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This work presents the results of a multidiscipinary study carried out in the southern branch of the Larderello geothermal field (Travale-Montieri area), which was based on the integration of field data with information on the deeper structures as derived from interpretation of seismic reflection profiles and the P-T t history of the metamorphic substratum as reconstructed from borehole data. Our data document that the structural and metamorphic signature of the metamorphic substratum is chiefly related to a prograde HT-LP metamorphic overprint, ranging in age from c. 2.8 to 0.7 Ma. The metamorphic climax was attained within the K-feldspar zone and equilibrated at P-T conditions of about 0.2 GPa and 650 [degrees]C. We interpret these new findings as evidence of Pliocene-Pleistocene thermal metamorphism associated with multiple granite intrusions at shallow levels in the crust. These results (1) add strength to the interpretations emphasizing the contribution of Neogene thermal metamorphism to the tectonometamorphic signature of the basement rocks found at depth in the Larderello geothermal field, and (2) provide insights on the thermal structures of the crustal section hosting the geothermal field and on the modes through which the long-lived positive thermal anomaly operated in southern Tuscany.

We describe the evolution of the volcanic activity and deformation patterns observed at Mount Etna during the July-August 2001 eruption. Seismicity started at 3000 m below sea level on 13 July, accompanied by moderate ground swelling. Ground deformation culminated on 16 July with the development of a NE-SW graben c. 500 m wide and c. 1 m deep in the Cisternazza area at 2600-2500 m above sea level on the southern slope of the volcano. On 17 July, the eruption started at the summit of Mount Etna from the SE Crater (central-lateral eruptive system), from which two radial, c. 30 m wide, c. 3000 m long fracture zones, associated with eruptive fissures, propagated both southward (17 July) and northeastward (20 July). On 18 July, a new vent formed at 2100 m elevation, at the southern base of the Montagnola, followed on the next day by the opening of a vent further upslope, at 2550 m (eccentric eruptive system). The eruption lasted for 3 weeks. Approximately 80% of the total lava volume was erupted from the 2100 m and the 2550 m vents. The collected structural data suggest that the Cisternazza graben developed as a passive local response of the volcanic edifice to the ascent of a north-south eccentric dyke, which eventually reached the ground surface in the Montagnola area (18-19 July). In contrast, the two narrow fracture zones radiating from the summit are interpreted as the lateral propagation, from the conduit of the SE Crater, of north-south- and NE-SW-oriented shallow dykes, 2-3 m wide. The evolution of the fracture pattern together with other volcanological data (magma ascent and effusion rate, eruptive style, petrochemical characteristics of the erupted products, and petrology of xenoliths within magma) suggest that the eccentric and central-lateral eruptions were fed by two distinct magmatic systems. Examples of eccentric activity accompanied by central-lateral events have never been described before at Etna. Keywords: Mount Etna, July-August 2001 Eruption, magmas, dykes.