Paleomagnetic and Rock Magnetic Characterization of the Pietre Cotte Lava Flow (Vulcano, Italy)

Active emplacement of silicic lava flows has rarely been observed. To understand their dynamics is essential to study past and inactive flows. The Pietre Cotte lava flow, a glass-rich rhyolitic flow emplaced around 1740 CE at Vulcano (Italy), represents one of the best exposed and continous example of silicic lava flow. This lava flow is characterized by a single lobe around 380 m long with a constant width of about 170 m. A complex emplacement history composed by a series of deformation phases was reconstructed by structural and textural data. Evidence of extensional (e.g. tension gashes and stretched vesicles) and compressional (i.e. folds) regimes were observed and associated to local variations in water content, strain rate and/or temperature. We performed rock magnetic and paleomagnetic analyses to provide additional constraints to the emplacement dynamics of the Pietre Cotte lava flow, both in term of deformation events and emplacement time. Magnetic mineralogy experiments reveal the presence of low coercivity phases, such as magnetite. Anisotropy of magnetic susceptibility (AMS) at the flow front and within the lava flow is characterized by magnetic foliation and lineation parallel to the flow banding and flow direction, respectively. The magnetic fabrics at the lateral margins of the lava flow reveal the superposition of local variations with magnetic fabric consistent with ramps and folds, remarking local variations in the deformation regimes. Anisotropy of remanence (ARM) experiments at different coercivity windows show significant agreements with the AMS at site level. Instead, the partial ARM in the coercivity window 100 - 40 mT is characterized by a relatively high dispersion of the axes. The demagnetization pattern is well defined at all sites, showing only one magnetization component pointing straight to the origin of the Zijderveld diagrams. Within-site directions are well clustered, whereas small variations among sites are detected. We suggest that detailed rock magnetic and paleomagnetic investigation of silicic lava flow mutually constrain the structural and textural data and unravel the local variations in the deformation regimes, providing significant insights on the emplacement dynamic of lava flows.