CHARACTERIZING THE ASYMMETRY OF AN OROGENIC WEDGE: LOOKING AT THE CLIMATE AND TECTONIC CONTROLS ON WEDGE GEOMETRY

We found a direct correlation between a climate gradient and the style and rates of deformation in the Eastern Cordillera of the Northern Andes. This cordillera is a two-sided orogenic wedge trending SW-NE that in cross section shows a symmetrical doubly verging tectonic style with an asymmetric topographic profile. Across this cordillera there is a SE-NW precipitation gradient that ranges from 8 to 2 m/yr from east to the central plateau and to the west.

We compared the spatial distribution of geomorphic elements and indexes with ancient and recent deformation fields to determine if the present landscape is inherited from ancient deformation or it is a response to the present tectonic-climate coupling. We mapped the distribution of knickpoints, changes in local and geophysical relief, basin circularity and hypsometry, and stream concavity and steepness and tried to correlate these maps with the distribution of ancient mapped faults and with the maps of current strain derived from earthquake and geodetic data.

Our correlations show that the eastern retro-wedge developed a higher, steeper topography that corresponds to higher precipitation. The western pro-wedge is not as homogeneous in its topographic distribution. In the southern end of the pro-wedge, lower precipitation correlates with smaller relief and gentler slopes. However, in the central and northern part, lower precipitation correspond to areas of deep, incised valleys with high relief and steeper slopes.

On both sides of the orogen river profiles of major streams are segmented by major knick points. Knick points are aligned parallel to the trend of the orogen, with the average relief of every knick point being much higher in the east than in the west. Knickpoint alignments are much longer in the west than in the east, then following elongated faults in the west and segmented faults in the east. The distribution of steeper areas and knick points coincides with short term strain maps that show high strain concentrated along the frontal folds and faults of the pro-wedge, whereas in the retro-wedge areas with higher strains do not always correlate to the location of faults. Along the retro-wedge higher precipitation correlates with distributed deformation and overall intense denudation. In the pro-wedge lower precipitation does not always correlate with the degree of deformation and the intensity of denudation.