Tectonic implications of the jurassic magmatism and the metamorphic record at the southern Colombian Andes

Abstract

The Jurassic magmatism and metamorphism of Colombia result from the convergent relation between the Farallón plate and the northwestern continental margin of South America. However, the geodynamic process that generated both magmatism and metamorphism is still unclear. Field relations, U–Pb geochronology and trace elements in zircons, whole-rock geochemistry, and mineral chemistry from a series of plutonic and metamorphic rocks found in Nariño and Putumayo regions (southern Colombia) were used to constrain their composition, age, relation, and tectonic setting, as well correlate them with the Jurassic continental magmatic arc of Colombia. The plutonic rocks vary compositionally from diorite to granite. Whole-rock geochemical analyses show relative enrichment of Large Ion Lithophile Elements (LILE) and Light Rare Earth Elements (LREE) compared with High Field Strength Elements (HFSE) and Heavy Rare Earth Elements (LREE), and negative Nb and Ti anomalies, which reveal that the samples were formed in a volcanic arc setting. U–Pb zircon geochronology indicates that the granitoids crystallized during the Late Jurassic (ca. 163-153 Ma). On the other hand, the metamorphic rocks are hornblende-biotite schists that yield a U–Pb age of 160.8 ± 0.8 Ma, considered the crystallization age of the protolith. Pressure-temperature (P-T) calculations indicate that the schists underwent metamorphism at ~700 °C and 0.45 GPa.The results obtained enable us to correlate the granitoids with the Jurassic magmatic arc of the Colombian Andes. Furthermore, the hornblende-biotite schist is probably contemporaneous with amphibolites and metapelites reported farther north in the Central Cordillera (Cajamarca Complex), which indicates that they could be part of a regional scale metamorphic belt either exposing different structural levels or recording metamorphic conditions from different positions in an arc-related setting.