Uplift and denudation of the Antioquia Eastern Massif (Colombia) from fission-tracks thermochronology

Fission-track dating and thermochronology have been used to assess the low-thermal history of some plutonic rocks intruded into the Antioquia Eastern Massif as defined by Gerardo Botero. These techniques enable us to gain a better understanding of the orogenic process that shaped the northern Colombian Central Cordillera. Samples were collected from the Antioqueño Batholith, Sonsón Batholith, and the smaller igneous bodies: La Unión, San Diego, Altavista and Ovejas, all intruded during the Late Cretaceous. Zircon fission track ages vary from 46.4±1.1 Ma to 64.0±1.3 Ma. Mean track lengths are very homogeneous, with variations from 13.9±1.6 μm to 14.6±1.3 μm. The results of thermal annealing modeling carried out with the AFTSolve program show three main segments: 1) Significant decrease in temperature from 240°C to ~50°C in the middle to late Eocene at maximum cooling rates of 50°C/Ma; 2) A period of thermal stability extending into the Middle Miocene; and 3) a final cooling segment through to surface temperature (20°C) at cooling rates of about 4°C/Ma. Results were interpreted as coincident with the Pre-Andean (middle Eocene) and the Eu-Andean (late Miocene-Pliocene) orogenies. This last pulse is related to the recent orogeny that exhumed the analyzed samples, occurring between 3 and 5 Ma ago, interpreted as the maximum time for the formation of the “Central Cordillera” erosion surface and its subsequent superimposed relief. The intermediate quiescent period did not record the Oligocene Proto-Andean orogeny. The tectonic phases produced episodes of uplift and denudational response at maximum rates of 2000 and 160 m/ Ma, respectively, using an assumed geothermal gradient of 25ºC/km.