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21.
Abstract A recent K–Ar study elucidated that eruptive style in the eastern Izu peninsula changed from polygenetic to monogenetic volcano at 0.3–0.2 Ma. To narrow down the time of change, we determined 10 K–Ar ages on Togasayama Andesite of Amagi volcano, the youngest polygenetic volcano in the area, and Togasayama Monogenetic Volcano, one of the oldest monogenetic volcanoes in the area, which overlies a part of the Togasayama Andesite. Dating results showed that the Togasayama Andesite effused at least from 0.34 to 0.20 Ma, whereas the Togasayama Monogenetic Volcano erupted at 0.26–0.29 Ma, suggesting that the northern part of the Togasayama Andesite effused after the eruption of the Togasayama Monogenetic Volcano. Considering previous data, it is therefore inferred that change of eruptive style in the eastern Izu area occurred during the period 0.29–0.20 Ma, with considerable overlap of both polygenetic and monogenetic volcanism. 相似文献
22.
有机碳同位素示踪古环境变化研究 总被引:4,自引:0,他引:4
对有机碳同位素示踪环境变化的原理、研究对象、取得的进展和存在的问题等进行了详细研究,认识到C~H键比C-O键有利于富集^12C,从而导致生物或有机碳δ^13C为极低的负值,使有机碳与无机碳之间存在显著的碳同位素差异。光合作用类型的不同使植物分为C3,C4和CAM3种类群,并导致不同类群的植物具有不同的碳同位素组成,C3植物δ^13C=-20‰~-32‰,平均-28‰,而C4植物δ^13C=-9‰~-17‰,平均-14‰。气候环境的差异影响了光合作用的类型和强度,使不同环境的植物类群特征不同,不仅造成植物组合的碳同位素组成不同,而且导致不同食性的动物牙齿等化石的碳同位素组成的差异,甚至相应的无机碳同位素的变化,因此生物链及其衍生物的碳同位素研究也就成为反演某一地区或某一时期气候环境的有效手段。被作为研究对象的地质记录可分为有机和无机两类,有机类主要包括树轮等植物化石、牙齿等动物化石、煤等陆相沉积有机质、海相沉积有机质、土壤(前者的衍生物),这些研究对象分别适合于目的不同的环境研究,并获得了较好的效果。进而发现有机碳同位素在研究重大生物灭绝事件、C4植物起源、地球早期生命起源、地外生命存在与否、矿产资源形成时的有机质作用等问题上将有重要作为。 相似文献
23.
NEKVASIL H.; DONDOLINI A.; HORN J.; FILIBERTO J.; LONG H.; LINDSLEY D. H. 《Journal of Petrology》2004,45(4):693-721
Experimental simulation of incremental crystal fractionationof a hy-normative hawaiite indicates that the spectrum of compositionsfrom mildly alkalic hawaiite to sodic rhyolite found in silica-saturatedalkalic suites of the ocean islands and continental hotspotsand rifts can be produced by fractionation at 9·3 kbarwith bulk water contents > 相似文献
24.
A method for calculating effective bulk composition modification due to crystal fractionation in garnet-bearing schist: implications for isopleth thermobarometry 总被引:11,自引:1,他引:11
T. P. Evans 《Journal of Metamorphic Geology》2004,22(6):547-557
Quantitative P–T path determination in metamorphic rocks is commonly based on the variation in composition of growth‐zoned garnet. However, some component of growth zoning in garnet is necessarily the result of an effective bulk composition change within the rock that has been generated by crystal fractionation of components into the core of garnet. Therefore, any quantitative calculation of the P–T regime of garnet growth should be completed using an accurate assessment of the composition of the chemical system from which garnet is growing. Consequently, a method for calculating the extent of crystal fractionation that provides a means of estimating the composition of the unfractionated rock at any stage during garnet growth is developed. The method presented here applies a Rayleigh fractionation model based on measured Mn content of garnet to generate composition v. modal proportion curves for garnet, and uses those curves to estimate the vectors of crystal fractionation. The technique is tested by calculating the precision of the equilibrium between three garnet compositional variables within the chemical system determined to be appropriate for each of a series of microprobe analyses from garnet. Application of the fractionation calculations in conjunction with the P–T estimates based on intersecting compositional isopleths provides a means of calculating P–T conditions of garnet growth that is based on individual point‐analyses on a garnet grain. Such spatially precise and easily obtainable P–T data allow for detailed parallel studies of the microstructural, the P–T, and the chemical evolution of metamorphosed pelites. This method provides a means of studying the dynamics of orogenic systems at a resolution that was previously unattainable. 相似文献
25.
26.
Under Rayleigh equilibrium condition, stable isotopic ratio in residual water increases with the decrease of the residual water proportion f exponentially, and the fractionation rate of stable isotopes is inversely proportional to temperature. However, under kinetic evaporation condition, the fractionation of stable isotopes is not only related to the phase temperature but also influenced by the atmospheric humidity and the mass exchange between liquid and vapor phases. The ratio δ in residual water will not change with f after undergoing evaporation of a long time for great relative humidity. The rate that the evaporating water body reaches isotopic steady state is mainly dependent on the relative humidity in atmosphere. The analysis shows that the actual mean linear variety rates, about -30.0, of the δ18O in residual water versus the residual water proportion at Nagqu and Amdo stations are consistent with the simulated process under temperature of 20 oC and relative humidity of 50%. The distillation line simulated under Rayleigh equilibrium condition is analogous to the global meteoric water line (MWL) as the temperature is about 20 oC. Under non-equilibrium condition, the slope and constant values of distillation line are directly proportional to temperature and relative humidity. According to the basic data, the simulated distillation line is very consistent with the actual distillation line of Qinghai Lake. 相似文献
27.
Paul J. Sylvester 《Geostandards and Geoanalytical Research》2005,29(1):41-52
This annual review of laser-ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) covers the year 2003. Significant advances were made in understanding laser-sample interactions. In particular, research defined the distribution of particle sizes produced by the interplay of laser wavelength, laser pulse width and the gas environment of ablation. A link between particle sizes and elemental and isotopic fractionation at both the ablation site and in the ICP was established. Experimental 15 7 nm and femtosecond laser systems were tested with promising results. The number of applications of LA-ICP-MS in geology and environmental Earth science continued to grow with particular interest in element concentration and isotope ratio profiling of materials, linking composition to time scales. In situ isotopic ratio measurements were increasingly made using multicollector magnetic sector ICP-MS instruments. Other applications of wide interest included bulk sampling of rocks and ores prepared as lithium borate glasses; low level analysis of platinum-group elements, rhenium and gold in sulfides, metal and silicates; in situ uranium-lead zircon geochronology; and melt and fluid inclusion analysis. 相似文献
28.
29.
Multi-isotope (H, O, S, Sr, Pb) systems coupled with conventional (major and trace element) hydrogeochemical analysis were applied to determine the origin of water, to model water-rock-tailings interactions and for source apportionment of sulfur and associated toxic metals in the mining region of Taxco, Guerrero in southern Mexico. Oxygen and H isotopes indicate that meteoric water in the zone is rainwater undergoing varying degrees of isotopic fractionation by atmospheric evaporation whereas Sr isotopes trace the interaction of pristine water from volcanics of the regional recharge zone and subsequently flowing through sandstone and shale to spring points. Leachates form from two distinctive sources (spring water and surface water) having differential interactions with bedrocks prior to entering the tailings. Compared to pristine water, leachates are enriched in sulfate, metals (e.g. Fe, Mn, Pb and Zn) and metalloids (e.g. As). The sulfur isotopic composition of ore-sulfides, leachates, secondary precipitates, regional surface water and hypogenic sulfates is described in terms of a two-component mixing model with shale of Mexcala and limestone of Morelos formations representing the light and heavy end-members, respectively, whereas Sr isotopic composition is bracketed combining three lithogenic (Mexcala/Morelos, Tilzapotla and Taxco Schist) sources. Finally, leachates have a mixture of lead from ore-sulfides and Taxco Schist Formation (Family I) or from ore-sulfides alone (Family II). The application of multiple environmental isotopic techniques is an outstanding tool for elucidating complex interactions of water with bedrocks and tailings and for determining the source of sulfur and toxic metal from mining and other metal polluted environments. 相似文献
30.
Ablation Characteristic of Ilmenite using UV Nanosecond and Femtosecond Lasers: Implications for Non‐Matrix‐Matched Quantification 下载免费PDF全文
Zhen Li Zhaochu Hu Detlef Günther Keqing Zong Yongsheng Liu Tao Luo Wen Zhang Shan Gao Shenghong Hu 《Geostandards and Geoanalytical Research》2016,40(4):477-491
Ilmenite (FeTiO3) is a common accessory mineral and has been used as a powerful petrogenetic indicator in many geological settings. Elemental fractionation and matrix effects in ilmenite (CRN63E‐K) and silicate glass (NIST SRM 610) were investigated using 193 nm ArF excimer nanosecond (ns) laser and 257 nm femtosecond (fs) laser ablation systems coupled to an inductively coupled plasma‐mass spectrometer. The concentration‐normalised 57Fe and 49Ti responses in ilmenite were higher than those in NIST SRM 610 by a factor of 1.8 using fs‐LA. Compared with the 193 nm excimer laser, smaller elemental fractionation was observed using the 257 nm fs laser. When using 193 nm excimer laser ablation, the selected range of the laser energy density had a significant effect on the elemental fractionation in ilmenite. Scanning electron microscopy images of ablation craters and the morphologies of the deposited aerosol materials showed more melting effects and an enlarged particle deposition area around the ablation site of the ns‐LA‐generated crater when compared with those using fs‐LA. The ejected material around the ns crater predominantly consisted of large droplets of resolidified molten material; however, the ejected material around the fs crater consisted of agglomerates of fine particles with ‘rough' shapes. These observations are a result of the different ablation mechanisms for ns‐ and fs‐LAs. Non‐matrix‐matched calibration was applied for the analysis of ilmenite samples using NIST SRM 610 as a reference material for both 193 nm excimer LA‐ICP‐MS and fs‐LA‐ICP‐MS. Similar analytical results for most elements in ilmenite samples were obtained using both 193 nm excimer LA‐ICP‐MS at a high laser energy density of 12.7 J cm?2 and fs‐LA‐ICP‐MS. 相似文献