A set of magnetic measurements (hysteresis loops, thermomagnetic curves, magnetic susceptibility, anhysteretic and isothermal remanences) were performed for samples collected from stratigraphic layers (basal ash, L1, 2a and 2b) of the Campanian Ignimbrite (CI) and from its marine equivalent, the Y5 tephra layer. Day plots, Lowrie–Fuller tests and interparametric ratios demonstrate that the carrier of the remanence is low Ti-magnetite with grain size mostly characterized by pseudo-single-domain (PSD) grains. The magnetite content increases toward the top, particularly in the uppermost 2b layer which is also characterized by smaller grain size. The distribution of the magnetic content is different among the different layers and it may reflect a primary signature as well as post-depositional transformation such as zeolitization and/or maghemitization. The magnetic data confirm the correlation between the CI and the Y5 tephra layer and indicate that a unique eruption was responsible for their emplacement. First-order reversal curve (FORC) diagrams clearly display that the plinian basal ash can be considered the only true source for the marine tephra layer. The results demonstrate the potential of magnetic methods to characterize pyroclastic flow deposits and provide support for the identification and correlation of distal tephra.
Figures & Tables
The Use of Palaeomagnetism and Rock Magnetism to Understand Volcanic Processes
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.