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Paleomagnetic determination of emplacement temperatures of pyroclastic deposits: an under-utilized tool |
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| Authors: | Greig A Paterson Andrew P Roberts Conall Mac Niocaill Adrian R Muxworthy Lucia Gurioli José G Viramonté Carlos Navarro Shoshana Weider |
| Institution: | 1. National Oceanography Centre, University of Southampton, European Way, Southampton, SO14 3ZH, UK 2. Department of Earth Sciences, University of Oxford, Oxford, OX1 3PR, UK 3. Department of Earth Science and Engineering, Imperial College, London, SW7 2AZ, UK 4. Department of Geology and Geophysics, SOEST, University of Hawaii, 1680 East-West Road, Honolulu, HI, 96822, USA 5. Instituto Geonorte, Universidad Nacional de Salta, Av. Bolivia, 5150–4400, Salta, República Argentina 6. Observertorio Vulcanólogico, Universidad de Colima, Av. Gonzalo de Sandoval 444, Colima, Colima, CP. 28045, Mexico |
| Abstract: | Paleomagnetic data from lithic clasts collected from Mt. St. Helens, USA, Volcán Láscar, Chile, Volcán de Colima, Mexico and Vesuvius, Italy have been used to determine the emplacement temperature of pyroclastic deposits at these localities and to highlight the usefulness of the paleomagnetic method for determining emplacement temperatures. At Mt. St. Helens, the temperature of the deposits (T dep ) at three sites from the June 12, 1980 eruption was found to be ≥532°C, ≥509°C, and 510–570°C, respectively. One site emplaced on July 22, 1980 was emplaced at ≥577°C. These new paleomagnetic temperatures are in good agreement with previously published direct temperature measurements and paleomagnetic estimates. Lithic clasts from pyroclastic deposits from the 1993 eruption of Láscar were fully remagnetized above the respective Curie temperatures, which yielded a minimum T dep of 397°C. Samples were also collected from deposits thought to be pyroclastics from the 1913, 2004 and 2005 eruptions of Colima. At Colima, the sampled clasts were emplaced cold. This is consistent with the sampled clasts being from lahar deposits, which are common in the area, and illustrates the usefulness of the paleomagnetic method for distinguishing different types of deposit. T dep of the lower section of the lithic rich pyroclastic flow (LRPF) from the 472 A.D. deposits of Vesuvius was ~280–340°C. This is in agreement with other, recently published paleomagnetic measurements. In contrast, the upper section of the LRPF was emplaced at higher temperatures, with T dep ~520°C. This temperature difference is inferred to be the result of different sources of lithic clasts between the upper and lower sections, with the upper section containing a greater proportion of vent-derived material that was initially hot. Our studies of four historical pyroclastic deposits demonstrates the usefulness of paleomagnetism for emplacement temperature estimation. |
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