Abstract

ALCALA-REYGOSA, Jesús; VAZQUEZ-SELEM, Lorenzo  and  ZAMORANO, José Juan. Dating the late Holocene lava flows of the Citlaltépetl volcano (Orizaba Peak) by means of the ³⁶Cl cosmogenic isotope and lichenometry, and implications on eruptive chronology. Bol. Soc. Geol. Mex [online]. 2020, vol.72, n.1, e260919.  Epub Dec 22, 2020. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2020v72n1a260919.

In this study we tested whether young (Holocene) lava flows can be confidently dated based on the preservation of the primary geomorphological features, the stratigraphic position and historical records. To verify this hypothesis, we combined in situ-produced cosmogenic 36Cl exposure dating and lichenometry on two lava flows from the last eruptive cycle of Citlaltépetl (Pico de Orizaba), called Lava flow “A” and “B”, previously attributed to 16th and 17th century eruptions, respectively. On lava flow “A”, the measured in situ-produced 36Cl concentrations lead to a mean age of 3.03 ± 0.70 ka, while lichenometry yields a minimum age of ~1,130 years. Regarding lava flow “B”, the measured in situ-produced 36Cl concentrations lead to a mean age of 1.45 ± 0.35 ka, whereas lichenometry gives a minimum age of ~1,000 years. The exposure ages derived from these methods indicate that both lava flows are significantly older than previously thought and therefore the combination of the preservation of the primary geomorphological features, the stratigraphic position and the historical records is not enough to determine their ages. Overall, the combination of in situ-produced 36Cl cosmic ray exposure dating and lichenometry, used for the first time in Mexico and supported by geomorphological, stratigraphic and historical record criteria, has a considerable potential for dating purposes and it could be useful to refine the eruptive history of other Mexican volcanoes.

Keywords : Lava flows; in situ-produced cosmogenic ³⁶Cl; lichenometry; lichen Rhizocarpon geographicum; Late Holocene.

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