Cenozoic Exhumation of the Sierra Nevada De Santa Marta, Colombia: Implications on the Interactions Between the Carribean and South American Plate

Since the Late Maastrichian, the interactions of the Caribbean and South American plates have controlled the formation of different orogenic events along this continental margin. Understanding the thermal and exhumation history of these mountain ranges provides major insights to the particular tectonic configuration that trigger their evolution. The scarcely known Sierra Nevada de Santa Marta massif show evidences of extensive Cretaceous to Eocene magmatism. Contact metamorphism and Al-in-hornblende geobarometry from arc granitoids (65-50 Ma), indicates pressures of 4-7 Kb, and 12-18 Km of unroofing since the Paleogene. Published K-Ar ages suggest cooling below 250°C at about 48 m.y. Considering an arc geothermal gradient of ~50° C, a minimum exhumation rate of 0.7 Km/Ma between 65-48 Ma can be determined. Zircon and apatite (U-Th)/He analyses from granitoids samples collected along a NW-SE profile yielded ages of 20-26 Ma and 8-15 Ma respectively. These results suggest exhumation rates of 0.16 Km/Ma until the Late Oligocene, that increased in the Middle-Late Miocene, where exhumation rates rise to 0.33 Km/Ma, similarly as including todays exposure level. Within a plate tectonic perspective, the Eocene exhumation is related to the post-collisional effects of the Caribbean accretion plus the magmatic underplating in a newly formed subduction zone. The relatively lower exhumation rates for the Oligocene and Miocene in comparison with the previous event, must be a consequence of the changes in the Caribbean-South American convergence towards a more transtensional relation, that shut down arc magmatism. The increase in the exhumation rate from the Miocene to Recent represents additional changes in the plate convergence relations that end-up with the subduction of the buoyant Caribbean plate under South America, responsible for ongoing uplift and lack of isostatic equilibrium. The Caribbean exhumation rates also suggest that Santa Marta was isolated from the Andean geodynamics since the Eocene.