Adria Plate Research Articles

The Role of Adria Plate Lithospheric Structures on the Recent Dynamics of the Central Mediterranean Region.

The Tertiary tectonic evolution of the Central Mediterranean has been relatively well constrained by abundant geological data. Yet, several uncertainties persist about the mechanisms that led to the present‐day surface morphology and deep slab geometry. Here, we combine geodynamic and seismological numerical modeling techniques to reproduce the recent large‐scale evolution of the Central Mediterranean and the associated strain‐induced upper mantle fabrics and seismic anisotropy. 3D thermo‐mechanical subduction models were designed and calibrated according to paleogeographic‐tectonic reconstructions and seismological observations available in the literature. It is found that, although the opening of back‐arc extensional basins in response to the retreat of the Ionian slab is a common feature in all models, structural heterogeneities within the Adria plate and/or the geometry of its Tyrrhenian passive margin profoundly impact on the segmentation of the subducting slab and the amount of Ionian trench retreat. More, in general, this study highlights the importance of coupling geodynamic and seismological modeling to better constrain the tectonic evolution of complex convergent margins such as the Central Mediterranean.

Migration of Late Miocene to Quaternary alkaline magmatism at the Alpine-Pannonian transition area: Significance for coupling of Adria plate motion with the Alpine-Carpathian front

Within-plate migration of alkaline basaltic centers is generally related to translation of the lithosphere with a hot spot above a largely stationary mantle plume. Here, we report, for the first time, a hitherto unrecognized migration of small-sized Late Miocene to Early Quaternary alkali-basaltic volcanic centers at the transition from Eastern Alps to Pannonian Basin. The volcanic centers migrated along the South Burgenland High in a regular sequence over a 95 km distance from NNE to SSW between 11 Ma and 1.7 Ma. The basaltic magmatism was also associated with thinning of the crust and lithosphere and an increase of the thermal gradient. In detail, three stages of migration are recognized as follows: (i) Stage 1 with a 55 km SSW-towards shift of volcanism between 11 and 5 Ma; (ii) Stage 2 with a ~ 35 km-WSW shift and enlargement of the distribution of volcanic centers between ca. 5 and 3.5 Ma; and (iii) Stage 3 with a S-directed shift of ca. 25 km between 3.5 and 1.7 Ma. The Stage 1 shift of alkali-basaltic volcanism can be also observed in the Little Hungarian Plain and South Slovakia–Nógrád volcanic fields, and the Stage 2 in the Balaton-Bakony of the Pannonian Basin (north of Lake Balaton). We propose that this pattern and mechanism of migration of the volcanic centers along the South Burgenland High resulted from thermally induced progressive thinning of the lithosphere over a mantle plume underneath the ALCAPA block, which was moving from SSW to the NNE between 11 and 1.7 Ma. The migration was interrupted by a marked eastward shift between 5 and 3.5 Ma (Stage 2). The migration of volcanic centers correlates with orientation and timing of regional shortening phases and inversion of the Alpine-Carpathian-Pannonian system although the overall amount of shortening remains uncertain. The deformation events allow to correlate Adria motion with deformation along the frontal parts of Eastern Alps, and Western and Eastern Carpathians across the western Pannonian Basin.

The Variscan subduction inheritance in the Southern Alps Sub-Continental Lithospheric Mantle: Clues from the Middle Triassic shoshonitic magmatism of the Dolomites (NE Italy)

Although often speculated, the link between the Middle Triassic shoshonitic magmatism at the NE margin of the Adria plate and the subduction-related metasomatism of the Southern Alps Sub-Continental Lithospheric Mantle (SCLM) has never been constrained. In this paper, a detailed geochemical and petrological characterization of the lavas, dykes and ultramafic cumulates belonging to the shoshonitic magmatic event that shaped the Dolomites (Southern Alps) was used to model the composition and evolution of the underlying SCLM in the time comprised between the Variscan subduction and the opening of the Alpine Tethys. Geochemical models and numerical simulations enabled us to define that 5–7% partial melting of an amphibole + phlogopite-bearing spinel lherzolite, similar to the Finero phlogopite peridotite, can account for the composition of the primitive Mid-Triassic SiO2-saturated to -undersaturated melts with shoshonitic affinity (87Sr/86Sri = 0.7032–0.7058; 143Nd/144Ndi = 0.51219–0.51235; Mg # ~ 70; ~1.1 wt% H2O). By taking into account the H2O content documented in mineral phases from the Finero phlogopite peridotite, it is suggested that the Mid-Triassic SCLM source was able to preserve a significant enrichment and volatile content (600–800 ppm H2O) for more than 50 Ma, i.e. since the slab-related metasomatism connected to the Variscan subduction. The partial melting of a Finero-like SCLM represents the exhaustion of the subduction-related signature in the Southern Alps lithosphere that predated the Late Triassic-Early Jurassic asthenospheric upwelling related to the opening of the Alpine Tethys.

Porphyroclasts: Source and Sink of Major and Trace Elements During Deformation-Induced Metasomatism (Finero, Ivrea-Verbano Zone, Italy)

Petrographic and geochemical data for mylonites from a metric-scale shear zone in mantle peridotites from the Finero massif (Southern Alps) record large mineralogical and geochemical modifications compared to surrounding coarse-grained ultramafic rocks, which were pervasively deformed in presence of hydrous melts. The mylonites are composed by olivine and orthopyroxene and, less frequently, clinopyroxene, phlogopite, and pargasite porphyroclasts enclosed in a fine-grained matrix of phlogopite and olivine, with subordinate amounts of orthopyroxene, clinopyroxene, pargasite, and chromite. P-T estimates indicate that deformation occurred under granulite- to upper-amphibolite facies conditions. Field relationships and U-Pb dating indicate that the shear zone was active during Lower Jurassic and/or later, in an extensional setting at the western margin of the Adria plate, which led to the opening of the Alpine Tethys. The major and trace element composition of the porphyroclasts in the mylonites significantly differ from those in the hosting coarse-grained ultramafics. Porphyroclasts were chemically active during deformation acting as source (diffusion-out) or sink (diffusion-in) for some trace elements. The chemical modifications were promoted by the interaction with aqueous fluids and the composition varied from mantle- (enriched in Ni, Co, Li, Na, REE, Y, and Sr) to crustal-derived (enriched in Zn, K, Al, Ti, and Fe).

Brittle vs. ductile strain during the synorogenic exhumation of HP-LT rocks: An example from the Lungro-Verbicaro Unit mylonites (northern Calabria, Italy)

We present a study on the mylonites exposed in the Cirella area along the Tyrrhenian coast of northern Calabria (southern Italy), in order to understand the role of ductile and brittle deformation on the exhumation process of these rocks. The analyzed shear zone is located in the footwall of a regional tectonic contact between metaophiolites (Ligurian Complex) on the top, and the continental Lungro-Verbicaro Unit (Adria plate) at the bottom. The latter consists of a metasedimentary succession with Triassic shallow-water carbonates at the base of it, evolving upward to Jurassic-lower Miocene slope to deep basin carbonates and foredeep siliciclastic rocks. Both oceanic and continental successions are characterized by high-pressure and low-temperature (HP-LT) metamorphism. The analyzed mylonites show different degrees of strain, ranging from protomylonites to ultramylonites, the latter characterized by well-marked foliation and stretching lineations. Several micro- and mesoscale progressive deformation structures, including two fold sets, S-C’ structures are present in these rocks, and a late oblique foliation, indicating a NW sense of shear. A successive shortening stage produced thrust faults and related folds, indicating a tectonic transport toward SE. We associate the mylonitic deformation with the activity of the overlying detachment fault, which is responsible for the synorogenic exhumation of the Lungro-Verbicaro Unit during the Miocene time. However, the ductile strain, recorded by the studied mylonites, accounted for a small displacement during the exhumation of this tectonic slice. In fact, the calculated displacement achieved by the Lungro-Verbicaro Unit, during exhumation, is much larger than the one estimated considering only the ductile zones activity. This evidence suggests that, synchronously with ductile strain, brittle deformation occurred along the detachment fault located at the top of the thrust sheet. In addition, a severe erosion due to the tectonic exhumation of the HP-LT rocks (in the late Miocene) produced a large amount of clastic sediment that filled the extensional basins widespread in northern Calabria.

Crustal Thickness Beneath the Dinarides and Surrounding Areas From Receiver Functions

AbstractKnowledge about the crustal thickness is one of the key elements in the reconstruction of the regional tectonic history. The Dinaric mountain belt is one of the most enigmatic segments of the Alpine‐Mediterranean collision zone, characterized by large variations in crustal thickness and not studied sufficiently. We present a new Moho depth map for the wider Dinarides region which was created using teleseismic earthquake recordings from 87 permanent and temporary seismic stations in the region. Teleseismic data were analyzed using the receiver function method to extract converted P to S waves.The resulting Moho topography fits well within a structural framework comprising a thicker crust under the Dinarides, which gradually becomes thinner toward the Pannonian and Adriatic domains. The profiles crossing the northwestern Dinarides are marked by a relatively sharp decrease in crustal thickness north of the main thrust front. This transition is followed by significant crustal thinning toward the Pannonian basin. The Mohorovičić discontinuity lies the deepest in the central and southern Dinarides, at depths of over 55 km. Here similarly to the northwestern segment we observe a jump in the crustal thickness when transitioning toward the Internal Dinarides, which hints at possible underthrusting (or subduction) of the Adria plate in this region. Moho depths in the transition zone toward the Pannonian basin and in the Pannonian basin proper vary between 25 and 35 km. In the Adriatic domain, we find crustal thickness ranging from 30 km to more than 45 km around the Central Adriatic islands.

Upper mantle deformation signatures of craton–orogen interaction in the Carpathian–Pannonian region from SKS anisotropy analysis

SUMMARYSince the Mesozoic, central and eastern European tectonics have been dominated by the closure of the Tethyan Ocean as the African and European plates collided. In the Miocene, the edge of the East European Craton and Moesian Platform were reworked in collision during the Carpathian orogeny and lithospheric extension formed the Pannonian Basin. To investigate the mantle deformation signatures associated with this complex collisional-extensional system, we carry out SKS splitting analysis at 123 broad-band seismic stations in the region. We compare our measurements with estimates of lithospheric thickness and recent seismic tomography models to test for correlation with mantle heterogeneities. Reviewing splitting delay times in light of xenolith measurements of anisotropy yields estimates of anisotropic layer thickness. Fast polarization directions are mostly NW–SE oriented across the seismically slow West Carpathians and Pannonian Basin and are independent of geological boundaries, absolute plate motion direction or an expected palaeo-slab roll-back path. Instead, they are systematically orthogonal to maximum stress directions, implying that the indenting Adria Plate, the leading deformational force in Central Europe, reset the upper-mantle mineral fabric in the past 5 Ma beneath the Pannonian Basin, overprinting the anisotropic signature of earlier tectonic events. Towards the east, fast polarization directions are perpendicular to steep gradients of lithospheric thickness and align along the edges of fast seismic anomalies beneath the Precambrian-aged Moesian Platform in the South Carpathians and the East European Craton, supporting the idea that craton roots exert a strong influence on the surrounding mantle flow. Within the Moesian Platform, SKS measurements become more variable with Fresnel zone arguments indicating a shallow fossil lithospheric source of anisotropy likely caused by older tectonic deformation frozen in the Precambrian. In the Southeast Carpathian corner, in the Vrancea Seismic Zone, a lithospheric fragment that sinks into the mantle is sandwiched between two slow anomalies, but smaller SKS delay times reveal weaker anisotropy occurs mainly to the NW side, consistent with asymmetric upwelling adjacent to a slab, slower mantle velocities and recent volcanism.

New insights on the Adria plate geodynamics from the northern Adriatic perspective

Abstract The interpretation of approximately 1300 km of multichannel seismic data, acquired in the northern Adriatic Sea, revealed that the Apennine foredeep in the northern Adriatic does not show any evidence of tilting since Early Pliocene, suggesting that slab retreat cannot be the geodynamic driving force for the northern Adriatic subsidence and for the northern Apennine kinematic since that time. Moreover, the presence of two fault systems that developed since the Pliocene indicates that the northern Adriatic underwent intraplate deformation during the Plio-Pleistocene. These considerations suggest that, since Early Pliocene, subduction below the northern Apennine ceased, and that the Adria Plate movements were mainly driven by the kinematics of the adjacent plates, particularly by the Nubia-Europe convergence. At present, on the basis of the foredeep setting, four distinct sectors can be recognized in the Adriatic foreland: Po Plain, northern, central and southern Adriatic, separated by major tectonic lineaments. The northern Adriatic differs from the two adjoining sectors because its foredeep deposits are still well preserved. In the Po Plain in fact, the Adriatic foredeep is almost totally incorporated into the Alpine and Apennine chains while in the central Adriatic, it is affected by a considerable intraplate deformation (e.g. the Mid Adriatic Ridge). In this framework, the northern Adriatic region may be regarded as a triangular shaped sector indented below the Southern Alps to the north and the northern Dinarides to the north-east and bounded to the west by the Schio-Vicenza fault system and to the south-east by the Kvarner fault.

Interaction of B-rich supercritical magmatic fluids with granite: first report of dumortierite in Larderello, Italy

In a peraluminous two-mica monzogranite cored at 4.5 km depth in well Radicondoli 29, dumortierite occurs together with andalusite, Li-rich tourmaline, fluorite and fluorapatite. The average composition is SiO2: 30.9, Al2O3: 58.6, FeO: 0.44, MgO: 0.47, CaO: 0.02, F: 0.15. Dumortierite crystallized from supercritical magmatic fluids at T =520-620°C, P = 100 ± 30 MPa. Synthetic fluid inclusions yielded T = 510 ± 10°C, P = 42 ±3 MPa at 2.9 km depth in well Venelle 2. All data suggest present-day T = 450-550°C, P = 40-80 MPa. The supercritical magmatic fluids were hypersaline brines with ~ 30 wt % LiCl and up to 2.4 wt % F, extreme contents that can be found only in pegmatites, aplites and leucogranites. Larderello granites derived from partial melting of a lower crust made up of interlayered metasediments and amphibolites. Extensive melting took place in the lower crust during the last 10 Ma owing to extensional tectonics, lithosphere thinning, roll back or break down of the west merging Adria plate and swelling of the asthenosphere below the western side of the Apennines.

Subduction Zones Interaction Around the Adria Microplate and the Origin of the Apenninic Arc

AbstractThe study of slab‐slab interactions has come to the front of geodynamics researches to explain geological and geophysical observations from tectonically complex areas. Here we aim to better understand the geodynamics of the Central Mediterranean, where the Adria plate subducts on its two opposite sides. Additionally, the slab below the Central South Apennines has been progressively breaking off during the last 3 Myr. The role of a slab window in a single slab or in an outward dipping double‐sided subduction system is addressed by analog models at the scale of the upper mantle, realized using glucose syrup and silicone putty, to model the interaction between the Earth's mantle and the lithosphere. Our results show that the presence of a slab window modifies the pattern of mantle circulation, as well as the trench geometry and kinematics. In particular, the opening of the slab window induces the formation of two arcs flanking the window, while the mantle flows through it and turns toward the arcs, creating a small‐scale toroidal flow. The effect of a slab window is more pronounced on double subduction systems, as the outflow through the window is amplified, while internal deformation is induced in the plate by the opposite slab pull force. These experimental results suggest that the origin of the Apenninic and the Calabrian arcs is the result of the formation of a slab window, providing a new interpretation of the surface deformation and the SKS shear wave splitting pattern of the Adria microplate.

Evidence of Permian magmatism in the Alpi Apuane metamorphic complex (Northern Apennines, Italy): New hints for the geological evolution of the basement of the Adria plate

The occurrence of metavolcanic rocks within the Paleozoic basement of the Alpi Apuane metamorphic complex has been known since long time. Among them, some massive porphyritic tourmaline-bearing rocks cropping out in the southern sector of the Alpi Apuane present some distinctive and peculiar features, differing from the better known middle Ordovician metarhyolites of the “Porfiroidi e scisti porfirici” Fm. The porphyritic tourmaline-bearing rocks belong to the recently proposed Fornovolasco Metarhyolite Fm. They are granular to porphyritic, with phenocrysts of quartz (often with magmatic embayment), pseudomorphosed feldspars, and mica (both biotite and muscovite), in a groundmass formed by quartz, white mica, albite, and K-feldspar. Tourmaline (schorl-dravite in composition) is an abundant accessory mineral, in some cases forming cm-sized spots. The studied rocks plot into the rhyolite field of the Total Alkali vs Silica classification diagram. They show a peraluminous nature, having an Alumina Saturation Index ranging from 1.3 and 3.2. Their trace-element signature is that typical of highly evolved orogenic magmas. Laser ablation-ICP-MS U—Pb datings on zircon suggest a Permian crystallization age (weighted average ages of the four samples ranging from 292 and 271 Ma), thus relating these rocks to a post-Variscan magmatism. This new dating represents the very first evidence of a Permian magmatism in the pre-Triassic basement of the Northern Apennines. The potential relationships between Permian felsic magmatism and the ore genesis in the Alpi Apuane metamorphic complex are also discussed.

Miocene basin opening in relation to the north-eastward tectonic extrusion of the ALCAPA Mega-Unit

AbstractThe opening and evolution of the Western Carpathians Miocene basins was closely related to the north-eastward tectonic extrusion of the ALCAPA Mega-Unit lithosphere caused by the final stage of collision of the Eastern Alpine–Western Carpathian orogenic system with the European Platform and Alpine convergence with the Adria plate. The roll back effect of the oceanic or thinned continental crust of the Magura–Krosno realms, subduction below the front of the Carpathians in the north-east, east and relative plate velocities led to gradual stretching of the overriding micro-plates (defined as the ALCAPA and Tisza Dacia Mega-Unit). Diverse movement trajectories of the ALCAPA crustal wedge individual segments (Eastern Alps, Western Carpathians, and Northern Pannonian domain) were accompanied by several counter-clockwise rotational phases. Beside the interpreted Early Miocene “en-block” counter-clockwise rotation, most of the rotations in the Central Western Carpathians were caused by “domino-effect tectonics” inside strike-slip zones and took part in the basin opening, which was in most cases followed by rapid subsidence.

Aeromagnetic Investigation of the Central Apennine Seismogenic Zone (Italy): From Basins to Faults

AbstractWe report on a high‐resolution, low‐altitude aeromagnetic investigation of the central Apennine extensional seismogenic zone, hit by destructive historical earthquakes including the 2009 L'Aquila seismic sequence. Central Apennines are predominantly made by thick (>4 and possibly up to 12 km) packages of shelf and deep marine limestones and dolomites of Mesozoic age, unconformably covered by upper Pliocene‐Holocene continental sediments lying on (often active) normal fault hanging walls. Seismogenic faults cut the carbonates down to 10‐ to 12‐km depth, where the brittle‐ductile transition occurs. Aeromagnetic data were collected during June 2014 with a cesium magnetometer, along 200‐m‐spaced flight lines. Apart from a regional 80‐nT anomaly that we modeled at 30‐ to 40‐km depths in the lower crust of the Adria plate, weak magnetic residuals are observed. As expected, normal faults cutting the diamagnetic carbonates lack any magnetic fingerprint. However, shallow continental basins yield clear anomalies of 2‐ to 8‐nT intensity, as they contain both residual soils and tephra erupted after 0.7 Ma by volcanoes from the Tyrrhenian margin of Italy. Basin margins imaged by aeromagnetism mirror the geometry of their causative normal faults. Thus, aeromagnetic residuals document many of the central Apennine normal faults that were active during the last ~3 Ma. Most prominent anomalies reflect basins formed after 0.7 Ma, as their magnetization is significantly higher than that of older continental basins. We conclude that rectilinear boundaries of most prominent anomalies reflect faults formed after 0.7 Ma, thus probably seismogenic.

Refertilized mantle keel below the Southern Alps domain (North-East Italy): Evidence from Marosticano refractory mantle peridotites

The Veneto Volcanic Province (VVP), a Cenozoic magmatic province in northeastern Italy, is one of the widest volcanic areas of the Adria plate. It consists of five main magmatic districts, and its most primitive products commonly host mantle xenoliths. In this study, we present a newly discovered xenolith suite from the Marosticano district that contains peridotites with compositional characteristics of mineral assemblages that provide insight into an unexpected nature of the sub-continental lithospheric mantle (SCLM) of the Adria plate. In contrast to xenoliths from other VVP sites previously studied (i.e., Val d'Adige and Lessini Mts.), Marosticano xenoliths exhibit highly refractory compositions typical of on-craton peridotites. High olivine forsteritic contents (Fo: 91–93) indicate high degrees of partial melting (>25%) that should have been associated with the complete consumption of clinopyroxene. Major and trace element compositions further link these peridotite fragments to early Proterozoic cratonic mantle. The occurrence of clinopyroxene within such rocks suggests Marosticano clinopyroxene testify to a metasomatic legacy. The i) LREE-enrichments of Marosticano clinopyroxene and ii) the dissolved CO2 mole fractions (up to 1.0) for the inferred clinopyroxene-forming melt are consistent with carbonatite/CO2-rich silicatic melts as metasomatic agents. The latter could be responsible for the equilibrium temperatures (1033–1117°C) and oxidizing conditions [ΔlogfO2 (FMQ)=−0.6−+1.1], anomalously high for a cratonic environment but similar to the off-craton VVP xenoliths. The cratonic signature and carbonatite/CO2-rich silicate metasomatism found together in the Marosticano mantle xenoliths reveal that ancient features can be preserved in SCLM in a young, active geodynamic setting such as the Adria plate boundary. In this framework Lessini Mts. and Val d'Adige xenoliths could be interpreted as circumcratonic reminiscent domains affected by refertilization due to infiltration of asthenosphere-derived melts, rather than newly accreted “off-craton” SCLM. These new interpretations could be useful for completing the reconstruction of the Africa/Eurasia interplay during the Alpine collision.

A Revised Subduction Inception Model to Explain the Late Cretaceous, Double‐Vergent Orogen in the Precollisional Western Tethys: Evidence From the Northern Apennines

AbstractThe Meso‐Cenozoic alpine belts of the Mediterranean area are characterized by complex architectures, result of a complex subduction and collision evolution that preserve also a legacy of the rifting‐related configuration of the continental margins. The Northern Apennines is a segment of these belts originated during closure of the Ligure‐Piemontese ocean and collision between the Europe and Adria plates. The different configuration of the Adria and Europe margins, inherited from asymmetric rifting, is recorded in the Ligurian Units that preserve incorporation into the subduction factory of fragments of the oceanic domain (Internal Ligurian Units) and portions of the Ocean‐Continent Transition Zone (OCTZ) toward Adria (External Ligurian Units). We provide here unpublished data on the stratigraphy and sedimentology of these units, together with a review of what is already established in literature. Both data sets combined testify that at 80 Ma, an accretionary prism was growing between the deposition basins of the two groups of units and fed both basins with clasts from the ocean realm, the continental crust, and the subcontinental mantle. We propose that closure of the Ligure‐Piemontese ocean occurred through subduction that nucleated at the transition from the oceanic plate and the thinned Adria margin and developed a double‐vergent prism by accreting oceanic material and continental extensional allochthons from the OCTZ. We believe the revised site of subduction initiation, and the precollisional architecture, inherited from the rifting and spreading phases, allows reconciling most of the discrepancies between the various interpretations proposed in literature for the precollisional evolution of the Apennines.

Orogen-parallel brittle extension as a major tectonic imprint in the Neogene evolution of the south-western Alpine arc

We present a new analysis of the late Alpine brittle deformation in the southern branch of the western Alpine arc, focusing on the stack of internal metamorphic nappes east of the Argentera external crystalline massif. The regional-scale fault network is dominated by a NW–SE-striking right-lateral fault system that follows the general curvature of the arc and controls the overall morphology of the area. A second fault set strikes N–S and is mainly represented by normal faults which accommodate orogen-parallel extension. Structural analysis and paleostress tensors derived from inversion of fault-slip data reveal a complex pattern of deformation involving extensional and strike-slip deformation events. The orogen-parallel extension previously described in the internal zones at the east of the Pelvoux massif is confirmed further south, and we show that it is combined with right-lateral strike-slip deformation that increases in intensity towards the south-west. The stability of the minimum stress axis (σ3) direction suggests that extensional and transcurrent regimes are contemporaneous and highlights regional interferences between inner brittle extension, parallel to the strike of the belt, and the strike-slip strain field driven by the counterclockwise rotation of the Apulia–Adria plate. The curved geometry of the belt constrains the direction of extension and the coupling relationship between the internal and external Alpine zones. We propose that the Neogene tectonic history is a result of the unique curved tectonic architecture of the south-western Alps with respect to the rotation of the Apulia–Adria indenting plate. The southern tip of the western Alpine arc represents a transitional zone between extension in the inner chain and strike-slip/compression in the outer parts.

Triassic Succession of Zelovo Area (Svilaja Mt. - Karst Dinarides, Croatia): A Sedimentary Record from the Epeiric to Isolated Carbonate Platform Transition

The Zelovo area on the foothills of Svilaja Mt. is a well-known area of the thick succession of the Triassic strata. It is composed of Lower Triassic mixed carbonate and siliciclastic beds that were deposited within the epeiric platform depositional realm situated in an equatorial area along the northern Gondwana shelf. The overlying Anisian and Ladinian carbonate beds with pelagic and sporadic more intense pyroclastic characteristics belong to another paleogeographic entity known as the Adria plate, i.e. huge depositional area of the isolated carbonate Southern Tethyan Mega platform. This Lower and Middle Triassic epeiric platform-isolated platform sequence was emerged during Late Ladinian and then submerged again due to Norian transgression, marking renewed carbonate deposition within the isolated carbonate platform realm up to the end of Cretaceous.

The boeotian flysch revisited: New constraints on ophiolite obduction in central Greece

This paper reports new data on biostratigraphy, stratigraphy and syn-sedimentary deformation of the so-called “Boeotian Flysch” cropping out in key areas in Central Greece (Levadhia, Parnassus, Iti). Because of its age, sedimentary evolution and mechanisms of the syn-sedimentary deformation, the Boeotian Flysch represents a key element providing useful hints on the Cretaceous paleogeography reconstruction of the Dinaric-Hellenic Chain and in particular on the obduction at the Jurassic-Cretaceous transition in the eastern continental margin of the Adria plate. We provide here a new detailed study of different features of the Boeotian Flysch, with particular emphasis on reconstructing and dating its stratigraphy. In particular, we recognized two distinct turbiditic systems: the Lower Boeotian Flysch (Tithonian?-Aptian) and the Upper Boeotian Flysch (Cenomanian-Coniacian), which are separated by a main unconformity marking a sedimentary hiatus lasting from Aptian p.p. to Albian. By means of the improvement of the age, stratigraphy and deformation history of this syn-tectonic turbidite deposit, we therefore contribute to better define the chronology of the early phases of continental stage of obduction, and the following continental collision between Adria and Eurasia. The analyses of the collected data allowed us to propose for the Boeotian Flysch a deposition within an obduction-related foredeep basin associated with a flexural depression/flexural bulge due to crustal loading of westerly-directed ophiolite obduction.

Results and significance of crustal data obtained with active seismic methods

The main results from active seismic prospecting in the Alps revealed the deep structure of the chain. Reflection seismic and wide-angle reflection/refraction methods, complementary in terms of penetration and resolution, can give a complete picture of the whole crust. Receiver functions analysis may confirm the interpretation models and link seismic section to teleseismic traveltimes tomographic images of the velocity distribution within the upper mantle. The active seismic shows that the brittle mantle of the Adria plate behaves as a strong indenter decoupling the European lower crust and Moho from the inner part of the orogen. Crustal scale faults offsetting the Moho characterize the chain with the continental lithosphere of the European plate underthrusting Adria.

Can We Consider the 1951 Caviaga (Northern Italy) Earthquakes as Noninduced Events?

Online Material: Table of Mercalli–Cancani–Sieberg (MCS) intensities, onset times and associated phases, complete parameter sets for each 1951 location and computation of the isostatic stress variation due to unloading in the upper crust. On the night of 15–16 May 1951, two moderate earthquakes with estimated magnitudes of M w 5.4 and 4.5 occurred in northern Italy, about 40 km southeast of Milan, close to the small town of Caviaga. They were recorded by several observatories worldwide, as reported by the International Seismological Summary (ISS) On‐Line Bulletin (ISS, 1951; International Seismological Centre [ISC], 2011). Despite the moderate magnitudes, these two events caught the attention of seismologists and have been studied in detail, in particular by Caloi et al. (1956), because they were close to Caviaga in an area that was assumed to be aseismic. Moreover, their shallow hypocenters (∼5 km in Caloi et al. , 1956) indicated a possible anthropogenic source, related to wells for gas withdrawal (Fig. 1; see Data and Resources). Figure 1. (top) Maps of the area of interest, showing the tectonic setting and seismicity between 1981 and 2012 (Italian Seismological Instrumental and Parametric Data‐Base Working Group, see Data and Resources; Catalogue of Italian Seismicity, Castello et al. , 2006). Symbols in color indicate earthquakes (circles for M w>2.0 and squares for M w>4.5). Symbols are scaled with magnitude and colors accord to depth scale. Focal mechanisms are for seismicity with M w>4.5 from 1977 to present (Pondrelli et al. , 2006). Top left inset: The black box is the study area and the red dashed line marks the boundary of the Adria plate. The (red) tectonic structures and (light green lines) geological sections are extracted from Pieri and Groppi (1981) and Cassano et al. (1986). Top right map: Blue stars indicate the original locations of the events …