Abstract
The Tyrrhenian margin of Central Italy underwent extension during Pliocene and Quaternary. Extension occurred mainly through NWâSE normal faults, bordering a sequence of Plio-Quaternary basins. These basins are offset by coeval NEâSW faults, which show strikeâslip and normal motions and have been interpreted as transfer faults. Plio-Quaternary volcanic activity along the margin occurred along a NWâSE belt, systematically in correspondence with NEâSW transverse systems. The Campi Flegrei Volcanic District (CFVD), on the Southern Tyrrhenian margin, consists of an active NEâSW volcanic ridge developed along NEâSW fractures. We performed a structural field analysis with analogue and mechanical models to investigate the role of transverse structures upon volcanism at Campi Flegrei. Field analysis at Campi Flegrei recognized NEâSW and, to a lesser extent, coeval NWâSE active fractures. Analogue experiments have simulated the development of transfer fault systems in brittle extensional domains. The experiments show that subvertical transfer faults connect offset adjacent normal faults dipping 60°. The mechanical model is based on the stress equations in uniaxial lithostatic conditions and absence of regional stresses. It shows how pre-existing subvertical fractures require the smallest magmatic pressures to be penetrated. For a given magmatic pressure, subvertical fractures might be penetrated more deeply, tapping more easily primitive magmas. These results suggest that the CFVD is located along a NEâSW transfer zone connecting NWâSE regional normal faults. Volcanic activity along such NEâSW trend would be induced by the subvertical dip of the transfer faults. The subvertical dip of transfer faults also suggests an explanation for the emission of the more primitive products along NEâSW systems at Campi Flegrei. These considerations find a wider application on the remaining volcanic districts of the margin, located in the same overall structural setting.
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