Discussion on 'Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism' by Oyarzun et al. (Mineralium Deposita 36: 794-798, 2001)

摘要

In a recent thought-provoking article, Oyarzun et al. (2001) argue that Late Eocene-Early Oligocene fast, oblique convergence between the South America and Nazca-Farallon plates led to flat subduction and direct melting of the subducting plate. The result of this process was the formation of adakite magmas which generated giant porphyry copper deposits related to the Late Eocene-Early Oligocene structural belt of northern Chile, known as the West Fissure fault system. Unfortunately, no additional information was presented by Oyarzun and co-workers to distinguish whether this adakitic signature, or TTG-type magmatism as described by Cornejo and Matthews (2000) at the El Salvador deposit, reflects melting of the base of an overthickened crust, high-pressure crystallization of mantle-derived hydrous magmas, or slab melting followed by crustal contamination during ascent through the Andean crust. Furthermore, current contrasting views on flat-slab subduction settings introduce additional uncertainties to the model proposed by Oyarzun and co-workers.