Grenvillian granulite-facies metamorphism in the Arequipa Massif, Peru: a Laurentia-Gondwana link

Abstract

The Arequipa Massif is a major component of the Central Andean orogenic basement, extensively exposed along the coast of southern Peru in the vicinity of the Arica Bight and Bolivian Orocline. The southern part of the massif is dominated by granulitic gneisses, for which a ca. 1900 Ma age for metamorphism of a slightly older protolith has been accepted on the basis of Rb-Sr whole-rock isochrons and bulk U-Pb zircon dating. New U-Pb single-grain zircon geochronology, however, reveals two Mesoproterozoic granulite-facies domains: 1200 Ma to the NE of Quilca (16° 44'S, 72° 24'W), and 970 Ma in the vicinity of Mollendo (16° 58'S, 72° 03'W). These ages correspond to the major metamorphic events represented in the Grenville Province of North America and lend credence to proposed reconstructions, based on sparse isotopic data, that Grenvillian metamorphic belts underlie the western margins of South American cratons and constituted the conjugate rifted margin of eastern Laurentia. The protolith ages of the samples further substantiates the proposed Neoproteozoic reconstruction. In both domains of the massif, the orthogneisses have zircon upper intercept ages of about 1950 Ma and the paragneisses contain younger detrital zircons suggesting sedimentation in the early Mesoproterozoic. Correlative zircon ages are found in the Makkovik-Ketilidian belt and the adjacent Trans-Labrador Batholith of eastern Laurentia. The Arequipa Massif is therefore envisaged to represent an exotic terrane that originated as the tip of a pre-Grenville Laurentian promontory, comprising Labrador, Greenland and Scotland, that was embedded into the proto-Andean margin during the Grenville Orogeny.