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In situ U/Pb dating of impact‐produced zircons from the Vargeão Dome (Southern Brazil)
Author(s) -
Nédélec Anne,
Paquette JeanLouis,
Yokoyama Elder,
Trindade Ricardo I. F.,
Aigouy Thierry,
Baratoux David
Publication year - 2013
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12066
Subject(s) - geology , breccia , lava , geochemistry , basalt , large igneous province , impact structure , rhyolite , zircon , igneous rock , volcano , baddeleyite , flood basalt , impact crater , volcanic rock , volcanism , paleontology , magmatism , astrobiology , physics , tectonics
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.