MAGMATIC AND TECTONIC FRAMEWORK OF PORPHYRY-COPPER PROVINCES IN NORTHWESTERN MEXICO AND SOUTHERN PERU: SIMILARITIES AND DIFFERENCES

NW Mexico and southern Peru host two of the most important porphyry-copper provinces on Earth. Both regions formed in geodynamic settings that share some similarities and differences during the porphyry emplacement and supergene enrichment. In both cases, a long-lived subduction zone (at least 200 My), calk-alkaline magmatism, a thick continental crust and landward arc migration due to progressive slab flattening are observed. All these features created excellent conditions to generate porphyry-copper clusters including giant (>2.5 Mt Cu) to super-giant (> 25 Mt Cu) individual deposits. The moment and duration of emplacement of the mineralizing pulses are similar (between 75 and 52 Ma in NW Mexico and 82 to 52 Ma in SW Peru). Such copper clusters require particular conditions of the magmatic system above the subducting slab to guarantee the arrival in subsurface environment of large amounts of copper derived from the asthenospheric mantle. In NW Mexico it has been proposed that a slab tear south of the Colorado Plateau flat-slab favored the renewal of asthenospheric mantle to the system. In southern Peru, the genesis of porphyry copper mineralization process is considered as resulting from extreme upper crustal shortening that allowed development of large, confined and shallow magmatic chambers from which copper-rich fluids were released to form large porphyry copper system. However, there are no convincing evidence of such large-scale shortening during this period. After porphyry emplacement, supergene enrichment is needed to reach economic ore grades. In NW Mexico, the mineralized systems were exhumed during regional large-scale extension that favored supergene enrichment processes. In southern Peru, moderate extension occurred just after porphyry emplacement, during an episode of flat-slab subduction. This episode induced regional uplift in the upper plate that may have been critical to exhume and enrich the mineralized deposits.