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One of the major issues of the evolution of continental lithospheres is the detachment of the lithospheric mantle that may occur under certain conditions and its impact on the surface. In order to investigate the dynamics of continental delamination, we performed a parametric study using physically scaled laboratory models. The adopted setup is composed of a three-layers visco-elastic body (analog for upper crust, lower crust, lithospheric mantle) locally thickened/thinned to simulate a density anomaly (lithospheric root) and an adjacent weak zone, lying on a low viscosity material simulating the asthenosphere. The results emphasize the interplay between mantle flow, deformation, surface topography and plate motion during a three-phases process: (1) a slow initiation phase controlled by coupling and bending associated with contraction and dynamic subsidence, (2) lateral propagation of the delamination alongside with extension and a complex topographic signal controlled by coupling and buoyancy, while poloidal mantle flow develops around the tip of the delaminating lithospheric mantle, and (3) a late phase characterized by a counterflow that triggers retroward motion of the whole model. A semiquantitative study allows us to determine empirically two parameters: (1) an initiation parameter that constrains the propensity of the delamination to occur and correlates with the duration of the first stage, (2) a buoyancy parameter characterizing the delamination velocity during late stages and therefore its propensity to cease. Finally, we point out similarities and differences with the Sierra Nevada (California, USA) in terms of topography, deformation and timing of delamination.

Absolute plate motion models with respect to a deep mantle reference frame (e.g., hot spots) typically contain some net rotation (NR) of the lithosphere. Global mantle flow models for the present-day plate setting reproduce similarly oriented NRs but with amplitudes significantly smaller than those found in some high NR Pacific hot spot reference frames. It is therefore important to understand the mechanisms of NR excitation, which we attempt here with two-dimensional cylindrical models of an idealized Pacific domain. We study the influence of slab properties, oceanic ridge position, continental keels, and a weak asthenospheric layer on NR and trench migration. Fast slab return flow develops in models with stiff slabs and moderate slab dips. Rapid NRs, comparable to the high NR Pacific hot spot reference frames, are primarily induced by asymmetric slab dips, in particular a shallow slab beneath South America and a steep slab in the western Pacific. A scaling relationship links the amplitude of NR to plate size, slab dip angle, and slab viscosity. Asymmetric ridge positions also promote NR through asymmetric plate sizes. Continental keels have less impact, in contrast to what has been found in earlier global studies. Several models yield unidirectional Pacific trench motions, such as slab advance in the western Pacific and, simultaneously, slab retreat in the eastern Pacific. Our model provides a physical explanation for NR generation in the present-day Pacific setting and hints at mechanisms for the temporal evolution of the basin. RI Becker, Thorsten/A-6665-2010; Moresi, Louis/H-1390-2011

""High-energy seismicity is historically recorded in Tripolitania, Libya suggesting that. this area, far from Mediterranean convergent margin, is currently deforming. How this deformation. relates to surrounding tectonics of the Africa-Europe convergence is still poorly known. Here, we. use remote sensing image analysis and structural survey to show the recent deformation history that. affected Tripolitania and reactivated the western bordering structures of Sirte Basin. This tectonic. regime onset long after the Paleocene–Oligocene deformation correlated to the Hellenic subduction. evolution (Libyan tectonics have been quiescent since then) and is compatible with age and. trends of the Sicily Channel rift zone, a deformational belt that developed across the Maghrebian. chain. We show that the continuity of this belt reaches farther than that previously acknowledged,. as far as c. 1400 km from the collisional front. We speculate on the causes of deformation in this. remote area, suggesting that the extensional belt formed in response to the strong slab-pull gradients. at the central Mediterranean subduction margin which followed the progressive closure of the. oceanic basin.""

We describe the origin and evolution of a travertine deposit located 20 km east of Rome (Italy), near Tivoli. Borehole analysis reveals that the Tivoli travertine body was deposited in a 20-km2 basin, has an average thickness of 50 m and is thicker (more than 80 m) along a steeper base along the west north–south striking side. Structural analysis reveals that this north–south Q1 oriented margin is controlled by dextral strike–slip faults and associated N20–408E oblique and normal faults and joint system that serve as a preferential pathway for hydrothermal circulation, linked to mixing between a shallow fresh water table and deeper circuit. The age of the travertine was calculated by means of U-series disequilibrium, with the beginning and end of the deposition dated at c. 120 and 30 ka, respectively. Five unconformities within the travertine sequence may be linked to erosional episodes related to fluid discharge and low sea level. We conclude that the growth of the Roman thermogene travertine, and therefore the upwelling of hydrothermal fluid along the fault zone, was favoured by a warm and humid climate.

Recent geodetic data are compatible with NNE– SSW tectonic extension at a rate of ∼5 mm/yr in Sicily, southern Italy, within a broader region of net active compression along the Nubian plate margin (northern Africa). The structures that accommodate such extensional regime and its cause are still unknown. From field structural surveys and seismological analyses, the geometry, kinematics, structural architecture, and seismic potential of an extensional seismic zone linking Cefalù and Mount Etna in central eastern Sicily are defined. The zone includes high‐angle WNW striking normal and right‐lateral strike‐slip faults and subordinate north and NNE striking strike‐slip faults either right or left lateral. The occurrence of small discontinuous faults and the absence of related depressions and sedimentary basins suggest that the extensional regime is still in an incipient stage. The ongoing seismic activity possibly reactivates preexisting faults. Instrumentally and historically recorded earthquakes are lower than about 6 in magnitude, and destructive events are historically unknown since at least 1300 A.D. This apparent upper bound of earthquake magnitudes is consistent with the maximum magnitude values estimated from the length of the longest mapped faults and sources of seismic swarms, which all together suggest a value between 6 and 6.5 as the maximum expected magnitude that can be proposed at the present stage of investigation for earthquakes in the study area. Lateral extension on preexisting faults and upwelling of melt mantle material beneath Mount Etna are considered viable processes to explain, at least in part, the active extensional tectonics along the Cefalù‐Etna seismic zone. Strike‐slip seismic faulting beneath Mount Etna may be part of a previously proposed diffuse transfer zone affecting northeastern Sicily and including the Tindari Fault.

The southernmost segment of the Andes of southern Patagonia and Tierra del Fuego forms a ∼700 km long orogenic re-entrant with an interlimb angle of ∼90° known as Patagonian orocline. No reliable paleomagnetic evidence has been gathered so far to assess whether this great orogenic bend is a primary arc formed over an articulated paleomargin, or is due to bending of a previously less curved (or rectilinear) chain. Here we report on an extensive paleomagnetic and anisotropy of magnetic susceptibility (AMS) study carried out on 22 sites (298 oriented cores), predominantly sampled in Eocene marine clays from the external Magallanes belt of Tierra del Fuego. Five sites (out of six giving reliable paleomagnetic results) containing magnetite and subordinate iron sulphides yield a positive fold test at the 99% significance level, and document no significant rotation since ∼50 Ma. Thus, the Patagonian orocline is either a primary bend, or an orocline formed after Cretaceous–earliest Tertiary rotations. Our data imply that the opening of the Drake Passage between South America and Antarctica (probably causing the onset of Antarctica glaciation and global climate cooling), was definitely not related to the formation of the Patagonian orocline, but was likely the sole consequence of the 32±2 Ma Scotia plate spreading. Well-defined magnetic lineations gathered at 18 sites from the Magallanes belt are sub-parallel to (mostly E–W) local fold axes, while they trend randomly at two sites from the Magallanes foreland. Our and previous AMS data consistently show that the Fuegian Andes were characterized by a N–S compression and northward displacing fold–thrust sheets during Eocene–early Miocene times (50–20 Ma), an unexpected kinematics considering coeval South America–Antarctica relative motion. Both paleomagnetic and AMS data suggest no significant influence from the E–W left-lateral Magallanes–Fagnano strike–slip fault system (MFFS), running a few kilometres south of our sampling sites. We thus speculate that strike–slip fault offset in the Fuegian Andes may range in the lower bound values (∼20 km) among those proposed so far. In any case our data exclude any influence of strike–slip tectonics on the genesis of the great orogenic bend called Patagonian orocline.

A variety of atypical plume-like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed, and seismological imaging has shown ubiquitous small-scale convection in the uppermost mantle in regions such as the Mediterranean region, the western US, and around the western Pacific. We argue that the three-dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics. The testable surface expressions of this process are the outsidearc alkaline volcanism, topographic swell, and low-velocity seismic anomalies associated with partial melt. Using three-dimensional, simplified numerical subduction models, we show that focused upwellings can be generated both ahead of the slab in the back-arc region (though ~five times further inward from the trench than arc-volcanism) and around the lateral edges of the slab (in the order of 100 km away from slab edges). Vertical mass transport, and by inference the associated decompression melting, in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities. The upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation. We discuss representative case histories from the Pacific and the Mediterranean where we find possible evidence for such slab-related volcanism.

Subduction of oceanic lithosphere and deep slabs control several aspects of plate tectonics. We review models of subduction dynamics that have been studied over the last decade by means of numerical and analog experiments. Regional models indicate that trench rollback, trench curvature, and back-arc deformation may be explained by fl uid slabs that are ~250–500 times stiffer than the upper mantle. Slab width and, more importantly, rheology determine the role of viscous bending, poloidalsinking fl ow and toroidal-rollback stirring, and interactions of the slab with the higher viscosity lower mantle. Several of these contributions can be represented by a local sinking velocity. Back-arc deformation may then result from an imbalance if larger-scale plate forcing leads to deviations of the convergence rate from the local equilibrium. Lateral viscosity variations (LVVs) are also key for understanding plate driving forces. The realism of global circulation computations has advanced and such models with weak zones and other LVVs have lead to an improved match to observed plate tectonic scores. Those include the correlation with plate motions, the magnitude of intraplate deformation, and oceanic to continental plate velocity ratios. Net rotation of the lithosphere with respect to the lower mantle may be caused jointly by regional slab forcing and the stirring effect of cratonic keels. However, slab models have so far only produced net rotations that are small compared to recent hotspot reference-frame models. Progress in the next years will likely come from a better understanding of slab strength, which is still uncertain since large-scale subduction zone observables and laboratory results do not put strong constraints on slab rheology. Importantly, circulation models with an improved representation of convergent margins will help to close the gap between regional and global approaches to subduction, and to better understand the potential role of the overriding plate.

The Apennine belt represents a typical orogenic segment of the western Mediterranean, characterized by the tectonic convergence between European and Africa plates after oceanic subduction. Both oceanic- and continent-derived metamorphic complexes, considered as the remnants of the subduction-exhumation cycle, crop out in the inner sectors of the Apennine belt, where extensional deformation has dominated since the Early Oligocene. We review the available structural, metamorphic and geochronological data coming from these metamorphic complexes in order to provide a kinematics reconstruction accounting for the tectono-metamorphic evolution of the Apennines, from oceanic subduction to final extensional reworking. During the Eocene, oceanic rocks were progressively subducted down to eclogite-facies conditions following a subductiontype metamorphic gradient. The transition from oceanic- to continental-subduction was coeval with a transition from subduction-type to Barrovian-type metamorphic gradient. Continental collision, at the Eocene-Oligocene boundary, post-dated the syn-orogenic exhumation of HP-rocks and was synchronous with the onset of post-orogenic extension in the hinterland domains. Extensional deformation migrated to the east, following the forelandward migration of the thrust system at the trench. The concomitance of extension and compression is here related to fast rollback of the subducting plate and delamination of the lithospheric mantle below the subducted continental crust. Implications on how the subduction tectonics, syn-orogenic exhumation and post-orogenic extension could have controlled the circulation of HP-rocks in the developing Apennines are also discussed. © The Geological Society of London 2009.

The Apennine belt represents a typical orogenic segment of the western Mediterranean, characterized by the tectonic convergence between European and Africa plates after oceanic subduction. Both oceanic- and continent-derived metamorphic complexes, considered as the remnants of the subduction-exhumation cycle, crop out in the inner sectors of the Apennine belt, where extensional deformation has dominated since the Early Oligocene. We review the available structural, metamorphic and geochronological data coming from these metamorphic complexes in order to provide a kinematics reconstruction accounting for the tectono-metamorphic evolution of the Apennines, from oceanic subduction to final extensional reworking. During the Eocene, oceanic rocks were progressively subducted down to eclogite-facies conditions following a subductiontype metamorphic gradient. The transition from oceanic- to continental-subduction was coeval with a transition from subduction-type to Barrovian-type metamorphic gradient. Continental collision, at the Eocene–Oligocene boundary, post-dated the syn-orogenic exhumation of HP-rocks and was synchronous with the onset of post-orogenic extension in the hinterland domains. Extensional deformation migrated to the east, following the forelandward migration of the thrust system at the trench. The concomitance of extension and compression is here related to fast rollback of the subducting plate and delamination of the lithospheric mantle below the subducted continental crust. Implications on how the subduction tectonics, syn-orogenic exhumation and post-orogenic extension could have controlled the circulation of HP-rocks in the developing Apennines are also discussed.

We report new paleomagnetic and structural data from late Cretaceous to Mio-Pliocene continental sandy/silty sedimentary rocks from the Eastern Cordillera (central Andes). Here, N–S to NNE– SSW ridges hosting Paleozoic basement and upper Cretaceous continental red beds overthrust thick adjacent Cenozoic basins. Pretilting (and likely primary) reliable directions gathered at 15 sites document 45.9 ± 9.4, 30.1 ± 23.9, and 15.4 ± 19.3 clockwise (CW) rotations with respect to South America occurring after the late Cretaceous (80 Ma), Oligo-Miocene (20–30 Ma), and late Miocene- Pliocene (5–10 Ma), respectively. Conversely, four upper Cretaceous sites from the walls of a N–S leftlateral strike-slip fault (Yavi–Abra Pampa fault) yield a null rotation. About 20 km to the west, flower structures and subvertical syntectonic strata dated at 14.26 ± 0.19 Ma are exposed along the subparallel Abra Moreta left-lateral strike-slip fault. Relying on data from the literature on the period when deformation began, we suggest that since Eo- Oligocene times (30–40 Ma) the Eastern Cordillera has undergone a regional CW rotation of 40–50, synchronous with crustal shortening and large-scale bending of the Andean salient. The CW rotation is possibly still active today, as documented by regional GPS data from the Andes. Since 15 Ma ago, the activity of N–S left-lateral strike-slip faults induced counterclockwise rotations along the fault zone, locally annulling the regional CW rotation. In agreement with a previous model, we speculate that mid-Miocene strike-slip activity accommodated the progressive southward spreading of the Altiplano- Puna high-altitude plateau, laterally migrating from the overthickened crustal region of the salient apex.

European Geosciences Union, General Assembly 2013, 07 – 12 April 2013,Vienna | Austria, Multi-seismic experiments acquired across the central and southern part of the Iberian Peninsula provide a new insight into the structure and nature of the lithosphere beneath these areas. Normal incidence and wide-angle seismic reflection data acquired in the area resolve the internal architecture and constrain the distribution of the physical properties along an almost 280 km long transect that samples the major tectonic domains of the Central Iberian Zone (CIZ) and the associated suture (e.g., the Central Unit, CU). A high quality image, ~230 km long, down to 45 km depth (~15 s TWTT) is provided by the normal incidence data set. Based on the reflectivity characteristics, the image can be divided into an upper and mid-lower crust, ~13 km and ~18 km thick, respectively. The wide-angle seismic transect extended the crustal section towards the north across the Madrid Basin. This, latter data set also sample the CIZ until the CU. This is ~280 km long profile which provides very strong constraints on the distribution of physical properties (P wave and S wave velocities, Poisson's ratio) of the upper lithosphere. The PiP and PmP seismic phases constrain two discontinuities: the brittle to ductile discontinuity at ~13-19 km and the Moho boundary at ~31-35.5 km. Currently both appear to act as decoupling surfaces and are interpreted to represent levels of lithological/rheological variations. The internal structure of the Moho is further discussed taking into account the characteristics of the PmP reflections. Furthermore, low fold wide-angle P and S wave stacks reveal a marked crust-mantle transition which is most probably 5-6 km thick and relatively complex structure. The geometrical relationships of this structure with the crustal fabrics of the normal incidence image suggest that the Moho is most probably a result of the re-equilibration and/or other lithospheric processes active after the Variscan collision.

EGU General Assembly 2014, 27 April - 2 May, 2014 in Vienna, Austria, The African continent shows striking topographic features and has recently been target of numerous geophysical and seismic studies to determine its crustal structure, locally and regionally. Observation of surface tectonics coupled with knowledge of variations in crustal thickness provide a top to bottom frame to investigate sub-crustal processes, which affect the uppermost lithosphere and control today’s African topography. As the significance of previous models of crustal thickness in Africa is debatable and favors premature conclusions here our motivation is to address the detailed structure of the African lithosphere revealing Moho and LAB geometry using 1D modeling of elevation, geoid and thermal data including the thermotectonic age of the crust as well as age and thickness of sediments to better account for lateral variations in crustal density. The four-layered model is composed of crust and lithospheric mantle plus sea water and asthenosphere, assuming Airy isostasy and is benchmarked against a detailed compilation of seismic Moho data from active and passive seismic experiments across the continent and its margins. Relating better surface topography with the depth of the Moho and the LAB contributes to improve knowledge on the lithospheric structure in Africa that mainly comes from global models, such as CRUST1.0, regional tomography models and gravity modeling, which unfortunately miss a proper relation between elevation, mean crustal density and crustal thickness. Our approach therefore is seen to support the discussion around the strongly debated processes responsible for the anomalous high elevation especially in the south eastern part of Africa and the observed undulations in Moho depth from about 20 km below the extended regions of the East African Rift System to 50 kilometers underneath the thickest Proterozoic belts. By linking differences in age, density and thermal state of the lithosphere with topography and geoid we want to provide new information especially for the data remote areas in Northern and Central Africa.

European Geosciences Union, General Assembly 2014, Vienna,Austria , 27 April – 02 May 2014, Despite increasing efforts in seismic surveying and geophysical studies to unravel the structure of the African lithosphere, vast areas of the African continent, especially in the central part, still lack reliable data on Moho and LAB depth. As Africa offers provoking conditions to investigate the relation between deep and upper mantle thermal and/or compositional anomalies and its anomalous regional long wavelength topography we present insights into the continent’s crustal and lithospheric thickness. For this purpose we address the 1D study of the detailed structure of the African lithosphere (Moho and LAB geometry) applying a four-layered model composed of crust and lithospheric mantle plus sea water and asthenosphere, assuming Airy isostasy and using, as constraints, elevation, geoid and thermal data. Furthermore, to better verify the crustal thickness model we test it against a comprehensive compilation of existing Moho depth estimates from active and passive seismic studies across the continent. Additionally existing models of thermo-tectonic age of crust, sediment thickness and the thermo-chemical state of mantle domains from global and regional tomography are used to discuss the strongly debated processes responsible for the today’s bimodal distribution of basin-and swell topography.

Subduction zones are not static features, but trenches retreat (roll back) or advance. Here, we investigate the dominant dynamic controls on trench migration by means of two- and three-dimensional numerical modeling of subduction. This investigation has been carried out by systematically varying the geometrical and rheological model parameters. Our viscoplastic models illustrate that advancing style subduction is promoted by a thick plate, a large viscosity ratio between plate and mantle, and a small density contrast between plate and mantle or an intermediate width (w 1300 km). Advancing slabs dissipate 45% to 50% of the energy in the system. Thin plates with relatively low viscosity or relatively high density, or wide slabs (w 2300 km), on the other hand, promote subduction in the retreating style (i.e., slab roll-back). The energy dissipated by a retreating slab is 35% to 40% of the total dissipated energy. Most of the energy dissipation occurs in the mantle to accommodate the slab motion, whereas the lithosphere dissipates the remaining part to bend and ‘‘unbend.’’ With a simple scaling law we illustrate that this complex combination of model parameters influencing trench migration can be reduced to a single one: plate stiffness. Stiffer slabs cause the trench to advance, whereas more flexible slabs lead to trench retreat. The reason for this is that all slabs will bend into the subduction zone because of their low plastic strength near the surface, but stiff slabs have more difficulty ‘‘unbending’’ at depth, when arriving at the 660-km discontinuity. Those bent slabs tend to cause the trench to advance. In a similar way, variation of the viscoplasticity parameters in the plate may change the style of subduction: a low value of friction coefficient weakens the plate and results in a retreating style, while higher values strengthen the plate and promote the advancing subduction style. Given the fact that also on Earth the oldest (and therefore probably stiffest) plates have the fastest advancing trenches, we hypothesize that the ability of slabs to unbend after subduction forms the dominant control on trench migration

This work presents the results from a multidisciplinary study carried out in the southern branch of the Larderello geothermal field (Travale-Montieri area) that is based on the integration of field data with information of 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, spanning 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 650°C (garnet-biotite thermometry) and 0.2 GPa (andalusite stability field). We interpret these new findings as the evidence of Pliocene-Pleistocene thermal metamorphism associated with multiple granite intrusions at shallow levels in the crust. These results (i) add strength to the interpretations emphasising the role of Neogene thermal metamorphism on the tectono-metamorphic signature of the basement rocks found at depth in the Larderello geothermal field; and (ii) 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.

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 8C. 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

The controversial relationship between the orogenic segments of the Western Alps and the Northern Apennines is here explored integrating recently published 3D tomographic models of subduction with new and re-interpreted geological observations from the eclogitic domain of the Voltri Massif (Ligurian Alps, Italy), where the two belts joint each other. The Voltri Massif is here described as an extensional domain accommodating the opposing outward migration of the Alpine and Apennine thrust fronts, since about 30–35 Ma. Using tomographic images of the upper mantle and paleotectonic reconstructions, we propose that this extensional setting represents the surface manifestation of an along strike change in polarity of the subducted oceanic slab whose polarity changed laterally in space and in time. Our tectonic model suggests that the westward shift of the Alpine thrust front from the Oligocene onward was the consequence of the toroidal asthenospheric flow induced by the retreat of the Apenninic slab.

Laboratory models have been conducted to improve our understanding of the role that the resistance of the slab to bending and its coupling to the ambient mantle play in subduction dynamics over geological time scales. Our models are set up with a viscous plate of silicone (lithosphere) subducting under negative buoyancy in a viscous layer of glucose syrup (mantle). For our study, the lithosphere/upper mantle viscosity contrast has been systematically varied, from ~10 to ~105 in order to explore the parameter space between weak and strong slab dynamics. We found that subduction is characterized by a retreating mode for viscosity ratios N104, by the coexistence of a retreating mode and an advancing mode for viscosity ratios between ~104 and ~102, and quasi-stationary, Rayleigh–Taylor like behaviour for ratios b102. By combining our experimental results and kinematic data from current subduction zones in four reference frames which differ in the amount of net rotation, we infer that a lithosphere/upper mantle viscosity contrast of 150–500 is necessary to obtain realistic trench/subducting plate velocity ratios as well as the variability of subduction styles observed in nature.

30-35 Ma ago a major change occurred in the Mediterranean region, from a regionally compressional sub- duction coeval with the formation of Alpine mountain belts, to extensional subduction and backarc rifting. Backarc ex- tension was accompanied by gravitational spreading of the mountain belts formed before this Oligocene revolution. Syn-rift basins formed during this process above detachments and low-angle normal faults. Parameters that control the formation and the kinematics of such flat-lying detachments are still poorly understood. From the Aegean Sea to the Tyrrhenian Sea and the Alboran Sea, we have analysed onshore the deformation and P-T-t evolution of the ductile crust exhumed by extension, and the transition from ductile to brittle conditions as well as the relations between deep defor- mation and basin formation. We show that the sense of shear along crustal-scale detachments is toward the trench when subduction proceeds with little or no convergence (northern Tyrrhenian and Alboran after 20 Ma) and away from the trench in the case of true convergence (Aegean). We tentatively propose a scheme explaining how interactions between the subducting slab and the mantle control the basal shear below the upper plate and the geometry and distribution of detachments and associated sedimentary basins. We propose that ablative subduction below the Aegean is responsible for the observed kinematics on detachments (i.e. away from the trench). The example of the Betic Cordillera and the Rif orogen, where the directions of stretching were different in the lower and the upper crust and changed through time, is also discussed following this hypothesis.

Seismological and structural data are used to constrain the active tectonics of the Nubia plate compressive margin in southern Italy. In this region, compressional displacements have resumed at the rear of the Maghrebian orogenic wedge since about 700–500 ka and are presently accommodated along a seismic belt in the south Tyrrhenian area, where a passive margin has developed during late Neogene-Quaternary times. Earthquake data from the south Tyrrhenian belt are analyzed with Bayloc, a probabilistic nonlinear location method. Results show that the seismic belt is segmented and involves a series of NE-SW and NW-SE elongated clusters. The NE-SW clusters are interpreted as high-angle reverse fault zones verging toward the southeast, whereas the perpendicular clusters are interpreted as possible strike-slip fault zones transferring the contractional displacements to advanced segments of the belt in the southeast. Brittle deformations observed in the Quaternary volcanic island of Ustica are consistent with the geometry and kinematics of the seismic belt deduced from the seismological data. The south Tyrrhenian active belt may constitute an early stage of subduction of the Tyrrhenian oceanic crust beneath Sicily. A similar scenario has been hypothesized also for the westward prolongation of the south Tyrrhenian belt off the Algerian coast. By integrating instrumental and historical seismic data with tectonic evidences, we infer that the south Tyrrhenian belt is probably capable of producing earthquakes with a maximum size close to magnitude 7. The analyzed data suggest a multifault system behavior for the studied compressional belt. This inference is important to estimate and mitigate the seismic and tsunamic hazards in such a densely populated region.

Plate tectonic history, geological, geochemical (element and isotope ratios), and seismological (P-wave tomography and SKS splitting) data are combined with laboratory modeling to present a three-dimensional reconstruction of the subduction history of the central Mediterranean subduction. We  nd that the dynamic evolution of the Calabrian slab is characterized by a strong episodicity revealed also by the discrete opening of the Tyrrhenian Sea. The Calabrian slab has been progressively disrupted by means of mechanical and thermal erosion leading to the formation of large windows, both in the southern Tyrrhenian Sea and in the southern Apennines. Windows at lateral slab edges have caused a dramatic reorganization of mantle convection, permitting in ow of subslab mantle material and causing a complicated pattern of magmatism in the Tyrrhenian region, with coexisting K- and Na-alkaline igneous rocks. Rapid, intermittent avalanches of large amounts of lithospheric material at slab edges progressively reduced the lateral length of the Calabrian slab to a narrow (200 km) slab plunging down into the mantle and enhancing the end of the subduction process.

A combination of statistical studies on present-day subduction zones and three-dimensional (3D) laboratory models is performed with the aim to clarify the way that plate kinematics control the geometry of the slab and the overriding plate deformation in subduction zones. In 3D laboratory models, the analogue of a two layer linearly viscous lithosphere–upper mantle system is achieved by means of silicon putty glucose syrup tank experiment. The subducting and overriding plate velocities are systematically changed by exploring the variability field of natural plate kinematics. Both statistical and modelling approaches recognize the importance of overriding plate motion on subduction process behavior: (1) trenches migrate at a rate close to the overriding plate motion, but always move slower than the overriding plates. The mechanism at work is a direct consequence of “slab anchoring” opposed by both lithosphere and mantle viscous resistance and is responsible for overriding plate deformation and slab geometry variability. (2) An overriding plate shortens when the overriding plate moves toward the trench and conditions that are favourable for overriding plate extension are created when the overriding plate moves away from the trench. (3) Shallow and steep dips are found if the overriding plate moves toward and away from the trench, respectively.

Plate tectonic history, geological, geochemical (element and isotope ratios), and seismological (P-wave tomography and SKS splitting) data are combined with laboratory modeling to present a three-dimensional reconstruction of the subduction history of the central Mediterranean subduction. We fond that the dynamic evolution of the Calabrian slab is characterized by a strong episodicity revealed also by the discrete opening of the Tyrrhenian Sea. The Calabrian slab has been progressively disrupted by means of mechanical and thermal erosion leading to the formation of large windows, both in the southern Tyrrhenian Sea and in the southern Apennines. Windows at lateral slab edges have caused a dramatic reorganization of mantle convection, permitting inflow of subslab mantle material and causing a complicated pattern of magmatism in the Tyrrhenian region, with coexisting K- and Na-alkaline igneous rocks. Rapid, intermittent avalanches of large amounts of lithospheric material at slab edges progressively reduced the lateral length of the Calabrian slab to a narrow (200 km) slab plunging down into the mantle and enhancing the end of the subduction process.

Three-dimensional dynamically consistent laboratory models are carried out to model the large-scale mantle circulation induced by subduction of a laterally migrating slab. A laboratory analogue of a slab–upper mantle system is set up with two linearly viscous layers of silicone putty and glucose syrup in a tank. The circulation pattern is continuously monitored and quantitatively estimated using a feature tracking image analysis technique. The effects of plate width and mantle viscosity/density on mantle circulation are systematically considered. The experiments show that rollback subduction generates a complex three-dimensional time-dependent mantle circulation pattern characterized by the presence of two distinct components: the poloidal and the toroidal circulation. The poloidal component is the answer to the viscous coupling between the slab motion and the mantle, while the toroidal one is produced by lateral slab migration. Spatial and temporal features of mantle circulation are carefully analyzed. These models show that (1) poloidal and toroidal mantle circulation are both active since the beginning of the subduction process, (2) mantle circulation is intermittent, (3) plate width affects the velocity and the dimension of subduction induced mantle circulation area, and (4) mantle flow in subduction zones cannot be correctly described by models assuming a two-dimensional steady state process. We show that the intermittent toroidal component of mantle circulation, missed in those models, plays a crucial role in modifying the geometry and the efficiency of the poloidal component.

Uno dei maggiori problemi nel restauro o nella gestione dei Beni Culturali è l'analisi non distruttiva dei materiali costituenti il manufatto, litoidi o non, che e volte deve essere effettuata senza la distruzione di frazioni anche piccolissime, o, in casi estremi, senza nessuna manipolazione dell'oggetto di cui si desidera conoscere la natura o la composizione. Un esempio di quest'ultimo caso è rappresentato dall'analisi dei marmi della Pietà Rondanini e di un frammento recentemente ritrovato (Mantura, 1973) e conservato presso la galleria Borghese raffigurante la testa e una spalla del Cristo, attribuito alla stessa Pietà, di dimensioni di circa 60 cm. All'osservazione macroscopica, il marmo con cui erano stati ottenuti i due manufatti sembrava essere lo stesso, ed una loro diversificazione poteva essere effettuata, al di fuori di ogni ambiguità, solo attraverso un esame di qualche caratteristica microscopica o microchimica peculiare del materiale. Tale problema poteva essere risolto solo attraverso una analisi della roccia con cui i due pezzi erano stati ottenuti, ma qualunque tipo di analisi analisi avrebbe comportato una seppur piccola manipolazione del pezzo, e questo non era possibile. A questo punto si è pensato di sfruttare una proprietà fisica particolare dei materiali geologici: la radioattività.

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 NW-SE 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 NW-SE 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.

The western Mediterranean subduction zone (WMSZ) extends from the northern Apennine to southern Spain and turns around forming the narrow and tight Calabrian and Gibraltar Arcs. The evolution of the WMSZ is characterized by a first phase of orogenic wedging followed, from 30 Ma on, by trench retreat and back-arc extension. Combining new and previous geological data, new tomographic images of the western Mediterranean mantle, and plate kinematics, we describe the evolution of the WMSZ during the last 35 Myr. Our reconstruction shows that the two arcs form by fragmentation of the 1500 km long WMSZ in small, narrow slabs. Once formed, these two narrow slabs retreat outward, producing back-arc extension and large scale rotation of the flanks, shaping the arcs. The Gibraltar Arc first formed during the middle Miocene, while the Calabrian Arc formed later, during the late Miocene-Pliocene. Despite the different paleogeographic settings, the mechanism of rupture and backward migration of the narrow slabs presents similarities on both sides of the western Mediterranean, suggesting that the slab deformation is also driven by lateral mantle flow that is particularly efficient in a restricted (upper mantle) style of mantle convection.