New fission-track age constraints on the exhumation of the central Santander Massif: Implications for the tectonic evolution of the Northern Andes, Colombia

Abstract

The Late Cretaceous to late Neogene exhumation history of the central Santander Massif in the Northern Andes of Colombia is controlled by the geodynamic interactions between the Caribbean, South American and Nazca plates, as well as the Neogene collision and accretion of the Panama arc. Slab-breakoff of the Caribbean plate, with the tip of the slab tear presently being located beneath Bucaramanga, and the east-west oriented Caldas tear are the main structures relating seismic activity and Late Miocene to Pleistocene magmatic/hydrothermal activity and associated gold mineralization in the central Santander Massif.Here we present new apatite (AFT) and zircon fission-track (ZFT) data from 18 samples collected along two profiles in the California–Vetas block (including the Rio Charta), to the south of the Rio Charta fault, and from Bucaramanga to Picacho on the western flank of the central Santander Massif. The fission-track data are used for time–temperature history modelling and for estimating long-term average exhumation rates. The California–Vetas block in the central Santander Massif to the north of the Rio Charta fault cooled rapidly at a rate of about 24°C/Myr between 10 and 5Ma. Fast cooling was not related to post-magmatic cooling or hydrothermal activity, but rather to exhumation, with rates based on apatite fission-track cooling ages on the order of 0.3–0.4km/Myr. However, long-term average exhumation rates since the Late Cretaceous, based on zircon fission-track data, were only on the order of 0.1–0.2km/Myr. Our data indicate that next to the Rio Charta fault also the Surata fault contributed to the exhumation of the California–Vetas block.The western flank of the central Santander Massif, shows a more complete thermal history along the Bucaramanga–Picacho profile, with the exposure of an exhumed zircon fission-track partial annealing zone. Thermal history modelling of zircon fission-track data of this profile shows that after burial and heating from about 150Ma on cooling at rates of 7–10°C/Myr started at about 25Ma. For the lower part of the profile, the early Miocene ZFT ages indicate exhumation at rates of 0.3–0.5km/Myr along the Bucaramanga fault, but were only about 0.1km/Myr on the high plateau of the central Santander Massif.