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Paleomagnetic data collected in the last 30 years indicate that a simple orocline model is not sufficient to describe the complex evolution of the Calabrian Arc. Present-day curvature of the Calabrian Arc is the result of a different tectonic history between the edges of the arc, namely the Southern Apennines and Sicily, and its core, the Calabria-Peloritani Domain. These differences mirror the structural architecture and deep lithospheric configuration of the Calabrian Arc, which are related to the geometry and evolution of the Ionian subduction system. In particular, the presence of lateral heterogeneities in the subducting lithosphere and the subsequent progressive decrease in width of the trench during subduction are likely the main causes of Calabrian Arc formation and of its present-day narrow tight shape.

An integrated structural and paleomagnetic study was carried out on Neogene-Quaternary elastic sedimentary sequences exposed in north Calabria to define the brittle postorogenic evolution of the inner sector of the Calabrian arc. The structural, mineralogical, and magnetic fabric data presented in this paper suggest that the post-orogenic basins of north Calabria originated and developed under an extensional tectonic regime that has been active since the middle Miocene. Results were used to define the spatial and temporal evolution of the extensional fault systems in the framework of extensional processes active in the backarc region of the southeastward-migrating Apennine subduction system. Our data indicate that regional backarc extension operated in the brittle crust, and the data trace a continuous evolution from low- to high-angle extensional faulting. Paleomagnetic data show that this continuous extensional process was accompanied by complex interactions among fault-bounded crustal blocks. In fact, the extensional domain is subdivided into different structural compartments, separated by the adjustment in the fault strike imposed by the regional rotation pattern. Keywords: extension tectonics, Calabria, Italy, paleomagnetism, magnetic susceptibility, anisotropy, neutron diffraction analysis.

Fissure eruptions may provide important information on the shallow propagation of dikes at volcanoes. Somma-Vesuvius (Italy) consists of the active Vesuvius cone, bordered to the north by the remnants of the older Somma edifice. Historical chronicles are considered to define the development of the 37 fissure eruptions between A.D. 1631 and 1944. The 1631 fissure, which reopened the magmatic conduit, migrated upward and was the only one triggered by the subvertical propagation of a dike. The other 25 fissure eruptions migrated downward, when the conduit was open, through the lateral propagation of radial dikes. We suggest two scenarios for the development of the fissures. When the summit conduit is closed, the fissures are fed by vertically propagating dikes. When the summit conduit is open, the fissures are fed by laterally propagating dikes along the volcano slopes. Consistent behaviors are found at other composite volcanoes, suggesting a general application to our model, independent of the tectonic setting and composition of magma. At Vesuvius, the historical data set and our scenarios are used to predict the consequences of the emplacement of fissures after the opening of the conduit. The results suggest that, even though the probability of opening of vents within the inhabited south and west slopes is negligible, the possibility that these are reached by a lava flow remains significant. Keywords: fissures, dike propagation, conduit, Vesuvius.

[1] The Hyblean Plateau in southeastern Sicily, Italy, consists of an isolated and elevated forebulge structure formed since the early Miocene time by bending the foreland lithosphere below the advancing Maghrebian thrust-fold belt. The Hyblean forebulge is presently located in front of an orogenic recess and partly surrounded by two orogenic salients. We analyzed magnetic (anisotropy of magnetic susceptibility) and structural (joints, faults, slickenside lineations, and bed attitudes) fabric data from Neogene carbonate rocks exposed atop the Hyblean forebulge. Results showed unidirectional fabrics developed in response to a NWSE extension at the end the of early Miocene time and beginning of middle Miocene time, and duple-to-multiple fabrics developed in response to major NWSE and NE-SW extensions from the Langhian time onward. We interpreted these results as the evidence for the growth of a doubly plunging forebulge due to the presence of foreland crustal heterogeneities, which enhanced differential retreating processes of the foreland along the subduction zone and the subsequent formation of orogenic salients and recesses. A semianalytical model shows that the observed brittle deformations potentially involved a significant thickness of the carbonate sedimentary cover, thereby reducing the lithosphere flexural rigidity and enhancing its bending aptitude. Citation: Billi, A., M. Porreca, C. Faccenna, and M. Mattei (2006), Magnetic and structural constraints for the noncylindrical evolution of a continental forebulge (Hyblea, Italy), Tectonics, 25, TC3011, doi: 10.1029/2005TC001800.

Paleomagnetic analysis from lower Pleistocene (Sicilian) mudstones in the Sant'Arcangelo basin (Southern Apennines, Italy) shows no vertical-axis rotations. These results define the upper time constraint on the 23[degrees] counterclockwise rotations previously measured in the underlying lower Pleistocene (Santernian-Emilian) units of the Sant'Arcangelo basin. These rotations occurred before the Jaramillo subchron in a time span of Keywords: paleomagnetism, fast tectonic rotations, early Pleistocene, Southern Apennines, slab breakoff.

We report on a palaeomagnetic study of upper Miocene sediments from the Amantea basin, located on the Tyrrhenian coast of Calabria. The magnetic mineralogy is dominated by greigite and subordinate magnetite in the Tortonian-Messinian clays (ten sites), and by hemoilmenite and magnetite in the underlying sands and volcanic ashes (three sites), which have not been dated. Data from the Tortonian-Messinian clays pass both a reversal and a fold test, and define a 19[degrees] [+ or -] 11[degrees] clockwise rotation (with respect to the geocentric axial dipole field direction) for the whole basin. The variable amounts of westward declinations observed in the underlying sands and volcanic ashes can be due to (1) a large counterclockwise rotation episode occurring before the clockwise rotation, (2) the effects of a transitional geomagnetic field in these rapidly deposited sediments, or (3) the observed complex magnetic mineralogy. These new results, when compared with previous palaeomagnetic studies from other Calabrian basins, show that the Neogene drifting of the Calabro-Peloritan block from the eastern margin of Sardinia to the present-day position was accompanied by a (probably Pleistocene) 15-20[degrees] rigid clockwise rotation recorded in both the Tyrrhenian and Ionian margins. This tectonic regime is shown to be very different from the one observed by previous studies in the northern Tyrrhenian domain, where large rotations associated with thrust sheet activity in the external Apennines were coeval with the onset of an irrotational extensional regime in the Tuscan and Latium Tyrrhenian margins. Palaeomagnetism thus confirms the significant geodynamical differences between the southern and northern Tyrrhenian Sea spreadings. Keywords: Calabria, Neogene, palaeomagnetism, tectonics.