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561.
562.
The available data on the destructive intermediate earthquakes (M ? 634) in the Vrancea, Romania, region have been examined with the aim of revealing some time-magnitude regularities. The basic idea is that the total sequence (? 1100–1973 yr.), which appears as random, could be decomposed in some regular source-components which, by extrapolation, are superimposed to predict the future total sequence.The common nature of faulting (reverse dip-slip) and inferred regularities in the time-magnitude pattern of destructive Romanian earthquakes — (a) three active (seismic) time-bands alternating with quiet periods, the existence of (b) “quasicycles” and of (c) “supercycles” — led to the following predictions: (1) the occurrence of a shock with M ≈ 634 ? 7 in 1980 ± 13 years; and (2) later earthquakes are predicted in 2005, in 2030–2040 (M ≈ 634 ? 7), and one with nearly maximum magnitude (M = 712?734) in 2070–2090.In every century, about 40 years represent a time interval of high seismic danger for Romania and, according to the proposed long-term time-magnitude model, three destructive earthquakes arc to occur in (and/or near) the evidenced seismic periods P1, P2 and P3.It is shown that, taking into account the actual difficulties involved in the earthquake prediction, the Vrancea destructive earthquake of March 4, 1977 (M = 7.1) was quite successfully predicted.  相似文献   
563.
Electronic and Mössbauer absorption spectra and electron microprobe data are correlated for iron-bearing orthopyroxenes. The correlation provides a means of quantitatively determining the distribution of Fe2+ between the M(1) and M(2) sites of orthopyroxene crystals from electronic spectra and electron microprobe analysis. The electronic spectra are used to analyze the changes in the Fe2+ distribution produced during heating experiments and confirm earlier results from Mössbauer spectra. Two components of the spin-allowed transition of Fe2+ in the M(1) site are identified at about 13,000 cm?1 and 8,500 cm?1 in γ. Molar absorptivity (?) values for all spin-allowed Fe2+ absorption bands in the near-infrared region are determined. The M(2) Fe2+ band at ~5,000 cm?1 in β is the analytically most useful for site occupancy determinations. It remains linear with concentration (?=9.65) over the entire compositional range. The band at ~10,500 cm?1 in α is the most sensitive to M(2) Fe2+ concentration (?=40.8), but deviates from linearity at high iron concentrations. The origins of spin-forbidden transitions in the visible region are examined.  相似文献   
564.
565.
566.
Olivine clasts, which have mantles formed by reaction of the olivine with the breccia matrix, are present in the high-grade thermally metamorphosed Apollo 14 breccias. The mantled olivine clasts are most abundant in 14311, but they are also present in 14304 and 14319. Typically the mantles consist of two zones: an inner corona containing pyroxene, ilmenite and commonly plagioclase, and an outer light-colored halo where the matrix is depleted in ilmenite. The growth of the coronas involved matrix-to-corona diffusion of TiO2 and corona-to-matrix diffusion of MgO and FeO. These diffusive fluxes can be attributed to chemical potential gradients developed between mineral assemblages in local equilibrium at the olivine-corona boundary and the matrix.  相似文献   
567.
The use of Schlumberger and dipole arrays for crustal-scale resistivity soundings is considered. Advantages and disadvantages of the two methods are described. The depth to which resistivity may be determined from field measurements is discussed as well as the determination from the sounding curves of various parameters associated with layered structure. The interpretation of experimental data using reference curves as well as two approaches used in computer assisted interpretation are discussed.  相似文献   
568.
Prior experimental work has shown that in the laboratory the mineralogy of eclogites is sensitive to the ratio of CaO ∶ MgO ∶ FeO and that the reaction pyroxene + kyanite?garnet + quartz proceeds to the right at high pressures in rocks rich in magnesium and to the left in rocks rich in calcium and iron. Typical basalts crystallized at high pressure never contain kyanite. The chemistry and mineralogy of a large number of naturally occurring eclogites show they belong to three classes.
  1. Kyanite-free magmatic eclogites, rich in magnesium, from:
  2. kimberlites
  3. dunites and serpentinites.
  4. Kyanite-bearing eclogites and grosspydites rich in CaO and low in FeO with intermediate MgO from:
  5. kimberlites
  6. gneisses.
  7. Kyanite-free eclogites of metamorphic origin rich in iron with low magnesium and intermediate amounts of calcium from:
  8. glaucophane schists
  9. gneisses.
  相似文献   
569.
George W. DeVore 《Lithos》1983,16(4):255-263
The hydrated altered basalts of the oceanic crust, if subducted, could release large volumes of water during their phase transformations and partial melting reactions. If heat from shear strain recrystallizations largely heats the altered basaltic layer, only a 2 km thick layer could be heated significantly before the slab reaches 80–125 km depth. Most of the released waters should be driven into the deeper but cooler regions at the slab and andesitic-tonalitic partial melts should form in the heated altered basalt layer. Large volumes of water initially at the surface could be added to the mantle and tonalitic partial melts could be lost from the oceanic crust and added to the continental plate and could account for continental growth.  相似文献   
570.
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