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Cretaceous record from a Mariana to an Andean–Type Margin in the Central Cordillera of the Colombian Andes
By Agustín CARDONA , Santiago LEÓN, Juan S. JARAMILLO, Víctor VALENCIA, Sebastian ZAPATA, Andrés PARDO–TRUJILLO, Axel K. SCHMITT, Dany MEJÍA and Juan Camilo ARENAS
The Cretaceous tectonic evolution of the western margin of South America is marked by the shift from an extensional convergent margin towards a more compressional setting that marks the awakening of the Andean orogeny. In the Colombian Andes, this changing scenario is recorded in the Cretaceous sedimentary and magmatic rocks of the Central Cordillera. There, a review of field relationships, together with the analysis of integrated provenance constraints, including sandstones petrography and detrital zircon geochronology from various localities, suggest that during the Early Cretaceous, until the Albian – Aptian, siliciclastic basin filling is characterized by a transgressive fining–upward trend, with a prominent first cycle quartzose provenance that indicates strong chemical weathering of the source areas. Jurassic, Triassic and older detrital zircon U–Pb ages suggest that the igneous and metamorphic rocks forming the basement of the Central Cordillera were the main sources. Furthermore, the presence of Early Cretaceous detrital ages spanning between 120 Ma and 100 Ma, together with interlayered volcanic rocks at the top of the sequence, characterized by a mixed arc–like, MORB and E–MORB geochemical signatures, can be related to the evolution of an extensional arc with an associated back–arc basin formation. Plutonic rocks with ca. 98 Ma crystallization ages show Nd, Sr, Hf and O isotopic evidence for the existence of a thinned continental crust that may account for the dominant mantle signature. By ca. 90 Ma the Early Cretaceous sedimentary sequences were deformed and intruded by plutonic rocks, which conversely, show an isotopic fingerprint characteristic of crustal signatures that can be explained by the involvement of a thicker crust that promoted melt interaction with the more radiogenic host rocks.
This tectonic change from a Mariana to an Andean–type subduction style was probably triggered by regional–scale plate kinematic re–organizations as suggested by the existence of coeval similar tectonic scenarios along the entire South–American margin, and marks the set–up for the construction of the Andean chain.
Keywords: tectonic style, zircon U–Pb geochronology, whole–rock geochemistry, petrography, Central Cordillera, Colombian Andes, intra–arc basin, back–arc basin, intra–oceanic terrane, tectono–stratigraphic domains.