Publication: The Arequipa Massif of Peru: New SHRIMP and isotope constraints
on a Paleoproterozoic inlier in the Grenvillian orogen
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2010
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Elsevier Science B.V., Amsterdam.
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Abstract
The enigmatic Arequipa Massif of southwestern Peru is an outcrop of Andean basement that underwent
Grenville-age metamorphism, and as such it is important for the better constraint of Laurentia–Amazonia
ties in Rodinia reconstruction models. U–Pb SHRIMP zircon dating has yielded new evidence on the evolution
of the Massif between Middle Paleoproterozoic and Early Paleozoic. The oldest rock-forming
events occurred in major orogenic events between ca. 1.79 and 2.1 Ga (Orosirian to Rhyacian), involving
early magmatism (1.89–2.1 Ga, presumably emplaced through partly Archaean continental crust), sedimentation
of a thick sequence of terrigenous sediments, UHT metamorphism at ca. 1.87 Ga, and late felsic
magmatism at ca. 1.79 Ga. The Atico sedimentary basin developed in the Late-Mesoproterozoic and detrital
zircons were fed from a source area similar to the high-grade Paleoproterozoic basement, but also
from an unknown source that provided Mesoproterozoic zircons of 1200–1600 Ma. The Grenville-age
metamorphism was of low-P type; it both reworked the Paleoproterozoic rocks and also affected the Atico
sedimentary rocks. Metamorphism was diachronous: ca. 1040 Ma in the Quilca and Camaná areas and
in the San Juán Marcona domain, 940 ± 6 Ma in the Mollendo area, and between 1000 and 850 Ma in the
Atico domain. These metamorphic domains are probably tectonically juxtaposed. Comparison with coeval
Grenvillian processes in Laurentia and in southern Amazonia raises the possibility that Grenvillian
metamorphism in the Arequipa Massif resulted from extension and not from collision. The Arequipa Massif
experienced Ordovician–Silurian magmatism at ca. 465 Ma, including anorthosites formerly considered
to be Grenvillian, and high-T metamorphism deep within the magmatic arc. Focused
retrogression along shear zones or unconformities took place between 430 and 440 Ma.