Abstract
The southern foothills of the Fuegian Andes are bounded by the Beagle Channel (BC), a conspicuous E-W longitudinal basin, controlled by a large transcurrent fault system, which extends from the Atlantic to the Pacific Ocean. The northern shore of the Beagle Channel’s central segment is characterized by several E-W oriented valleys, parallel to the main basin, which are interspersed with a series of oblique NW trending lineaments that extend across the mountain belt. A geoelectrical survey was carried out in order to investigate the shallow architecture of such sets of linear morphologies. The principal E-W lineament system was characterized by conspicuous sub-vertical resistivity contrasts, interpreted as fractured zones associated with fault strands of the main strike-slip Beagle Channel system, whereas the oblique NW-SE trending set of lineaments revealed slightly different resistivity patterns, with vertical displacements and less abrupt contrasts. These resistivity patterns, in combination with the widespread occurrence of normal faulting in the area, allowed to infer an extensional control over the oblique depressions. These morphological features were related to oblique transverse faults that segment two sub parallel E-W fault systems. The oblique faults were probably developed along inherited structural anisotropies and can be extended well beyond the BC shoreline to the NW. Both geophysical and field evidence suggest a post-glacial deformation along the area.
Highlights
In densely forested areas with sparse outcrops, heavily weathered or in locations of difficult access, the combination of traditional field geology with geophysical techniques, such as seismic, electrical, magnetometric or gravimetric surveys, constitute a valuable approach to explore the subsurface continuity of geological features observed in the outcrop and the remote sensing images
There is a growing body of literature that recognises the wide amount of advantages that this method offers: it is highly sensitive to the electrical properties of materials, it is of relatively fast acquisition, and it has been largely applied to map a variety of geological problems such as tracing fault zones and fracture systems, estimation of the bedrock depth, investigation of sedimentation and infilling processes and analysis of landslides or glacial landforms among others (Caputo et al, 2003; Comas et al, 2004; Fazzito et al, 2009; Maillet et al, 2005; Storz et al, 2000; Tassone et al, 2010)
The geophysical and outcrop data collected along the northern shore of the Beagle Channel (BC) made possible the subsurface recognition of several structures covered by Quaternary sedimentation or dense forests
Summary
In densely forested areas with sparse outcrops, heavily weathered or in locations of difficult access, the combination of traditional field geology with geophysical techniques, such as seismic, electrical, magnetometric or gravimetric surveys, constitute a valuable approach to explore the subsurface continuity of geological features observed in the outcrop and the remote sensing images. The surveyed area lies within the Fuegian Andes orogenic belt, an E-W trending fold and thrust belt, which is crosscut to the south and to the north by noticeable longitudinal morphostructures developed along regional fault zones (Fig. 1). NW trending depressions, highly oblique to the BCFS, are common in the central segment of the Beagle Channel. These features contain plenty of evidence of recent modelling by glacial erosion, but the nearly rectilinear geometries and parallelisms existing among them suggest that a structural control may have played a major role in their development. Its nature, geological processes and relationship with the strike-slip related deformation has received scant attention in the research literature
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