The nine elastic constants of andalusite and sillimanite have been determined, using the technique of Brillouin scattering. They are, in megabars, for andalusite: c11=2.334, c22=2.890, c33=3.801, c44=0.995, c55=0.878, c66=1.123, c23=0.977, c13=1.162, c12=0.814; for sillimanite: c11=2.873, c22=2.319, c33=3.884, c44=1.224, c55=0.807, c66=0.893, c23=1.586, c13=0.834, c12=0.947. Both structures are characterized by chains of edge-linked coordination octahedra extending parallel to the crystallographic c direction, cross-linked by polyhedra of lower coordination. In each structure the stiffness measured parallel to c is greater than that measured normal to c. The shear moduli can be directly correlated with the relative rigidity of the cross-linking structures. 相似文献
The seismic probing of the crust and upper mantle in Canada started in 1938 and since then has involved many government and university groups using a wide variety of techniques. These have included simple profiling with both wide and narrow station spacing, areal time-term surveys, detailed deep reflection experiments, very long-range refraction studies and the analysis of surface wave dispersion between stations of the Canadian Standard Network.
A review of the published interpretation leads to the general conclusion that:
1. (1) Pn-velocities vary from a value possibly as low as 7.7 km/sec under Vancouver Island to 8.6 km/sec and higher in the extreme eastern part of the shield and some parts of the Atlantic coast.
2. (2) Large areas of Canada have a crustal thickness of 30–40 km, with Vancouver Island, the southwestern Prairies, the Lake Superior basin and parts of the eastern shield of Quebec being thicker. No continental area in Canada is known to have a crust thinner than 29 km.
3. (3) The Riel discontinuity — a deep intra-crustal reflector and sometime refractor, is widely reported in the Prairies and Manitoba. It is not seen to the north in the vicinity of Great Slave Lake, nor in the Hudson Bay, Lake Superior and Maritime regions, nor in the interior of British Columbia. It may be present in some areas of the eastern shield.
4. (4) As experiments have become more detailed, crustal structures of greater complexity have been revealed. The concept that crustal structure becomes simpler with increasing depth is apparently unfounded.
Long-range refraction studies suggest that the Gutenberg P-wave low-velocity channel is poorly developed under the Canadian Shield. The analysis of the dispersion of surface waves, however, suggests that the channel is better developed for S-waves, and is present throughout the country. The lid of the channel is deepest under the central shield and shallowest under the Cordillera. 相似文献
Multiple linear regression analysis has been applied to the geometric and chemical variables in sodic plagioclases in order to determine their relative effects on individual T-O bond lengths in the Al1+xSi3?xO8 tetrahedral framework. Using data from crystal structure analyses of low and high albite, An16 and An28, and assuming that low albite is completely ordered, 1 $$\begin{gathered} {\text{T}} - {\text{O = 1}}{\text{.568}} + {\text{[(0}}{\text{.122) x (Al content of the T site)]}} \hfill \\ {\text{ }} - {\text{[(0}}{\text{.037) x (}}\Delta {\text{{\rm A}l}}_{{\text{br}}} )] + [0.063){\text{ x }}(\Sigma {\text{[}}q{\text{/(Na,Ca}} - {\text{O)}}^{\text{2}} ])] \hfill \\ {\text{ }} + {\text{[(0}}{\text{.029) x (}} - {\text{1/cosT}} - {\text{O}} - {\text{T)]}} \hfill \\ \end{gathered}$$ where the Al content of a particular tetrahedral (T) site can be estimated from empirically-derived determinative curves, where Δ Albr is a linkage factor to account for the Al content of adjacent tetrahedral sites, where the formal charge on the (Na1?xCax) atom is q=1+x, and where T-O-T is the inter-tetrahedral angle involving the T-O bond. For sodic plagioclases it is essential to know only the anorthite content and the 2Θ131-2Θ1¯31 spacing (CuKα radiation) in order to determine the independent variables in this equation and thus to evaluate the individual T-O distances. The 64 individual T-O distances predicted for the four sodic plagioclases by this equation agree well with the observed T-O bond lengths (σ=0.004 Å; r=0.994), and the method has been used by way of example to rationalize the T-O bond lengths in analcime (cf. Ferraris, Jones and Yerkess, 1972). 相似文献
Eighteen international reference standards, mostly geochemical standards, have been analysed for boron using prompt-gamma neutron activation analysis (PGNAA). There is good agreement between the results for samples with high boron abundances and the few published values using PGNAA and other methods. However, correlation is poor at low boron abundances, especially in those standards with low boron/sodium ratios. Corrections for sodium interference on boron have been critically evaluated and the data corrected using two different methods. 相似文献
Formation of deep basins on continental crust in fold belts is often explained by stretching. This mechanism inevitably produces large deformations in the upper crust. No deformations typical of significant stretching were revealed in the predominant part of deep basins on continental crust in the Alpine Belt. This means that these basins were not produced by stretching. Most basins were formed during a short period of time of a few million years. The short duration of the subsidences eliminates thermal relaxation as the mechanism. The space and time relationships between the subsidence and orogeny and the profile of the basin floor exclude thrust loading as a cause of formation for practically all large basins. Gabbro to eclogite transformation is suggested as a mechanism of rapid subsidence. This occurs under the upwelling of hydrous asthenosphere at moderate temperature to the base of the crust. Eclogite sinking into the mantle results in a strong attenuation of the crust and lithosphere, which permits intense subsequent folding. The major part of deep basins in continental crust that formed by rapid subsidence was intensely shortened in the Alpine Belt. Significant crustal shortening did not spread over the cratonic lithosphere. 相似文献
Here we report on a set of six apatite reference materials (chlorapatites MGMH#133648, TUBAF#38 and fluorapatites MGMH#128441A, TUBAF#37, 40, 50) which we have characterised for their chlorine isotope ratios; these RMs span a range of Cl mass fractions within the apatite Ca10(PO4)6(F,Cl,OH)2 solid solution series. Numerous apatite specimens, obtained from mineralogical collections, were initially screened for 37Cl/35Cl homogeneity using SIMS followed by δ37Cl characterisation by gas source mass spectrometry using both dual‐inlet and continuous‐flow modes. We also report major and key trace element compositions as determined by EPMA. The repeatability of our SIMS results was better than ± 0.10‰ (1s) for the five samples with > 0.5 % m/m Cl and ± 0.19‰ (1s) for the low Cl abundance material (0.27% m/m). We also observed a small, but significant crystal orientation effect of 0.38‰ between the mean 37Cl/35Cl ratios measured on three oriented apatite fragments. Furthermore, the results of GS‐IRMS analyses show small but systematic offset of δ37ClSMOC values between the three laboratories. Nonetheless, all studied samples have comparable chlorine isotope compositions, with mean 103δ37ClSMOC values between +0.09 and +0.42 and in all cases with 1s ≤ ± 0.25. 相似文献
The East Pacific Rise (EPR) at 9°50'N hosts a hydrothermal vent field (Bio9) where the change in fluid chemistry is believed to have caused the demise of a tubeworm colony. We test this hypothesis and expand on it by providing a thermodynamic perspective in calculating free energies for a range of catabolic reactions from published compositional data. The energy calculations show that there was excess H2S in the fluids and that oxygen was the limiting reactant from 1991 to 1997. Energy levels are generally high, although they declined in that time span. In 1997, sulfide availability decreased substantially and H2S was the limiting reactant. Energy availability dropped by a factor of 10 to 20 from what it had been between 1991 and 1995. The perishing of the tubeworm colonies began in 1995 and coincided with the timing of energy decrease for sulfide oxidizers. In the same time interval, energy availability for iron oxidizers increased by a factor of 6 to 8, and, in 1997, there was 25 times more energy per transferred electron in iron oxidation than in sulfide oxidation. This change coincides with a massive spread of red staining (putative colonization by Fe-oxidizing bacteria) between 1995 and 1997. For a different cluster of vents from the EPR 9°50'N area (Tube Worm Pillar), thermodynamic modeling is used to examine changes in subseafloor catabolic metabolism between 1992 and 2000. These reactions are deduced from deviations in diffuse fluid compositions from conservative behavior of redox-sensitive species. We show that hydrogen is significantly reduced relative to values expected from conservative mixing. While H2 concentrations of the hydrothermal endmember fluids were constant between 1992 and 1995, the affinities for hydrogenotrophic reactions in the diffuse fluids decreased by a factor of 15 and then remained constant between 1995 and 2000. Previously, these fluids have been shown to support subseafloor methanogenesis. Our calculation results corroborate these findings and indicate that the 1992-1995 period was one of active growth of hydrogenotrophic communities, while the system was more or less at steady state between 1995 and 2000. 相似文献
An experiment, in which an iron-nickel-copper sulphide melt was heated with synthetic chromite and then cooled, showed that substantial quantities of chromite had dissolved in the melt and had then recrystallized as euhedral crystals rimmed with magnetite. This experiment suggests that the unusual chromite (low in Mg and Al) which is associated with the sulphide phase in Western Australian nickel ores may have formed in a similar way.J.M.R. carried out the experimental part of this investigation as a post-graduate student at Flinders University, South Australia, working under a CSIRO extramural grant. 相似文献