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Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation

Chew, David
Kirkland, Christopher
Goodhue, Robbie
Published in Geology. 2007, vol. 35, no. 12, p. 1095
Abstract The Chiquerío Formation in southern Peru records the only documented Neoproterozoic glacial episode in the entire Andean Belt. We present U-Th-Pb secondary ion mass spectrometry (SIMS) detrital zircon ages and C isotopic data from the tillite and its overlying dolomite cap, the San Juan Formation. Two prominent negative C isotopic excursions are documented: an older excursion (δ13C = −2‰) in the cap-carbonate unit overlying the tillite, and a younger excursion (δ13C = −8‰) in a laminated limestone unit 700 m up sequence. In both cases, δ13C values recover to 2‰. U-Th-Pb SIMS detrital zircon results from the tillite (both matrix and interbedded turbiditic sandstones) indicate a restricted age distribution of 950-1300 Ma. Turbiditic dolomitic sandstones overlying the younger (−8‰) carbon isotope excursion yield a similar 950-1300 Ma peak, but also contain grains dated as 1600-2000 Ma and 700-820 Ma. The detrital zircon geochronology and C isotope chemostratigraphy are consistent with the Chiquerío Formation being equivalent to the ca. 700 Ma Sturtian glacial. The younger negative C isotope excursion is delimited by the youngest detrital zircon (697 ± 11 Ma) in overlying strata. A correlation with the 635 Ma Marinoan glacial is inferred, although no unequivocal glaciogenic strata have been identifi ed. The detrital zircon data are consistent with derivation from the Proto-Andean margin, despite the Chiquerío Formation unconformably overlying basement gneisses of the 1800-2000 Ma Arequipa-Antofalla basement (AAB), which is exotic to Amazonia. This implies the Chiquerío Formation and AAB were proximal to the proto-Andean margin during Neoproterozoic glaciation, and supports paleogeographic reconstructions that favor AAB accretion to the Amazonian craton during the 1000-1300 Ma Grenville-Sunsas orogeny.
Keywords NeoproterozoicProto-AndesCap carbonateGlacialAmazoniaProvenance
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Research group Isotope Geochemistry, Geochronology and Thermochronology
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CHEW, David et al. Neoproterozoic glaciation in the Proto-Andes: Tectonic implications and global correlation. In: Geology, 2007, vol. 35, n° 12, p. 1095. https://archive-ouverte.unige.ch/unige:28474

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Deposited on : 2013-06-10

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