Low-grade Metamorphism of Cretaceous Basins from the Colombian Andes: Testing Tectonic Models with Paleogeothermal Gradients

Abstract:

The Cretaceous tectonic evolution of the northern Andes include the formation of several sedimentary basins interpreted formed in rift or arc-back-arc settings. Such basin were formed in association with the subduction of the Pacific plate, the opening of the Caribbean or the growth of allocthonous oceanic arcs and were extensively deformed in the Late Cretaceous initiation of Andean orogeny.

Tectonic models for these basins have been mainly postulated from the stratigraphic interpretations or regional characterization of the tectonomagmatic affinity of volcanic rocks. Less attention have been paid on the pontential to evaluate the tectonic history from the characterization of the paleothermal record recorded in diagenetic and very low grade metamorphic evolution of the pelitic rock.

In the Central Cordillera outcrops two main Albian Cretaceous units: the Abejorral formation which is characterized by a pelitic succession with minor sandstones beds and the Quebradagrande Complex that include intercalations of volcanic and pelitic rocks. Such relatively deep accumulation environment is contemporaneous with shallow carbonates and pelitic succesions in the Eastern Cordillera of the Colombian Andes.

Rocks from the Eastern Cordillera that have been widely characterized due to their relation with petroleum exploration are characterized limited development of cleavage and well defined sedimentary structures. In contrast field field relations have shown that the central Cordillera units are characterized by the development of a well defined slaty cleavage, limited development of quartz veins.

Published vitrinite constraints from the Eastern Cordillera have revealed very high burial temperatures which is compatible with proposed extensional setting during burial and accumulation. New illite and chlorite mineralogical characterization is being obtained on the Abejorral and Quebradagrande formation in order to test if the low grade metamorphic record still preserved the high geothermal gradient expected from an accumulation environment and the quick transition from extension to compression.