Andean-type convergent continental margins (upper volcanic-sedimentary level)

Abstract

Andean-type (for short) convergent continental margins and their metallogeny are magnificently displayed in the cordilleras of South and North America, especially in the portion of the Andes between Ecuador and Santiago. The latter is thus a model of a long-lasting, persistent (for 570 million years; Petersen, 1999) convergent continental plate margin that is easy to delimit. This is not the case of the numerous geologically older disrupted margins that have been repositioned and re-integrated since their origin; the Kazakhstan or Iran–Afghanistan Blocks (microcontinents?) come to mind. As this is a “convenience” chapter, the emphasis is on the rock- and ore-forming environments and processes that are characteristic of the model Andean arcs, that are: broad magmatic arcs developed over craton-ward thickening continental crust; subaerial calc-alkaline volcanism; terrestrial sedimentation in mountainous setting. Some rock and ore settings in the young island arc systems (Chapter 5) that are (almost) identical to the Andean settings, like the continental crust-influenced magmatism in mature (Japan-style) island arcs, are included here. In the ancient terrains modified by dispersion and accretion in particular, it is virtually impossible to distinguish between magmatic arcs formerly attached to a continent and former island arcs. On the other hand most marine rock- and ore-forming environments (as in the marine forearc), even if attached to Andean margins, are described in Chapter 5 and their ancient counterparts in Chapter 9.