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241.
The effect of fluids on recrystallization behaviour is well known; however, the detailed microscale distribution of fluid in grain boundaries and the influence of fluid on grain boundary migration are still unresolved. In this study, in‐situ deformation experiments in transmitted light microscopy were undertaken, as this allows continuous and direct observation of the whole range of processes involved in fluid‐assisted grain boundary migration. A new see‐through deformation apparatus was developed to enable the control of fluid pressure. Bischofite containing small amounts of aqueous fluid was deformed at temperatures between 50 and 90 °C, over a range of fluid pressure from 0.5 to 1 MPa, and strain rates of 5 × 10?6 to 1 × 10?4 s?1. The rates of grain boundary migration were measured at different temperatures and strain rates. Detailed observations during and after the deformation illustrate the evolution of migrating fluid‐filled grain boundaries and show that the incorporation of fluids from inclusions as well as their pinch‐off is dependent on the grain boundary velocity, the thickness of the grain boundary and the size and shape of the inclusions. Direct evidence is presented for the contraction of the grain boundary fluids into isolated inclusions after equilibrium conditions are attained. 相似文献
242.
Abstract. Scanning electron microscopy-cathodoluminescence (SEM-CL) imaging of vein quartz in the Cu-mineralised, Shuteen Complex (South Gobi, Mongolia) has revealed a complex history of crystal growth, dissolution and microfracture healing, associated with several hydrothermal events that could not be detected using other observational techniques (e.g. transmitted/reflected light microscopy, back-scattered electron imaging, or secondary electron imaging).
The quartz initially grew as CL-bright/grey crystals in a 345±30C liquid reservoir, as inferred by the analysis of primary liquid fluid inclusions (average Th of 343C; 6.6∼7.7 wt% NaCleq ). Quartz precipitation occurred at the edge of the crystals as reservoir fluids cooled to 260±25C, as indicated by micron-scale CL-dark/CL-bright quartz growth bands containing abundant fluid inclusions (with an average Th values of 261C). Pressure fluctuations were the likely cause of dissolution, as SEM-CL imaging reveals the quartz have corroded or rounded crystal edges, and precipitation of later quartz into open space. SEM-CL imaging shows the quartz contains healed microfractures that trapped low salinity fluids (3.9 wt% NaC1eq ) with Th values of 173±15C.
SEM-CL imaging provides a means of deciphering the thermal and chemical evolution of the fossil Shuteen hydrothermal system, and the nature of hydrothermal quartz vein-forming processes, by facilitating the correlation of distinct fluid inclusion populations and their relative chronology, with specific hydrothermal events. 相似文献
The quartz initially grew as CL-bright/grey crystals in a 345±30C liquid reservoir, as inferred by the analysis of primary liquid fluid inclusions (average Th of 343C; 6.6∼7.7 wt% NaCl
SEM-CL imaging provides a means of deciphering the thermal and chemical evolution of the fossil Shuteen hydrothermal system, and the nature of hydrothermal quartz vein-forming processes, by facilitating the correlation of distinct fluid inclusion populations and their relative chronology, with specific hydrothermal events. 相似文献
243.
This paper describes palynological evidence for what appears to be comparatively large-scale human impact in the catchment of the Sungai Niah in the wet tropical lowland swamp forests of Sarawak, Malaysian Borneo close to the Great Cave of Niah. Pollen associated with cleared landscapes and rice cultivation is evident in the sedimentary record from before 6000 cal yr B.P. Human activity seems to have been associated with changes in sedimentary regime, with peat-dominated environments being replaced diachronously by clay-dominated deposition. This may reflect anthropogenic soil erosion in the catchment of the Sungai Niah. 相似文献
244.
We analyze multicolor observations of the blazar ON 231 obtained during coordinated observations in 1994–2002. On average, the spectral energy distribution of the variable component in the optical range remains constant, and can be represented
by the power law F
ν ∼ ν
−0.85. Since the radiation of the blazar is strongly polarized, there is no doubt that the variable emission that is responsible
for the activity of the blazar is synchrotron radiation. There are small but significant season-to-season variations in the
spectral index. 相似文献
245.
The main argument against the idea that the intense radio emission observed from active regions on the Sun and flare stars is electron-cyclotron maser (ECM) radiation is that such radiation should be strongly absorbed in higher-lying layers where the condition for the cyclotron resonance at harmonics of the electron gyrofrequency is fulfilled. Cyclotron absorption lowers the efficiency of ECM radiation virtually to zero for a broad range of angles between the direction of propagation of the radiation and the magnetic field. Less severe absorption is possible only in narrow angular “windows” along (for ordinary and extraordinary waves) and perpendicular to (for ordinary waves) the magnetic field. However, the ECM radiation that is generated does not fall into these windows of transparency due to the kinematic conditions corresponding to coronal magnetic traps. We investigate the efficiency of induced scattering of ECM radiation on ions in the equilibrium plasma in the source. Under certain conditions, induced scattering leads to the formation of a condensate of ECM radiation with the direction of its wave vectors approximately along the magnetic field, enabling the escape of the radiation through windows of transparency. The most favorable conditions for this phenomenon are realized for ordinary waves. We estimate the optical depths of the sources of the ECM radiation to the scattering and the angular width of the condensate for ordinary and extraordinary waves for the cases of the flare radio emission of the star AD Leo and the sources of type I noise storms in the solar corona. In both cases, the polarization of the emergent radiation should correspond to the ordinary wave. 相似文献
246.
B. A. Elliott W. H. Peck O. T. Rämö M. Vaasjoki M. Nironen 《Mineralogy and Petrology》2005,85(3-4):223-241
Summary Oxygen isotope ratios of igneous zircon from magmatic rocks in Finland provide insights into the evolution and growth of the
Precambrian crust during the Svecofennian orogeny. These data preserve magmatic δ18O values and correlate with major discontinuities in the lower crust. Oxygen isotope ratios of zircon across the 1.88–1.87 Ga
Central Finland granitoid complex (CFGC) range from 5.50‰ to 6.84‰, except for three plutons in contact with the adjacent
greenstone and metasedimentary belts (δ18O(Zrc) = 7.60‰–7.78‰). There is a systematic variation in δ18O(Zrc) with respect to geographic location in the CFGC, ranging from 6.60±0.23‰ (σ) in the northeast to 5.90±0.40‰ in the
west-southwest. These values correlate with a change in crustal thickness and shift in geochemical composition. The oxygen
isotope composition of the 1.65–1.54 Ga rapakivi granites and related rocks in southern Finland show a decreasing trend from
north to south, independent of their emplacement age. The southern anorogenic granite group has an average δ18O in zircon of 6.14±0.07‰ and the northern anorogenic group has an average δ18O in zircon of 8.14±0.59‰. This difference reflects the boundary between island arc terrains accreted during the Paleoproterozoic.
Deceased 相似文献
247.
High-resolution historical records from Pettaquamscutt River basin sediments: 2. Pb isotopes reveal a potential new stratigraphic marker 总被引:2,自引:0,他引:2
Ana Lúcia Lima Bridget A. Bergquist Matthew K. Reuer Francis O. Dudas Timothy I. Eglinton 《Geochimica et cosmochimica acta》2005,69(7):1813-1824
A high-resolution record of Pb deposition in Rhode Island over the past 250 yr was constructed using a sediment core from the anoxic Pettaquamscutt River basin. The sedimentary Pb concentration record shows the well-described maximum associated with leaded gasoline usage in the United States. Diminished Pb variability during recorded periods of local industrial activity (1735 to 1847) supports the greater importance of regional atmospheric lead transport vs. local inputs. The Pb isotopic composition at this site shows a clear maximum in anthropogenic 206Pb/207Pb in the mid-1800s. Similar peaks have also been observed in sediments from Chesapeake Bay and the Great Lakes, suggesting a common source. Possible causes for this event include mining and smelting of Pb ores in the Upper Mississippi Valley district, which accounted for almost all Pb production in the United States in that period. The timing of this event can provide an important stratigraphic marker for sediments deposited in the past 200 yr in the Northeastern United States. The downcore profile of anthropogenic 206Pb/207Pb provides a classic example of how changes in the mixture of ores for production of tetraethyl lead caused a regional-scale shift in the sedimentary record, and suggests that coal could have played a secondary role in Pb emissions after 1920. 相似文献
248.
Ya.P. Malovitskiy E.M. Emelyanov O.V. Kazakov V.N. Moskalenko G.V. Osipov K.M. Shimkus I.S. Chumakov 《Marine Geology》1975,18(5):231-261
According to geophysical data, the Mediterranean Sea depressions are noted for a peculiar type of the earth's crust. The sedimentary rock sequence is of great thickness (8–15 km) and is of platform-type dislocation. Several structural stages are distinguished in the sedimentary complex. The youngest of them are the Messinian (evaporite) and Pliocene—Quaternary stages. The consolidated part of the earth's crust shows small thickness and is divided into large blocks. Vertical dislocations of the large crustal blocks which were conditioned by condensation—rarefaction and the upper mantle substance migration were at the base of Mediterranean sea floor transformation. 相似文献
249.
Slope stability FEM analysis and retaining wall design: a case study of clinker in Benxi of Liaoning
Aref M. O. AL-JABALI Lei NIE Jianlei LIU Huangping DING Nengjuan ZHOU Mohammed HAZAEA 《世界地质(英文版)》2008,11(2)
Stability is always the most important problem after high slope was excavated. The study analyzed the stress and strain inside the slope by Finite Element Method (FEM) and carried through stress distribution and failure zone, then analyzed the stability of the slope using three different methods and came to the conclusion that it is in unstable condition, so the designed retaining wall was put forward which makes the slope stable. 相似文献
250.