ASSESSING THE THERMOTECTONIC HISTORY OF COLOMBIA’S WESTERN CORDILLERA THROUGH THERMOCHRONOLOGY/GEOCHRONOLOGY IN PLUTONIC MASSIFS AND SEDIMENTARY BASINS: TECTONIC, GEOMORPHIC AND CLIMATIC IMPLICATIONS

Colombia’s Western Cordillera (WCo) displays characteristics of a volcanic arc accreted to the South American margin. It is built on Late Jurassic-Cretaceous oceanic crust covered by Cretaceous sedimentary rocks of oceanic and continental affinity. These Mesozoic units are intruded by plutonic masses of intermediate to mafic composition. Our U/Pb ages in magmatic zircons indicate discrete pulses of magmatism in the Albian-Cenomanian (Sabana Larga and Mistrató batholits), Early Eocene (Mandé Batholith), and Early to Late Miocene (Farallones del Citará Batholith, Tatamá, Tamesis and La Horqueta stocks, etc.). This cordilleran segment is directly linked to the accretion of the Panama Chocó Block (PCB), whose time of collision is still controversial. Topographically, the WCo exhibits sierra-like morphology, local relief in excess of 3000 m, and a longitudinal profile with elevations of ~ 4000 m (on the plutonic massifs) and axial depressions as low as 500 m. The WCo is a major orographic barrier trapping Pacific moisture and turning western Colombia into one of the wettest regions on earth. The Chocó Basin (CB) is a forearc structure located directly to the west of the WCo. Our provenance analyses indicate the latter as the source of detrital material. The lithologic, structural, and topographic milieu on this understudied segment of the Andean range allowed us to produce geochronology and thermochronology data for seven plutonic units and one sedimentary unit from outcrop samples, as well as for borehole sedimentary samples derived from the ~3 km-deep Choco-1-STP drill. We use our datasets to derive time-temperature histories providing a detailed record of uplift and exhumation that delineates the interesting co-evolution of the WCo and the CB. Significant cooling events (uplift-exhumation) are found at ~ 62, 43, 25, 16, 10, and 5 Ma. These events are typical of the Andean orogenetic phases in Colombia and are related to regional geodynamic process including accretion of oceanic crust, changes in convergence parameters (velocity and obliquity), Nazca-Farallon breakup, PCB collisional episodes, and subduction of anomalous/buoyant oceanic crust. A persistent pulse of uplift-exhumation is identified at ~ 9-10 Ma. We link this pulse to the establishment of the WCo as the topographic barrier it embodies today.