Fabrizio Pepe

Rifted margin formation in the south Tyrrhenian Sea: A high‐resolution seismic profile across the north Sicily passive continental margin

A new, 150 km long seismic line across the continental margin of north Sicily has been acquired and interpreted. The overall structure of the margin is controlled by extension, which caused crustal thinning and widespread normal faulting. Two main thinned zones are observed in the south in correspondence with the Cefalu basin and farther to the north at the continent-ocean transition. Zones of thinned crust coincide with zones of intense normal faulting. Extension began in late Tortonian times and caused the opening of the Cefalu basin controlled by a northward dipping listric fault. Messinian stretching affected most of the future margin and provoked a widening of the Cefalu basin and normal faulting in the north. Following a phase of relative quiescence in the early Pliocene, renewed extension determined further opening of the Cefalu basin and subordinate normal faulting in the north. Here, however, the record is unclear because of the emplacement of the calc-alkaline Sisifo volcano with associated volcanoclastic deposits. Breakup took place in the late Pliocene and was followed by the deposition of postrift Pleistocene sediments. At the lithospheric scale the sites of extension/thinning did not migrate during rifting. On the smaller scale, on the contrary, the Cefalu basin displays a remarkably systematic pattern of migration toward the foot-wall of the listric fault, which controlled the opening of the basin. The spacing of 4–6 km between faults is also quite systematic. Elongation experienced by the continental part of the margin (presently ∼97 km) has been derived by comparing the present-day and the preextensional lengths and is ∼10 km. The corresponding strain rate is 5×10−16 s−1.

Architecture and Neogene to Recent evolution of the western Calabrian continental margin: An upper plate perspective to the Ionian subduction system, central Mediterranean

The western Calabria continental margin forms the transition between the Pliocene to Recent Marsili spreading center and continental Calabria, all parts of the upper plate of the Ionian subduction zone. Integrating high-resolution and crustal seismic images constrained by gravity modeling, we provide a detailed reconstruction of the architecture of the margin and develop a new scheme for its Miocene to present evolution. This time span encompasses the continent-continent collision between Africa and Eurasia, subsequent orogenic collapse and rifting apart between the two continental masses, and the Pliocene to Recent emplacement of oceanic crust in the Vavilov and Marsili basins. The crust of the margin thins from the Calabria coast (∼25 km) to the Marsili continent-ocean transition (∼12 km). On the whole, upper and lower crusts thin proportionally with pure shear geometry. The continental margin is covered by an Oligocene(?) to present sedimentary succession reaching a maximum thickness of ∼6.0 km in the Paola Basin. During the Miocene the continental margin experienced regional shortening accommodated by a large number of mainly west vergent thrusts possibly associated with the late stages of the Kabilo-Calabrian chain. Shortening continued through Pliocene to Recent but was accommodated by a limited number of west vergent thrust faults located in the western part of the margin and by a few tens of kilometers wide syncline located in the eastern part of the profile. The accommodation space created in the syncline core hosted a ∼4.5 km thick, Plio-Quaternary sedimentary succession, the Paola Basin. No significant extensional fault is observed along the profile. Miocene to Recent subsidence was controlled by (1) a short-wavelength component related to shortening and responsible for the formation of the Paola Basin syncline and, possibly, contributing to the uplift of onshore Calabria and (2) a long-wavelength component responsible for the regional subsidence and oceanward tilting of the Calabria margin. Short-wavelength subsidence ended in the late Pliocene, but long-wavelength downward movements persisted and even accelerated during late Pliocene(?) to Quaternary times when the present-day bathymetry was achieved. Both horizontal deformations and vertical movements are difficult to explain in the context of a normal back-arc basin without taking into consideration patterns of secondary mantle flow generated by the retreat of the subducting slab.

An active oblique-contractional belt at the transition between the Southern Apennines and Calabrian Arc: the Amendolara Ridge, Ionian Sea, Italy.

High-resolution, single-channel seismic and multibeam bathymetry data collected at the Amendolara Ridge, a key submarine area marking the junction between the Apennine collision belt and the Calabrian subduction forearc, reveal active deformation in a supposedly stable crustal sector. New data, integrated with existing multichannel seismic profiles calibrated with oil-exploratory wells, show that middle to late Pleistocene sediments are deformed in growth folds above blind oblique-reverse faults that bound a regional pop-up. Data analysis indicates that ~10 to 20 km long banks that top the ~80 km long, NW-SE trending ridge are structural culminations above en echelon fault segments. Numeric modeling of bathymetry and stratigraphic markers suggests that three 45° dipping upper crustal (2–10 km) fault segments underlie the ridge, with slip rates up to ~0.5 mm/yr. Segments may be capable with M ~ 6.1–6.3 earthquakes, although an unknown fraction of aseismic slip undoubtedly contributes to deformation. The fault array that bounds the southern flank of the ridge (Amendolara Fault System) parallels a belt of Mw < 4.7 strike-slip and thrust earthquakes, which suggest current left-oblique reverse motion on the array. The eastern segment of the array shows apparent morphologic evidence of deformation and might be responsible for Mw ≤ 5.2 historic events. Late Pliocene-Quaternary growth of the oblique contractional belt is related to the combined effects of stalling of Adriatic slab retreat underneath the Apennines and subduction retreat of the Ionian slab underneath Calabria. Deformation localization was controlled by an inherited mechanical interface between the thick Apulian (Adriatic) platform crust and the attenuated Ionian Basin crust.

Structural architecture and active deformation pattern in the northern sector of the Aeolian-Tindari-Letojanni fault system (SE Tyrrhenian Sea-NE Sicily) from integrated analysis of field, marine geophysical, seismological and geodetic data

Framed in the current geodynamics of the central Mediterranean, the Aeolian-Tindari-Letojanni fault system is part of a wider NW-SE oriented right-lateral wrench zone which accommodates diverging motion between regional-scale blocks located at the southern edge of the Calabrian Arc. In order to investigate the structural architecture and the active deformation pattern of the northern sector of this tectonic feature, structural observations on-land, high and very-high resolution seismic reflection profiles, swath bathymetry and seismological and geodetic data were merged from the Lipari-Vulcano volcanic complex (central sector of the Aeolian Islands) to the Peloritani Mountains across the Gulf of Patti. Our interpretation shows that the active deformation pattern of the study area is currently expressed by NW-SE trending, right-transtensional en-echelon fault segments whose overlapping gives rise to releasing stepover and pull-apart structures. This structural architecture has favored magma and fluid ascent and the shaping of the Lipari-Vulcano volcanic complex. Similarly, the Gulf of Patti is interpreted as an extensional relay zone between two overlapping, right-lateral NW-SE trending master faults. The structural configuration we reconstruct is also supported by seismological and geodetic data which are consistent with kinematics of the mapped faults. Notably, most of the low-magnitude instrumental seismicity occurs within the relay zones, whilst the largest historical earthquakes (1786, Mw=6.2; 1978, Mw=6.1) are located along the major fault segments.

Granulometry, mineralogy and trace elements of marine sediments from the Gulf of Milazzo (NE Sicily): evaluation of anthropogenic impact

Granulometry, mineralogy, and trace element concentrations are determined in marine sediments from thirty-six sampling sites in the littoral environment of the Gulf of Milazzo (NE Sicily). Sediment samples were collected in August 2008, along 18 seaward transects, at water depths of ‐10, ‐20 and ‐30 m, by using a Van Veen grab. Grain-size analysis shows predominance of sand (56%) and silt (35%) fractions with respect to clay (7%) and gravel (2%) fractions. Bulk mineralogical analysis documents the presence of quartz, micas, feldspars, calcite, and chlorite, which reflect erosion processes affecting the Kabilian-Calabrian Units. Concentrations of most trace elements in the deeper sediments were notably higher than shallower ones, due to the gradual increase of the fine fraction (<63 mm). Concentrations of Cr, Ni, Pb and, at lesser extent, Zn and Cu in the <63 mm fraction appear to be potentially hazardous, exceeding national and international regulatory guidelines, both close to the Milazzo industrial area and at Capo Rasocolmo. Trace element mean values from the Gulf of Milazzo are comparable with those measured in polluted sediments collected in the Gulf of Palermo and Augusta Bay with a moderate enrichment in Zn. Differ ent sources of trace elements and different geochemical mechanisms are probably responsible of this distribution. Among these sources and mechanisms, local anthropogenic inputs, different contents of organic matter, and surface water circulation may be invoked.