Global correlation of the Vazante Group, São Francisco Basin, Brazil: Re–Os and U–Pb radiometric age constraints |
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| Authors: | Karem Azmy Brian Kendall Robert A Creaser Larry Heaman Tolentino F de Oliveira |
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| Institution: | aDepartment of Earth Sciences, Memorial University of Newfoundland, St. John's, NL A1B 3X5, Canada;bSchool of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287-1404, USA;cDepartment of Earth & Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada;dVotorantim Metais, P.O. Box 03, 38780-000 Vazante, MG, Brazil |
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| Abstract: | The Vazante Group consists of Precambrian carbonate-dominated platform deposits that extend along more than 300 km in the external zone of the Brasilia Fold Belt of the São Francisco Basin in east central Brazil. The sequence is about 4.8 km thick and contains a preserved glaciomarine diamictite unit (containing dropstone) at the top and a lower diamictite unit at the bottom. Previous C- and Sr-isotope profiles suggested the correlation of the upper diamictite unit with the “Sturtian” glacial event (ca. 750–643 Ma). However, new Re–Os isotope data from the shales associated with the upper diamictites yield radiometric age estimates between 993 ± 46 and 1100 ± 77 Ma. U–Pb measurements on a suite of clear euhedral zircon crystals that were separated from the same shales associated with the upper diamictite and from the arkosic sandstone above the lower diamictite yield ages as young as 988 ± 15 and 1000 ± 25 Ma, respectively. Based on the Re–Os and U–Pb ages, the best age estimate of the Vazante Group is constrained to be  1000–1100 Ma and thus the two diamictite units are not correlative with the Sturtian glaciation(s) but most likely are records of glacial events that occurred during the late Mesoproterozoic. |
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| Keywords: | Mesoproterozoic Carbonates Glaciation Re– Os U– Pb Vazante Group Brazil |
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