Magmatic evolution of the Cerro Toro granite, a complex Ordovician pluton of northwestern Argentina

Abstract The Cerro Toro granitoids range in composition from granite to gabbro and enclose abundant igneous and metamorphic enclaves that are assimilated in varying degree. The host rocks were intensely heated by intrusion of the Cerro Toro pluton, with local formation of anatexites. Geochronologic determinations point to an initial Sr ratio of 0.70967 ± 0.00043 and an age of 456 ± 14 Ma (Ordovician). The geochemical and field relationships between the acidic and basic members point to strong interactions between different unconsolidated magmas, with an extreme local fluidity that resulted in a gneiss-like aspect—although without cataclasis. Geochemical evidence indicates that the Cerro Toro granite was emplaced in a magmatic arc, at relatively deep crustal levels, under conditions close to anatexia.