The link between metamorphism, volcanism and geotectonic setting during the evolution of the Andes

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Abstract
Summary: A low-grade, non-deformational, regional metamorphism ranging from burial to ocean-floor type characterizes the Andean range. Longitudinal variations exist, coinciding with changes in the chemistry of the volcanic suites involved, both trends being controlled by the geotectonic setting. The study of Cretaceous volcanic rocks in Colombia, Peru and Chile indicates that: (i) ocean-floor metamorphism (high- T gradients) correlates with tholeiitic volcanism in marginal basins where the continental crust was eliminated or extremely attenuated; (ii) burial metamorphism (low- to moderate- T gradients) correlates with calc-alkaline to shoshonitic volcanism in ensialic, aborted, marginal basins with moderate thinning of the continental crust. The metamorphism in the Andes, which is characterized by a counter-clockwise P-T-t path, started during the initial stages of basin formation and preceded the orogenic activity, contrary to the development in compressional geotectonic settings.