Adakitic signal linked to Gondwanan porphyry type deposits from the Andean Frontal Cordillera of Argentina

摘要

The Yalguaraz Cu - (Mo) porphyry deposit, genetically linked to the early Permian magmatism (279.9 +/- 3.2 Ma), is located at the eastern margin of the Andean Frontal Cordillera of Argentina, 15 km north of the Permian San Jorge Cu porphyry deposit. The geochemistry of this Gondwanan metal-bearing magmatism reveals an arc affinity and an adakite-like signature. The petrogenetic analysis of these rocks also suggests assimilation of the continental crust in the source magmas and a change in the residual mineralogy from amphibole +/- plagioclase in San Jorge magmas, to garnet in Yalguaraz magmas. This change to a higher-pressure residual mineralogy suggests increasing crustal thickness, which is consistent with regional geodynamic changes including progressive shallowing probably due to the subduction of an aseismic ridge south of 31 degrees S in the Andes of Argentina during the lower Permian.