Geologic structure of the northern margin of the Chihuahua trough: Evidence for controlled deformation during Laramide Orogeny

摘要

In this article we studied the northern part of the Laramide foreland of the Chihuahua Trough. The purpose of this work is twofold; first we studied whether the deformation involves or not the basement along crustal faults (thin- or thick- skinned deformation), and second, we studied the nature of the principal shortening directions in the Chihuahua Trough. In this region, style of deformation changes from motion on moderate to low angle thrust and reverse faults within the interior of the basin to basement involved reverse faulting on the adjacent platform. Shortening directions estimated from the geometry of folds and faults and inversion of fault slip data indicate that both basement involved structures and faults within the basin record a similar Laramide deformation style. Map scale relationships indicate that motion on high angle basement involved thrusts post dates low angle thrusting. This is consistent with the two sets of faults forming during a single progressive deformation with in - sequence - thrusting migrating out of the basin onto the platform. We found that the style of deformation in the Chihuahua trough is variable. In places such as the East Potrillo Mountains and Indio Mountains is typical of the thin- skinned style, associated with the Cordilleran thrust belt, while in other places, the thick - skinned deformation present is typical of the Laramide orogeny in the southern Rocky Mountains. The Franklin Mountains record the transition from thick- to thin - skinned deformation. We notice that this difference in the style of deformation is related to the thickness of the Cretaceous section within the Chihuahua trough. On the other hand, the orientation of the shortening direction can be explained based on the geometry of the trough and especially the strike of its eastern margin. Along strike variations in shortening direction and kinematics are controlled by the curved northeast margin of the trough and reflect stress reorientation along the weak interface between the strong platform and weak basin interior. These processes were wide spread affecting the 300 km long eastern margin of the Chihuahua trough between El Paso and the Big Bend region of west Texas.