Geologic mapping of the basement of the Paris basin (France) by gravity- and magnetic-data interpretation
Published:January 01, 1985
N. Debeglia, C. Weber, 1985. "Geologic mapping of the basement of the Paris basin (France) by gravity- and magnetic-data interpretation", The Utility of Regional Gravity and Magnetic Anomaly Maps, William J. Hinze
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Simultaneous interpretation of gravity and magnetic data, taking into account all available information (geology, borehole, and nonconfidential seismic surveys), has been carried out with the help of potential-field transformation, modeling, and inversion software. Geophysical synthesis led to the delineation of a geologic map of the pre-Triassic basement of the Paris basin and to the delineation of the most important structural features of the Hercynian and Caledonian Ranges in France between outcropping Paleozoic massifs. Recent boreholes, drilled at the end of this synthesis, largely confirm the proposed interpretation. Thanks to simultaneous gravity and magnetic inversion, models of the Magnetic Anomaly of the Paris Basin can be proposed, and the origin of this anomaly can be related to a scheme of the structural evolution of the basin.
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The Utility of Regional Gravity and Magnetic Anomaly Maps
The first composite magnetic-anomaly map of the conterminous United States and adjacent offshore areas has been published at a color-contour interval of 200 gammas and at the scale and projection of other national geologic and geophysical maps for easy comparison. This map, despite the inconsistent characteristics of the surveys from which it was compiled, is useful in providing a regional framework for the interpretation of magnetic studies of limited areas, in selecting areas for more detailed magnetic investigations, and in studying the distribution and character of regional geologic features.
The map has a wide variation of magnetic-anomaly patterns, trends, and types, thus reflecting the diversity of the geologic terranes of the United States. In general, the anomaly pattern east of the Cordillera in the craton and in the Appalachian Mountains consists of more and greater intensity anomalies. The muted nature of the anomalies of much of the Cordillera is a result of several factors but appears to be primarily related to a decreased crustal magnetization caused by an abnormally shallow Curie isotherm. The anomalies of the Appalachian Mountains and the Cordilleran system primarily reflect the major structural patterns of the orogens, but important exceptions occur, such as those associated with rocks underlying thrust sheets in the Appalachian Mountains and westerly-striking anomaly trends in the Cordillera, which are correlated with igneous intrusives, faults, and mineral deposits.
The buried southern and eastern edges of the Pre-cambrian craton are indicated by changes in the magnetic anomalies and their dominant trends. Within the central United States, numerous regional magnetic-anomaly provinces are observed that reflect the long, complex history of the Precambrian basement rocks of the craton. These provinces are transected by conspicuous, intense, long, generally linear anomalies that originate from mafic extrusive or shallow intrusive igneous bodies within failed rifts, such as the Midcontinent rift system, the Southern Oklahoma aulacogen, and the Reelfoot rift buried beneath the Mississippi embayment. These are only a few of the many interesting regional geologic features that are observed on the composite magnetic-anomaly map of the United States.