The Arequipa Massif of Peru: New SHRIMP and isotope constraintsudon a Paleoproterozoic inlier in the Grenvillian orogen

摘要

The enigmatic Arequipa Massif of southwestern Peru is an outcrop of Andean basement that underwentudGrenville-age metamorphism, and as such it is important for the better constraint of Laurentia–Amazoniaudties in Rodinia reconstruction models. U–Pb SHRIMP zircon dating has yielded new evidence on the evolutionudof the Massif between Middle Paleoproterozoic and Early Paleozoic. The oldest rock-formingudevents occurred in major orogenic events between ca. 1.79 and 2.1 Ga (Orosirian to Rhyacian), involvingudearly magmatism (1.89–2.1 Ga, presumably emplaced through partly Archaean continental crust), sedimentationudof a thick sequence of terrigenous sediments, UHT metamorphism at ca. 1.87 Ga, and late felsicudmagmatism at ca. 1.79 Ga. The Atico sedimentary basin developed in the Late-Mesoproterozoic and detritaludzircons were fed from a source area similar to the high-grade Paleoproterozoic basement, but alsoudfrom an unknown source that provided Mesoproterozoic zircons of 1200–1600 Ma. The Grenville-ageudmetamorphism was of low-P type; it both reworked the Paleoproterozoic rocks and also affected the Aticoudsedimentary rocks. Metamorphism was diachronous: ca. 1040 Ma in the Quilca and Camaná areas andudin the San Juán Marcona domain, 940 ± 6 Ma in the Mollendo area, and between 1000 and 850 Ma in theudAtico domain. These metamorphic domains are probably tectonically juxtaposed. Comparison with coevaludGrenvillian processes in Laurentia and in southern Amazonia raises the possibility that Grenvillianudmetamorphism in the Arequipa Massif resulted from extension and not from collision. The Arequipa Massifudexperienced Ordovician–Silurian magmatism at ca. 465 Ma, including anorthosites formerly consideredudto be Grenvillian, and high-T metamorphism deep within the magmatic arc. Focusedudretrogression along shear zones or unconformities took place between 430 and 440 Ma.ud