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171.
U–Pb zircon ages of the Nakanogawa Group in the Hidaka Belt,northern Japan: Implications for its provenance and the protolith of the Hidaka metamorphic rocks
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Futoshi Nanayama Yutaka Takahashi Toru Yamasaki Mitsuru Nakagawa Hideki Iwano Tohru Danhara Takafumi Hirata 《Island Arc》2018,27(2)
Zircon U–Pb ages of two acidic tuff and two turbidite sandstone samples from the Nakanogawa Group, Hidaka Belt, were measured to estimate its depositional age and the development of the Hokkaido Central Belt, northeast Japan. In the northern unit, homogeneous zircons from pelagic acidic tuff from a basal horizon dated to 58–57 Ma, zircons from sandstone from the upper part of the unit dated to 56–54 Ma, and zircons from acidic tuff from the uppermost part dated to 60–56 Ma and 69–63 Ma. Both of the tuff U–Pb ages are significantly older than the youngest radiolarian fossil age (66–48 Ma). Therefore, the maximum depositional age of the turbidite facies in the northern unit is 58 Ma and the younger age limit, estimated from the fossil age, is 48 Ma. In the southern unit, homogeneous zircons from turbidite sandstone dated to 58–57 Ma. Thus the depositional age of this turbidite facies was interpreted to be 66–56 Ma from the fossil age, probably close to 57 Ma. Most of the zircon U–Pb ages from the Nakanogawa Group are younger than 80 Ma, with a major peak at 60 Ma. This result implies that around Hokkaido volcanic activity occurred mainly after 80 Ma. Older zircon ages (120–80 Ma, 180–140 Ma, 340–220 Ma, 1.9 Ga, 2.2 Ga, and 2.7 Ga) give information about the provenance of other rocks in the Hidaka Belt. It is inferred that the Nakanogawa Group comprises protoliths of the upper sequence of the Hidaka Metamorphic Zone, which therefore has the same depositional age as the Nakanogawa Group (66–48 Ma). The depositional ages of the lower sequence of the Hidaka Metamorphic Zone and the Nakanogawa Group are probably the same. 相似文献
172.
Hideki Iwano Tohru Danhara Yugo Danhara Saori Hirabayashi Toru Nakajima Harutaka Sakai Takafumi Hirata 《Island Arc》2020,29(1)
We present a new LA–ICP–MS system for zircon fission‐track (FT) and U–Pb double dating, whereby a femtosecond laser combined with galvanometric optics simultaneously ablates multiple spots to measure average surface U contents. The U contents of zircon measured by LA–ICP–MS and standardized with the NIST SRM610 glass are comparable to those measured by the induced FT method, and have smaller analytical errors. LA–ICP–MS FT dating of seven zircon samples including three IUGS age standards is as accurate as the external detector method, but can give a higher‐precision age depending on the counting statistics of the U content measurement. Double dating of the IUGS age standards gives FT and U–Pb ages that are in agreement. A chip of the Nancy 91500 zircon has a homogeneous U content of 84 ppm, suggesting the possibility of using this zircon as a matrix‐matched U‐standard for FT dating. When using the Nancy 91500 zircon as a U‐standard, a zeta calibration value of 42–43 year cm2 for LA–ICP–MS FT dating is obtained. While this value is strictly valid only for the particular session, it can serve as a reference for other studies. 相似文献
173.
A simplified physical model is proposed in this article to describe differences among basins in substance distributions which were not well described by previous simplified models. In the proposed model, the global ocean is divided into the Pacific/Indian Ocean (PI), the Atlantic Ocean (AT), the Southern Ocean and the Greenland/Iceland/Norwegian Sea. The model is consisted of five physical parameters, namely the air-sea gas exchange, the thermohaline circulation, the horizontal and vertical diffusions, and the deep convection in the high-latitude regions. Individual values of these parameters are chosen by optimizing model distribution of natural 14C as a physical tracer. The optimal value for a coefficient of vertical diffusion in the low-latitude region is 7.5 × 10–5 [m2s–1]. Vertical transports by the Antarctic Bottom Water and the North Atlantic Deep Water are estimated at 1.0 Sv and 9.0 Sv. Global-mean air-sea gas exchange time is calculated at 9.0 years. Using these optimal values, vertical profiles of dissolved inorganic carbon without biological production in PI and AT are estimated. Oceanic responses to anthropogenic fluctuations in substance concentrations in the atmosphere induced by the industrialization and nuclear bomb are also discribed, i.e., the effects appear significantly in AT while a signal is extremely weak in PI. A time-delay term is effective to make the PI water older near the bottom boundary. 相似文献
174.
Abstract: Synchrotron radiation-induced X–ray fluorescence (SR–XRF) and conventional X-ray fluorescence (XRF) analyses were applied to determine the distributions of iron, manganese, calcium, titanium, and silicon, and chemical forms of iron and trace manganese in three banded iron formation (BIF) samples. The XRF imagings on the weathered and altered BIF from the Cleaverville Formation (3. 3–3. 1 Gyr), Western Australia, showed redistributions of iron, calcium, and manganese with the disappearance of the primary bandings, while, in contrast, titanium preserved its primary depositional distribution. The XRF imagings on the BIF from the Hamersley Group (2. 5 Gyr), Western Australia, showed that manganese and titanium distribute originally at boundary region between the iron-rich mesoband and the silica-rich mesoband. The X-ray Absorption Near Edge Structure (XANES) analysis revealed that the chemical forms of manganese and iron well represent the rhythmic change of the bandings. 相似文献
175.
The responses of atmospheric pCO2 and sediment calcite content to changes in the export rain ratio of calcium carbonate to organic carbon are examined using
a diffusion-advection ocean biogeochemical model coupled to a one-dimensional sediment geochemistry model. Our model shows
that a 25% reduction in rain ratio decreases atmospheric pCO2 by 59 ppm. This is caused by alkalinity redistribution by a weakened carbonate pump and an alkalinity increase in the whole
ocean via carbonate compensation with decreasing calcite burial. The steady state responses of sedimentary calcite content
and calcite preservation efficiency are rather insensitive to the deepening of the saturation horizon of 1.9 km. This insensitivity
is a result of the reduced deposition flux that decreases calcite burial, counteracting the saturation horizon deepening that
increases calcite burial. However, in the first 10,000 years the effect of reduced calcite deposition on the burial change
is more prominent; while after 10,000 years, the effect of saturation horizon deepening is more dominant. The lowering of
sediment calcite content for the first 10,000 years is effectively decoupled from the 1.9 km downward shift of the saturation
horizon. Our results are in part a consequence of the more dominant role that respiration CO2 plays in sediment calcite dissolution over bottom water chemistry in our control run and support the decoupling of calcite
lysocline depth and saturation horizon shifts, as suggested originally by Archer and Maier-Reimer (1994) and Archer et al. (2000). 相似文献
176.
Tomoyuki Shikata Sou Nagasoe Tadashi Matsubara Yasuhiro Yamasaki Yohei Shimasaki Yuji Oshima Takuji Uchida Ian R. Jenkinson Tsuneo Honjo 《Journal of Oceanography》2008,64(3):355-365
In the present study, we have investigated the conditions influencing encystment and excystment in the dinoflagellate Gyrodinium instriatum under laboratory conditions. We incubated G. instriatum in modified whole SWM-3 culture medium and in versions of modified SWM-3 from which NO3
−, PO4
3−, NO3
− + PO4
3−, or Si had been omitted and observed encystment. Percentage encystment was high in the media without N and without P, while
the percentage encystment in the medium lacking both N and P was highest. Moreover, to investigate N or P concentration which
induced the encystment, Gyrodinium instriatum was also incubated in media with different concentrations of inorganic N and P; the concentrations of NO2
− + NO3
− and PO4
3− were measured over time. The precursors of cysts appeared within 2 or 3 days of a decrease in NO2
− + NO3
− or PO4
3− concentration to values lower than 1 μM or 0.2 μM, respectively. When cysts produced in the laboratory were incubated, we observed excystment after 8–37 days, without a mandatory
period of darkness or low temperature. We incubated cysts collected from nature at different temperatures or in the dark or
light and observed excystments. Natural cysts excysted at temperatures from 10 to 30°C, in both light and dark, but excystment
was delayed at low temperatures. These studies indicate that G. instriatum encysts in low N or P concentration and excysts over a wide temperature range, regardless of light conditions, after short
dormancy periods. 相似文献
177.
Concentration and stable isotopic compositions (δ
18O) of dissolved O2 were measured in seawater samples collected from the Philippine Sea in June 2006. The in-situ O2 consumption rate and the isotopic fractionation factor (α
r
) during dissolved O2 consumption were obtained from field observations by applying a vertical one-dimensional advection diffusion model to the
deep water mass of about 1000–4000 m. The average O2 consumption rate and α
r
were, respectively, 0.11 ± 0.07 μmol kg−1yr−1 and 0.990 ± 0.001. These estimated values agree well with values from earlier estimations of Pacific deep water. The in-situ O2 consumption rates are two or more times higher north of 20°N, although the value of α
r
was not significantly different between the north and south. Its levels varied rapidly in the water mass of less about 2000
m depth. These results suggest that organic matter from the continent imparts a meaningful contribution to the upper water
in the northern part of the area; it might produce the strong O2 minimum that is evident in the water mass from about 1000–2000 m in the northern part of the Philippine Sea. 相似文献
178.
Takehiko Suzuki Seiji Maruyama Tohru Danhara Takafumi Hirata Hiroshi Machida Fusao Arai 《第四纪科学杂志》2020,35(1-2):316-333
Tephra fingerprinting techniques contributing to volcanology and palaeoenvironmental studies have been developed using a combination of laser-ablation inductively coupled-plasma mass spectrometry (LA-ICP-MS) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). In particular, femtosecond LA-ICP-MS can determine major- and trace element abundances in individual glass shards. On the basis of the major oxide and trace element composition of the glass shards, using those methods, we re-examined the identification of four lower Pleistocene tephras originating from north-east Japan. All trace element abundances exhibited the typical pattern of tephras from the Hokkaido–Tohoku area, and major element concentrations were distinct. As a result, we re-examined the correlation of the widespread Tmg-R4 tephra (2.0 Ma), and newly defined the widespread Kd44-Naka tephra (1.968–1.781 Ma), both originating from the Sengan geothermal region. Furthermore, we re-examined identifications of Sr-Asn-Kd8 (1.219 Ma) and Sr-Kc-U8 (0.922–0.910 Ma) in central Japan, both derived from the Aizu volcanic region. The extensive distributions of the former two tephras suggest the occurrence of two large caldera-forming eruptions (Volcanic Explosivity Index 7) during a short period. Also, the distributions and volumes of the latter two tephras are broader and larger than those previously assumed. The results provide insight into large volcanic eruption history and terrestrial and marine palaeoenvironmental history. 相似文献
179.
Tatsuhiro Nishikiori Takejiro Takamatsu Ayato Kohzu Yasuhiro Nakajima Mirai Watanabe 《Environmental Earth Sciences》2012,67(5):1531-1545
Geological and geographical parameters including land use, stratigraphic structure, groundwater quality, and N- and O-isotopic compositions of nitrate in groundwater were investigated to elucidate the mechanism of groundwater pollution by NO3 ? in the agricultural area of Katori, Chiba, Japan. An aquitard distributed in the western part of the study area has produced two unconfined aquifers. The average concentrations of NO3 ? and dissolved oxygen (DO) were high in the aquifer above the aquitard (7.5 and 7.6 mg/L, respectively) and in the aquifer of the eastern part of the study area that was not influenced by the aquitard (11.9 and 7.8 mg/L, respectively); however, the levels in the aquifer under the aquitard were relatively low (2.2 and 3.7 mg/L, respectively). The δ15N and δ18O values of NO3 ? generally increased exponentially in the groundwater that flowed into the aquifer under the aquitard as the concentration of NO3 ? decreased, although this decrease in NO3 ? also occasionally occurred without isotopic changes. These results indicated that the aquitard prevented the penetration of NO3 ?, DO, and gaseous O2. Under the aquitard, denitrification and dilution with unpolluted water that entered from natural forested areas reduced the NO3 ? concentrations in the groundwater. The major sources of NO3 ? in groundwater in the study area were estimated to be NH4-chemical fertilizer, livestock waste, and manure. 相似文献
180.
César Augusto Moreira Antonio Celso de Oliveira Braga Letícia Hirata Godoy Diego de Sousa Sardinha 《Geofísica Internacional》2013,52(4):375-383
The geophysical methods are effective tools for determining changes in physical parameters of the geological environment, as soil or groundwater in the presence of contamination. This work consisted on analyzing the natural electric potential obtained over domestic solid waste ditches with controlled closure dates. The interpretation data suggest the generation of electric potential predominantly through the redox phenomenon, as opposed to the flow potential phenomenon. The statistical data analysis indicates a correlation between residence time of the waste and growing variations of voltage. In addition highlights that eight years are required to achieve the reported values for the area with absence of waste, time estimated for decomposition of most organic matter contained in the buried waste. 相似文献