Fault-controlled hydrothermal flow over a deep magmatic intrusion inferred by numerical modelling in a back-arc tectonic setting, SE Tyrrhenian Sea

Hydrothermal flow over a magmatic system is one of the main-explored topic by scientific community during the last decades. Here we analyze hydrothermal circulation above a deep magmatic structure located offshore Capo Vaticano promontory (western Calabria coast). The magmatic intrusion may be related to melt migration from a deeper melting region above the Ionian subducting plate. In order to explain observations, we combine geophysical data and numerical modelling. 2D Fluid flow modelling was performed by using the Computational Fluid Dynamics (CFD) software (ANSYS FLUENT), that uses as input: 1) a geological section of the area, from interpretation of a pre-stack depth migrated multichannel seismic profile. The selected seismic line crosses the structural high in front of Capo Vaticano promontory above the magmatic intrusion; and 2) the temperature and heat flow conditions at the boundaries of the model. Model results highlight that temperature and geothermal gradient are mainly controlled by fluid flow pattern, which in turn is affected by fault distribution, by rock permeability, by basement topography and sediment thickness. Depth distribution of hypocenters of instrumental earthquakes, recorded since 2000 (http://cnt.rm.ingv.it/iside) within the active Tyrrhenian back-arc basin, suggests a depth of subducting plate greater than 70 km beneath our study area. A sufficient depth to allow partial melting of the mantle above the slab. Melt migration through the mantle wedge at shallower level forms the magmatic intrusion inferred by magnetic anomalies. The Pliocene Western Offshore Fault (Pepe et al., 2013) and the currently active Ridge 1 Fault (Loreto et al., 2015a), intensely fracturing the continental crust, enhance deep hydrothermal circulation. This hypothesis agrees well with documented observations (Loreto et al., 2015b) and represents a step forward in the knowledge of the Apennine subduction system. Furthermore, it adds new data to the tectonic framework of the inner Calabrian Arc dissected by numerous seismogenic normal faults capable to trigger highly destructive earthquakes.