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Boekhout F.,Section of Earth and Environmental science | Sempere T.,Joseph Fourier University | Spikings R.,Section of Earth and Environmental science | Schaltegger U.,Section of Earth and Environmental science
Journal of South American Earth Sciences | Year: 2013

We present an integrated geochronological and sedimentological study that significantly revises the basin and magmatic history associated with lithospheric thinning in southern coastal Peru (15-18°S) since the onset of subduction at ~530Ma. Until now, estimating the age of the sedimentary and volcanic rocks has heavily relied on paleontologic determinations. Our new geochronological data, combined with numerous field observations, provide the first robust constraints on their chronostratigraphy, which is discussed in the light of biostratigraphical attributions. A detailed review of the existing local units simplifies the current stratigraphic nomenclature and clarifies its absolute chronology using zircon U-Pb ages. We observe that the Late Paleozoic to Jurassic stratigraphy of coastal southern Peru consists of two first-order units, namely (1) the Yamayo Group, a sedimentary succession of variable (0-2km) thickness, with apparently no nearby volcanic lateral equivalent, and (2) the overlying Yura Group, consisting of a lower, 1-6km-thick volcanic and volcaniclastic unit, the Chocolate Formation, and an upper, 1-2km-thick sedimentary succession that are in markedly diachronous contact across the coeval arc and back-arc. We date the local base of the Chocolate Formation, and thus of the Yura Group, to 216Ma, and show that the underlying Yamayo Group spans a >110Myr-long time interval, from at least the Late Visean to the Late Triassic, and is apparently devoid of significant internal discontinuities. The age of the top of the Chocolate Formation, i.e. of the volcanic arc pile, varies from ~194Ma to less than ~135Ma across the study area. We suggest that this simplified and updated stratigraphic framework can be reliably used as a reference for future studies. © 2013 Elsevier Ltd.

Boekhout F.,Section of Earth and Environmental science | Roberts N.M.W.,Kingsley Dunham Center | Gerdes A.,Goethe University Frankfurt | Gerdes A.,Stellenbosch University | Schaltegger U.,Section of Earth and Environmental science
Geological Society Special Publication | Year: 2015

Convergent continental margins are the primary host of both growth and loss of continental crust. Continental growth largely occurs via subduction-driven magmatism, whereas continental loss largely occurs via subduction erosion and sediment subduction. Because the latter typically involves partial recycling into magmas, both growth and loss of continental crust can be represented in the magmatic record. The degree of crustal recycling can be estimated from the initial Hf isotope signatures in both magmatic and detrital zircon grains. Recent insights into the geodynamic evolution of the Peruvian margin, in combination with a new dataset of Hf isotopic data on zircon from the Carboniferous to Early Cretaceous, enable us to (1) compare the geodynamic history of the southern Peruvian margin with its Hf isotopic evolution, and (2) quantify the crustal growth between 500 and 135 Ma. The data exhibit a correlation with trends in isotope composition v. time and reflect the dominantly extensional regime that prevailed from the onset of subduction from 530 Ma to c. 135 Ma. This study demonstrates that the Peruvian margin experienced continental growth with juvenile input to arc magmatism of 30-45% on average, and illustrates the use of U-Pb and Hf isotopes in zircon as a tool to trace episodes of crustal growth through time. © The Geological Society of London 2015.

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