Zircon fission-track (ZFT) dating of modern river sediments and bedrock outcrops provides information on the cooling of crustal rocks below about 240°C and their long-term exhumation history, given common geothermal gradients and orogenic cooling rates on the order of 15°C/Myr. In comparison to apatite fission-track and (U-Th)/He data, ZFT data are more reflective of regional scale tectonic events, because of the higher closure temperature of the ZFT method, which requires higher levels of exhumation to expose rocks with orogenic cooling ages at the surface.
Numerous detrital thermochronology studies in the Alps, Himalayas or Andes have shown that the age spectrum determined from modern river samples faithfully reflect the cooling age distribution in a given drainage area. However, often the question remains how the different age peaks, which can be discerned from peak fitting of the observed detrital age distribution, may be interpreted with respect to tectonic events and erosion.
New and published detrital ZFT data of the Rio Chicamocha drainage and the Rio Guitiquia and Rio Guayuribe, used in combination with published bedrock ZFT data of the Santander Massif and the Eastern Cordillera, show that both mountain belts experienced important cooling events but at different times. Whereas the western flank of the Santander Massif experienced an important pulse of exhumation at about 25 Ma, the eastern flank of the Eastern Cordillera shows evidence for significant cooling at about 15 Ma. Furthermore, the Santander Massif exhibits an almost complete exhumed ZFT partial annealing zone, which is somewhat tilted to the south. In contrast, the Eastern Cordillera shows a dissected exhumed partial annealing zone on its eastern flank.
In case of the two exhumed ZFT partial annealing zones, the comparison of the detrital and bedrock data shows that only the youngest detrital age peaks in each river sample reflect the most likely tectonically driven exhumation events. The older age peaks indicate zircons derived from with the exhumed partial annealing zones, and the oldest peaks reflect pre-orogenic cooling ages.
- Matthias Bernet1, Carlos Zuluaga2, Sergio Amaya3, Carolina Jimenez4, Mauricio Bermúdez5, Nicolas Villamizar4, Helbert García Delgado4, and Francisco Velandia6