Jambaló blueschist and greenschist protoliths in the Central Cordillera of the Colombian Andes and their tectonic implications for Late Cretaceous Caribbean-South American interactions

Whole-rock geochemistry and Nd isotopes were used to constrain the nature of the protoliths and provide clues on the metamorphic conditions of the Jambaló blueschists in the Central Cordillera (Colombian Andes). Blueschist-facies rocks and related greenschists belong to a Cretaceous–Paleocene subduction complex. The blueschist occurs as a lens surrounded by greenschist-facies rocks, suggesting that the latter resembles retrograde products of high-pressure rocks. The geochemical composition of blueschists and greenschists indicates similar protoliths, implying that the Jambaló rocks were probably part of a unique and coherent block exposed to different degrees of retrograde metamorphism. Th/La ratios above 0.19 and 143Nd/144Nd compositions of 0.51272 and 0.51259 indicate subduction zone sedimentary input or some crustal contamination, interpreted as the interaction of arc-derived sediments with basalts formed in a supra-subduction zone. The Jambaló schists may represent the youngest exposure of high-pressure metamorphic rocks along the Andes and records of Late Cretaceous Caribbean and South American convergence.