Internal framework and geochemistry of the Carboniferous Huaco granitic complex, Sierra de Velasco, NW Argentina

Fernando Guillermo Sardi, Pablo Grosse, Mamoru Murata, Rafael Pablo Lozano Fernández


The A-type Huaco granite complex of the Velasco range (Sierras Pampeanas of northwest Argentina) is conformed by a dominant facies and nine subordinate facies that display different temporal relations, textures and compositions. The dominant facies (Regional Porphyritic Granite; RPG) is a porphyritic two mica monzo- to syenogranite, with abundant microcline megacrysts up to 12 cm in size. It was emplaced in a dominant extensional setting and had a mainly crustal source but with participation of a mantle-derived component. The RPG transitions towards two coeval facies, at its margins (Border Granite; BG) and around Be-pegmatites (Adjacent Porphyritic granite; APG). These two facies have a finer-grained texture and smaller and less abundant megacrysts. They are also monzo- to syenogranites, but a slight decrease in the biotite/muscovite ratio is observed from the BG to the RPG to the APG. Trace element modeling and REE chemistry suggest that the RPG, BG and APG differentiated from the same magma source by fractional crystallization. The RPG contains tonalitic (TE) and felsic (FE) enclaves which are temporally early facies. The TE can be considered partially assimilated remnants of a mafic component in the genesis of the RPG, whereas the FE seem to be remnants of premature aplites. Five subordinate facies intrude the RPG and are hence temporally late facies: Be-pegmatites (BeP), felsic dykes (FD), dioritic dykes (DD), equiganular granites (EqG) and an orbicular granite pod (OG). The BeP, FD and OG can be considered final stages in the magmatic evolution of the granitic complex, evidencing the presence of abundant water and volatiles in the final stages of crystallization of the RPG. The EqG form small stocks that intrude the RPG and were possibly originated from purely crustal sources. The DD probably correspond to a younger unrelated episode of mafic magmatism.


REE and LIL composition, fractional crystallization model, granitic facies, Huaco granite, Velasco range, Sierras Pampeanas

How to cite this article Sardi, F., Grosse, P., Murata, M., and Lozano Fernández, R., 2018, Internal framework and geochemistry of the Carboniferous Huaco granitic complex, Sierra de Velasco, NW Argentina: Andean Geology, v. 45, no. 2, , doi: