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

Resumen

In this article we
studied the northern part of the Laramide foreland of the Chihuahua
Trough. The purpose of this work is twofold; fi rst 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 refl ect 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.