In situ U/Pb dating of impact‐produced zircons from the Vargeão Dome (Southern Brazil) |
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| Authors: | Anne Nédélec Jean‐Louis Paquette Elder Yokoyama Ricardo I F Trindade Thierry Aigouy David Baratoux |
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| Institution: | 1. Géosciences Environnement Toulouse (UMR5563), University of Toulouse, , France;2. Institut de Recherche en Astrophysique et Planétologie (UMR5577), University of Toulouse, , France;3. Magmas et volcans (UMR6524), University of Clermont‐Ferrand, , France;4. Instituto de Astronomia, Geofisica e Ciencias atmosfericas, University of S?o Paulo, , Brazil |
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| Abstract: | The Vargeão impact structure was formed in the Serra Geral basaltic and rhyodacitic to rhyolitic lava flows of southern Brazil, that belong to the Paraná‐Etendeka large igneous province. The Chapecó‐type rhyodacites contain small baddeleyite crystals recently dated at 134.3 (±0.8) Ma, which is regarded as the age of this acid volcanism coeval to the flood basalt eruption. Inside the impact structure, a brecciated rhyodacitic sample displays fine veinlets containing numerous lithic fragments in a former melt. This impact breccia contains newly formed zircons, either in the veins or at the contact between a vein and the volcanic matrix. The zircons are 10–50 μm in length, clear and nearly unzoned. In situ laser‐ablation dating of the zircons provides a concordant Early Aptian age of 123.0 ± 1.4 Ma that is regarded as the age of the impact event. As in situ age determination ensures the best possible selection of the analyzed mineral grains, the methodology employed in this study also represents a promising method for dating other impact structures. |
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