In situ U/Pb dating of impact-produced zircons from the Vargeão Dome (Southern Brazil)
Version of Record online: 19 FEB 2013
© The Meteoritical Society, 2013.
Meteoritics & Planetary Science
Volume 48, Issue 3, pages 420–431, March 2013
How to Cite
Nédélec, A., Paquette, J.-L., Yokoyama, E., Trindade, R. I. F., Aigouy, T. and Baratoux, D. (2013), In situ U/Pb dating of impact-produced zircons from the Vargeão Dome (Southern Brazil). Meteoritics & Planetary Science, 48: 420–431. doi: 10.1111/maps.12066
- Issue online: 18 MAR 2013
- Version of Record online: 19 FEB 2013
- Manuscript Accepted: 11 DEC 2012
- Manuscript Received: 26 JUN 2012
- Institut National des Sciences de l'Univers
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.