TECTONIC SETTING AND EVOLUTION OF LATE MIOCENE VOLCANISM AT MIDDLE CAUCA BASIN, COLOMBIA

In the Cauca Basin at Northwestern Colombia, between the Central and Western Colombian Cordilleras, outcrops a Late Miocene volcanic sequence. At the middle sector of this basin located between 5° to 6° North Lat. and 75° to 75°, 5 West Long., the sequence is constituted by the 10 to 6 Ma Combia Formation composed by thick tholeitic basaltic and basaltic andesite flows and basaltic pyroclastic currents, followed by a profusion of calc-alkaline dacitic domes and volcanic necks distributed simultaneously along this area between 8 to 6, 3 Ma. This volcanic arc sequence is related to the subduction of Nazca plate beneath South American plate.

Currently, a change in the angle of the subduction is recognized at 5°, 5 North Lat., normal to the south and flat to the north of this latitude, probably related to the so called Caldas tear and supported by seismic and GPS data. We have revised the volcanic mapping of this area in order to understand the chemical signature of the volcanic sequence and its relationship with this tectonic framework.

The middle sector of the Cauca basin represents an overlapping zone with a rhomboidal crossing geometry defined by conjugate the regional N-NE left strike – slip faults, known as Romeral or Silvia-Pijao; and NW-SE normal faults system. This configuration allowed the development of the magmatic accommodation space and controlled the transportation system of the magmas, which fed both the Combia Formation and the Late Miocene-Pliocene hypabissal bodies. It seems these magmatic events occurred under a transpresional regime developed during the Chocó-Panamá Block collision against the northwestern margin of South America at the middle? to late Miocene.

A faulted-controlled gold mineralization is spatially associated with some of the dacitic sub-volcanic bodies, developed at 6 Ma, which produced some of the best examples of mesothermal and epithermal low-sulfidation Au–Ag ores deposits and prospects in Colombia.

We summarize the tectonic and magmatic events in an event chart since the Early Miocene that shows the timing and interaction between tectonics, volcanism and the formation of ore deposits in the middle part of the Cauca Basin.