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  • GEOPHYSICS  (6)
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  • 1
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    Seismic properties of the crust and uppermost mantle of North America (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Seismic refraction profiles for the North American continent were compiled. The crustal models compiled data on the upper mantle seismic velocity (P sub n), the crustal thickness (H sub c) and the average seismic velocity of the crystalline crust (V sub p). Compressional wave parameters were compared with shear wave data derived from surface wave dispersion models and indicate an average value for Poisson's ratio of 0.252 for the crust and of 0.273 for the uppermost mantle. Contour maps illustrate lateral variations in crustal thickness, upper mantle velocity and average seismic velocity of the crystalline crust. The distribution of seismic parameters are compared with a smoothed free air anomaly map of North America and indicate that a complidated mechanism of isostatic compensation exists for the North American continent. Several features on the seismic contour maps also correlate with regional magnetic anomalies.
    Keywords: GEOPHYSICS
    Type: NASA-CR-175134 , NAS 1.26:175134
    Format: application/pdf
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  • 2
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    Relation of MAGSAT Anomalies to the Main Tectonic Provinces of South America (1984)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Comparison of MAGSAT scalar magnetic anomaly data to the main tectonic provinces and boundaries of South America reveals a number of geologic correlations. South America is divisible into a broad platform of Precambrian shields and cratons separated by Phanerozoic basins, grabens and aulacogens to the east, the Phanerozoic Patagonian Platform to the south, and the Mesozoic to Cenozoic Andean Fold Belt and Caribbean Mountain System to the west and north. The continental shields are mainly more magnetic then continental basins and orogenic belts. Cratons, mainly covered by younger sedimentary rocks, are generally associated with magnetic gradients. Most of the anomalies associated with the Patagonian Platform are positive and have higher amplitudes eastward away from the Andean Fold Belt. The northern Andes are coincident with positive magnetic anomalies, whereas the central and southern Andes are associated mainly with negative anomalies.
    Keywords: GEOPHYSICS
    Type: Texas Univ. Appl. of MAGSAT to Lithospheric Modeling in South America, Part 2; p 52-58|Ann. Intern. Meeting and Exposition of the Soc. of Exploration Geophysicists; Jan 01, 1982; Dallas, TX; United States
    Format: text
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  • 3
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    Satellite Elevation Magnetic and Gravity Models of Major South American Plate Tectonic Features (1984)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Some MAGSAT scalar and vector magnetic anomaly data together with regional gravity anomaly data are being used to investigate the regional tectonic features of the South American Plate. An initial step in this analysis is three dimensional modeling of magnetic and gravity anomalies of major structures such as the Andean subduction zone and the Amazon River Aulacogen at satellite elevations over an appropriate range of physical properties using Gaus-Legendre quadrature integration method. In addition, one degree average free-air gravity anomalies of South America and adjacent marine areas are projected to satellite elevations assuming a spherical Earth and available MAGSAT data are processed to obtain compatible data sets for correlation. Correlation of these data sets is enhanced by reduction of the MAGSAT data to radial polarization because of the profound effect of the variation of the magnetic inclination over South America.
    Keywords: GEOPHYSICS
    Type: Texas Univ. Appl. of MAGSAT to Lithospheric Modeling in South America, Part 2; p 33|IAGA Sci. Assembly; Aug 03, 1981 - Aug 15, 1981; Edinburgh
    Format: text
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  • 4
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    Correlation of Tectonic Provinces of South America and the Caribbean Region with MAGSAT Anomalies (1984)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Intensities of MAGSAT scalar magnetic anomaly data correlate with the main tectonic provinces of South America and the Caribbean region. Magnetic anomalies of the continents generally have higher amplitudes than oceanic anomalies. This is particularly evident in Central America and in the shield areas of South America. The Caribbean Sea and Gulf of Mexico are underlain by prominent magnetic minima. Within these oceanic areas, linear magnetic highs correlate with topographic ridges which separate the Gulf of Mexico, the Colombian Basin, and the Venezuelan Basin. The boundaries of the Caribbean plate occur along magnetic gradients which are particularly sharp along the northern and western margins of the plate, but gradational along the southern margin where they merge with the Andean Cordillera. The anomalies along the western margin of the South American plate are also distinct and appear to be separate from those of the adjacent ocean basin. Eastern South America is characterized by magnetic anomalies which commonly extend into the Atlantic Ocean.
    Keywords: GEOPHYSICS
    Type: Caribbean Geol. Conf.; Aug 01, 1983; Cartagena; Colombia|Texas Univ. Appl. of MAGSAT to Lithospheric Modeling in South America, Part 2; p 27-28
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  • 5
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    Structure of the southern Rio Grande rift from gravity interpretation (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Regional Bouguer gravity anomalies in southern New Mexico have been analyzed by two-dimensional wave number filtering and poly-nomial trend surface analysis of the observed gravity field. A prominent, regional oval-shaped positive gravity anomaly was found to be associated with the southern Rio Grande rift. Computer modeling of three regional gravity profiles suggests that this anomaly is due to crustal thinning beneath the southern Rio Grande rift. These models indicate a 25 to 26-km minimum crustal thickness within the rift and suggest that the rift is underlain by a broad zone of anomalously low-density upper mantle. The southern terminus of the anomalous zone is approximately 50 km southwest of El Paso, Texas. A thinning of the rifted crust of 2-3 km relative to the adjacent Basin and Range province indicates an extension of about 9 percent during the formation of the modern southern Rio Grande rift. This extension estimate is consistent with estimates from other data sources. The crustal thinning and anomalous mantle is thought to result from magmatic activity related to surface volcanism and high heat flow in this area.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 6157-616
    Format: text
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  • 6
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    Crustal structure of the Southern Rio Grande rift determined from seismic refraction profiling (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: As part of a major cooperative seismic experiment, a series of seismic refraction profiles have been recorded in south-central New Mexico with the goal of determining the crustal structure in the southern Rio Grande rift. The data gathered greatly expand the seismic data base in the area, and consist of three interlocking regional profiles: a reversed E-W line across the rift, an unreversed N-S axial line, and an unreversed SW-SE line. The reversed E-W line shows no significant dip along the Moho (32 km thick crust) and a 7.7 km/s Pn velocity. Results from the N-S axial line and the NW-SE line indicate an apparent Pn velocity of 7.95 km/s and significant dip along the Moho with crustal thinning toward the south and southeast. When interpreted together, these data indicate a crustal thinning in the southern rift of 4-6 km with respect to the northern rift and the adjacent Basin and Range province, and establish the regional Pn velocity to be approximately 7.7 km/s. These results suggest that the Rio Grande rift can be identified as a crustal feature separate and distinct from the Basin and Range province.
    Keywords: GEOPHYSICS
    Type: Journal of Geophysical Research (ISSN 0148-0227); 91; 6143-615
    Format: text
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