Erosion and regional exhumation of an Early Cretaceous subduction/accretion complex in the Northern Andes

A multi-technique provenance analysis, together with whole-rock geochemistry from arc related volcano-sedimentary rocks of the Albian-Aptian Quebradagrande Complex (Central Colombian Andes, Northern Andes), were conducted to reconstruct the tectono-stratigraphic relations with the adjacent Early Cretaceous subduction/accretion Arquia Complex, in order to understand the tectonic modification of the Andean margin before the onset of the Andean orogeny. The presence of olivine, spinel, serpentine, high-pressure garnets and glaucophane in the sandstones of the Quebradagrande Complex suggests that the subduction/accretion Arquia Complex was a major source area during basin filling. Carboniferous and older detrital zircons suggest that the pre-Cretaceous continental basement of the Colombian Central Cordillera, which limits the Quebradagrande Complex to the east, was also a major basin source. Whole-rock geochemistry from associated volcanic rocks, showing suprasubduction to NMORB signature, is characteristic of a magmatic arc formed in thinned continental crust. Integration of the results with the Early Cretaceous record of the Central Cordillera indicates that the continental margin experiences a major slab-roll back event that promotes extensional tectonics, affecting the arc and facilitating the exhumation of a subduction/accretion complex. During the Late Cretaceous, both complexes were deformed and a new magmatic arc was formed. The extensional tectonics reflects the complex plate kinematic readjustments that affected western South America during the Cretaceous. [GRAPHICS] .