In 1951–52, a nationwide sediment gauge network was initiated in Bulgaria. In 1992–93 a Computerized Information Base of Sediment Data for the Bulgarian rivers was developed. Some analysis has shown that the long term sequences of the annual suspended sediment load of the rivers are not homogeneous. The period 1980–90 has received special attention due to the anthropogenic generated randomeness of the hydrometeorological process on most of catchment areas across the country. Due to the anthropogenic impact, the sediment load assessments are strongly affected. The author has determined a new parameter — Partial Suspended Sediment yield — MR(°) that is formed in separate river reaches, bordered by any two adjacent gauges. The partial suspended sediment yield is zoned in selected grades instead of drawing isolines. A comparison among runoff (Q) and suspended load (R) for the rivers in Bulgaria reveals relationships that are in conformities with the process of suspended sediment formation. Some other empirical relationships of potential practical use for the Bulgarian rivers have been determined. The goal is to introduce some results of Bulgarian sediment studies to a Non-Bulgarian audience. 相似文献
Quartz grains in hydrothermally altered granites from the Isle of Skye are highly heterogeneous and not equilibrated in oxygen
isotope ratio at the 20 μm scale. Ion microprobe analysis of one grain shows a gradient of 13‰ over 400 μm and a greater range
in δ18O than all quartz previously analyzed on the Isle of Skye. Other crystals from the same outcrop are homogeneous. Digitized
cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable. The ion probe
analysis correlates low δ18O values on a micro-scale to one set of healed cracks. Thus, quartz exchanges oxygen isotopes primarily by solution and reprecipitation
along fractures, in contrast to more reactive feldspar that appears to exchange from the grain boundary inward. Macroscopic
models of isotope exchange are not realistic for these rocks; the flow of hydrothermal fluids was heterogeneous, anisotropic
and crack controlled.
Received: 23 October 1995/Accepted: 9 April 1996 相似文献
The melting reaction: albite(solid)+ H2O(fluid) =albite-H2O(melt) has been determined in the presence of H2O–NaCl fluids at 5 and 9.2 kbar, and results compared with those obtained in presence of H2O–CO2 fluids. To a good approximation, albite melts congruently at 9 kbar, indicating that the melting temperature at constant
pressure is principally determined by water activity. At 5 kbar, the temperature (T)- mole fraction (X(H2O) ) melting relations in the two systems are almost coincident. By contrast, H2O–NaCl mixing at 9 kbar is quite non-ideal; albite melts ∼70 °C higher in H2O–NaCl brines than in H2O–CO2 fluids for X(H2O) =0.8 and ∼100 °C higher for X(H2O) =0.5. The melting temperature of albite in H2O–NaCl fluids of X(H2O)=0.8 is ∼100 °C higher than in pure water. The P–T curves for albite melting at constant H2O–NaCl show a temperature minimum at about 5 kbar. Water activities in H2O–NaCl fluids calculated from these results, from new experimental data on the dehydration of brucite in presence of H2O–NaCl fluid at 9 kbar, and from previously published experimental data, indicate a large decrease with increasing fluid pressure
at pressures up to 10 kbar. Aqueous brines with dissolved chloride salt contents comparable to those of real crustal fluids
provide a mechanism for reducing water activities, buffering and limiting crustal melting, and generating anhydrous mineral
assemblages during deep crustal metamorphism in the granulite facies and in subduction-related metamorphism. Low water activity
in high pressure-temperature metamorphic mineral assemblages is not necessarily a criterion of fluid absence or melting, but
may be due to the presence of low a(H2O) brines.
Received: 17 March 1995/Accepted: 9 April 1996 相似文献
Dense sand-bentonite buffer (γd = 1.67Mg/m3) has been proposed in Canada as one of several barriers for isolating nuclear fuel waste. The buffer will be required to function under conditions of high total pressures and elevated temperatures approaching 100°C. Summary results are presented from two test programs: (1) isothermal consolidated undrained triaxial (CIU¯) tests; and (2) isothermal drained constant-p′ (CID) triaxial tests. Specimens were consolidated at effective stresses up to 9.0 MPa and temperatures up to 100°C.
The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressqf, and higher pore water pressure changesΔuf. The net result is curved peak strength envelops in plots ofqf versuspf′ that are higher at elevated temperatures, even though the strengths,qf of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes.
The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great. 相似文献
Neodymium and lead isotope and elemental data are presented for the Sebago batholith (293±2 Ma), the largest exposed granite
in New England. The batholith is lithologically homogeneous, yet internally heterogeneous with respect to rare earth elements
(REE) and Nd isotopic composition. Two-mica granites in the southern/central portion of the batholith (group 1) are characterized
by REE patterns with uniform shapes [CeN/YbN (chondrite normalized) = 9.4–19 and Eu/Eu* (Eu anomaly) = 0.27–0.42] and ɛNd(t) = −3.1 to −2.1. Peripheral two-mica granites (group 2), spatially associated with stromatic and schlieric migmatites,
have a wider range of total REE contents and patterns with variable shapes (CeN/YbN = 6.1–67, Eu/Eu* = 0.20–0.46) and ɛNd(t) = −5.6 to −2.8. The heterogeneous REE character of the group 2 granites records the effects of magmatic differentiation
that involved monazite. Coarse-grained leucogranites and aplites have kinked REE patterns and low total REE, but have Nd isotope
systematics similar to group 2 granites with ɛNd(t) = −5.5 to −4.7. Rare biotite granites have steep REE patterns (CeN/YbN = 51–61, Eu/Eu* = 0.32–0.84) and ɛNd(t) = −4.6 to −3.8. The two-mica granites have a restricted range in initial Pb isotopic composition (206Pb/204Pb = 18.41–18.75; 207Pb/204Pb = 15.60–15.68; 208Pb/204Pb = 38.21–38.55), requiring and old, high U/Pb (but not Th/U) source component. The Nd isotope data are consistent with magma
derivation from two sources: Avalon-like crust (ɛNd>−3), and Central Maine Belt metasedimentary rocks (ɛNd<−4), without material input from the mantle. The variations in isotope systematics and REE patterns are inconsistent with
models of disequilibrium melting which involved monazite.
Received: 8 December 1995 / Accepted: 29 April 1996 相似文献
Theoretical results show that the amplitude of a borehole source is reduced when the well in which it is operated is cased and cemented. This reduction is a strong function of the formation velocity and is more weakly dependent on the direction of propagation of the wave travelling from source to receiver and on the diameter of the borehole itself. We have tested these predictions with data gathered in a cross-hole seismic experiment conducted in two stages in 1990 and 1991. The source and receivers were located in the MIT/Stech 1-21A and MIT/Burch 1-20B wells at the Earth Resources Laboratory (ERL) test site in Michigan (USA). Though the source well (MIT/Stech 1-21A) was uncased in 1990, a steel casing and cement were added prior to the collection of data in 1991. Several receiver positions were reoccupied to compare data collected with the source in open and cased holes. Using a velocity model for this area and borehole diameter measurements from a calliper log, a compensation factor can be computed that will adjust the data collected in 1991 to have amplitudes comparable to that collected in the first stage of the experiment. The accuracy of the results demonstrates the validity of the theory, which can be very useful in better understanding seismic waveforms recorded in cross-hole experiments. 相似文献
Antenna field 2 of the Tromsø Heating facility consists of six rows of six horizontal crossed full wave dipoles aligned with the rows running geographic east-west. In previous experiments on ELF/VLF wave generation it has been the practice to feed the rows in parallel, with HF radiation amplitude modulated at the ELF/VLF frequency it was desired to radiate (AM configuration). Here we describe how the antenna array was also configured so that it could be fed with a continuous wave (CW) input power but still carry information at an ELF/VLF frequency. To effect this the three southern most rows of the antenna array were driven with a CW signal at 4.04 MHz and the three northernmost rows with a CW signal at frequency greater than 4.04 MHz by the ELF/VLF frequency it was desired to radiate (CW configuration). Experiments were performed with modulation/difference frequencies of 565 and 2005 Hz and the signals were received at the Lycksele Geophysical Observatory, 500 km south of the heating facility. The signals were typically 11 dB greater in the AM than the CW configuration, despite the fact that the average power delivered to the ionosphere in the CW configuration was four times that in the AM configuration. Significant harmonic radiation (both odd and even) was produced in the AM configuration but no harmonic radiation was detected in the CW configuration. A simple theory has been developed to model the fields produced by HF heating using the two techniques (AM,CW). A good agreement has been obtained between the experimental observations and model computations. The model has been extended to show how the relative efficiency of generation, AM/CW, varies with the frequency of the ELF/VLF radiation and HF antenna element spacing. Radiation patterns for the ‘ionospheric ELF/VLF antenna’ have also been derived for the two generation techniques. 相似文献