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221.
222.
Three planktonic foraminiferal species Globigerina bulloides, Neogloboquadrina pachyderma (d), and Globorotalia inflata collected from core-tops spanning 35° to 65°N in the North Atlantic were used for U/Ca and Mg/Ca and foraminiferal shell weight analyses. Except for U/Ca in G. bulloides calcified under warm conditions (>∼13 °C), U/Ca ratios in all three studied species increase with decreasing latitude and show strong positive correlations with Mg/Ca ratios. A dissolution effect on planktonic U/Ca is suggested by decreased shell weight and U/Ca and Mg/Ca ratios for shells from very deep water depth (>4.4 km) along the latitudinal transect. G. bulloides from down core samples in the North Atlantic show low U/Ca ratios during the last glacial and high ratios during the Holocene, similar to the Mg/Ca evolution trend. In general, our data indicate that the U incorporation into planktonic foraminiferal carbonates is strongly influenced by calcification temperature, although U/Ca in G. bulloides may be affected by seawater carbonate ion concentration under warm conditions and/or other factors. 相似文献
223.
The study of granitic plutons of the Baikal Highland and the Tien Shan has made it possible to establish new features of their posthumous (after incorporation into the consolidated Earth’s crust) structural reworking and to understand the implications of the cataclastic flow for the exhumation of the crystalline basement in the studied regions. It is shown that granitic plutons undergo appreciable structural transformation at the stages of tectonic reactivation that is significantly separated in time from the moment of formation of plutons as geological bodies. The 3D cataclastic deformation is the main mode of structural reworking of granitic plutons, while the cataclastic flow is the main form of their mobility. Newly recognized slice structures characterize the volumetric deformation of granites. 相似文献
224.
The structure of anomalously uplifted areas in transverse ridges of the Vema, S o Paulo, and Romanche fracture zones is considered. It is concluded that their formation and eventual development in the present-day structure of the central Atlantic bottom proceeded during two stages. The first stage that corresponds to a short period at the Tortonian-Messinian transition (10 Ma ago) was marked by transportation of deep-seated rocks into the upper part of the lithosphere along thrust faults with mass motion in the meridional direction along the axis of the Mid-Atlantic Ridge. The second stage was characterized by contrasting highamplitude vertical movements from 10 to 3 Ma ago. It is suggested that near-meridional compression in the domains surrounding the Western Tethys in the Tortonian-Messinian resulted in deformation of the upper lithosphere within large transform fracture zones of the central Atlantic. The deformation that occurred 10 Ma ago was a manifestation of the global neotectonic epoch of the Earth. 相似文献
225.
Sorption of Ni2+ on Na-rectorite as a function of contact time, temperature, pH and fulvic acid (FA)/humic acid (HA) was studied under ambient conditions. A pseudo-second-order rate equation was used to simulate the kinetic sorption. The removal of Ni2+ increased with increasing pH. The presence of FA/HA enhanced the sorption of Ni2+ at low pH values, whereas no drastic effect of FA/HA on Ni2+ uptake to rectorite was found at high pH values. The diffuse layer model (DLM) fitted the experimental data of Ni2+ sorption in the absence and presence of FA/HA very well with the aid of FITEQL 3.2. The Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were used to simulate the sorption isotherms of Ni2+ at different temperatures. The thermodynamic data (ΔH0, ΔS0, ΔG0) were calculated from the temperature dependent sorption isotherms and the results suggested that the sorption process of Ni2+ on rectorite was spontaneous and endothermic. The sorption and species of Ni2+ on rectorite in the presence and absence of FA/HA was also investigated and characterized by XPS. The spectroscopic analysis indicated no drastic structural changes of Na-rectorite and the sorption of Ni2+ mainly occurred on the surface and at the edge position of Na-rectorite. 相似文献
226.
V. S. Kulikov Ya. V. Bychkova V. V. Kulikova Yu. A. Kostitsyn O. S. Pokrovsky M. V. Vasil’ev 《Petrology》2008,16(6):531-551
The Ruiga differentiated mafic-ultramafic intrusion in the northwestern part of the Vetreny Belt paleorift was described for the first time based on geological, petrological, geochronological, and geochemical data. The massif (20 km2 in exposed area) is a typical example of shallow-facies peridotite-gabbro-komatiite-basalt associations and consists of three zones up to 810 m in total thickness (from bottom to top): melanogab-bronorite, peridotite, and gabbro. In spite of pervasive greenschist metamorphism, the rocks contain locally preserved primary minerals: olivine (Fo 75–86), bronzite, augite of variable composition, labradorite, and Cr-spinels. A mineral Sm-Nd isochron on olivine melanogabbronorite from the Ruiga Massif defines an age of 2.39 ± 0.05 Ga, while komatiitic basalts of the Vetreny Belt Formation were dated at 2.40–2.41 Ga (Puchtel et al., 1997). The rocks of the Ruiga intrusion and lava flows of Mt. Golets have similar major, rare-earth, and trace element composition, which suggests their derivation from a single deep-seated source. Their parent magma was presumably a high-Mg komatiitic basalt. In transitional crustal chambers, its composition was modified by olivine-controlled fractionation and crustal contamination, with the most contaminated first portions of the ejected melt. In terms of geology and geochemistry, the considered magmatic rocks of the Vetreny Belt are comparable with the Raglan Ni-PGE komatiite gabbro-peridotite complex in Canada (Naldrett, 2003). 相似文献
227.
The paper is devoted to the conditions under which opacite rims developed around hornblende grains in andesite of the catastrophic eruption (March 30, 1956) of Bezymyannyi volcano, Kamchatka. The opacite rims were produced by a bimetasomatic reaction between hornblende and melt with the development of the following zoning: hornblende → Px + Pl + Ti-Mag → Px + Pl → Px → melt. Biometasomatic reaction was accompanied by the active removal of CaO from the rim, addition of SiO2, and more complicated behavior of other components. The hornblende also shows reactions of its volumetric decomposition under near-isochemical conditions. The opacite rims developed under isobaric conditions, at a pressure of approximately 6 kbar. The main reason for the instability of the hornblende was the heating of the magma chamber from 890 to 1005°C due to new hot magma portion injection. The time interval between the injection and the start of eruption was estimated from the thickness of the opacite rims and did not exceed 37 days. Hence, the March 30, 1956, eruption was not related to the volcanic activity in November of 1955 but to the injection of a fresh magma portion in February–March of 1956. 相似文献
228.
Vittorio Zanon Fátima Viveiros Catarina Silva Ana Rita Hipólito Teresa Ferreira 《Natural Hazards》2008,45(1):19-31
A detailed study was carried out on a piece of land that had been struck by lightning during the violent rainstorm that raged
over the Island of S?o Miguel (Azores Archipelago) in late October 2006. Temperature and gas measurements (CO2, CO, H2S and CH4) were performed in four study trenches, dug in an area of ∼3 m2, where an underground fire had been initiated by the impact with a lightning stroke, followed by the emission of a column
of gases and smoke. The soil under study was originally a well-pedogenized about 80 cm thick bed, made of volcanic clayey
to silty tephra fallouts and contained 5.5–9.7% of organic matter. The underground fire was monitored for one week and revealed a peak release of
404 ppm CO and 3.4% CO2 originating from a horizon located about 45 cm under the soil surface. Measurements of temperature, performed one week after
the impact, indicated a maximum value of 326°C inside the soil, while 516.5°C were measured on the surface of a lava block
interred about 20 cm under the surface. Subsequently, a stratigraphic and sedimentologic study proved the role of the grain-size
of the soil and of the organic matter content of the different horizons of the impact area, in determining the ratio between
anoxic/oxidised combustion conditions and in the progress of the process itself. It was also noticed that combustion was not
total all over in the soil bed and that the process had slightly migrated toward SW during the observation period. The combustion
process went on for about ten days, in spite of several other violent rainstorms, until it was artificially extinguished through
the excavations made to obtain study trenches. This particular circumstance evidenced the potential natural hazard represented
by this kind of atmospheric event, especially in a land where the volcanic nature of the soil may easily mislead inexperienced
observers and, consequently, delay proper action. 相似文献
229.
含硫化物脉状矿床成矿流体的中阶段 δD亏损:实例与原因 总被引:2,自引:0,他引:2
很多含硫化物脉状金银矿床的成矿过程可以大致分为3个阶段,从早到晚分别以形成黄铁矿-石英组合、多金属硫化物和碳酸盐网脉为标志.所谓中阶段δD亏损,是指在成矿流体δ18O逐渐降低(或升高)时,中阶段δD同时低于早阶段和晚阶段的δD.列举了一些矿床的氢氧同位素研究结果,例证了这种现象的存在;根据中阶段伴随大量硫化物沉淀的事实,认为硫化物沉淀时流体中H2S或HS-的H 被金属离子置换出来,H 加入到流体系统后导致了流体的中阶段δD亏损.对不同温度H2O-H2S体系1000In ot值的概算显示,在200-650℃温度范围,H2S或HS-的δD低于H2O的δD约211‰~478%‰,H2S或HS-中H 的少量释放即可导致流体水δD的显著降低.因此建议,成矿流体从早到晚δ18O逐渐降低,中阶段δD亏损的规律,可以作为含硫化物脉状矿床氢氧同位素演化的概念性模型. 相似文献
230.