Thermoremanent Magnetization in Volcanic Rocks and Emplacement Temperature Estimates
2015. "Thermoremanent Magnetization in Volcanic Rocks and Emplacement Temperature Estimates", The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes, M. H. Ort, M. Porreca, J. W. Geissman
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The temperature of the deposits (Tdep) emplaced by the pyroclastic density current (PDC) generated by the seven major explosive eruptions from Somma–Vesuvius during the last 22 kyr were investigated using the thermal remanent magnetization (TRM) of lithic clasts embedded within the deposits. New data are presented for the Pomici di Base, Greenish Pumice, Mercato and 1631 AD deposits and compared to the literature data from the Avellino, 79 AD-Pompeii and 472 AD-Pollena eruptions. The Tdep mainly fall in the range 270–370 °C and no significant correlation is evidenced between sedimentological features, eruptive and depositional processes and the final Tdep. The admixture of ambient air during the run-out appears the most effective process to cool the temperature of the ash and gases of the PDC, and is therefore the main factor affecting the deposit temperature.
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This volume provides a synopsis of current research on volcanic processes, as gained through the use of palaeomagnetic and rock magnetic techniques. Thermoremanent magnetization information provides a powerful means of deciphering thermal processes in volcanic deposits, including estimating the emplacement temperature of pyroclastic deposits, which allows us to understand better the rates of cooling during eruption and transport. Anisotropy of magnetic susceptibility and anisotropy of remanence are used primarily to investigate rock fabrics and to quantify flow dynamics in dykes, lava flows, and pyroclastic deposits, as well as identify vent locations. Rock-magnetic characteristics allow correlation of volcanic deposits, but also provide means to date volcanic deposits and to understand better their cooling history. Because lava flows are typically good recorders of past magnetic fields, data from them allow understanding of changes in geomagnetic field directions and intensity, providing clues on the origin of Earth’s magnetic field.