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Title

U-Pb geochronologic evidence for the evolution of the Gondwanan margin of the north-central Andes

Authors
Chew, D. M.
Kosler, J.
Whitehouse, M. J.
Gutjahr, M.
Miskovic, A.
Published in Geological Society of America Bulletin. 2007, vol. 119, no. 5-6, p. 697-711
Abstract We investigated the Neoproterozoic-early Paleozoic evolution of the Gondwanan margin of the north-central Andes by employing U-Pb zircon geochronology in the Eastern Cordilleras of Peru and Ecuador using a combination of laser-ablation-inductively coupled plasma-mass spectrometry detrital zircon analysis and dating of syn- and posttectonic intrusive rocks by thermal ionization mass spectrometry and ion microprobe. The majority of detrital zircon samples exhibits prominent peaks in the ranges 0.45-0.65 Ga and 0.9-1.3 Ga, with minimal older detritus from the Amazonian craton. These data imply that the Famatinian-Pampean and Grenville (= Sunsas) orogenies were available to supply detritus to the Paleozoic sequences of the north-central Andes, and these orogenic belts are interpreted to be either buried underneath the present-day Andean chain or adjacent foreland sediments. There is evidence of a subduction-related magmatic belt (474-442 Ma) in the Eastern Cordillera of Peru and regional orogenic events that preand postdate this phase of magmatism. These are confi rmed by ion-microprobe dating of zircon overgrowths from amphibolite-facies schists, which reveals metamorphic events at ca. 478 and ca. 312 Ma and refutes the previously assumed Neoproterozoic age for orogeny in the Peruvian Eastern Cordillera. The presence of an Ordovician magmatic and metamorphic belt in the north-central Andes demonstrates that Famatinian metamorphism and subduction-related magmatism were continuous from Patagonia through northern Argentina to Venezuela. The evolution of this extremely long Ordovician active margin on western Gondwana is very similar to the Taconic orogenic cycle of the eastern margin of Laurentia, and our fi ndings support models that show these two active margins facing each other during the Ordovician.
Keywords GondwanaAndesPeruGeochronologyZirconPaleozoic
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Research group Isotope Geochemistry, Geochronology and Thermochronology
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CHEW, D. M. et al. U-Pb geochronologic evidence for the evolution of the Gondwanan margin of the north-central Andes. In: Geological Society of America Bulletin, 2007, vol. 119, n° 5-6, p. 697-711. https://archive-ouverte.unige.ch/unige:28490

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Deposited on : 2013-06-10

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