Paleomagnetically inferred ages of a cluster of Holocene monogenetic eruptions in the Tacambaro-Puruaran area (Michoacan, Mexico): Implications for volcanic hazards

摘要

The paleomagnetic dating procedure was applied to a cluster of four partly overlapping monogenetic Holocene volcanoes and associated lava flows, namely La Tinaja, La Palma, Mesa La Muerta, and Malpais de Cutzardndiro, located in the Tacambaro-Puruaran area, at the southeastern margin of the Michoacan-Guanajuato volcanic field. For this purpose, 21 sites distributed as far apart as possible from each other were sampled to obtain a well-averaged mean paleomagnetic direction for each single lava flow. For intensity determinations, double-heating Thellier experiments using the IZZI protocol were conducted on 55 selected samples. La Tinaja is the oldest of these flows and was dated by the C-14 method at similar to 5115 +/- 130 years BP (cal 4184-3655 BCE). It is stratigraphically underneath the other three flows with Malpais de Cutzarondiro lava flow being the youngest. The paleomagnetic dating procedure was applied using the Matlab archaeo-dating tool in couple with the geomagnetic field model SHA.DIF.14k. Accordingly, for La Tinaja several possible age ranges were obtained, of which the range 3650-3480 BCE is closest to the C-14 age. Paleomagnetic dating on La Palma produced a unique age range of 3220-2880 BCE. Two ages ranges of 2240-2070 BCE and 760-630 BCE were obtained for Mesa La Muerta and a well-constrained age of 420-320 BCE for Malpais de Cutzarondiro. Although systematic archaeological excavations have so far not been carried out in this area, it is possible that the younger eruptions were contemporary to local human occupation. Our paleomagnetic dates indicate that all four eruptions, although closely clustered in space, occurred separately in time with varying recurrence intervals ranging between similar to 300 and similar to 2300 years. This finding should be considered when constraining the nature of the magmatic plumbing system and developing a strategy aimed at reducing risk in the volcanically active Michoacan-Guanajuato volcanic field, where several young monogenetic volcano clusters have been identified recently. These enigmatic small "flare-ups" (outbursts of small pods of magma in geologically short periods of time within a small area) have also been encountered in other subduction-related volcanic fields around the globe (e.g. Cascades arc in the western U.S.A.) and still require to be investigated by geophysical and petrological means in order to understand their origin. (C) 2017 Elsevier B.V. All rights reserved.