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981.
Gábor Dobosi Pamela D. Kempton Hilary Downes Antal Embey-Isztin Matthew Thirlwall Peter Greenwood 《Contributions to Mineralogy and Petrology》2003,144(6):671-683
Mafic granulite xenoliths from the lower crust of the Pannonian Basin are dominated by LREE-depleted bulk-rock compositions. Many of these have MORB-like 143Nd/144Nd but 87Sr/86Sr is elevated relative to most MORBs. Their '18O values cover a wide range from +3.8 to +9.5. A group of LREE-enriched mafic granulites have higher 87Sr/86Sr (0.704-0.708) and lower 143Nd/144Nd (0.5128-0.5124), with higher '18O values on average (+7.8 to +10.6) than the LREE-depleted granulites. The LREE-enriched granulites are, however, isotopically similar to newly discovered metasedimentary granulite xenoliths. A sublinear correlation in )Hf-)Nd isotope space has a shallower slope than the crust-mantle array, with the metasedimentary rocks forming the low )Hf end member; the radiogenic end is restricted to the LREE-depleted granulites and these overlap the field of MORB. Pb isotopes for the LREE-depleted samples are less radiogenic on average than those of the LREE-enriched and metasedimentary xenoliths, and metasedimentary granulites have consistently higher 208Pb/204Pb. The wide range in '18O over a restricted range in Nd and Sr isotope values, in combination with the predominance of LREE-depleted trace-element compositions, is consistent with an origin as a package of hydrothermally altered oceanic crust. The existence of '18O values lower than average MORB and/or mantle peridotite requires that at least some of these rocks were hydrothermally altered at high temperature, presumably in the oceanic lower crust. The low 143Nd/144Nd of the LREE-enriched mafic granulites cannot be explained by simple mixing between a LREE-depleted melt and an enriched component, represented by the recovered metasediments. Instead, we interpret these rocks as the metamorphic equivalent of the shallowest levels of the ocean crust where pillow basalts are intimately intercalated with oceanic sediments. A possible model is accretion of oceanic crustal slices during subduction and convergence, followed by high-grade metamorphism during the Alpine orogeny. 相似文献
982.
983.
Michael G. Davis Michael O. Garcia Paul Wallace 《Contributions to Mineralogy and Petrology》2003,144(5):570-591
Glasses from Mauna Loa pillow basalts, recent subaerial vents, and inclusions in olivine were analyzed for S, Cl, F, and major elements by electron microprobe. Select submarine glasses were also analyzed for H2O and CO2 by infrared spectroscopy. The compositional variation of these tholeiitic glasses is dominantly controlled by crystal fractionation and they indicate quenching temperatures of 1,115-1,196 °C. Submarine rift zone glasses have higher volatile abundances (except F) than nearly all other submarine and subaerial glasses with the maximum concentrations increasing with water depth. The overwhelming dominance of degassed glasses on the submarine flanks of Mauna Loa implies that much of volcano's recent submarine growth involved subaerially erupted lava that reached great water depths (up to 3.1 km) via lava tubes. Anomalously high F and Cl in some submarine glasses and glass inclusions indicate contamination possibly by fumarolic deposits in ephemeral rift zone magma chambers. The relatively high CO2 but variable H2O/K2O and S/K2O in some submarine rift zone glasses indicates pre-eruptive mixing between degassed and undegassed magma within Mauna Loa's rift system. Volatile compositions for Mauna Loa magmas are similar to other active Hawaiian volcanoes in S and F, but are less Cl-rich than Ll'ihi glasses. However, Cl/K2O ratios are similar. Mauna Loa and Ll'ihi magmas have comparable, but lower H2O than those from Kilauea. Thus, Kilauea's source may be more H2O-rich. The dissimilar volatile distribution in glasses from active Hawaiian volcanoes is inconsistent with predictions for a simple, concentrically zoned plume model. 相似文献
984.
Using analytic signal method, interpretation of pole-pole secondary electric potentials due to 2D conductive/resistive prisms
is presented. The estimated parameters are the location, lateral extent or width and depth to top surface of the prism. Forward
modelling is attempted by 2D-Finite Difference method. The proposed stabilised analytic signal algorithm (RES2AS) uses Tikhonov’s
regularization scheme and FFT routines. The algorithm is tested on three theoretical examples and field data from the campus
of Roorkee University. The stability of RES2AS is also tested on synthetic error prone secondary pole-pole potential data. 相似文献
985.
Mercury from mineral deposits and potential environmental impact 总被引:6,自引:0,他引:6
James J. Rytuba 《Environmental Geology》2003,43(3):326-338
986.
Models of the motion of the terrestrial reference frame with respect to an inertial frame can describe the motions of the Earth-Moon system, which are traditionally separated into precession, nutation, the polar motion, and rotation about the Earth’s axis. Existing theoretical models do not describe variations in the Earth-orientation parameters with the required accuracy, so that the current polar coordinates and duration of the day must be determined from observations. To improve theoretical models for the time dependence of the coordinates of the Earth’s pole, we examine the possible excitation of the Chandler wobble due to internal properties of the Earth-Moon system. A differential equation describing the parametric resonance in the Earth-Moon system is obtained for the first region of the parametric excitation. The solution of this equation analytically describes the finite amplitudes of the nonlinear conservative system. The theoretical results are compared with the empirical laws of Melchior deduced from observational data on the coordinates of the Earth’s pole. 相似文献
987.
988.
Environmental impact of heavy-metal dispersion in the Huerva River (Iberian Range,NE Spain) 总被引:1,自引:0,他引:1
P. Acero J. Mandado J. Gómez M. Gimeno L. Auqué F. Torrijo 《Environmental Geology》2003,43(8):950-956
In this study, the methodology of geochemical prospecting has been applied to the study of cadmium, lead, copper and zinc dispersion in the fine sediments of the upper course of the Huerva River (Iberian Range, NE Spain). The survey was organised in two stages: (1) general sampling along the river and its tributary channels, aimed at selecting the sections with the highest contents of the target elements, and (2) detailed study of those sections, aimed at an interpretation of possible positive geochemical anomalies and identification of their sources. The results of this study prove the existence of multiple and complex sources, with a significant influence of sources related to anthropogenic activity. However, the system shows a good ability to depurate itself under current conditions. 相似文献
989.
J. Fernández-Turiel C. Pérez-Miranda G. Almada M. Medina C. Riviere M. Gordillo 《Environmental Geology》2003,43(8):941-949
Spatial and temporal variations of Na, Mg, Si, K, Ca, SO42-, Cl-, HCO3-, Ag, Al, As, Au, B, Ba, Be, Bi, Br, Ce, Cd, Co, Cr, Cs, Cu, Dy, Er, Eu, F, Fe, Ga, Ge, Gd, Hf, Hg, Ho, I, La, Li, Mn, Mo, Nb, Nd, Ni, P, Pb, Pr, Rb, Sb, Sm, Sn, Sr, Ta, Tb, Te, Th, Ti, Tl, U, V, W, Y, Yb, Zn, and Zr were monitored through 37 sampling stations to determine the main aspects influencing the surface-water quality in the Salí River watershed (Tucumán Province, NW Argentina). The influence of the regional geological setting on water chemistry allows to distinguish three sub-basins. The interaction with sedimentary rocks was found to be dominant in the northern and central-eastern sub-basin as well as in the southern sub-basin, whereas the metamorphic-granitic basement of the Pampean Ranges was noted in the central sub-basin. In addition, anthropogenic activities affect the spatial variation of K, P, Mn, Rb, and Pb as well as dissolved oxygen concentrations and Eh. Temporal water-quality variation is related to the spatial distribution of precipitation and to the seasonal character of the main local industries (sugar cane, alcohol, citrus), increasing P and K concentrations and decreasing dissolved oxygen concentration and Eh in winter. Cl-, Na, SO42-, Al, As, B, Fe, Mn, Se and U concentrations exceed the regulated drinking-water thresholds at several sampling stations. 相似文献
990.
A series of yearly data on the concentration of radioactive carbon 14C in tree rings measured at the Tbilisi State University in 1983–1986 and covering the time interval 1600–1940 is statistically analyzed. We find evidence for a 22-year cyclicity in the intensity of Galactic cosmic rays (GCRs) during the Maunder minimum of the solar activity (1645–1715), testifying that the solar dynamo mechanism continued to operate during this epoch. Variations of Δ14C on timescales of tens and hundreds of years correlate well with the corresponding variations of the GCR intensity and solar activity, making radiocarbon a reliable source of information on long-timescale variations of solar activity in the past. Short-timescale (<30 years) fluctuations of Δ14C may be appreciably distorted by time variations not associated directly with solar activity; probable origins of this distortion are discussed. 相似文献