Abstract

RODRIGUEZ G, Gabriel; ZAPATA, Gilberto; ARANGO, María Isabel  and  BERMUDEZ, José Gilberto. PETROGRAPHIC, GEOCHEMISTRY AND GEOCHRONOLOGICAL CHARACTERIZATION OF PERMIAN GRANITOIDS ROCKS TO THE WEST OF LA PLATA AND PACARNÍ - HUILA, UPPER MAGDALENA VALLEY - COLOMBIA. bol.geol. [online]. 2017, vol.39, n.1, pp.41-68. ISSN 0120-0283.  https://doi.org/10.18273/revbol.v39n1-2017002.

La Plata Granite is a granitic series with a heterogeneous composition that is outcropping at the eastern flank of the Central Cordillera of Colombia in the Upper Magdalena Valley area, between the Cauca and Huila departments. It is composed of monzogranites, syenogranites, granodiorites and quartz monzonites. At its edges, the unit includes migmatites and granitoids rocks with folded, stromaticand nebulitic structures. These migmatitic rocks are composed of quartz feldespatic granofels representing the leucosome, and quartz feldespatic granofels with hornblende and biotite corresponding to melanosome. Both granitic and migmatitic rocks have a high K rich calc-alkaline affinity, with SiO₂ content ranging from 58,92% (migmatites) and 77,39% (sienogranite). These two groups of rocks exhibit correlation in Harker diagrams and indiscriminately placed between metaluminous and peraluminous series. Furthermore, in the multi-element diagrams, there is a difference between the granitic and migmatitic rocks signatures, showing parallelism between them, suggesting similar origins associated with a volcanic arc setting given the low contents of Nb, Ti and P for both groups of rocks. LA-ICP-MS U-Pb geochronology analysis in zircons obtained from seven (7) rocks yield similar crystallization ages for granites and migmatites; with ages of 268,3±2,0 Ma, 273,2±4,1 and 277,9±2,1 Ma for migmatitic rocks and 269,0±3,0 Ma, 270,0±2,7 Ma, 272,0±6,8 Ma and 274,8±2,3 Ma for the granitic rocks. Both groups point to inherited ages from the Permian to the Paleoproterozoic, which suggest the contribution of the continental crust blocks that appear to the east of the Permian rocks described in the present study.

Keywords : Permian rocks; geochemistry; geochronology.

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