Unveiling Turrialba (Costa Rica) volcano's latest geological evolution through new 40Ar/39Ar, ages
Abstract
Step-heating 40Ar/39Ar dating experiments on whole rock matrix were performed on samples from eight key lava flow units from Turrialba, the easternmost volcano of the Central Volcanic Range of Costa Rica. Our results, together with available corrected 14C ages, recent mapping and new geochemical analyses, are part of a study to reconstruct Turrialba’s evolution. The project is being conducted as part of wider studies because of the increase in volcanic activity during the last three years. The geochemical compositions of the lava flow units span the range from basalts to dacites, and commonly have high K2O concentrations, making them good candidates for 40Ar/39Ar radiometric dating. The ages reported here correspond to the Paleo Turrialba (600-250 ka) and Neo Turrialba (< 250 ka) temporal stages. Sample TUR-38 (251 ± 4 ka) belongs to the latest unit of Paleo Turrialba stage, known as Finca Liebres volcano, while the remaining seven samples belong to Neo Turrialba: TUR-30 (99 ± 3 ka), TUR-19 (90 ± 4 ka), TUR-32 (62 ± 2 ka) TUR-33 (61 ± 2 ka), TUR-12 (25 ± 1.9 ka), TUR-36 (10 ± 3 ka) and TUR-08 (3 ± 3 ka). All the obtained ages in this study are in agreement with the local stratigraphy and prior 14C age determinations, adding robustness to our results. According to ages obtained and the areal distribution of the sampled units, the most important construction period of the massif was during the Neo-Turrialba stage which has passed through two important constructing episodes, around 100-60 ka and 10 ka-present. Although our results include some very young ages, all of them meet the established evaluation criteria used for plateau and isochron ages, commonly used for 40Ar/39Ar dating. Furthermore, we used a protocol that closely monitors the mass spectrometer mass discrimination during the measurements to provide additional control. Three of the eight 40Ar/39Ar ages reported here are remarkably young (25 ka or less). Two of those are the samples with the highest values of K2O (3.27 and 3.56 wt%, respectively), while the other sample has 1.57 wt% K2O. These relatively high values of K2O, together with the mass discrimination protocol, are reasons we are confident that these results are real and not artifacts of some measurement bias. One lava flow from Turrialba was dated at 10 ± 3 ka, with a seven step plateau comprising of 99% of the total 39ArK, making this one of the youngest and most precise ages ever obtained by 40Ar/39Ar in Central America.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V23B2437R
- Keywords:
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- 1105 GEOCHRONOLOGY / Quaternary geochronology;
- 1194 GEOCHRONOLOGY / Instruments and techniques;
- 8488 VOLCANOLOGY / Volcanic hazards and risks;
- 8494 VOLCANOLOGY / Instruments and techniques