CENOZOIC COUPLING BETWEEN THE SOUTHERN CARIBBEAN AND THE NORTHWESTERN SOUTH AMERICAN PLATES CONSTRAINED BY APATITE FISSION TRACK THERMOCHRONOLOGY FROM THE SIERRA NEVADA DE SANTA MARTA (COLOMBIA)

The topographically prominent Sierra Nevada de Santa Marta (SNSM) Massif forms part of a faulted block of continental crust located along the northern boundary of the South American Plate with the Caribbean Plate and hosts the highest elevation in the world (5775m) whose local base is at sea level. The high elevation and prominent relief is testament to extensive surface and rock-uplift, which was accompanied by erosive exhumation resulting in the cooling of the Massif.

Apatite fission track (AFT) data obtained by the LA-ICP-MS method was collected from crystalline rocks in order to quantify the amount of cooling and exhumation of the SNSM. AFT age vs. elevation profiles along with inverse thermal history models show evidence of several cooling events during the Cenozoic, which shed light on the tectonic history of the plate boundary and the driving forces of rock uplift along this active margin.

Cooling and exhumation from ~65 to ~30 Ma is likely to have been driven by an increased coupling and underthrusting of the Caribbean Plate beneath South America, whereas cooling observed from ~30 to ~16 Ma in discrete regions of the Massif was related to an increased sinistral displacement of the bordering intracontinental Santa Marta–Bucaramanga Fault.

The late Oligocene – middle Miocene data reveal northwest directed propagation of exhumation within the SNSM, which is probably related to progressive thrust displacement. The displacing thrusts intersect the Santa Marta–Bucaramanga Fault, whose sinistral displacement probably provides the local driving force for the advance of exhumation within the SNSM.

In addition, we suggest that the high peaks of the SNSM formed when the present surface was at temperatures lower than 60°C, and there has been insufficient erosion (approximately <1.5km) to expose late Miocene and younger apatite partial annealing zones. Given the high erosional power of the climate in northern Colombia, this is indicative of very recent, rapid rock uplift, leaving insufficient time for erosion to expose rocks that cooled through the apatite partial annealing zone after ~16 Ma.