7 × 10−8 ms−1. Two outflows from this subsystem have different and variable fractions of a modern water component (bomb age), most probably originating from the bank infiltration of a nearby stream. 相似文献
10.
by Denis Cohen Mark Person Peng Wang Carl W. Gable Deborah Hutchinson ee Marksamer Brandon Dugan Henk Kooi Koos Groen Daniel Lizarralde Robert L. Evans Frederick D. Day-Lewis John W. Lane Jr. 《Ground water》2010,48(1):143-158
While the existence of relatively fresh groundwater sequestered within permeable, porous sediments beneath the Atlantic continental shelf of North and South America has been known for some time, these waters have never been assessed as a potential resource. This fresh water was likely emplaced during Pleistocene sea-level low stands when the shelf was exposed to meteoric recharge and by elevated recharge in areas overrun by the Laurentide ice sheet at high latitudes. To test this hypothesis, we present results from a high-resolution paleohydrologic model of groundwater flow, heat and solute transport, ice sheet loading, and sea level fluctuations for the continental shelf from New Jersey to Maine over the last 2 million years. Our analysis suggests that the presence of fresh to brackish water within shallow Miocene sands more than 100 km offshore of New Jersey was facilitated by discharge of submarine springs along Baltimore and Hudson Canyons where these shallow aquifers crop out. Recharge rates four times modern levels were computed for portions of New England's continental shelf that were overrun by the Laurentide ice sheet during the last glacial maximum. We estimate the volume of emplaced Pleistocene continental shelf fresh water (less than 1 ppt) to be 1300 km3 in New England. We also present estimates of continental shelf fresh water resources for the U.S. Atlantic eastern seaboard (104 km3 ) and passive margins globally (3 × 105 km3 ). The simulation results support the hypothesis that offshore fresh water is a potentially valuable, albeit nonrenewable resource for coastal megacities faced with growing water shortages. 相似文献
11.
P.C. Johnson R.A. Ettinger J.P. Kurtz R. Bryan J.E. Kester 《Ground Water Monitoring & Remediation》2009,29(1):153-159
The area surrounding the Colorado Department of Transportation Materials Testing Laboratory in Denver was the subject of intense investigation, involving the collection of thousands of ground water, soil-gas, and indoor air samples in order to investigate indoor air impacts associated with a subsurface release of chlorinated solvents. The preremediation portion of that data set is analyzed and reduced in this work to ground water–to-indoor air attenuation factors (αgw = the ratio of the measured indoor air concentration to the soil-gas concentration predicted to be in equilibrium with the local ground water concentration). The empirical αgw values for this site range from about 10−6 to 10−4 with an overall average of 3 × 10−5 (μg/L indoor air)/(μg/L soil gas). The analysis of this data set highlights the need for a thorough data review and data screening when using large data sets to derive empirical relationships between subsurface concentrations and indoor air. More specifically, it is necessary to identify those parts of the data that contain a strong vapor intrusion pathway signal, which generally will require concentrations well above reported detection levels combined with spatial or temporal correlation of subsurface and indoor concentrations. 相似文献
12.
Peter J. Valbracht Thomas Staudacher Alex Malahoff Claude J. Allgre 《Earth and Planetary Science Letters》1997,150(3-4):399-411
We report new noble gas fusion and crushing data for six pillow rim glasses, recovered between 3 and 5 km water depth on the south rift zone of Loihi Seamount, Hawaii. Helium abundances of the glasses vary from 0.3 to 2.3 μcc/g, with 4He/3He ratios between 30000 and 27000 (24–27 RA), similar to previously reported values. The neon data form a correlation line which is similar to the Loihi-Kilauea line reported by Honda et al. [1], but extends to much higher ratios, up to 12.9 and 0.0382 for the 20Ne/22Ne and 21Ne/22Ne ratios, respectively. This provides conclusive evidence for the suggestion that the Hawaiian plume, thought to originate in the lower mantle, has a solar-like 20Ne/22Ne composition [1], but a slightly higher 21Ne/22Ne ratio. 40Ar/36Ar ratios of the deep rift-zone glasses are as high as 2600, and show a positive correlation with neon isotopic ratios. In contrast to neon and argon, all xenon isotopic compositions are isotopically indistinguishable from air, which either suggests preferential atmospheric contamination of xenon, or could indicate an atmospheric xenon isotopic composition for the lower mantle. 相似文献
13.
Conglomerates of the Kuma Group, central Shikoku, southwest Japan contain Sanbagawa schist clasts with a variety of metamorphic grades and lithologies. K–Ar and 40 Ar/39 Ar dating of phengite show all the pelitic schist clasts from low- to high-grade zones have similar phengite ages (82–84 Ma) that are significantly older than those from the in situ Sanbagawa sequence of central Shikoku. This is because the Kuma–Sanbagawa sequence was exhumed earlier than the in situ Asemi sequence with an exhumation process intermediate between those for the Kanto Mountains and the in situ Asemi sequences. 40 A/39 Ar plateau ages (103 and 117 Ma) of phengite in amphibolites indicate the timing of the early stage of the exhumation of the metamorphic pile, probably close to the peak metamorphic age. 相似文献
14.
Yong-Jiang Liu Franz Neubauer Johann Genser Akira Takasu Xiao-Hong Ge Robert Handler 《Island Arc》2006,15(1):187-198
Abstract Pelitic schists from Qingshuigou in the Northern Qilian Mountains of China contain mainly glaucophane, garnet, white mica, clinozoisite, chlorite and piemontite. Isotopic age dating of these schists provides new constraints on the formation of the high-grade blueschists at Qingshuigou. White mica 40 Ar/39 Ar ages range from 442.1 to 447.5 Ma (total fusion age of single grain) and from 445.7 to 453.9 Ma (integrated age of white mica concentrates). These ages (442.1–453.9 Ma) represent the peak metamorphic ages or cooling ages of the blueschists during exhumation shortly after peak metamorphism. The 40 Ar/39 Ar dates in the present study are similar to ages previously reported for eclogites and blueschists in the area; this suggests that both the eclogites and pelitic sediments underwent high-grade metamorphism during the same subduction event. From this chronological evidence and the presence of well-developed Silurian remnant-sea flysch and Devonian molasse, it is concluded that the Northern Qilian Ocean had closed by the end of the Ordovician, and rapid orogenic uplift followed in the Devonian. 相似文献
15.
Noble gas concentrations and isotopic compositions have been determined for four submarine volcanic glasses from the Valu Fa Ridge (VFR) in the southern Lau Basin. The samples are the least differentiated ones from this area, and they display enrichments in fluid-mobile elements similar to the nearby island arc. 3He/4He ratios are slightly below average MORB (6.8–7.8 times atmospheric), whereas Ne, Ar, Kr, and Xe have isotopic compositions very similar to air. Together with previously published data from the Valu Fa Ridge and other spreading segments in the Lau Basin, our data show a systematic latitudinal variation of increasing Ne, Ar, Kr, and Xe abundances from north to south as well as Ne and Ar isotopic compositions changing from MORB-like to atmosphere-like in the same direction. Moreover, isotopic compositions and noble gas abundances of the lavas correlate strongly with Ba/Nb ratios and H2O concentrations. Based on these observations and mass balance arguments, we propose that the atmospheric noble gases come from the subducting oceanic crust and are not due to shallow contamination with air dissolved in seawater or assimilation of old crust. Our data suggest that the noble gases released from the subducting slab are atmospheric and thus contain little or no solar He and Ne. In addition to the fact that ratios of He to heavy noble gases are small in aged ocean crust, He has possibly fractionated from the other noble gases due to its higher diffusivity, and thus He transport from the subducting slab into the mantle wedge is probably insignificant. We propose that the 3He/4He ratios lower than MORB observed in the VFR lavas result from radiogenic ingrowth of He in a highly depleted, and hence degassed, mantle wedge after the enrichment of U and Th released from the downgoing slab. 相似文献
16.
U. Beyerle W. Aeschbach-Hertig M. Hofer D. M. Imboden H. Baur R. Kipfer 《Journal of Hydrology》1999,220(3-4):169-185
Noble gas isotopes (3He, 4He, Ne, Ar, Kr, Xe), tritium (3H), chlorofluorocarbons (CFCs) and dissolved oxygen (O2) were seasonally measured in a small groundwater system recharged by infiltration of river water at Linsental, northeastern Switzerland. All Groundwater samples contained an excess of atmospheric noble gases (‘excess air’) usually with an elemental composition equal to air. The concentrations of atmospheric noble gases in the groundwater were used to calculate the excess air component and the water temperature at recharge. The noble gas temperatures (NGTs) in the boreholes close to the river vary seasonally, however, the average NGT of all samples lies close to the mean annual temperature of the river water. Groundwater ages were calculated using the tritium/helium-3 (3H/3He) dating method. The water ages of the samples obtained near the river depend on the amount of recently infiltrated river water and are young during times of active river discharge. In contrast, the mean water age of about 3 years of the deep aquifer remained nearly constant over the sampling period. The observed CFC-11 (CFCl3) and CFC-12 (CF2Cl2) concentrations are significantly higher than the atmospheric equilibrium concentrations and therefore CFCs do not provide any direct information on the residence time of the groundwater. Nevertheless, the CFC excess in the groundwater shows a linear increase with the 3H/3He age. Additionally, both accumulation of radiogenic He (4Herad) and O2 consumption are strongly correlated with residence time. All these correlations can be interpreted either in terms of mixing of recently infiltrated river water with older groundwater or in terms of accumulation/consumption rates. 相似文献
17.
Mario Trieloff Joachim Kunz Claude J. Allgre 《Earth and Planetary Science Letters》2002,200(3-4):297-313
New noble gas data of ultramafic xenoliths from Réunion Island, Indian Ocean, further constrain the characteristics of primordial and radiogenic noble gases in Earth’s mantle plume reservoirs. The mantle source excess of nucleogenic 21Ne is significantly higher than for the Hawaiian and Icelandic plume reservoirs, similar to excess of radiogenic 4He. 40Ar/36Ar of the Réunion mantle source can be constrained to range between 8000 and 12 000, significant 129Xe and fission Xe excess are present. Regarding the relative contribution of primordial and radiogenic rare gas nuclides, the Réunion mantle source is intermediate between Loihi- and MORB-type reservoirs. This confirms the compositional diversity of plume sources recognized in other radioisotope systematics. Another major result of this study is the identification of the same basic primordial component previously found for the Hawaiian and Icelandic mantle plumes and the MORB reservoir. It is a hybrid of solar-type He and Ne, and ‘atmosphere-like’ or ‘planetary’ Ar, Kr, Xe (Science 288 (2000) 1036). 20Ne/22Ne ratios extend to maximum values close to 12.5 (Ne-B), which is the typical signature of solar neon implanted as solar corpuscular radiation. This suggests that Earth’s solar-type noble gas inventory was acquired by small (less than km-sized) precursor planetesimals that were irradiated by an active early sun in the accretion disk after nebular gas dissipation, or, alternatively, that planetesimals incorporated constituents irradiated in transparent regions of the solar nebula. Previously, such an early irradiation scenario was suggested for carbonaceous chondrites which follow common volatile depletion trends in the sequence CI–CM–CV–Earth. In turn, CV chondrites closely match Earth’s mantle composition in 20Ne/22Ne, 36Ar/22Ne and 36Ar/38Ar. This indicates that mantle Ar could well be a planetary component inherited from precursor planetesimals. However, a corresponding conclusion for mantle Kr and Xe is less convincing yet, but this may be just due to the lack of appropriate ‘meteoritic’ building blocks matching terrestrial composition. Alternatively, heavy noble gases in Earth’s mantle could be due to admixing of severely fractionated air, but this effect must have affected all mantle sources to a very similar extent, e.g. by global subduction before the last homogenization of the mantle reservoirs. 相似文献
18.
Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan 总被引：2，自引：0，他引：2
Kunio Fujimori Hiroshi Ishii Atsushi Mukai Shigeru Nakao Shigeo Matsumoto Yasuhiro Hirata 《Island Arc》2001,10(3-4):228-234
Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M 7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10−7 str (almost parallel to the fault) and tilt of approximately 1 × 10-7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water. 相似文献
19.
Sulfur isotopic characteristics of late Cenozoic ore deposits at the arc junction of Hokkaido, Japan
Abstract Sulfide minerals of late Cenozoic vein-type deposits of southwest Hokkaido and Kuril Islands yielded δ34 CDT S values of 2 to 8 permil, which are typical green-tuff values of magnetite-series igneous terrane. Sulfides of the Kitami district of northeast Hokkaido, on the other hand, are characterized by negative δ34 SCDT values, ranging from 0 to - 7 permil. This unique value among ore deposits in the late Cenozoic back-arc terranes in the Japanese Islands is considered to have resulted from extraction of 32 S enriched sulfur from the basement rocks, because of well-developed N-S fracturing in the basement, which is characteristic of the axial belt and Kitami district of Hokkaido. 相似文献
20.
T. Nakamori 《Island Arc》2001,10(1):1-8
Abstract Global carbonate accumulation rates on the surface of the earth, including not only platforms but also continental margin slopes and deep-sea from the Cretaceous to Present, are estimated by compiling previous geologic studies. These rates are revised, taking account of the erosional effect of the sediments on the platform and deep-sea. Long-term model carbonate fluxes from the ocean to the crust are calculated on the basis of the carbon cycle model (GEOCARB of Berner 1991 ). The rates based on the actual geologic data indicate much lower values than model fluxes, excluding the Pliocene and Quaternary. The discrepancy could be attributed to the two misunderstandings, namely an overestimate of carbonate accumulation rate for the Quaternary and an incorrect use of the higher Quaternary rate for a boundary condition of the model. The carbonate accumulation rate for the Pliocene to Quaternary is lowered from 29.8 × 1018 mol/Ma (modified from Opdyke & Wilkinson 1988 ) to 14.8 × 1018 mol/Ma in the present study, assuming that the rate from Quaternary to Pliocene is almost the same as the Miocene value. New model fluxes are recalculated with the new boundary condition in the Quaternary (14.8 × 1018 mol/Ma). Revised model fluxes show general trends of high rates in 120 Ma or 130 Ma, and a low rate in 0 Ma, and are in agreement with the accumulation rate pattern. 相似文献