TS7.9
vPICO presentations: Tue, 27 Apr
Following the Wilson Cycle theory, most rifts and rifted margins around the world developed on former orogenic suture zones (Wilson, 1966). This implies that the pre-rift lithospheric configuration is heterogeneous in most cases. However, for convenience and lack of robust information, most models envisage the onset of rifting based on a homogeneously layered lithosphere (e.g. Lavier and Manatschal, 2006). In the last decade this has seen a change, thanks to the increased academic access to high-resolution, deeply imaging seismic datasets, and numerous studies have focused on the impact of inheritance on the architecture of rifts and rifted margins. The pre-rift tectonic history has often been shown as strongly influencing the subsequent rift phases (e.g. the North Sea case - Phillips et al., 2016).
In the case of rifts developing on former orogens, one important question relates to the distinction between extensional structures formed during the orogenic collapse and the ones related to the proper onset of rifting. The collapse deformation is generally associated with polarity reversal along orogenic thrusts, ductile to brittle deformation and important crustal thinning with exhumation of deeply buried rocks (Andersen et al., 1994; Fossen, 2000). The resulting structural template commonly involves metamorphic core complexes, extensional shear zones and detachment faults superposed on inherited thrust assemblages (Fossen, 2000). On the other hand, the proximal domains of rifted margins often show only moderately reduced crustal thicknesses (Whitmarsh et al., 2001). The top basement geometries are typically summarized as series of tilted blocks, bordered by 'Andersonian-type' normal faults rooted in the brittle-ductile transition at mid-crustal levels, accounting for minor amounts of extension (the ‘stretching phase’ of Lavier and Manatschal, 2006). Thus, orogenic collapse and early rifting are considered to represent very different deformation modes with distinct structural geometries. We used the post-Caledonian Norwegian rift system to study the relationship between these two end-member forms of deformation.
Based on onshore and offshore observations from the Mid-Norwegian and North Sea extensional systems, and on numerical modelling experiments, we show that the near-coastal onshore and proximal offshore Norwegian area is floored by a unit of intensively sheared basement, mylonitic shear zones, core complexes and detachment faults that attest to significant crustal thinning. We describe how, when and where the post-Caledonian continental crust evolved from a context of orogenic collapse to one of continental rifting. We highlight the importance of a deformation stage that occurred between the collapse mode and the high-angle faulting mode often associated with early rifting of continental crust. This transitional stage - termed the reactivation phase - which we interpret as the earliest stage of rifting, includes unexpected large magnitudes of crustal thinning facilitated through the reactivation and further development of inherited collapse structures, including detachment faults, shear zones and metamorphic core complexes. The reduction of the already re-equilibrated post-orogenic crust to only ~50% of normal thickness over large areas, and considerably less locally, during this stage shows that the common assumption of very moderate extension in the proximal margin domain may not conform to margins that developed on collapsed orogens.
How to cite: Peron-Pinvidic, G., Osmundsen, P. T., Fourel, L., and Buiter, S.: From orogeny to rifting: when and how does rifting begin? Insights from the Norwegian ‘reactivation phase’., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-469, https://doi.org/10.5194/egusphere-egu21-469, 2021.
The Reykjanes Ridge is a spreading center that presents an opportunity to track the dynamic formation of structural and volcanic features at an asymmetric slow-spreading plate boundary. The ridge spans the northern ~1000 km of the Mid Atlantic Ridge and has been spreading at a full spreading rate of ~20 mm/year [1]. The characteristic along-ridge basement depth, crustal thickness, and chemical gradient have been variably attributed to an active mantle plume beneath Iceland, or a passive mantle anomaly pre-dating the rifting [1]. A unique feature of the ridge is that it spreads obliquely to the spreading axis: a consequence of the change in spreading direction from ~125o to ~100o due to the failure of the triple junction between the Greenland, Eurasian, and North American plates 37 Mya [2]. Along with the sudden change in orientation, disjunct ridge segments were formed and separated by transform faults which have been continuously eliminating from north to south, thereby re-establishing the original linear geometry of the ridge [1]. The Bight Transform Zone is the final remaining transform fault and constitutes the boundary between the southern Reykjanes Ridge and the northern Mid-Atlantic Ridge. Despite the termination of strike-slip transform fault motion, the ridge remains in a state of active tectonic deformation as demonstrated by the time-dependant orientations of linear structures, lengths of spreading segments, and deviation from the previously asserted linear continuity of the ridge. Investigating the relationship between structures, volcanism, and regional geodynamics is possible with the application of a novel remote-predictive geological mapping method based on interpretations from newly acquired bathymetric and acoustic backscatter data. Notably, the bathymetric data provides significant high-resolution coverage of both on-axis and off-axis regions, allowing us to track the evolution of the ridge for up to 13 Mya. The acoustic backscatter data aids in the interpretation of geologic features and terrains whose distribution and morphology reflect both present-day and historic ridge dynamics. This analysis will produce new insight into the on-going first and second-order deformation of the Reykjanes Ridge, its controls, and its effects on diffuse low-temperature vs. focused high-temperature hydrothermal venting.
[1] Martinez et al., 2020. Reykjanes Ridge evolution: Effects of plate kinematics, small-scale upper mantle convection, and a regional mantle gradient. Earth-Science Reviews.
[2] Jones, Stephen M., 2003. Test of a ridge–plume interaction model using oceanic crustal structure around Iceland. Earth and Planetary Science Letters.
How to cite: Panasiuk, S., Anderson, M. O., Höskuldsson, Á., Martinez, F., and Pałgan, D.: Remote-predictive geologic mapping of the Reykjanes Ridge: Implications for the volcanic and structural evolution of a slow-spreading Mid-Ocean Ridge, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3450, https://doi.org/10.5194/egusphere-egu21-3450, 2021.
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Extensional detachment faults accommodate high degrees of crustal thinning and exhumation, shaping largely the final architecture of magma-poor rifted margins. Great efforts have been directed to study extensional detachments based on offshore seismic surveys and onshore field analogues. However, little is known about the breakaway of these structures as well as their role and evolution during rifting and subsequent contractional reactivation.
In this work, we use the Le Danois-Labourd offshore-onshore natural laboratory (northern Spain) to explore the features characterising major Mesozoic extensional detachment faults and their fate during subsequent Alpine contractional reactivation. Both sites keep evidence of Mesozoic extensional detachment faulting and high degrees of crustal thinning, including exhumed mid-crustal granulites reworked as clasts into Apto-Albian syn-rift sediments, and show mild Alpine reactivation, corresponding at present-day to structural highs. Relying on the interpretation of high quality 2D seismic reflection profiles offshore and on field-based cross-sections onshore, we describe and compare the former rift architecture associated with these major detachment faults and the distribution of contractional structures at the two sites.
This combined study enable us to evidence strong structural similarities between the two sites and to propose that the Le Danois and the North Mauléon extensional detachment systems are major rift structures within the North Iberian rift system. We propose that they were responsible for high degrees of crustal thinning and the exhumation of mid-crustal rocks during the Late Aptian to Albian N-S directed extension. Major thrusts truncated the two extensional detachments during subsequent Alpine reactivation, leading to the uplift and tilting of the Le Danois and the Labourd rift-inherited crustal blocks. We suggest that the location of the two blocks at the termination of offset/overlapped hyperextended rift segments allowed for their preservation as mildly inverted structural highs, including rift-related structures.
How to cite: Cadenas, P., Lescoutre, R., and Manatschal, G.: Extensional detachments related to extreme crustal thinning and their fate during contractional reactivation: the Le Danois-North Mauléon offshore-onshore examples in north Iberia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8283, https://doi.org/10.5194/egusphere-egu21-8283, 2021.
With an increasing number of global and regional plate reconstruction models established in recent years, the motion of the Porcupine Bank, Irish Atlantic continental margin, underlain by orogeny-related pre-rift crustal basement terranes, have been investigated and restored as well. However, these reconstructed models of the Porcupine Bank margin mainly depend on potential field data analysis and lack seismic constraints, failing to reveal the role of inherited crustal sutures during rifting and associated crustal deformation over geological time. In this study, five deformable models with distinct structural inheritance trends are established in GPlates by adjusting a previously published regional restoration model for the North Atlantic realm. For each model, driving factors (e.g., such as whether the Orphan Knoll is included, the altered rotational poles of the Flemish Cap, and the motion of the eastern border of the Porcupine Basin) are also taken into consideration. Crustal thicknesses from gravity inversion and seismic refraction data modelling are compared against those from these deformable plate reconstruction models to identify the most geologically reasonable one. The resulting preferred model has the Porcupine Bank subdivided into four blocks with each experiencing polyphase rotations and shearing prior to final continental breakup, implying strong inheritance and segmentation of the Porcupine Bank and the Porcupine Basin. The derived reconstructed paleo-positions over time of the Flemish Cap and the Porcupine Bank within the deforming topological network reveal new and evolving conjugate relationships during rifting, which are assessed using regional seismic transects from both margins. Finally, extensional obliquity between both margins is quantitatively restored, showing time-variant orientations due to the rotation and shearing of associated continental blocks, which contributes to unraveling the spatial and temporal evolution of southern North Atlantic rifting during the Mesozoic, prior to the initiation of seafloor spreading.
How to cite: Yang, P., Welford, J. K., and King, M.: Assessing the rotation and segmentation of the Porcupine Bank, Irish Atlantic margin, during oblique rifting using deformable plate reconstruction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3043, https://doi.org/10.5194/egusphere-egu21-3043, 2021.
Continental rifts form across a mosaic of crustal units, each unit displaying properties that reflect their own unique tectonic evolution and lithology. The physiography of rift systems is largely reflective of this underlying crustal substrate, which may change over short distances along-strike of the rift. Pervasive, well-developed structural heterogeneities represent sites where strain may localise and may thus weaken a crustal volume. In contrast, relatively pristine areas of crust, such as igneous batholiths, contain few heterogeneities and may be considered relatively strong. Characteristic rift physiographies associated with these ‘strong’ and ‘weak’ crustal units, and how rift physiography changes across areas where these units are juxtaposed remain elusive.
In this study we use the 3D thermo-mechanical numerical code ASPECT to investigate how areas of differing upper crustal strength influence rift physiography. We extend a 500x500x100km volume, within which we define four 125km wide upper crustal domains of either ‘strong’, ‘normal’ or ‘weak’ crust. Crustal strength is determined by varying the initial plastic strain in the model across 5km blocks, producing a static-like pattern. Weak domains contain weakened blocks with large initial plastic strain values, creating large contrasts with adjacent blocks. In contrast, 5 km blocks within the strong domain have relatively low values of initial plastic strain, producing little variation between adjacent blocks.
Our modelling simulations reveal that strain rapidly localises onto high-displacement structures (equivalent to faults) in the weak domain. Fault spacing and the strain accommodated by each fault decreases in the normal domain, with the strong domain characterised by closely-spaced, low displacement faults approximating uniform strain. When heterogeneities are incorporated into the strong domain, we find that these rapidly localise strain, effectively partitioning the domain into a series of smaller, strong areas separated by faults. Faults are initially inhibited at the boundaries with adjacent stronger domains; as extension progresses, these faults break through the barrier and propagate into the stronger domains.
Our observations have important implications for rift system development, particularly in areas of highly heterogeneous basement. Studies have shown that the Tanganyika rift developed at high angles to cratonic and mobile belt basement terranes, with localisation inhibted in the stronger cratonic areas. Similarly, extension in the Great South Basin (GSB), New Zealand, initially localised in weak, dominantly sedimentary, terranes, compared to stronger, more homogenous granitic areas. Terrane boundaries in the GSB also inhibit the lateral propagation of faults. Comparing our model results with observations from these and other systems globally, we determine characteristic structural styles and examine how rift physiography varies across ‘strong’ and ‘weak’ crustal volumes.
How to cite: Phillips, T., Naliboff, J., McCaffrey, K., Pan, S., and van Hunen, J.: The influence of laterally varying crustal strength on rift physiography – Combining 3D numerical models and geological observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4492, https://doi.org/10.5194/egusphere-egu21-4492, 2021.
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In geodynamic numerical models, grain-size-independent dislocation creep often solely defines the governing crystal-plastic flow law in the upper mantle. However, grain-size-dependent diffusion creep may become the dominant deformation mechanism if grain size is sufficiently small. Previous studies implying composite diffusion-dislocation creep rheologies and fixed grain size suggest that the upper mantle is stratified with the dominant mechanism being dislocation creep at shallow depths and diffusion creep further down. Studies with variable grain size in the upper mantle depending on common grain-size evolution models demonstrate that the contrary might be the case, where diffusion creep is acting within the mantle lithosphere and dislocation creep in the asthenosphere below. Diffusion creep as a dominant mechanism has important implications for the overall strength of the lithosphere and therefore for the dynamic evolution of lithospheric-scale extension and orogeny.
To investigate the importance of grain size and the effects of resulting crystal-plastic creep within the upper mantle, we developed a two-dimensional thermo-mechanical numerical code based on the finite difference method with a fully staggered Eularian grid and freely advecting Lagrangian markers. The model implies a composite diffusion-dislocation creep rheology and a dynamic grain-size evolution model based on the paleowattmeter including recently published olivine grain growth laws.
Results of upper mantle extension indicate olivine grain sizes of ~7 cm for large parts of the upper mantle below the LAB, while in the lithosphere grain size ranges from ~1 mm at the Moho to ~5 cm at the LAB. This grain size distribution indicates that dislocation creep dominates deformation in the entire upper mantle. However, diffusion creep activates along lithospheric-scale shear zones during rifting where intense grain size reduction occurs to local stress increase. We furthermore test the implications of wet and dry olivine rheology and respective crystal growth laws and interpret their effects on large-scale tectonic processes. Our results help explain strain localization during extension by strength loss related to grain size reduction and consequent diffusion creep activation.
How to cite: Ruh, J. B., Tokle, L., and Behr, W. M.: Self-consistent grain size evolution controls lithospheric shear zone formation during continental rifting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9600, https://doi.org/10.5194/egusphere-egu21-9600, 2021.
Existing plate tectonic models rely on two essential features: (1) rigid tectonic plates and (2) very narrow plate boundaries where all deformation is localized. On the world geological map, plate boundaries are materialized by lines. Subduction plate boundaries, however, affect domains several hundred kilometers wide. In the upper plate of subduction zones, this deformation can result in the formation of orogenic-like compressive structures or extensional back-arc basins. In both cases, the respective contributions of slab movements, far-field stresses (i.e., boundary conditions) and tectonic inheritance in localizing strain in the upper plate are not yet well understood.
Located in the upper plate of the Late Triassic to Oligocene Neotethys subduction, the Iranian plateau records a long-lived convergence history, with numerous episodes of intraplate deformation. We herein focus on the Cretaceous back-arc opening (e.g., formation of the Nain-Baft marginal basin), whose possible triggers include a change in internal slab dynamics and/or regional-scale convergence dynamics (e.g., kinematics of the Neotethyan subduction, ridge subduction, opening of peripheral basins such as the Caspian Sea).
The Iranian plateau is part of a composite continental lithosphere made of blocks detached from Gondwana during the Paleozoic. It preserves evidence for structures inherited from the Precambrian Panafrican orogeny, as well as thinning and shortening during the opening and closure of the Paleotethys (during the Devonian and Late Triassic, respectively). Important lateral contrasts are observed after the Neotethys Permian rifting: the southwestern part (Sanandaj-Sirjan Zone) was thinned and filled with volcanic products, whereas the northeastern part (Kopeh-Dag and Yadz block) was thickened during the Late Triassic Cimmerian event. From NW to SE, deformation was also likely partitioned across large-scale strike-slip faults such as the Doruneh fault. These imprints make it difficult to assess the nature and extent of lateral heterogeneities in the crust, and in particular the variation of Moho depths prior to the Cretaceous extension.
In order to determine which parameters controlled the deformation of the Iranian upper plate, ultimately leading to localized back-arc extension along the Nain-Baft basin (i.e., SE of the Doruneh fault), we designed a parametric numerical study using the thermo-mechanical code pTatin2D, in which metamorphic reactions were implemented to model the subduction process realistically. Model results are evaluated based on the evolution of strain in the upper plate, in particular the characteristic size (~500 km) and duration of back-arc deformation (~30 Ma of extension prior to closure of this domain). The importance of structural inheritance is assessed by imposing either (1) a prexisiting crustal scale fault, (2) a partially thickened (3) or thinned crust. Those different tests allow to propose tentative geodynamic scenarios for the deformation of the upper plate Iranian plateau during the Cretaceous.
How to cite: Larvet, T., Le Pourhiet, L., and Agard, P.: Evolution of strain patterns in deforming upper plates in subduction zones: the case study of Cretaceous extension in the Iranian plateau, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11949, https://doi.org/10.5194/egusphere-egu21-11949, 2021.
The Taiwan orogen forms an active mountain range that has been evolving since the Late Miocene as a result of the oblique collision between the Luzon Arc, located in the Philippine Sea Plate, and the continental margin of the Eurasian Plate. Due to this configuration, some inherited structures from the continental margin are at high angle to the structural trend of the Taiwan thrust-and-fold belt and are thought to play an important role in present day tectonics. The inherited structures resulted from processes undergone by the Eurasian margin, such as rifting in the Early Eocene, and further local extension in the Middle Miocene. They comprise sub-vertical faults that are presently being reactivated and are actively involved in the evolution of the structure, seismicity and topography of Taiwan, causing transverse zones in its thrust-and-fold belt and foreland.
The key objective of this research is to help define the deep structure in southern Taiwan, as well as the location and kinematics of these inherited east-northeast striking faults. To achieve this goal, we undergo a multidisciplinary approach based on the analysis and modelling of gravity (free-air and Bouguer anomaly) and magnetic data. The application of analytical techniques, such as horizontal directional derivatives allows us to identify gradients that can be related to the geometry and minimum horizontal extent of these basement structures in the margin and in Taiwan. Forward modelling of gravity and magnetic data contributes further to provide a better-constrained quantitative approach to their depth as they appear to affect the top of the basement. Finally, these results have been integrated with structural studies and earthquake information in order to improve our understanding of the southern Taiwan and Eurasian continental margin structure.
The preliminary results allow us to discuss the limitations of vertical derivatives and residual potential field data when dealing with deep inherited basement structures. The present dataset has proven to be useful to discern the existence of a deformed reactivated basement in the foreland and frontal part of the Taiwan thrust-and-fold belt, and improve our comprehension of its crustal structure. Due to the limitations of potential field data as the depth of the source increases, the resolution diminishes towards the E of the thrust-and-fold belt.
This research is part of project PGC2018-094227-B-I00 funded by the Spanish Research Agency of the Ministry of Science and Innovation of Spain. Olivia Lozano acknowledges funding from the same agency through contract PRE2019-091431.
How to cite: Lozano, O., Ayarza, P., Alvarez-Marrón, J., and Brown, D.: Potential field constraints on the basement structure of the Taiwan thrust-and-fold belt: preliminary results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8280, https://doi.org/10.5194/egusphere-egu21-8280, 2021.
Late Mesozoic-Cenozoic plate convergence led to widespread intraplate deformation in Western-Central Europe during the Late Cretaceous-Paleogene and the Miocene until today reflecting the collision of Eurasia with Iberia-Africa and Adria, respectively. The resulting complex deformation pattern inside the plate boundary zone contrasts with a rather uniform orientation adjacent to the north. Although there is broad consensus that the orientation of the first-order stress is controlled by plate kinematics, there is no sufficient explanation for the variation of the stress field across the plate boundary. We model plate kinematic trajectories and analyze the spatial distribution of paleostress data from fault-slip inversion and tectonic stylolites. The comparison reveals the coexistence of two contrasting stress provinces in Europe throughout the Late Mesozoic-Cenozoic. Inside the diffuse plate boundary zone, trajectories of plate motion fit deformation patterns. Outside of that zone, however, there is significant deviation. Here deformation is mainly accommodated by the reactivation of Paleozoic shear zones. Thus, we argue that lithospheric-scale structural inheritance from the Pangea assemblage controls the stress-strain pattern of Western-Central Europe between the active plate boundary zone and the East European Craton since the Late Mesozoic.
How to cite: Stephan, T., Kroner, U., Köhler, S., Koehn, D., Bauer, W., and Stollhofen, H.: Lithospheric-scale anisotropies control first-order stress orientation during Cretaceous-Cenozoic plate kinematics in Western-Central Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-106, https://doi.org/10.5194/egusphere-egu21-106, 2021.
Africa-Eurasia plate convergence and the retreat of the subducting slab led to the consumption of the Tethys ocean lithosphere, which has now mostly disappeared below or accreted/exhumed within the Alps/Apennines. Slab tearing plays a major role in plate boundary evolution, asthenospheric upwelling, dynamic topography and magmatism. However, the role played by structural inheritance on the Africa plate is not well constrained. Based on seismological, geodetic and marine geophysical data, we analyse the pattern of crustal deformation in the Calabrian Arc and Sicily Channel, two key regions to unravel the complex Africa/Eurasia plate interaction in the central Mediterranean Sea.
The Calabrian Arc subduction-rollback system accommodates Africa/Eurasia plate convergence along thrust faults developing both in the frontal and inner domains of the accretionary wedge. However, the most intriguing and tectonically active features are represented by arc-orthogonal faults deforming the subduction system along a complex strike-slip/transtensional pattern that may have been the source of major earthquakes in the Calabrian Arc. Deformation along the lithospheric transtensional faults is punctuated by buried sub-circular magnetized bodies aligned with Mt. Etna, that were interpreted as serpentinite/mud diapirs intruding the subduction system from the lower plate mantle. These faults are part of the overall dextral shear deformation, resulting from differences in Africa-Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments of the Calabrian Arc. To the West, the Sicily Channel is part of the Pelagian block and experienced a lithospheric-scale continental rifting starting from the late Miocene with the development of NW-SE-trending tectonic depressions, bordered by crustal normal faults with variable throws. Our geophysical data, however, show that the most active tectonic feature in the area is a N-S trending and ~220-km-long lithospheric fault system characterized by volcanism, high heat flow and seismic activity. The NW-SE elongated rifting pattern, considered the first order structure in this region, appears currently inactive and sealed by undeformed Pleistocene deposits suggesting a recent change in structural development.
Seismological data show that the lithospheric boundaries present in the Calabrian Arc and Sicily Channel correlate well with spatial changes in the depth distribution of earthquakes and separate regions with different Moho depths and thickness of the seismogenic layer. We propose that these boundaries may represent long-lived inherited Mesozoic discontinuities controlling plate boundary evolution and neotectonics.
How to cite: Polonia, A., Artoni, A., Barberi, G., Billi, A., Gasperini, L., Palano, M., Sgroi, T., Spampinato, S., Sparacino, F., Torelli, L., and Ursino, A.: The role of structural inheritance on Africa-Eurasia plate boundary evolution and neotectonics in the central Mediterranean sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5574, https://doi.org/10.5194/egusphere-egu21-5574, 2021.
The fragmentation of the Adriatic plate and the sinking of the remnant Alpine Tethys and Ionian lithosphere give rise to passive subduction processes that, together with the collision of the African and European plates, characterize the Central Mediterranean area.
Circum - Mediterranean mountain ranges and Alboran, Balearic, Tyrrhenian and Hellenic back-arc basins are formed in this complex deformation system.
The evolution of the geodynamic processes that guided the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain are described in this work using the plate kinematics technique.
The study area has been divided into polygons (crustal blocks of microplates) after careful observation of the regional structures. The polygons are distinguished on the basis of the direction of the Tyrrhenian extension and the boundaries between them coincide with the large structures that characterize the Tyrrhenian-Apennine area.
The Tyrrhenian extension directions are indicators of the Euler poles of the individual polygons, in the Sardo-Corso block reference frame. The velocity ratios were determined by the slip vectors of the structures (plate boundaries) that separates the polygons. The rotation time and angle are determined respectively: using the stratigraphic records of the syn-rift sequences and comparing the crustal balance with the speed ratios.
At the end including the new kinematic framework in the global rotation model we were able to reconstruct the tectonic evolution of the central Mediterranean during the opening of the Tyrrhenian basin.
How to cite: Pierantoni, P. P., Penza, G., Macchiavelli, C., Schettino, A., and Turco, E.: Plate kinematic relationship between the Tyrrhenian basin and the Apennine chain (Central Mediterranean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14924, https://doi.org/10.5194/egusphere-egu21-14924, 2021.
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Sicily is in the centre of an area where complex geodynamic processes work together, these are: the Tyrrhenian-Apennine System evolution, the African-Ionian slab subduction and Africa-Europe collision.
During the last 5 Ma it was involved in a process of escape towards east-southeast: while on one side Africa acted as an intender pushing toward north, on the other side the fragmentation and retreat of the African-Ionian slab created space to the east.
The aim of this study is to reconstruct the kinematic evolution of Sicily, here considered as an independent plate starting from 5 Ma ago, and its role in the context of the Tyrrhenian-Apennine system.
The plates and microplate involved in the evolution are Europe, Africa and Calabria. The boundaries between these and Sicily are the margin of the Sicily microplate and are lithospheric structures known from the literature and identifiable from high resolution bathymetric maps, seismic sections, geodetic data, focal mechanism of recent earthquakes, gravimetric maps, lithosphere thickness maps and so on.
Briefly the margin between Sicily and Europe is along the Elimi chain, a E-W trending morpho-structure with transpressive kinematics, the margin with Calabria microplate is along the right-lateral Taormina line and the margin with Africa is expressed along the Malta Escarpment, south of Etna Mount, with transpressive kinematics and along the Sicily Channel, where a series of troughs (Pantelleria, Linosa and Malta) were interpreted in literature as pull-apart basins related to a dextral trascurrent zone.
The Euler pole of rotation between Sicily and Africa was found starting from the structures in the Sicily Channel and using the GPlates software, then we were able to find also Sicily-Europe and Sicily-Calabria poles and the respective velocity vectors and to compare these with the geological data and better refine the model.
How to cite: Penza, G., Pierantoni, P. P., Macchiavelli, C., and Turco, E.: Tectonic escape of Sicily Microplate in the context of Africa-Europe collision, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14921, https://doi.org/10.5194/egusphere-egu21-14921, 2021.
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In the collisional setting of the Northern Ionian Sea, the Calabrian Accretionary Wedge, which represents the Southeastward prolongation of the Southern Apennines, is facing directly the subducting Apula plate, which is mainly made of Mesozoic to Tertiary Carbonate Platform. The aim of this contribution is to illuminate the structures and stratigraphic relationships between the frontal part of the orogenic belt, the foredeep and adjacent Apulian foreland. Because of the lack of exploration wells in these deep offshore basins, a detailed seismic facies analysis of six multichannel seismic profiles has been carried out to define the tectonic-sedimentary evolution of the study area.
Seismic interpretation allows to identify four main structural domains. The highly tectonized accretionary wedge is characterized by compressive tectonics. A narrow foredeep basin is filled by a thick (1,5–0,9 s TWT) Pliocene-Holocene subhorizontal succession and lies above buried normal faults. A massive carbonate succession of the Apulian Platform, shows reef and carbonate platform margin facies. A layered carbonate succession of the Apulian Platform is characterized by ‘'intra-platform'’ facies and located in the easternmost portion of the area. Seismic stratigraphic analysis allows to define two main regional unconformities with characteristic relationships with structural trends: i) the Messinian unconformity, related to a regional and significant erosion associated to paleokarst processes on the exposed Mesozoic Apulian Platform, is cut by an array of normal faults affecting the entire Apulian foreland and by reverse faults in the accretionary wedge; ii) the middle Pliocene Unconformity, an angular and erosive unconformity truncating the Lower Pliocene reflectors, is affected by normal faults in the foreland and by compressive tectonics in the Calabrian wedge that is progressively advancing.
Seismic data analyses shows that the compressive tectonics is currently active in the Calabrian Accretionary Wedge and concentrated in the innermost domains where thrust faults deform the sea floor. The Mesozoic Apulian Platform is affected by normal faulting driven by flexural bending since Lower Pliocene. The new structural map shows that transpressive and positive inversion tectonics is a common deformational style in the foreland that can be associated with the Dinaric-Hellenic subduction, which is synchronous with respect to Calabrian subduction. According to these observations, the compressive tectonics affecting the Apulia plate can be interpreted as related to both the Calabrian and Dinaric-Hellenic shortening processes. The interference of these two orogenic wedges with the Apulia Plate plays an important role in defining the tectonic evolution of the Northern Ionian Sea.
How to cite: Chizzini, N., Artoni, A., Torelli, L., Polonia, A., Basso, J., and Gasperini, L.: The interaction between the Apula plate and the Calabrian Accretionary Wedge in the Northern Ionian Sea: tectonic-stratigraphic evolution and implications for subduction processes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8874, https://doi.org/10.5194/egusphere-egu21-8874, 2021.
In Northern Calabria, the Southern Apennines orogenic wedge bends and passes to the Calabrian Arc while they are both colliding with the subducting Apulia plate. The boundary between Southern Apennines and Calabrian Arc is commonly placed along the NW-SE trending Sangineto Lineament whose offshore prolongation is not clearly defined. A multi-scale seismic reflection dataset combined with exploration wells and seafloor bathymetry allowed us to define the post-Messinian tectono-sedimentary evolution of the Bradano Basin adjacent to the orogenic belt.
After Messinian times, two main tectono-sedimentary events deeply modified the Bradano Basin. During the first event (early Pliocene-early Pleistocene), a left-lateral transpressive system, about 20-30 km wide, was part of an oblique convergent margin along which the Southern Apennines and the Calabrian Arc collided; remnants of this transpressive system are now buried under the western portion of the Bradano Basin near the Calabrian margin. Shelf to deep marine turbiditic deposits were prevailing during this first event. Around the Pliocene-Pleistocene boundary (2.58 Ma), a sudden and widespread basin rearrangement occurred. During the second event (early Pleistocene-Present) the orogenic front of the Southern Apennines and the earlier transcurrent systems were suddenly translated to the NE of about 50 km and the left-lateral transpressive boundary between the Southern Apennines and Calabrian Arc became part of the orogenic wedge. During this second event, both upper and lower converging plates were shortened together along multiple detachments levels and out-of-sequence thrusts. The second tectono-sedimentary event is characterized by prograding deltaic and shelfal deposits that seal the earlier transpressive system and pass to deep marine deposits in the central part of the Bradano basin.
The study reveals that the eastern boundary between Southern Apennine and Calabrian Arc is a wide deformation belt including the Sangineto Lineament while the Messinian-Pliocene orogenic transpressive system is buried and translating toward the NE since Early Pleistocene.
How to cite: Artoni, A., Basso, J., Torelli, L., Polonia, A., Chizzini, N., Gasperini, L., and Carlini, M.: The post-Messinian translation of the Southern Apennines-Calabrian Arc in the Bradano basin (Northern Ionian Sea), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8451, https://doi.org/10.5194/egusphere-egu21-8451, 2021.
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During the Tertiary evolution of the Western Mediterranean subduction system, the orogenic accretion at the Maghrebian margin let the stacking of three main tectonic zones of the Rif fold-and-thrust belt: 1) the Internal Zone; 2) the “Maghrebian Flysch” Nappes; and 3) the External Zone. In this context, a migrating foreland basin system developed between the Maghrebian orogenic belt and the adjacent African Craton.
A comprehensive reconstruction of the foreland basin system of the Rif Chain for each phase of its accretional history is still missing. In this work, by integrating field observations with quantitative biostratigraphic data from calcareous nannofossils assemblages, sandstone composition, and detrital zircon U-Pb geochronology from selected stratigraphic successions, we reconstruct the foreland basin system that in the early Miocene developed in front of the growing Rif orogen. The analyzed successions are representative of (1) the “Beliounis Facies”, made of quartz-arenites and litharenites (Numidian-like “mixed succession”), from the Predorsalian Unit; (2) the “Mérinides Facies”, made of a Numidian-like “mixed succession”, from the “Maghrebian Flysch Basin”; and (3) the classical “Numidian Facies”, exclusively made of quartzarenites, from the Intrarifian Tanger Unit.
The petrographic analyses and the detrital zircon U-Pb ages show the provenance of the quartzarenites of the “Numidian Facies” from the African Craton, whereas the sublitharenites and feldspathic litharenites, of both the “Mérinides Facies” and “Beliounis Facies”, show provenance from a cratonic area and the growing and unroofing Rif Chain, respectively.
The Alpine signature of the detrital grains sedimented into the foredeep deposits of the early Miocene orogenic system of the Rif Chain is from the feldspathic litharenites of both the Mérinides Facies and the Beni Ider Flysch. Both show Mesozoic and Cenozoic U-Pb zircon populations, with a large population of zircons centered at ca. 32 Ma. The U and Th concentration, the Th/U ratio, and the REE pattern of this population of zircons suggest a possible source area from Oligocene doleritic rock intrusions, similar to the magmatic dyke swarms (diorite) cropping out in the Malaga region ( SE Spain).
The biostratigraphic analyses pinpoint the same age for the arrival of the quartz grains in the Numidian, Mérinides, and Beliounis deposits, indicating about 1 Myr for their sedimentation (ca. 20-19 Ma, early Burdigalian). Together with field evidence, the biostratigraphic results point to an autochthonous deposition of the Numidian Sandstones on top of the Tanger Unit, allowing to delineate the early Burdigalian foreland basin system of the Rif Chain. The foreland depozone involved the Tanger Unit and received the “Numidian Facies” deposits ; the foredeep depozone hosted about 2000 m of the “Mérinides Facies” and the Beni Ider Flysch, and developed on the so-called “Flysch Basin Domain”; and, finally, the wedge-top depozone, characterized by the “Beliounis Facies”, developed on top of the Predorsalian Unit.
The Numidian Sandstones and the Numidian-like deposits analyzed in Morocco show the same age of similar deposits from Algeria, Tunisia, and Sicily, suggesting a comparable early Burdigalian tectono-sedimentary evolution along the southern branch of the Western Mediterranean subduction-related orogen.
How to cite: Abbassi, A., Cipollari, P., Fellin, M. G., Zaghloul, M. N., Guillong, M., El Morabet, M., and Cosentino, D.: The Numidian Sand Event in the Burdigalian Foreland Basin System of the Rif (Morocco) in a source-to-sink perspective, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15312, https://doi.org/10.5194/egusphere-egu21-15312, 2021.
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The Alpine-Mediterranean belt is remarkable because of the strong arcuation of its subduction front and the abundance of extensional basins developed within an overall compressional setting. Both resulted from rapid slab rollback and trench retreat especially in Neogene time, accompanied by upper-plate extension and the opening of the Western Mediterranean basins. The Strait of Sicily is a very interesting geological area in the Western-Central Mediterranean, as it has undergone tectonic extension and opening of a rift zone (Sicily Channel Rift Zone, SCRZ) on the lower plate (Africa) of the subduction zone, marked by the Gela Front and the Calabrian Accretionary Wedge, located south and south-east of Sicily, respectively. Furthermore, the SCRZ is important for understanding and quantifying the independent motion and counter-clockwise rotation of the Adriatic plate in Neogene time (Le Breton et al. 2017). However, the exact timing, tectonic style and amount of deformation along the SCRZ remain unclear.
To tackle these questions, we re-evaluate multichannel seismic reflection profiles across the SCRZ (CROP seismic lines M24 and M25), as well as a series of seismic lines correlated with boreholes data from the VIDEPI project (www.videpi.com). Main stratigraphic horizons and tectonic structures are mapped in a 3D database using the MOVE Software (provided by Petex). Preliminary results indicate ~30 km of NE-SW extension through the Pantelleria Rift and onset of syn-rift deposition during the upper Messinian, which could be related with the fast slab retreat of the Calabrian Arc.
References:
Le Breton E., M.R. Handy, G. Molli and K. Ustaszewski (2017). Post-20 Ma motion of the Adriatic plate – new constrains from surrounding orogens and implications for crust-mantle decoupling, Tectonics, doi:10.1002/2016TC004443
How to cite: Le Breton, E., Carlini, M., Neumeister, R., Ecke, J., Chizzini, N., Torelli, L., and Artoni, A.: Lower plate extension of a retreating subduction zone: case study of the Sicily Channel Rift Zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12579, https://doi.org/10.5194/egusphere-egu21-12579, 2021.
The Apennines form an active fold and thrust belt that develops as part of the W-Mediterranean subduction zone. The evolution of the collisional system is driven by the retreating subduction of the alpine Tethys, which has caused the migration of compressive fronts and the opening of the Liguro-Provençal and Tyrrhenian back-arc basins, along with the rotation and translation of the Sardinia-Corsica and Calabria blocks. The Apennines make the northern limb of the Apennines-Calabria-Sicily orocline, developed due to the differential SE-ward retreat of the subduction system. In such a context, the central-southern Apennine system develops a foreland basin floored by a subaerial forebulge unconformity followed by a trinity of diachronous lithostratigraphic units: (i) shallow-water carbonates, (ii) hemipelagic marls, and (iii) siliciclastic turbidites. Previous studies have used the following datasets for reconstructing the evolution of the orogenic-foreland basin system: paleomagnetic data; the age of the siliciclastic syn-orogenic deposits filling the foredeep and wedge-top depozones; the age of the late-orogenic extensional basins. In this study, we highlight the importance of dating with high precision the onset of the Apennine orogenesis by means of Sr-isotope stratigraphy applied to the first carbonate sediments overlying the forebulge unconformity. In this regard, we have investigated a transect of the Apennine belt, extending from inner to outer sectors, in order to constrain the timing and style of migration of the belt and foreland basin. Our results show progressive rejuvenation of the forebulge unconformity toward the outer portions of the belt. More importantly, we highlight a time delay between the onset of syn-orogenic shallow-water carbonate deposition and the onset of siliciclastic turbidite deposition that ranges between 1 and 11 myr. In detail, the trends in the delay point at three main evolutive steps: 1) rapid evolution from forebulge to foredeep during the Burdigalian, 2) higher delays from the Serravallian until the latest Miocene, and 3) progressive decrease of the delay from the Zanclean. We associate the different velocity of migration with the differential slab retreat and spreading of the back-arc basins.
How to cite: Sabbatino, M., Tavani, S., Vitale, S., Corradetti, A., Consorti, L., and Parente, M.: Spatial-temporal migration of the central-southern Apennine belt and foreland basin system (Italy) constrained by Sr-isotope stratigraphy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10302, https://doi.org/10.5194/egusphere-egu21-10302, 2021.
We present a structural study on late Miocene-early Pliocene out-of-sequence thrusts affecting the southern Apennine chain. The analyzed structures are exposed in the Campania region (southern Italy). Here, leading thrusts bound the N-NE side of the carbonate ridges that form the regional mountain backbone. In several outcrops, the Mesozoic carbonates are superposed onto the unconformable wedge-top basin deposits of the upper Miocene Castelvetere Group, providing constraints to the age of the activity of this thrusting event. We further analyzed the tectonic windows of Giffoni and Campagna, located on the rear of the leading thrust. We reconstructed the orogenic evolution of this part of the orogen. The first was related to the in-sequence thrusting with minor thrusts and folds, widespread both in the footwall and in the hanging wall. A subsequent extension has formed normal faults crosscutting the early thrusts and folds. All structures were subsequently affected by two shortening stages, which also deformed the upper Miocene wedge top basin deposits of the Castelvetere Group. We interpreted these late structures as related to an out-of-sequence thrust system defined by a main frontal E-verging thrust and lateral ramps characterized by N and S vergences. Associated with these thrusting events, LANFs were formed in the hanging wall of the major thrusts. Such out-of-sequence thrusts are observed in the whole southern Apennines and record a thrusting event that occurred in the late Messinian-early Pliocene. We related this tectonic episode to the positive inversion of inherited normal faults located in the Paleozoic basement. These envelopments thrust upward crosscut the allochthonous wedge, including, in the western zone of the chain, the upper Miocene wedge-top basin deposits. Finally, we suggest that the two tectonic windows are the result of the formation of an E-W trending regional antiform, associated with a late S-verging back-thrust, that has been eroded and crosscut by Early Pleistocene normal faults.
How to cite: Stefano, V., Ernesto Paolo, P., Tramparulo, F. D., and Ciarcia, S.: The Late Miocene-Early Pliocene out-of-sequence thrusting event: new insights into the tectonic evolution of the southern Apennines (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-803, https://doi.org/10.5194/egusphere-egu21-803, 2021.
Cenozoic units from thrust-top and foredeep basins provide crucial information for constraining the progressive evolution of the Southern Apennine thrust and fold belt and, more in general, the geodynamic evolution of the Mediterranean area. For this reason, we have analysed the stratigraphic and tectonic setting of deep-sea Cenozoic units exposed in the southeastern sector of the Agri Valley (Basilicata, Southern Italy), in an area located immediately north of the Montemurro village, between the Costa Molina and Monte dell’Agresto localities. These units have not been studied in detail so far and different interpretations are reported in the literature. The study was based on an accurate field survey which led to a new geological map and to the reconstruction of the stratigraphic and structural setting of the area. Results of the field survey were constrained by well, seismic and new biostratigraphic data kindly provided by Eni. In our study, we focussed on the Albidona Formation, which was deposited in a thrust-top basin on the Liguride accretionary wedge, formed above the NW-dipping subduction of the Ligurian Tethys Ocean during the Late Cretaceous? - Early Miocene. Facies characteristics and age determinations allowed the differentiation of the Albidona Formation in two members, with the older one, identified as Member B-C (Lutetian) consisting of alternating marls, sandstones and clays and the younger one, identified as Member D (Barthonian/Priabonian), consisting in alternating sandstones and conglomerates. In particular, the presence of marker horizons such as a pebbly mudstone containing ophiolite debris strongly helped in the structural reconstructions. By this means, we recognized the presence of two folding phases affecting the Albidona Formation. Moreover, the geometrical relationships between the two members and the overlying Miocene Gorgoglione Formation allowed recognising two major NE-trending normal faults, which crosscut the aforementioned structures. These data provide new indications on the tectonic setting and the evolution of the Southern Apennines thrust and fold belt.
How to cite: Prosser, G. and Palladino, G.: Stratigraphic and Structural setting of Cenozoic deep-sea units from the Agri valley (southern Apennines, Italy), recording the tectonic evolution of the Southern Apennines., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13381, https://doi.org/10.5194/egusphere-egu21-13381, 2021.
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More than half a century of investigations on the chemical and isotopic compositions and on geochronological data of the Cenozoic magmatic rocks in the Alps and the transition to the Apennine will be summarized. The Alps itself are dominated by a calc-alkaline series between ~42 and 30 Ma, which we summarized as Periadriatic magmatism. This magmatism includes also eroded volcanic parts and several dykes in the Southern Alps and Tyrol. In addition, Sesia Zone magmatic rocks are characterized by ultrapotassic, shoshonitic and calc-alkaline rocks between 33 and 30 Ma. Two other magmatic provinces are located in between the Alps and the Apennine: (1) Veneto volcanic province (=VVP; nephelinites, basanites and alkali basalts between 52 and 30 Ma); (2) Mortara volcano (~28 Ma). Another group is the Esterél magmatic province, which is located in the Alps and their direct foreland, but are not related to Alpine geodynamics. These are basalts, andesites and dacites with mantle signature developed between 40 and 20 Ma. In the hanging plate of the early Apennine geometry, some minor volcanic activity is preserved in Sardinia. The major volume of Apennine magmatism itself (Elba etc.) is Late Miocene-Pleistocene in age and is related to roll back dynamics of the Apennine.
The Eocene/Oligocene Periadriatic magmatism of the Alps requires significant melt production in the crust combined with some ACF processes. This is possible by infiltration of fluids in the mantle wedge and the lower crust and a change of P-T conditions in the mantle. Their calc-alkaline character is related to Na-dominated input in the mantle and crust, which is commonly inferred to result from subduction of oceanic units. Ultrapotassic melts in the Sesia-unit most likely result from infiltration of K-dominated fluids, related to dehydration of continental material. The dynamics of Apennine and possible related forearc extension would allow an extensional related magmatism in the Esterél. This magmatism overlap in time with Alpine magmatism, and require a small-scale mantle dynamic due to the development of two slabs. In addition, the VVP and the Mortara volcano are located on the non deformed continental fragment of Adria between the Alps and Apennine. This area is characterized by overfilled basins and local magmatism inside the Adriatic continental plate.
The sometimes minor preserved volumes, but well constrain timing of magmatic rocks at the interaction between Alps and Apennine give insights in the lower crust/mantle dynamics at Oligocene/Early Miocene times. These interpretations may differ from models based on upper crustal tectonics, due to the decoupling between upper crust and lower crust/mantle.
How to cite: Berger, A.: Cenozoic magmatism in the Alps with special reference to the Ligurian knot, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-537, https://doi.org/10.5194/egusphere-egu21-537, 2021.
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The Alps and the westernmost part of Apennines physically join in NW Italy (Piemonte), where the Apennine thrusts interfered, since Late Oligocene, with both the inner boundary faults of the uplifting Alps axial belt and the outer fronts of the Alpine antithetic retrobelt (the Southern Alps). As the two orogenic belts had been intergrowing since the late Oligocene, coeval syn-orogenic basins developed on both, either as separate depocenters or, more frequently, to form a continuous sedimentary domain, strongly controlled by the tectonic evolution of the Alps-Apennines orogenic system. These syn-orogenic basins both recorded the main stages of the Alps (neoAlpine events) and Apennines tectonic evolution, whose evidence (mostly represented by regional-scale unconformities) can be correlated within each basin and across them. Correlations (in terms of sharing common geologic events) can be found also with the middle Eocene to lower Oligocene basal part of the Alpine foreland basin succession, which extended continuously on the external side of the Western Alps. This contribution will briefly discuss this complex matter in an integrated Alpine-Apennines perspective and in the frame of the post-Eocene evolution of the Western Mediterranean area.
How to cite: Piana, F., d'Atri, A., and Irace, A.: On the syn-orogenic basins of the Alps-Apennines tectonic system in NW Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14220, https://doi.org/10.5194/egusphere-egu21-14220, 2021.
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The Northern Apennines are an accretionary wedge formed in response to the Late Cretaceous-Eocene closure of the Ligurian-Piedmont ocean and the subsequent Oligocene-Miocene convergence and collision between Africa and Europe. The wedge is formed by a stack of different paleogeographic units which, from the innermost to the outermost and from top to bottom, are: (i) the Ligurian Domain (formed by Jurassic ophiolites and their Cretaceous-to-Paleocene sedimentary cover); (ii) the Sub-Ligurian Domain (Paleocene-to-lower Miocene deep marine sediments and turbidites); (iii) the Tuscan-Umbria-Marche Domain (mostly including Jurassic-to-Oligocene platform and basinal carbonate successions, overlain by Miocene-Pliocene turbidites). The wedge is shaped by WNW-ESE-striking and SW-dipping thrusts, accommodating a general northeastward tectonic transport. Atop of the deformed Ligurian Domain there occur the Epiligurian Units, which consist of middle Eocene-upper Miocene bathyal to shallow-water siliciclastic deposits infilling wedge-top basins. These Units presently fill in separate basins with poor lateral interconnectivity due to erosion and deformation. Since the Miocene, thrusting toward the (eastern) orogenic foreland occurred simultaneously with extension in the (western) hinterland domain, causing the formation of NW-SE-striking normal faults. Presently, focal mechanisms of the stronger earthquakes constrain dominant thrusting associated with NE-SW regional shortening, whereas the extensional regime controls the seismicity along the axial portion of the wedge. This recently launched study aims to better characterize the deformation structures affecting the Epiligurian Units in the internal and external sectors of the Northern Apennines (Emilia-Romagna Region) with the goal to provide a comprehensive syn-to-post accretion evolutionary scenario for these shallow basins. In particular, deformation structures affecting these wedge-top sequences of the inner (southwestern) side of the wedge are being studied by their systematic geometric and kinematic multiscalar and multitechnique characterization. Top-to-the NE, WNW-ESE-striking thrusts/reverse faults, dipping moderately to SSW are defined by planar slip surfaces associated with thin clastic damage zones. Top-to-the SE, ENE-WSW-striking thrusts/reverse faults, are instead generally devoid of well-developed damage zones. These contractional faults are systematically cut by NW-SE and NE-SW-striking normal and oblique faults systems, characterized by mutually intersecting fault planes accommodating centimetric to decimetric throws. Associated with the extensional structures occur widespread cataclastic and disaggregation deformation bands. They are found as either single bands or clusters, cutting across upper Eocene coarse-grained sandstones. Our preliminary results show that the Epiligurian Units experienced a complex tectonic evolution, including NNE-SSW shortening followed by NE-SW extension. The structural record of these wedge top basins is useful to infer the kinematics and rate of wedge build up and tearing down during the progressive evolution of the continental collision. The Epiligurian Units can thus be considered as useful gages of the deformation history of the Northern Apennines wedge, with noteworthy implications on its current seismotectonic setting.
How to cite: Stendardi, F., Vignaroli, G., and Viola, G.: Structural characterization of the wedge - top Epiligurian Units in the framework of the Northern Apennines tectonic evolution (northern Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-381, https://doi.org/10.5194/egusphere-egu21-381, 2021.
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The Neogene and Quaternary tectonic evolution of the inner Northern Apennines (i.e southern Tuscany and northern Tyrrhenian Sea), as well as its crustal features (i.e. low crustal thickness, Neogene-Quaternary magmatism, widespread geothermal anomalies, lateral segmentation of the stacked tectonic units, extensive deep sedimentary basins), are framed in different geodynamic scenarios: compressional, extensional or both, pulsing. Consequently, the basin and range structure that characterises the northern Tyrrhenian Sea and southern Tuscany is considered as a consequence of (i) out-of-sequence thrusts and related thrust-top-basins, (ii) polyphased normal faulting that formed horst and graben structures or (iii) a combination of both. This paper provides a new dataset from a sector of the eastern inner Northern Apennines (i.e. Monti del Chianti - Monte Cetona ridge) contributing to this scientific debate. New fieldwork and structural analysis carried out in selected areas along the ridge allowed to define the chronology of the main tectonic events on the basis of their influence on the marine and continental sedimentation. The dataset supports for early Miocene - (?) Serravallian in-sequence and out-of-sequence thrusting. Thrusting produced complex staking patterns of Tuscan and Ligurian Units. Extensional detachments developed since later middle Miocene and controlled the Neogene sedimentation in bowl-shaped structural depressions, later dissected by normal faults enhancing the accommodation space for Pliocene marine deposits in broad NNW-trending basins (Siena-Radicofani and Valdichiana Basins). In this perspective, no data supports for active, continuous or pulsing, compressional tectonics after late Serravalian. As a result, in the whole inland inner Northern Apennines the extensional tectonics was continuously active at least since middle Miocene and controlled the basins development, magmatism and structure of the crust and lithosphere.
How to cite: Brogi, A.: Late evolution of the inner Northern Apennines from the structure of the Monti del Chianti-Monte Cetona Ridge (Tuscany, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1764, https://doi.org/10.5194/egusphere-egu21-1764, 2021.
The tectonic setting of Neogene is under debate, being interpreted as a contractional, pulsing or extensional framework. On the key-areas to unravel this issue is the Gavorrano monzogranite, located nearby the Tyrrhenian seacoast, in the inner zone of the Northern Apennines (southern Tuscany), where a Neogene monzogranite body (estimated in about 3 km long, 1.5 km wide, and 0.7 km thick) emplaced during early Pliocene. This magmatic intrusion is partially exposed in a ridge bounded by regional faults delimiting broad structural depressions. A widespread circulation of geothermal fluids accompanied the cooling of the magmatic body and gave rise to an extensive Fe-ore deposit (mainly pyrite) exploited during the past century. Data from a new fieldwork dataset, integrated with information from the mining activity, have been integrated to refine the geological setting of the whole crustal sector where the Gavorrano monzogranite was emplaced and exhumed. Our review, implemented by new palynological, petrological and structural data pointed out that: i) the age of the Palaeozoic phyllite (hosting rocks) is middle-late Permian, thus resulting younger than previously described (i.e. pre-Carboniferous); ii) the P-T conditions at which the metamorphic aureole developed are estimated at about 660 °C and at a maximum depth of c. 5 km; iii) the tectonic evolution which determined the emplacement and exhumation of the monzogranite is constrained in a transfer zone, in the frame of the extensional tectonics affecting the area continuously since Miocene.
How to cite: Liotta, D., Caggianelli, A., Brogi, A., Zucchi, M., Spina, A., Capezzuoli, E., Casini, A., and Buracchi, E.: Neogene tectonics during granite emplacement in Northern Apennines: the case of the Gavorrano monzogranite (southern Tuscany, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1491, https://doi.org/10.5194/egusphere-egu21-1491, 2021.
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Exhumation and cooling of upper crustal plutons is generally assumed to develop in the brittle domain, thus determining an abrupt passage from crystallization to faulting. To challenge this general statement, we have applied an integrated approach involving meso- and micro-structural studies, thermochronology, geochronology and rheological modeling. We have analyzed the Miocene syn-tectonic Porto Azzurro pluton on Elba (Tuscan archipelago – Italy), emplaced in an extensional setting, and have realized that its fast exhumation is accompanied by localized ductile shear zones, developing along dykes and veins, later affected by brittle deformation. This is unequivocally highlighted by field studies and the analysis of microstructures with EBSD. In order to constrain the emplacement and exhumation rate of the Porto Azzurro pluton we performed U-Pb zircon dating and (U+Th)/He apatite thermochronology. It results in a magma emplacement age of 6.4 ± 0.4 Ma and an exhumation rate of 3.4 to 3.9 mm/yr. By thermo-rheological modeling we were able to establish that localized ductile deformation occurred at two different time steps: within felsic dykes when the pluton first entered into the brittle field at 380 kyr, and along quartz-rich hydrothermal veins at c. 550 kyr after pluton emplacement. Hence, the major conclusion of our data is that ductile deformation can affect a granitic intrusion even when it is entered into the brittle domain in a fast exhuming extensional regime.
How to cite: Spiess, R., Langone, A., Caggianelli, A., Stuart, F. M., Zucchi, M., Bianco, C., Brogi, A., and Liotta, D.: Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1316, https://doi.org/10.5194/egusphere-egu21-1316, 2021.
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In the Iano area (Southern Tuscany) a small tectonic window of Tuscan metamorphic units is observed. This belongs to the northernmost part of the so-called Mid-Tuscan ridge and, during Pliocene, formed a submarine high, now defining the easternmost shoulder of the Volterra Pliocene basin. The area gives the opportunity to investigate the complete cycle of negative inversion from crustal thickening to crustal thinning, which characterizes Southern Tuscany. Our new data focus on the western margin of the Iano ridge, and in particular on a system of high angle normal faults that represents the youngest structures of the investigated area. These structures, deformed low angle regional detachments locally juxtaposing the uppermost units of contractional nappe stack (the ophiolite-bearing Ligurian units), with the Tuscan metamorphic units, with an almost complete excision of at least 3.5 Km thick Mesozoic to Tertiary Tuscan nappe succession. The high angle normal faults show variable Plio-Quaternary vertical displacements from few meters to about 500 meters, and acted as pathways for the upwelling of hydrothermal fluids, as revealed by Pleistocene travertine deposits, hydrothermal alteration and occurrence of different generations of fluid inclusions in hydrothermal veins associated with these fault systems. Fluid inclusions were studied in quartz veins hosted in the Verrucano metasediments forming the top of the Tuscan metamorphic unit, as well as in some carbonate lithotypes (Cretaceous to Tertiary in age) of the overlying Tuscan Nappe. Two different kinds of fluid inclusions were documented. The Type 1 are multiphase (liquid + vapor + 1 daughter mineral) liquid-rich fluid inclusions whereas the Type 2 are two-phase (liquid + vapor) liquid-rich fluid inclusions. Type 1 fluid inclusions are primary in origin and were found only in quartz veins present in Verrucano metarudites, whereas Type 2 fluid inclusions occur in quartz veins present in both Verrucano phyllites and quartzites and in the carbonate units of the Tuscan Nappe. These are secondary and can be furthermore distinguished in two sub-populations (Type 2a and Type 2b) on the basis of petrographic observation and microthermometric data. Fluid inclusion investigation evidenced an evolution of the hydrothermal fluids from relatively high-T (~265°C) and hypersaline (35 wt.% NaClequiv.) fluids trapped at about 100 MPa, to lower temperature (~195°C) and salinity (~9.5 wt.% NaClequiv.) fluids, having circulated in the high-angle fault system. Based on the new data and a revision of the local tectonic setting a fluid-rock interaction history has been reconstructed with new hints and constraints for the Plio-Quaternary extensional history of the Volterra basin.
How to cite: Fulignati, P., Zucchi, M., Brogi, A., Capezzuoli, E., Liotta, D., Sarti, G., and Molli, G.: Fluid flow and faulting history of the Iano tectonic window (Southern Tuscany, Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4423, https://doi.org/10.5194/egusphere-egu21-4423, 2021.
Extensional tectonics and related magmatism affecting continental crust can favour the development of geothermal systems. Granitoids intruded in the upper crust represent the main expression of magmatism; they are strictly controlled by brittle structures during their emplacement and exhumation. The cooling of the magmatic bodies produce a thermal perturbation in the hosting rocks resulting in thermo-metamorphic aureoles of several meter thick, usually characterised by valuable ore deposits. After the emplacement and during the cooling stage such granitoids can promote the geothermal fluids circulation mainly through the fault zones. In case of favourable geological and structural conditions, geothermal fluids can be stored in geological traps (reservoirs), generally represented by rock volumes with sufficient permeability for storing a significant amount of fluid. Traps are confined, at the top, by rocks characterised by low, or very low permeability, referred to as the cap rocks of a geothermal system. Several studies are addressed to the study of fluid migration through the permeable rock volumes, whereas few papers are dealing with fluid flow and fluid-rock interaction within the cap rocks.
In this presentation, an example of fault-controlled geothermal fluid within low permeability rocks is presented. The study area is located in the south-eastern side of Elba Island (Tuscan Archipelago, Italy), where a succession made up of shale, marl and limestone (Argille a Palombini Fm, early Cretaceous) was affected by contact metamorphism related to the Porto Azzurro monzogranite, which produced different mineral assemblages, depending on the involved lithotypes. These metamorphic rocks were dissected by high-angle normal faults that channelled superhot geothermal fluids. Fluid inclusions analyses on hydrothermal quartz and calcite suggest that at least three paleo-geothermal fluids permeated through the fault zones, at a maximum P of about 0.8 kbar. The results reveal how brittle deformation induces fluid flow in rocks characterised by very low permeability and allow the characterisation of the paleo-geothermal fluids in terms of salinity and P-T trapping conditions.
How to cite: Zucchi, M.: Geothermal manifestations in the Tyrrhenian area: the role of faults in channelling superhot geothermal fluids, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1668, https://doi.org/10.5194/egusphere-egu21-1668, 2021.
The “Livorno-Empoli” fault represents the westernmost segment of one a major transversal structure of the inner Northern Apennines the so-called “Livorno-Sillaro Line” a regional structure described in the literature, for a long time (e.g., Ghelardoni, 1967; Bortolotti, 1966; Bernini et al., 1991; Cantini et al., 2001; Pascucci et al., 2007; Rosenbaum, Agostinetti, 2015). In the frame of our ongoing studies, in this contribution, we will focus on the short term history of this regional fault. A new stratigraphic-sequence frame for the late-Quaternary deposits has been developed by using the different facies associations as defined through a large surface database analysis. Moreover, a correlation has been done between subsoil deposits and the outcropping sediments on the hilly areas (Livorno, Pisa, and Cerbaie hills) surrounding the Arno valley.
Additionally, a morphotectonic analysis of the hydrographic networks and relief distribution has been done the Lidar data (DTM), supplied by the Tuscany Region, at the 2 m and 10 m of resolution. Specifically, the river system is particularly sensitive to deformation processes. The fluvial streams are in fact characterized by low geomorphological inertia and, therefore, by response times of a few hundred thousand years to the tectonic processes ongoing.
As a result of the integrated multidisciplinary analysis, it was possible to highlight the evidence of middle Pleistocene-Holocene tectonics of the “Livorno-Empoli Fault” until now neglected by the literature.
References
Ghelardoni, R. (1967) Osservazioni sulla tettonica trasversale dell’Appennino Settentrionale. Bollettino della Societa Geologica Italiana, 84, 1–14.
Bortolotti V. (1966) – La tettonica trasversale dell’Appennino – La linea Livorno-Sillaro. Bollettino della Società Geologica Italiana, Vol.85, pp. 529-540, 3 ff., 1 tav.
Bernini, M., Boccaletti, M., Moratti, G., Papani, G., Sani, F., & Torelli, L. (1991). Episodi compressivi neogenico-quaternari nell’area estensionale tirrenica. Dati in mare e a terra. Memorie della Società Geologica Italiana 1990, 45, 577–589.
Cantini P., Testa G., Zanchetta G. & Cavallini R. The Plio-Pleistocenic evolution of extensional tectonics in northern Tuscany, as constrained by new gravimetric data from the Montecarlo Basin (lower Arno Valley, Italy). Tectonophysics, 2001, 330, 25-43.
Pascucci V.; Martini I.P.; Sagri M.; Sandrelli F. Effects of transverse structural lineaments on the Neogene-Quaternary basins of Tuscany (inner Northern Apennines, Italy). Sedimentary Processes, Environments and Basins: A Tribute to Peter Friend, 2007,
Rosenbaum, G.; Agostinetti., N.P. (2015). Crustal and upper mantle responses to lithospheric segmentation in the northern Apennines. Tectonics, 34, 648–661, doi:10.1002/2013TC003498.
How to cite: Sarti, G., Giannico, V. G., Pittaro, D., Porta, L., and Molli, G.: Sedimentary record and the late - Quaternary tectonics of the “Livorno-Empoli Fault” (Northern Tuscany, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8433, https://doi.org/10.5194/egusphere-egu21-8433, 2021.
As part of an ongoing project of mapping, structural studies and fault characterization we present an updated tectonic scheme and data set for the active fault systems that shaped the inner portion of the Apennines north of the Arno river. Geomorphology, stratigraphy of Plio-Quaternary sediments, GPS data, historical and instrumental seismicity have been reviewed and combined with structural studies to define the neotectonic history of the investigated region. Within the studied area, first-order physiographic and structural features allow to define different structural domains related to a set of ranges with a dominant NW-SE direction separated by intramontane or continental/marine morphotectonic depressions of the Lunigiana, Garfagnana, Lucca-Mt.Albano, La Spezia-Carrara and the off-shore Viareggio basin. The main boundary faults and internal fault segments of the different structural domains were described while the Plio-Quaternary sedimentary records has been used to constrain their long to short term deformation and rates, with the aim to improve current Italian catalogues - DISS (INGV) and Ithaca (ISPRA) - with some utilities for the seismic microzonation local projects. Moreover, our work aims to draw the attention of the scientific community to the seismotectonics of a region in which the seismic hazard is largely considered medium to low despite the occurrence, one century ago, of one of the most destructive earthquakes that have struck the Italian peninsula, the 1920 Fivizzano EQ, with an estimated Mw 6.5 similar to the main shock of the 2016 Central Italy seismic sequence.
How to cite: Molli, G., Bennett, R., Malavieille, J., Serpelloni, E., Storti, F., Bigot, A., Pinelli, G., Giacomelli, S., Angeli, L., Giampietro, T., Lucca, A., and Porta, L.: Active Fault Systems in the inner North West Apennines: an updated view, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1473, https://doi.org/10.5194/egusphere-egu21-1473, 2021.
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We present the results of a detailed geological mapping project performed in the southernmost part of the Sibillini Mts., where the Sibillini Thrust (ST), one of the longest compressional structures of the Central Apennines, crops out. In the studied area the Meso-Cenozoic Umbria-Marche carbonate succession overthrusts the Messinian siliciclastic deposits of the adjacent Laga foredeep Basin. After the Messinian/Pliocene compressional tectonic phase, linked with the development of essentially W-dipping thrust systems, the E-verging Apennines accretionary wedge was affected by a Quaternary extensional tectonic phase during which SW-dipping normal fault systems developed. Among these normal faults, the Mt. Vettore extensional system (which includes the Castelluccio Plain fault (CPF) and the Mt. Vettoretto fault (MVF)) is one of the most important, being capable to produce destructive earthquakes (Mw 6.5 October 20, 2016). A long-lasting debate exists in literature concerning the cross-cutting relationships between the ST and the Mt. Vettore normal fault system: i.e., the thrust was alternatively considered as being nondisplaced by the normal faults or variously displaced with throws ranging between ~200 m and >2 km. Unfortunately, where normal faults should cut the thrust, a thick debris cover hides the tectonic structures and only speculative hypotheses can, thus, be done about this issue. In addition, important evidence of pre-thrusting extension is known in the area, that make difficult to discriminate the effective Quaternary activity of faults if the intersection with the compressional structures is not exposed. The aim of this study is to constrain the position of the ST under the debris cover and its relationship with the CPF and MVF, based on the following field data: i) thrust plane attitude; ii) position of the Laga Fm. outcrops, representing the footwall of the ST; iii) hanging wall anticline geometry; iv) geometry of normal faults and their recent activity; v) thickness of the Castelluccio Plain Quaternary infill at the hanging wall of the ST. The thrust position under the debris cover has been determined considering the variation of the hanging wall anticline geometry. In fact, where the Jurassic-Paleogene basinal formations crop out, the hanging wall anticline is well developed with vertical to overturned forelimb and fold axis essentially parallel to the thrust trend. This is crucial, because the occurrence in the field of an incomplete anticline (i.e., lacking the vertical to overturned forelimb) juxtaposed to the Laga Fm. (originally the footwall of the thrust) suggests the displacement of the anticline by a normal fault, allows us to infer the cross-cutting relationship between the tectonic lineaments and to estimate Quaternary normal fault throws. We conclude that the ST was displaced by the CPF with max throw ~250 m, which is consistent with the thickness of the Quaternary infill of the Castelluccio Plain. Both the CPF and the ST are in turn cut by the MVF (the youngest fault of the area, active in the 2016 earthquake) with a ~50 m throw, and is also inferred to partly reuse with negative inversion the ST plane where the plane geometry was favorable to extension.
How to cite: Simone, F., Francesca, S., Franco, C., Sabina, B., Valeria, R., and Stefania, S.: Cross-cutting relationships between the Sibillini Mts. Thrust and Mt. Vettore normal fault system (Central Apennines, Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2319, https://doi.org/10.5194/egusphere-egu21-2319, 2021.
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The Quaternary Volsci Volcanic Field (VVF) represents one of the products of the west-directed subduction of the Adriatic slab that drove the development of the Apennine mountain belt in central Italy. Here, we present new results on the eruptive history and the diatreme processes of exemplar tectonically controlled carbonate-seated maar-diatreme volcanoes. The VVF is defined by phreatomagmatic surge deposits, rich in accidental carbonate lithics, and subordinate Strombolian scoria fall deposits and lava flows, locally sourced from some tens of monogenetic eruptive centers, mostly consisting of small volume (0.01-0.1 km3) tuff rings and scoria cones. In light of new 40Ar/39Ar geochronological data and compositional characterization of juvenile eruptive products, we refine the history of VVF activity and envisage the implications on the pre-eruptive magma system and the continental subduction processes involved. Leucite-bearing, high-K (HKS) magmas mostly fed the early phase of activity (∼761–539 ka); primitive, plagioclase-bearing (KS) magmas appeared during the climactic phase (∼424–349 ka), partially overlapping with HKS ones, and then prevailed during the late phase of activity (∼300–231 ka). As the volcanic centers cluster along high-angle faults, we investigate the relationships between faulting and explosive magma-water interaction, as well as the distribution pattern of the eruptive centers. New field data allowed to retrieve the fold-and-thrust belt structure associated with the eruptive centers. Analysis of componentry, grain-size, degrees of whiteness and roundness of carbonate lithic inclusions, along with their micropaleontological features, has allowed to establish volcano tectonic correlations. In our interpretation, the clustering of eruptive centers is controlled by tectonic features. Specifically, a first order control is tentatively related to crustal laceration and deep magma injection along a ENE-trending Quaternary lateral tear in the slab and to Mesozoic rift-related normal faults. A second-order control is provided by orogenic structures (mainly thrust and extensional faults). In particular, magma-water explosive interaction occurred at multiple levels (< 2.3 km depth), depending on the structural setting of the Albian-Cenomanian aquifer-bearing carbonates, which are intersected by high-angle faults. The progressive comminution, rounding and whitening of entrained carbonate lithics allow us to trace multistage diatreme processes. Finally, our findings bear implications on volcanic hazard assessment in the densely populated (> 0.4 million people) areas of the Volsci Range and adjoining Pontina Plain and Middle Latin Valley.
How to cite: Cardello, G. L., Marra, F., Palladino, D., Consorti, L., Gaeta, M., Sottili, G., Carminati, E., and Doglioni, C.: The Volsci Volcanic Field (central Italy): Anatomy of a tectonically controlled, carbonate-seated, volcanic activity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16190, https://doi.org/10.5194/egusphere-egu21-16190, 2021.
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Paleogeographic reconstruction and recognition of the tectono-metamorphic evolution of ancient orogenic belt is often complex. The combination of an adequate amount of paleomagnetic, metamorphic, structural and geochronological data is necessary. Fundamental data derive from the study of regional-scale shear zones, that can be directly observed, by combining detailed field work with structural analysis, microstructural analysis and petrochronology. The Southern European Variscan Belt in the Mediterranean area was partially overprinted by the Alpine cycle (Stampfli and Kozur, 2006) and correlations are mainly based on lithological similarities. Little attention has been paid to the compatibility of structures in the dispersed fragments. A main debate is the connection among the Corsica-Sardinia Block (CSB), the Maures-Tanneron Massif (MTM) and the future Alpine External Crystalline Massifs (ECM) (Stampfli et al., 2002; Advokaat et al., 2014) and if these sectors were connected by a network of shear zones of regional extent, known as the East Variscan Shear Zone (EVSZ).
We present a multidisciplinary study of shear zones cropping out in the CSB (the Posada-Asinara shear zone; Carosi et al., 2020), in the MTM (the Cavalaire Fault; Simonetti et al., 2020a) and in the ECM (the Ferriere-Mollières and the Emosson-Berard shear zones; Simonetti et al., 2018; 2020b).
Kinematic and finite strain analysis allowed to recognize a transpressional deformation, with a major component of pure shear and a variable component of simple shear, coupled with general flattening deformation. Syn-kinematic paragenesis, microstructures and quartz c-axis fabrics revealed that shear deformation, in all the studied sectors, occurred under decreasing temperature starting from amphibolite-facies up to greenschist-facies. A systematic petrochronological study (U-Th-Pb on monazite collected in the sheared rocks) was conducted in order to constrain the timing of deformation. We obtained ages ranging between ~340 Ma and ~320 Ma. Ages of ~340-330 Ma can be interpreted as the beginning of the activity of the EVSZ along its older branches while ages of ~320 Ma, obtained in all the shear zones, demonstrate that they were all active in the same time span.
The multidisciplinary approach revealed a similar kinematics and tectono-metamorphic evolution of the studied shear zones contributing to better constrain the extension and timing the EVSZ and to strength the paleogeographic reconstructions of the Southern Variscan belt during Late Carboniferous time, with important implications on the evolution of the Mediterranean area after the Late Paleozoic. This case study demonstrates how paleogeographic reconstructions could benefit from datasets obtained from large-scale structures (i.e., shear zones) that can be directly investigated.
Advokaat et al. (2014). Earth and Planetary Science Letters 401, 183–195
Carosi et al. (2012). Terra Nova 24, 42–51
Carosi and Palmeri (2002). Geological Magazine 139.
Carosi et al. (2020). Geosciences 10, 288.
Simonetti et al (2020a). International Journal of Earth Sciences 109, 2261–2285
Simonetti et al. (2020b). Tectonics 39
Simonetti et al. (2018). International Journal of Earth Sciences. 107, 2163–2189
Stampfli and Kozur (2006). Geological Society, London, Memoirs 32, 57–82
Stampfli et al. (2002). Journal of the Virtual Explorer 8, 77
How to cite: Simonetti, M., Carosi, R., Montomoli, C., and Iaccarino, S.: The role of regional-scale shear zones in paleogeographic reconstructions: the case study of the Variscan belt in the Mediterranean area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8673, https://doi.org/10.5194/egusphere-egu21-8673, 2021.
The Pre-Mesozoic units exposed in the inner Northern Apennines mostly consist of middle-late Carboniferous-Permian successions unconformably deposited on a continental crust consolidated at the end of the Variscan (i.e. Hercynian) orogenic cycle (Silurian-Carboniferous). In the inner Northern Apennines, exposures of this continental crust, Cambrian?-early Carboniferous in age, have been described in the Northern Tuscany, Elba Island (Tuscan Archipelago) and, partly, in scattered and isolated outcrops of southern Tuscany. In this contribution, we reappraise the most significative succession (i.e. Risanguigno Formation) exposed in southern Tuscany and considered by most authors as part of the Variscan Basement. New stratigraphic and structural studies, coupled with palynological analyses, allow us to refine the age of the Risanguigno Fm and its geological setting and evolution. Based on the microfloristic content, the structural setting and the fieldwork study, we attribute this formation to late Tournaisian-Visean (middle Mississipian) time interval and conclude it is not showing evidence of a pre-Alpine deformation. These results, together with the already existing data, allow us to presume that no exposures of rocks involved in the Variscan orogenesis occur in southern Tuscany.
How to cite: Capezzuoli, E., Spina, A., Brogi, A., Liotta, D., Bagnoli, G., Zucchi, M., Molli, G., and Regoli, R.: Reconsidering the Variscan basement of southern Tuscany (inner Northern Apennines), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1675, https://doi.org/10.5194/egusphere-egu21-1675, 2021.
Recent biostratigraphic and sedimentological studies in the inner Northern Apennines (Italy) permit to refine the upper Palaeozoic successions of southern Tuscany, allowing new hypothesis to frame these formations in the palaeogeographic scenario inherited by the Variscan orogenesis. The Tuscan pre-Triassic successions, now exposed in the Monticiano-Roccastrada Unit, are generally barren or scarce in term of biomineralized fossiliferous content. They were mostly affected by HP-LT to LP-HT metamorphism that, together with their limited exposures, made difficult the stratigraphic correlations. This presentation is focused on three units (i.e. Falsacqua, Torrente Mersino and Carpineta formations) which age attribution and correlation were strongly debated. The Falsacqua Formation is mainly characterized by black to dark-grey phyllite, metasiltstone and metasandstone with dark metacarbonate intercalation. Due to the lack of biomineralized fossil content, by lithostratigraphic correlation with other Tuscan successions, this formation was referred to late Carboniferous-early Permian or Devonian. The Torrente Mersino Formation mainly consists of black to dark-grey quartz-phyllite, quartz metaconglomerate, light-grey quartzite, green phyllite and quartzite and light-grey phyllite. This formation is barren of fossil content and has been alternately assigned to Ordovician-Silurian, Silurian-Devonian, late Carboniferous-Permian and Triassic by lithostratigraphic correlation with other Tuscan and Sardinian successions. The Carpineta Formation is characterized by graphite-rich mudstones with carbonate-siltitic nodules. This unit was referred to the upper Visean-Serpukhovian based on its palaeontological content within the carbonate nodules. The first finding of a well-preserved microflora of middle Permian age in the Falsacqua and Torrente Mersino formations and of middle-late Permian age in the Carpineta Formation adds more constrains to the age attribution. This new age assignment permits to correlate the investigated Falsacqua and Torrente Mersino formations with the coeval ones belonging to southern Tuscany (i.e. Farma and Poggio al Carpino formations) and Elba Island (Rio Marina Formation) characterized by a similar microfloral content and to support a younger deposition of the Carpineta Formation than the Farma Formation one. Moreover, the occurrence of Gondwana-related sporomorphs in all the considered formations proposes a new palaeogeographic scenario for the northern Gondwana margin. Specifically, the present integrated study suggests that the northern margin of Gondwana fragmented through a series of transtensional phases. In this framework, the investigated upper Palaeozoic formations recorded marine siliciclastic sedimentation within either coeval pull-apart basins or laterally related facies of the same basin.
How to cite: Spina, A., Aldinucci, M., Brogi, A., Capezzuoli, E., Cirilli, S., and Liotta, D.: Permian sporomorphs from upper Palaeozoic succession of Southern Tuscany (Italy): new constraints for the stratigraphy and palaeogeographic setting of the Tuscan Domain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2112, https://doi.org/10.5194/egusphere-egu21-2112, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.