Evolution of the northern Andean Flat Slab Segment

In the northern Andean block the subducting Nazca plate contains a flat slab segment that notably influences the structural styles of the mountain belts of the Southamerican plate. A seismotectonic break at approximately 4°N is often referred to as the Caldas Tear. In contrast to the obvious aseismic ridges associated with the southern edges of the Peruvian and Chilean flat slab segments, there is no distinct single oceanic feature that limits the size of the North Andean flat slab segment. Instead, a ridge-transform system can be extrapolated into the inboard domain of the trench. This explains the presence of the Istmina Transverse Range along a transform-parallel sector, as well as the Miocene Combia volcanic province where this transform-parallel sector turns into the ridge-parallel discontinuity of the Caldas Tear. Folding of the forearc basins and the Eastern Cordillera of the retroarc domain provides evidence of a margin-wide, NW-SE contractional regime, which has been independently documented by regional paleostress determinations. Further structural evidence for oblique convergence comes from a clear collisional feature formed by a sweeping linear transform fault, which is now situated beneath the Istmina Transverse Range. This feature resulted in a triangular re-entrant of the Western Cordillera, causing it to bend around the Transverse Range. On the retroarc side, the southward propagation of the flat slab segment is evident in fold terminations within the Eastern Cordillera, as well as in the relay pattern of frontal thrust faults at its foothills. The southern morphotectonic break of the Caldas Tear juxtaposes the intramontane Bogotá basin, which belongs to the flat-slab segment, with a folded flank of an E-vergent anticlinorium that marks the deformational style related to the steeply dipping Nazca plate. In our contribution, we depict representative, but less evolved transverse lineaments of the Eastern Cordillera and characterize their deformation style. We also observe the local presence of salt nappes and compare the retarded vs. accelerated intrusive ascent of magmatic manifestations, discussing their relevance with respect to possible plate configurations that suggest lithospheric tearing or bending. The guiding question that informs our research is whether these surface processes provide insight into time slices of the evolving flat slab segment.