EVOLUCIÓN ESTRUCTURAL DEL COMPLEJO ÍGNEO HUACO, SIERRA DE VELASCO, LA RIOJA

MACCHIOLI GRANDE, M.; ALASINO P.H.; ROCHER, S.; LARROVERE, M.A.; DAHLQUIST J.A.; REINOSO CARBONELL, V.

Congreso; XX Congreso Geológico Argentino; 2017

The Huaco Igneous Complex is one of several Early Carboniferous granitic massifs emplaced at shallow levels that outcrop in Sierras Pampeanas (NW Argentina). It comprises three plutonic units, named Huaco, Sanagasta and La Chinchilla. Huaco and Sanagasta units are porphyritic biotite monzo to syenogranites emplaced in Ordovician-Silurian metamorphic rocks. La Chinchilla unit is a monzogranite that intrudes Huaco unit. The latter shows discordant relationships with host rockfabrics in sharp contacts in the north, as medium to shallow-dipping sheets, generating an interdigitated pattern.Host rock fabrics near the contact keep the NW-SE regional foliation. Conversely, the Sanagasta unit exhibits vertical contacts with the mylonites in the SW region, which occur as concordant anastomosed sheets. Moreover, in the SE of this unit, the host rock nearby the contact is locally deflected. Numerous blocks of mylonites appear in both units. La Chinchilla unit shows sharp discordant relations with Huaco unit. The observed features allow us to proposea fragile emplacement mechanism for both Huaco and La Chinchilla units, developing a tabular geometry.Sanagasta unit, in contrast, reveals a fragile-ductile emplacement style which leads to a cylindrical body. This switch in the emplacement style is due to the Huaco unit intruding a relatively cold upper crust and Sanagasta unitemplacing in a thermally mature system. Later, after 10 My of magmatic inactivity, the upper crust returns to normal thermal conditions and La Chinchilla unit intrudes in a fragile manner.