Decoding geochemical and gamma-spectrometric signatures from lavas and sand injectites at the base of the Paraná volcanic province, Novo Hamburgo, Brazil
| Autor: | Sérgio Benjamin Baggio, Sandro Kucera Duarte, Léo Afraneo Hartmann |
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| Rok vydání: | 2012 |
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| Zdroj: | International Geology Review. 55:510-524 |
| ISSN: | 1938-2839 0020-6814 |
| DOI: | 10.1080/00206814.2012.746804 |
| Popis: | Two fundamental issues in the understanding of processes active at the onset of volcanism in the Parana volcanic province of South America are the description of individual lava flows and the relationships between the lavas and the underlying loose erg sand. In the Novo Hamburgo region, Brazil, four Cretaceous lavas cover the erg and are well exposed in large quarries. One basalt flow (51.52 wt.% SiO2) and three basaltic andesites (52.28–55.74 wt.% SiO2) of the low-Ti Gramado chemical type are present. Outstanding, partly silicified sand injectites are also exposed, including 100 m-long (1–2 m thick) extrudites and one sill of similar dimensions (up to 5 m thick) as well as their feeding dikes and smaller sills. The feeder dikes display funnel shapes near the lower contact of the sand extrudites. Gamma-ray emission rates of the four flows are 79, 128, 95, and 97 counts per second from the first to the fourth flow. A vertical basalt dike (47.10 wt.% SiO2) cuts the Incopel flow in the Sultepa quarry and has... |
| Databáze: | OpenAIRE |
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