Estimation of the slab position beneath northwestern South America from receiver function analysis

Abstract:

Colombia presents an environment with a very active and complex geodynamical context that includes the subduction of both the Nazca and Caribbean plates beneath the South American plate. The displacement of the Wadati-Benioff zone and lack of volcanism north of 5°N correspond to a dramatic change in the subduction angle, and the potential existence of two distinct segments in the Nazca Plate (i.e., Bucaramanga and Cauca segments separated by the Caldas tear), presenting a flat subduction to the north and a normal subduction to the south.

In order to identify possible converted phases in the slab, a single station analysis of radial P receiver functions (RFP) was performed for four profiles, two crossing the Bucaramanga segment, and two for the Cauca segment. Based on previous studies on the structure of the crust and upper mantle, it is possible to relate deep phases in the RFP profiles to the subducted Nazca lithosphere for most of the stations used. Interpreting the four profiles, for the stations north of the Caldas tear the possible phases related to the slab are located at depths less than 100 km, showing a subhorizontal subduction; while the stations south of the tear exhibit more complexity due to the interferences of multiples overlapping with deep phases. However, the identified phases show a deepening tendency towards the east, interpreted as a conversion in the Nazca plate. To better constrain the slab position, we also carried out common converted point stacks and a joint inversion of surface wave dispersion curves with receiver functions.

The analysis of deep phases by RFP in Colombia is then complex due to the high deformation in the crust and the irregularity of its thickness. Therefore, further studies with other receiver function methods of analysis are necessary to corroborate and draw more detailed conclusions on the position of the Nazca plate beneath northwestern South America.