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1.
Dispersed and concretionary pyrite in chert–clay–carbonate and carbonate rocks of the Abalak Formation (Salym oil field) have been studied. The study was conducted using Scanning Electron Microscopy (SEM), Electron Probe Microanalysis (EPMA), and high spatial resolution Secondary Ion Mass Spectrometry (Nano-SIMS). As a result, three morphological groups of pyrite have been distinguished: large cubic crystals, framboidal pyrite, and fine-crystal aggregates that replace organic remnants. The sulphur isotope ratio allows one to distinguish two genetic types of pyrite. The source of the sulphur for the first genetic group was H2S produced by bacterial sulphate reduction, while the second group pyrite was formed with sulphur as a product of thermochemical sulphate reduction.  相似文献   
2.
Chemical and isotopic compositions of the Acropora nobilis skeleton were analyzed at various spatial resolutions to investigate the mechanism by which elements are incorporated into the skeleton. Chemical and isotopic profiles along growth axes of axial and radial corallites did not show seasonal variation, with the exception of the δ18O profile of the axial corallite. Detailed observations of the skeletal structure revealed that the skeletal density increased with distance from the tip because secondarily precipitated aragonite (here called the “infilling” skeleton) filled pore spaces in the “framework” skeleton. Microscale element analyses revealed that main part of the infilling skeleton had lower Mg/Ca and higher Sr/Ca and U/Ca than the framework skeleton. At microscale, Sr/Ca and U/Ca were positively correlated with each other, and negatively correlated with Mg/Ca but only weakly. The results showed that the infilling skeleton differed significantly from the adjacent framework skeleton in terms of not only formation chronology but also chemical composition, and that the bulk composition was influenced by the infilling/framework skeletal ratio. In order to use the Acropora skeleton as a paleoclimate archive, the relationship between environmental factors and the chemical composition of each skeletal component needs to be established.  相似文献   
3.
The atmospheric 3He/4He ratio has been considered to be constant on a global scale, because the residence time of helium is significantly longer than the mixing time in the atmosphere. However, this ratio may be decreasing with time owing to the anthropogenic release of crustal helium from oil and natural gas wells, although this observation has been disputed. Here, we present the 3He/4He ratios of old air trapped in historical slags in Japan and of modern surface air samples collected at various sites around the world, measured with a newly developed analytical system. In air helium extracted from metallurgical slag found at refineries in operation between AD 1603 and 1907 in Japan, we determined a mean 3He/4He ratio of (5106 ± 108) × 10-5 RHESJ (where RHESJ is the 3He/4He ratio of the Helium Standard of Japan), which is consistent with the previously reported value of (5077 ± 59) × 10-5 RHESJ for historical slags in France and United Arab Emirates and about 4% higher than that of average modern air, (4901 ± 4) × 10-5 RHESJ. This result implies that the air 3He/4He ratio has decreased with time as expected by anthropogenic causes. Our modern surface air samples revealed that the 3He/4He ratio increases from north to south at a rate of (0.16 ± 0.08) × 10-5 RHESJ/degree of latitude, suggesting that the low 3He/4He ratio originates in high-latitude regions of the northern hemisphere, which is consistent with the fact that most fossil fuel is extracted and consumed in the northern hemisphere.  相似文献   
4.
We have collected 34 hot spring and mineral spring gases and waters in the Chugoku and Kansai districts, Southwestern Japan and measured the 3He/4He and 4He/20Ne ratios by using a noble gas mass spectrometer. Observed 3He/4He and 4He/20Ne ratios range from 0.054 Ratm to 5.04 Ratm (where Ratm is the atmospheric 3He/4He ratio of 1.39 × 10−6) and from 0.25 to 36.8, respectively. They are well explained by a mixing of three components, mantle-derived, radiogenic, and atmospheric helium dissolved in water. The 3He/4He ratios corrected for air contamination are low in the frontal arc and high in the volcanic arc regions, which are consistent with data of subduction zones in the literature. The geographical contrast may provide a constraint on the position of the volcanic front in the Chugoku district where it was not well defined by previous works. Taking into account the magma aging effect, we cannot explain the high 3He/4He ratios of the volcanic arc region by the slab melting of the subducting Philippine Sea plate. The other source with pristine mantle material may be required. More precisely, the highest and average 3He/4He ratios of 5.88 Ratm and 3.8±1.6 Ratm, respectively, in the narrow regions near the volcanic front of the Chugoku district are lower than those in Kyushu and Kinki Spot in Southwestern Japan, but close to those in NE Japan. This suggests that the magma source of the former may be related to the subduction of the Pacific plate, in addition to a slight component of melting of the Philippine Sea slab.  相似文献   
5.
A large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau.In this study,11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones(XSH-ANHFZ)and analyzed for chemical and isotopic compositions.The δ18H_(2O) and δDH_(2O) values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes.Most water samples are significantly enriched in Na+ and HCO3 due to the dissolution of regional evaporites,carbonates and Na-silicates.3He/4He ratios of the gas samples are 0.025-2.73 times the atmospheric value.The 3He/4He ratios are high in the Kangding region where the dense faults are distributed,and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones(XSHFZ).Hydrothermal fluids have dissolved inorganic carbon(DIC)concentrations from 2 to 42 mmol L-1,δ13CDIC from -6.9‰ to 1.3‰,δ13CCO_(2) from -7.2‰ to -3.6‰ and Δ14C from -997‰ to -909‰.Combining regional geochemical and geological information,the CO2sources can be attributed to deep-sourced CO2from mantle and metamorphism of marine carbonate,and shallow-sourced CO2from the dissolution of marine carbonate and biogenic CO2.The mass balance model shows that 11±6% of the DIC is sourced from the dissolution of shallow carbonate minerals,9±8% formed by pyrolysis of sedimentary organic matter,80±9% derived from deep metamorphic origin and mantle-derived CO2.Among them,the deep-sourced CO2in Anninghe fault zones(ANHFZ)is merely metamorphic carbon,whereas ca.12% and ca.88% of the deep-sourced CO2in the XSHFZ are derived from the mantle and metamorphic carbon,respectively.The average deep-sourced CO2flux in the Kangding geothermal field is estimated to be 160 ta-1.If all the hot springs in various fault zones in the southeastern margin of the Tibetan Plateau are taken into account,the regional deep-sourced CO2flux would reach ca.105 ta-1.These results show that the deep-sourced CO2released from nonvolcanic areas might account for a considerable proportion of the total amount of global deep-sourced carbon degassing,which should be paid more attention to.  相似文献   
6.
The Precambrian/Cambrian (PC/C) boundary is one of the most important intervals for the evolution of life, represented by prominent biological evolution from the first appearance of soft-bodied animals from the late Neoproterozoic to the sudden diversification of animals with mineralized skeletons in the Cambrian. In South China several areas contain many fossils and are well exposed, suitable for the investigation of PC/C boundary. However, geochronological relationships are still poorly known because of lack of combined detailed investigations of internal structures of zircons and in-situ U–Pb dating.We focus on the internal structure of zircons from a tuff layer within Bed 5 in the Meishucun section on which we undertook cathodoluminescence (CL) imaging and in-situ U–Pb dating with LA-ICP-MS and nano-SIMS. Over 600 zircons from the tuff layer were classified into three types based on their CL images: oscillatory rims, inherited cores and dull structures. U–Pb dating of the internal structure of the zircons by LA-ICP-MS clearly shows a distinct unimodal age population dependent on the structure: 531 ± 17 Ma for the oscillatory rims and 515 Ma for the dull structures. The clear oscillatory zonation, the prismatic morphology, and their occurrence indicate that the oscillatory rims were formed from felsic magmatism, and that the U–Pb nano-SIMS age of 536.5 ± 2.5 Ma records the depositional age of the tuff. Our results indicate that the PC/C boundary is situated below Bed 5, and therefore the bottom of Zone 1 (Marker A) is more appropriate for the PC/C boundary than is the top of Zone 1 (Marker B). The age of a positive anomaly (P2) in the early Cambrian is estimated to be ca. 536 Ma.  相似文献   
7.
A quadrupole-based mass spectrometric system for determining noble gas (He, Ne, Ar, Kr and Xe) abundances in a liquid sample has been developed and applied to seawater equilibrated with the atmosphere at several temperatures. After known amounts of isotopic spikes (22Ne, 36Ar, 86Kr and 124Xe) were introduced into the preparation vacuum line, dissolved gases were extracted from seawater and well mixed with the spikes by ultrasonic vibration. Noble gases were purified using three-stage hot Ti getters and separated by two activated charcoal traps held at low temperature (liquid nitrogen and dry ice—ethanol). Noble gas abundances were measured by a relatively inexpensive quadrupole mass spectrometer based on the isotope dilution technique. Precisions obtained by repeated measurements for He, Ne, Ar, Kr and Xe are 1.5%, 0.4%, 0.4%, 0.4% and 0.6%, respectively. Noble gas abundances in air-saturated seawater at eight temperature steps (1.0°C, 5.5°C, 10.0°C, 14.4°C, 17.0°C, 21.3°C, 24.6°C, and 29.6°C) were measured using the analytical system. The overall variation of the abundances with temperature agrees well with those of NaCl brines reported in the literature. We propose here new constants to fit observed data to empirical equation of noble gas solubility in seawater with its temperature variation.  相似文献   
8.
We have collected fifty-five seawater samples at seven stations at various depths in the Yamato and Japan Basins of the Japan Sea and measured their helium isotopic ratios. The 3He/4He ratios vary from 0.997 Ratm to 1.085 Ratm where Ratm is the atmospheric ratio. The maximum 3He excesses about 8%, are observed at mid-depth (1000 m), and these values are significantly lower than those observed in deep Pacific waters. This implies that mantle-derived helium in deep Pacific water cannot enter the Japan Sea since it is an almost landlocked marginal sea. The observed 8% excess 3He may be attributable to the decay product of tritium. Slightly higher 3He/4He ratios in the Bottom Water were observed in the Yamato Basin than in the Japan Basin. The ventilation ages of seawater shallower than 1000 m are calculated as about 5 to 20 years, which is consistent with the CFC ages reported in the literature. There is a positive correlation between the apparent oxygen utilization and 3H-3He ages. The estimated oxygen utilization rate from the correlation in a layer between 500 m and 1000 m is about 3 μmol/kg/yr, which is similar to that in the eastern subtropical North Atlantic.  相似文献   
9.
We have measured helium isotopic ratios of thirty-seven Pacific water samples from various depths collected in adjacent regions of Honshu, Japan. The 3He/4He ratios vary significantly from 0.989 R atm to 1.208 R atm where R atm is the atmospheric ratio of 1.39 × 10−6. The mid-depth (750–1500 m) profile of 3He/4He ratios at ST-1 located Northwestern Pacific Ocean east of Japan (Off Joban; 37°00′ N, 142°40′ E) is significantly different from that at ST-2 of the Northern Philippine Sea south of Japan (Nankai Trough; 33°07′ N, 139°59′ E), suggesting that these waters were separated by a topographic barrier, the Izu-Ogasawara Ridge. Taking 3He/4He data of the Geosecs expeditions in the western North Pacific, an extensive plume of 15% excess 3He relative to the air may be traced at ST-1 over 12,000 kilometers to the northwest of the East Pacific Rise where the mantle helium may originate. The 20% excess found at ST-2 may be attributable to the additional source of the subduction-type mantle helium in the Okinawa Trough. A 15% excess of 3He has also been discovered at a depth of about 1000∼1500 m at ST-3 adjacent to Miyakejima Island (33°57′ N, 139°22′ E) and ST-4 of Sagami Bay (35°00′ N, 139°22′ E). It is confirmed that mid-depth all over the western North Pacific water is affected by the mantle helium with a high 3He/4He ratio. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
10.
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