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The outline of the buried Ouachita orogenic belt in Texas follows an ancient continental edge that has been involved in lithosphere plate interaction since late Precambrian time. Gravity and magnetic measurements along the central Texas part of the trend, combined with limited seismic and well information, indicate that the complex has been offset along a persistent zone of weakness during its history. The offset relationship of the gravity and magnetic anomaly patterns and their relationship, in turn, to the geology of this zone of weakness indicate a series of basement displacements through time. A broad negative gravity anomaly is related to the overthrust package developed during the collision phase. Broad magnetic anomalies are related to slivers of basement caught u in the collision. A belt of positive gravity anomalies is related to a concentration of dense rocks created during the collision phase, or to a mantle welt created during the pull-apart phase. Short-wavelength dipole magnetic anomalies are related to shallow volcanics extruded during this pull-apart phase. The detail in these patterns may provide a framework for interpretation of basement uplift and fracture patterns involved in the offset zone.
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