Chapter 14
Two Cretaceous Subduction Events in the Central Cordillera: Insights from the High P–Low T Metamorphism
By Camilo BUSTAMANTE
and Andres BUSTAMANTE
Pages 278–299
Manuscript accepted October 29, 2018
Abstract
The scarcity of high–pressure metamorphic rocks at the Earth’s surface due to the specific conditions required for their formation and preservation makes it difficult to access the information about subduction zones that they can provide. The northern Andes are characterized by several occurrences of blueschists and, in more minor proportions, eclogites, whose origins are yet to be unraveled. The metamorphic rocks found herein include the Pijao amphibolitized eclogites, Barragán blueschists and associated garnet–amphibolites, and Jambaló blueschists found in Colombia as well as the Raspas Metamorphic Complex in Ecuador. All these rocks have been correlated into a single Late Cretaceous high–pressure metamorphic belt based on regional geochemistry and geochronological data. A compilation of the most recent whole–rock geochemistry and Ar–Ar and Lu–Hf ages from the three high–pressure sequences in Colombia indicates that at least two different subduction events have been recorded in the Central Cordillera of Colombia. The first event, involving subduction and collision, occurred at ca. 130–120 Ma and is represented by the Pijao, Barragán, and Raspas high–pressure rocks, which have N–MORB–like protoliths and are contemporaneous with the end of the arc–related magmatism of the northern Andes, related to an oblique convergence between the Farallón Plate and the continental margin of South America. The second event of subduction is represented only by the Jambaló blueschists at ca. 70–60 Ma, whose protolith is akin to basalt formed in a plume–influenced intra–oceanic arc that was accreted to the continental margin. No reliable correlation is possible for these rocks as yet.
Keywords:blueschist, eclogite, northern Andes, high–pressure metamorphism.