/pdf/reconciling-plate-tectonic-reconstructions-of-alpine-tethys-1do3i5vm2t.pdf

Reconciling plate-tectonic reconstructions of Alpine Tethys with the geological–geophysical record of spreading and subduction in the Alps

We present a tectonic synthesis and an animation of the tectonics of the western Mediterranean since the Oligocene. This work is based on data derived from different geological datasets, such as structural geology, the distribution of metamorphic rocks, magmatic activity, sedimentary patterns, palaeomagnetic data and geophysics. Reconstruction was performed using an interactive software package (PLATYPLUS), which enabled us to apply rotational motions to numerous microplates and continental terranes involved in the evolution of the western Mediterranean basins. Boundary conditions are provided by the relative motions of Africa and Iberia with respect to Europe, and the Adriatic plate is considered here as an African promontory. The reconstruction shows that during Alpine orogenesis, a very wide zone in the interface between Africa and Europe underwent extension. Extensional tectonics was governed by rollback of subduction zones triggered by gravitational instability of old and dense oceanic lithosphere. Back-arc extension occurred in the overriding plates as a result of slow convergence rates combined with rapid subduction rollback. This mechanism can account for the evolution of the majority of the post-Oligocene extensional systems in the western Mediterranean. Moreover, extension led to drifting and rotations of continental terranes towards the retreating slabs in excess of 100-800 km. These terranes - Corsica, Sardinia, the Balearic Islands, the Kabylies blocks, Calabria and the Rif-Betic - drifted as long as subduction rollback took place, and were eventually accreted to the adjacent continents. We conclude that large-scale horizontal motions associated with subduction rollback, back-arc extension and accretion of allochthonous terranes played a fundamental role during Alpine orogenesis.

Reconstruction of the tectonic evolution of the western Mediterranean since the Oligocene

This article reviews geologic and other evidence constraining the thickness of the principal slip zone (PSZ) that accommodates the bulk of coseismic shear displacement during an individual rupture event. Surface deformation from rupturing may occupy swaths tens of meters or more in width, but trenches across active faults generally reveal that incremental slip is accommodated by a PSZ that is tens of centimeters or less in thickness. Geomorphic evidence, coupled with the observations from trenching, suggest a PSZ may stay well localized for distances of several kilometers through many rupture episodes. Mine exposures and exhumed fault zones demonstrate that PSZs separating different lithologies within the “fault core,” although contained within “damage zones” of variably fractured rock ranging up to hundreds of meters in thickness, often comprise just a few centimeters of gouge/ultracataclasite that have accommodated large finite displacements (>1 km). Microstructural studies demonstrate incremental slip localized still further down to 1–10 mm, as do other fault-rock assemblages (slickensides and slickenfibers, fault-veins of pseudotachylyte friction-melt, intravein septa in hydrothermal fault infills). The accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone, with extreme localization to less than 1 cm not uncommon. However, some distributed coseismic shear may also develop, especially at rupture irregularities. Coseismic reduction of shear resistance from friction-melting (Δ T ∼ 1000°C) or from transient thermal pressurization of aqueous fluids (Δ T ∼ 100°C) requires slip during moderate-to-large earthquakes ( u > 1 m) to be restricted to narrow zones, respectively a few centimeters or tens of centimeters in thickness. Given the evidence for slip localization, the apparent scarcity of pseudotachylyte suggests either that seismic friction-melting is a rare phenomenon, or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones.

Thickness of the Seismic Slip Zone

[1] We present the first regional map of CO2 Earth degassing from a large area (most of central and south Italy) derived from the carbon of deep provenance dissolved in the main springs of the region. The investigation shows that a globally significant amount of deeply derived CO2 (10% of the estimated global CO2 emitted from subaerial volcanoes) is released by two large areas located in western Italy. The anomalous flux of CO2 suddenly disappears in the Apennine in correspondence to a narrow band where most of seismicity concentrates. Here, at depth, the gas accumulates in crustal traps generating CO2 overpressurized reservoirs which induce seismicity.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2004GL019480

Carbon dioxide Earth degassing and seismogenesis in central and southern Italy

The Apenninic foreland shows two distinct structural signatures comparing the central Adriatic Sea and the Puglia region. During the Pliocene-Pleistocene the central Adriatic underwent high subsidence rates due to the eastward rollback of the hinge of the west dipping Apenninic subduction. The Puglia region and the Bradanic foredeep are located southward along strike in the same foreland, but, in contrast with the central Adriatic, after Pliocene-early Pleistocene subsidence they underwent uplift since the middle Pleistocene. The geometry and the kinematics of the frontal accretionary wedge and related foreland changed from that moment on between the two areas. At the front of the central northern Apennines, off scraping and subsidence continued, whereas the foredeep and foreland of the southern Apennines were buckled. Those differences are interpreted as being due to the larger subduction hinge rollback rate since middle Pleistocene of the central Adriatic lithosphere (70 km thick) with respect to the thicker Puglia (110 km). The different thicknesses of the continental crust and lithosphere were inherited from the Mesozoic rifting that disrupted the Adriatic plate. The different thicknesses appear to have controlled the variable degree of flexure of the lithosphere and its asthenospheric penetration rate. The Tremiti E–W alignment is the right-lateral lithospheric transfer zone of those different tectonic regimes. The consequent different dip of the subduction in the two sections (steeper west of Puglia) could also explain the lower elevation of the southern Apennines, compared to their central-northern sector.

The Puglia uplift (SE Italy): An anomaly in the foreland of the Apenninic subduction due to buckling of a thick continental lithosphere

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Different styles of deformation in the calabrian arc (Southern Italy): Implications for a seismotectonic zoning

Structural setting of the Apennine-Maghrebian thrust belt

Since early Pliocene times the Apenninic chain has been dissected by normal faults propagating towards the Adriatic foreland. In the Tyrrhenian Sea extension involved deep crustal sections, whereas in the ‘Central Apennines Downfaulted Area’ it affected the shallow crust. The Tyrrhenian back-arc domain is connected to the overall flexural retreat of the Adriatic–Apulia plate in front of the Apenninic collisional wedge. In the outer Apenninic belt thin-skinned delamination and gravitational collapse occurred in the hanging wall of a thickened wedge, overthrusting the uplifted, buoyant crust of the Apulia foreland. Differential sinking velocity of the foreland plate results from the inherited competence contrast between the rigid Gargano–Apulia carbonate platform to the south, and the low-competence lithology of the pelagic sequence of the Adriatic basin to the north. During late Messinian–early Pliocene times this palaeogeographical boundary acted as a lithospheric tear, separating segments of the Apulia plate subjected to different subduction modes.

Depth and modes of Pliocene–Pleistocene crustal extension of the Apennines (Italy)

Character of the stress field in the Calabrian Arc and Southern Apennines (Italy) as deduced by geological, seismological and volcanological information

Livio Vezzani

Papers

Geology and Tectonic Evolution of the Central-Southern Apennines, Italy

Different styles of deformation in the calabrian arc (Southern Italy): Implications for a seismotectonic zoning

Structural setting of the Apennine-Maghrebian thrust belt

Depth and modes of Pliocene–Pleistocene crustal extension of the Apennines (Italy)

Character of the stress field in the Calabrian Arc and Southern Apennines (Italy) as deduced by geological, seismological and volcanological information