Present knowledge of the magmatic evolution of the Eastern Cordillera of Peru

Abstract

The studies which have been carried out in the Eastern Cordillera of Peru over the past 20 years prove the existence of at least three orogenic cycles: the Late Precambrian, the Hercynian and the Andean, each one accompanied by a more or less abundant magmatism. (1) The Precambrian. Leaving aside the prasinites, possibly derived from synsedimentary volcanites, Precambrian magmatism (in the Huanuco region) consists of: a meta-igneous ultramafic to mafic association (serpentinites, meta-gabbros, meta-diorites); syntectonic meta-tonalites; and post-tectonic dioritic and granitic intrusive bodies. (2) The Hercynian (550 to 220 m.y.). From the Cambrian to the Upper Devonian the existence of a synsedimentary magmatism is known. Syntectonic granites were emplaced during the Eohercynian phase, but the major part of magmatism is of a Late Permian to Early Trias age, and is characterized by the intrusion of granitoids and by volcanism of calc-alkaline tendency. It appears that the nepheline syenite of Macusani may belong to a terminal episode of this magmatic period. (3) During the Andean evolution there is considerably less magmatism in the Eastern Cordillera than during the preceding cycles. Plutonism, which is essentially acid, is only well represented in central Peru. Volcanic rocks are more abundant and more widely distributed. Knowledge of the Precambrian is still insufficient to enable us to place the magmatism of this orogenic belt in a geodynamic context. It seems that the Hercynian magmatism is related to extension episodes affecting a continental crust. On the other hand, it is probable that the Andean magmatism of the Eastern Cordillera is linked, at least indirectly, to the presence of an active convergent margin to the west of Peru, dating from the Mesozoic.