Asymmetric exhumation and topographic development of the Santa Marta range, southern Caribbean Plate: Inferences from modeling of bedrock and detrital thermochronometry
Résumé
Episodic tectonic deformation along the southern Caribbean plate has resulted from the northeastward propagation of its leading edge. The transition from subduction to transform motion against the South American Plate has driven asymmetric exhumation and topographic development from northern Colombia to Venezuela and Trinidad. Here, we present a reconstruction of the tectonic evolution at the southwestern sector of this margin, in the Santa Marta Sierra Nevada (SNSM) in northern Colombia. The SMSN is an up to 5.8-km high and small (~14,500 km2) mountain range whose development is initially associated with arc-continent collision since Late Cretaceous and later on with srike-slip tectonics along the southern Caribbean plate. Inverse 1D modeling of bedrock AFT, AHe, and ZHe thermochronology in selected localities reveals rapid Oligocene-Middle Miocene (35-15 Ma) cooling associated with transtensional deformation, followed by slower cooling thereafter. Three-dimensional thermokinematic modeling further constrains exhumation rates to 0.6-0.8 mm/yr during this peak exhumation period and reveals that at least 50% of the modern topography is as old as 20 Ma. Despite the prominent topography and tropical climate, Quaternary catchment-wide denudation rates of up to 0.3 km/My derived from 10Be data in modern sediment of selected catchments document that slow cooling and denudation have prevailed since ~15 Ma. In addition, we applied inverse modeling of cosmogenic radionuclide-derived denudation rates with bedrock and detrital zircon U-Pb data from the same catchments to document the locus of modern denudation. Having independently constrained either (A) the thermal history or (B) the locus of modern denudation in selected catchments, we used AFT and AHe detrital data of modern sediment to infer either A or B in other catchments where we lack such information. Our combined results (1) provide a proof-of-concept of the applicability of modeling modern fluvial sediment thermochronology to infer exhumation patterns and (2) place time constraints to the passage of the transition from subduction to transform motion along the southwestern Caribbean-South America margin.