GRAUCH, V. J. S., U. S. Geological Survey, Denver, CO
ABSTRACT: Comparing Shallow Versus Deep Fault Patterns in the Albuquerque Basin using Aeromagnetic and Gravity Data
High-resolution aeromagnetic data have been collected over most of the Albuquerque basin. These data show expressions of numerous faults that offset basin fill or volcanic rocks. Many of the faults were previously unknown or known only in isolated places due to widespread cover. Depth estimates indicate the magnetic sources at the fault boundaries do not extend deeper than 500-600 m below the surface. The faults are commonly sinuous and linearly extensive, up to 50 km in length. Some of them display anastomizing or en echelon patterns. The faults generally strike northerly except near significant bends in the basin boundaries and in the northern part of the basin where clusters of faults alternate between northeasterly and northwesterly orientations.
In contrast, isostatic residual gravity data for the Albuquerque basin resolve major basin- or subbasin-bounding faults and other structures involving the basement, up to 5 km depth. Many of these structural trends are oriented in a generally northerly direction, similar to the shallow fault patterns. Major differences involve northeast and northwest trends of subbasin boundaries in the north-central part of the basin. The shallow faults cross these boundaries without change in orientation, although in places the spacing or number of faults appears to vary near the boundaries instead. Along the eastern boundary of the basin south of Albuquerque, both deep and shallow expression of faults trend northerly. However, the gravity data indicate that major displacement at depth is more than 1 km west of the presumed basinbounding fault at the surface. The discrepancies between the orientation or location of deep versus shallow faults must reflect a changing history of basin formation through time.
AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico