939 resultados para VP-SEM-EDS
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Fil: Ivars, Lorena Ángela.
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From January to March 1987, heat flow measurements were tried at four sites (Sites 689, 690, 695, and 696) during ODP Leg 113, in the Weddell Sea, Antarctica. At Site 690 (Maud Rise), a convex upward shaped temperature vs. depth profile was observed. This profile cannot be explained by steady-state conduction through solid materials only. We conclude that the minimum heat flow value at Site 690 is 45 mW/m2. A prominent bottom simulating reflector (BSR) was observed at 600 mbsf at Site 695. However, the observed temperature is too high to explain the BSR as a gas hydrate. The origin of the BSR remains unknown, although it is probably of biogenic origin as observed in the Bering Sea during DSDP Leg 19. After correcting for the effects of sedimentation, heat flow values at Sites 695 and 696 are 69 and 63 mW/m2, respectively. Furthermore, we compiled heat flow data south of 50°S. In the Weddell Sea region, the eastern part shows relatively low heat flow in comparison with the western part, with the boundary between them at about 15°W longitude.
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Seismic velocities have been measured at confining pressures to 600 MPa for eight samples of sheeted dike rock obtained from Hole 504B during Leg ODP 111. The compressional- and shear-wave velocities are, in general, higher than the velocities measured in overlying dike rocks obtained from the hole during DSDP Leg 83. The velocity gradients observed in Layer 2C result from decreasing porosity with depth and increasing metamorphic grade. The laboratory-measured velocities of the Leg 111 dike rocks are similar to those of dike rocks reported for the Bay of Islands, Samail, and Troodos ophiolites.
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A knowledge of rock stress is fundamental for improving our understanding of oceanic crustal mechanisms and lithospheric dynamic processes. However, direct measurements of stress in the deep oceans, and in particular stress magnitudes, have proved to be technically difficult. Anelastic strain recovery measurements were conducted on 15 basalt core samples from Sites 765 and 766 during Leg 123. Three sets of experiments were performed: anelastic strain recovery monitoring, dynamic elastic property measurements, and thermal azimuthal anisotropy observations. In addition, a range of other tests and observations were recorded to characterize each of the samples. One common feature of the experimental results and observations is that apparently no consistent orientation trend exists, either between the different measurements on each core sample or between the same sets of measurements on the various core samples. However, some evidence of correspondence between velocity anisotropy and anelastic strain recovery exists, but this is not consistent for all the core samples investigated. Thermal azimuthal anisotropy observations, although showing no conclusive correlations with the other results, were of significant interest in that they clearly exhibited anisotropic behavior. The apparent reproducibility of this behavior may point toward the possibility of rocks that retain a "memory" of their stress history, which could be exploited to derive stress orientations from archived core. Anelastic strain recovery is a relatively new technique. Because use of the method has extended to a wider range of rock types, the literature has begun to include examples of rocks that contracted with time. Strong circumstantial evidence exists to suggest that core-sample contractions result from the slow diffusion of pore fluids from a preexisting microcrack structure that permits the rock to deflate at a greater rate than the expansion caused by anelastic strain recovery. Both expansions and contractions of the Leg 123 cores were observed. The basalt cores have clearly been intersected by an abundance of preexisting fractures, some of which pass right through the samples, but many are intercepted or terminate within the rock matrix. Thus, the behavior of the core samples will be influenced not only by the properties of the rock matrix between the fractures, but also by how these macro- and micro-scale fractures mutually interact. The strain-recovery curves recorded during Leg 123 for each of the 15 basalt core samples may reflect the result of two competing time dependent processes: anelastic strain recovery and pore pressure recovery. Were these the only two processes to influence the gauge responses, then one might expect that given the additional information required, established theoretical models might be used to determine consistent stress orientations and reliable stress magnitudes. However, superimposed upon these competing processes is their respective interaction with the preexisting fractures that intersect each core. Evidence from our experiments and observations suggests that these fractures have a dominating influence on the characteristics of the recovery curves and that their effects are complex.
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Fil: Barandica, María Guadalupe.
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Fil: Ibach, Hermann.
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Fil: Martin De Blassi, Fernando.
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Fil: Peretó Rivas, Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas
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Fil: Massini Correas, Carlos I.. Universidad de Mendoza
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Fil: Massini Correas, Carlos I.. Universidad de Mendoza
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Delineating the interrelationships between tectonics, sedimentation, and geotechnical properties is particularly important for areas subjected to the dynamic affects of convergence. DSDP Leg 66 drilling within the Middle America Trench complex provided a unique opportunity to investigate these interrelationships along a transect of eight drill sites beginning on the trench outer slope and traversing the trench, trench inner slope, and upper continental slope. Investigations of other convergent margins suggest that deformation occurs most rapidly along the lower trench inner slope and is reflected by the geotechnical properties (Carson, 1977; Seely, 1977; and von Huene, 1979). This study focuses on the geotechnical properties of Middle America Trench sediments and the possible affects of convergence on these properties.