Provenance of the early Paleozoic Ollantaytambo Formation, southern Peru: the U-Pb and Hf isotope evidence of detrital zircons

Abstract

The plate-tectonic setting of the Ordovician sedimcntary basin of southem Peru and northem Bolivia has been diversely intcrpreted as that of an intracmtonic marginal basin, an aulaoogen, a backarc rift or a passive margin (see summary in Bahlburg et al., 2006). The basin developed on a crustal collage represented by the Arequipa Massif as part of the Arequipa Terrane to the west and the Amazonia craton to the east (Fig. 1). The Arequipa Massif in tum, is part of a 1.9 to 1.8 Ga are terrane (Loewy and Bahlburg, 2007), which is considered to have docked against the SW Amazonia craton in Grenvillian time leading to the formation of the Sunsás orogenic belt in southwestem Brazil and eastem Bolivia (Fig. 1; Lithedand et al., 1989; Loewy et al., 2004). Geochronologic data demonstrated that early Paleozoic granitoids intruded into the Arequipa Massif have an Ordovician age (473-440 Ma, Womer' et al., 2000; Loewy et al., 2004). Early results of an ongoing geochemical study characterize these rocks as having formed in a magmatic are environment (Loewy and Bablburg, unpublished data). The only evidence of early Paleozoic volcanism in the northcm central Andes of northem Bolivia and southern Pero is represented by the mafic to intermediate lapilli tuffs of the Ordovician Ollantaytambo Formation and Umachiri beds in the Cordillera Oriental and Altiplano of southern Peru (Bahlburg et al., 2006).