MORPHOTECTONIC RESPONSE (UPLIFT/EXHUMATION) OF LITHO-TECTONIC BLOCKS ADJACENT TO ANTIOQUEñO PLATEAU (NORTHERN ANDES): A THERMOCHRONOLOGY ANALYSES APPROACH ON CRETACEOUS AND PERMIAN INTRUSIVES

Our undergraduate investigation deals with the need to create more coherent thermotectonic models that explain the co-evolution of juxtaposed morphotectonic provinces within the Antioquia Central Massif, which is an igneous/metamorphic province located in the northern portion of the Central Cordillera of Colombia. This cordilleran segment includes the Antioqueño Plateauas an elevated erosional surface (~2500 mean elevation), and the adjacent Cauca and Magdalena Inter-Andean valleys, to the west and east respectively. Lack of detailed vertical profiles for thermochronology analyses along the steep Cauca river depression preclude the generation of morphotectonic models that explain the juxtaposition of these dissimilar, major geomorphic features. We use the relief differences and lithologic composition of several fault-bound blocks within the Cauca river trough to collect samples along vertical profiles on the Amaga Stock (Triassic), Pueblito Diorite (E-Cretaceous), and Heliconia Diorite (L-Cretaceous) to conduct: a) apatite (Ap) and zircon (Zrn) fertility/grain quality assessment, b) U/Pb Zrn geochronology and (U-Th)/He + fission track thermochronology in Ap and Zrn, and c) evaluate the morphotectonic history (uplift-exhumation-fault reactivation) of said blocks as a response to accretionary and subduction (compression- transpression) tectonics in western Colombia.

We collected a total of 19 samples (18 rock samples and one detrital sample, ~5 kg each) as follows: 12 in the Stock of Amaga, 4 in the Pueblito Diorite, 2 in the Heliconia Diorite, and 1 detrital sediment sample in the Quebrada Sinifaná. Samples were subjected to mineral separation though conventional gravimetric (water table, gold pan, heavy liquids) and magnetic susceptibility (Frantz Isodynamic®) procedures to obtain Ap and Zrn separates. Mineral fractions were scanned/hand-picked under reflected and transmitted light at high magnifications and SEM-CL to select adequate grains for He and FT analyses. Preliminary results of this study will be presented including new thermochronology and geochronology datasets and HeFTy® models that help elucidating the tectonothermal and morphotectonic history of litho-tectonic blocks on the tectonically active edge adjacent to the MCA at the eastern margin of the Cauca River trough.