Geophysics of the rifts associated with the Sirt Basin (North Africa) and the Anadarko Basin (North America).

摘要

In this study, a significant amount of geophysical and geological data has been gathered for both the Sirt and Anadarko basins. The primary intent of most of the geophysical data gathered in the Sirt basin (North Africa) and the Anadarko basin (North America) areas was petroleum oriented. The purpose of this study was to analyze these rifted areas of North Africa and North America.;For the Sirt basin area, an integrated analysis of subsurface and geophysical data was conducted using gravity, seismicity, and heat flow data. These data suggest that the Sirt basin has a number of features in common with modern and older continental rifts throughout the world. The Bouguer gravity map indicates that the Sirt basin is marked by elongate regional gravity maxima and minima trending NW-SE showing a strong correlation with the structural highs and lows known from drilling. This map also shows that the Hun graben is marked by a long wavelength negative gravity anomaly and very steep gravity gradients which delineate faults along the sides. Large deep-seated structures are also predominant on the Bouguer gravity map. Thus in some cases, it is very difficult to recognize smaller or shallower features. The third order polynomial surface map was chosen as the best approximation of the regional gravity field over the Sirt basin area.;The seismicity indicates that the rift margins, especially the western margin, are still tectonically active. The first motion results suggest strike-slip and normal faulting is occurring throughout the region. The waveform modeling results for the 1935 mainshock and the two largest aftershocks suggest a strike-slip mechanism with one fault plane similar to the strike of the eastern edge of the Hun graben. The seismic observations suggest that both the NW-SE distinctive faults seen in the gravity and associated NE-SW trending cross faults seen on geologic maps continue to play an important role in the western Sirt basin. Although these faults were normal faults from Cretaceous through Eocene time, they appear to behave as strike-slip faults in the present stress-regime.;The heat flow data show above average heat flow values in portions of the rift. The thick (;The Southern Oklahoma Aulacogen (SOA) area was analyzed through subsurface and geophysical data. The earth model indicates that the SOA has experienced an impressive amount of modification of the crust. When reactivated by late Paleozoic events at the continental margin, vertical displacements alone exceeded 12 km. Quaternary stratigraphic relationships and ten ;Seismic and gravity data suggests that the Anadarko basin shows a striking lack of symmetry with a great truncation at the south side of the basin along the frontal fault zone. Seismic data also indicates that the base of the crust is layered and transitional in character rather than a simple sharp boundary. The Moho is about 45 km deep beneath the frontal thrust zone of the Wichita uplift shallowing to about 41 km in both ends of the modeled line. (Abstract shortened by UMI.)