Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling

The recent advances in experimental petrography together with the information derived from the super-deep drilling projects have provided additional constraints for the interpretation of refraction and reflection seismic data. These constraints can also be used in the interpretation of magnetic and gravity data to resolve nonuniqueness. In this study, we re-interpret the magnetic and gravity data of the Italian peninsula and neighbouring areas. In view of the constraints mentioned above, it is now possible to find an agreement between the seismic and gravity models of the Central Alps. By taking into account the overall crustal thickness, we have recognized the existence of three types of Moho: 1) European which extends to the north and west of the peninsula and in the Corsican-Sardinian block. Its margin was the foreland in the Alpine Orogeny and it was the ramp on which European and Adriatic mantle and crustal slices were overthrusted. This additional load caused bending and deepening and the Moho which now lies beneath the Adriatic plate reaching a maximum depth of approximately 75 km. 2) Adriatic (or African) which lies beneath the Po plain, the Apennines and the Adriatic Sea. The average depth of the Moho is about 30-35 km below the Po plain and the Adriatic Sea and it increases toward the Alps and the Tyrrhenian Sea (acting as foreland along this margin). The maximum depth (50 km) is reached in Calabria. 3) Pery-Tyrrhenian. This is an oceanic or thinned continental crust type of Moho. It borders the oceanic Moho of the Tyrrhenian Sea and it acquires a transitional character in the Ligurian and Provençal basins (<15 km thickness) while further thickening occurs toward the East where the Adriatic plate is overthrusted. In addition, the interpretation of the heat flow data appears to confirm the origin of this Moho and its geodynamic allocation.

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Neogene kinematics of the Giudicarie Belt and eastern Southern Alpine orogenic front (Northern Italy)

10.5194/se-2021-19 ◽

2021 ◽

Author(s):

Vincent F. Verwater ◽

Eline Le Breton ◽

Mark R. Handy ◽

Vincenzo Picotti ◽

Azam Jozi Najafabadi ◽

...

Keyword(s):

Cross Sections ◽

Eastern Alps ◽

Strike Slip ◽

Fault System ◽

Late Oligocene ◽

Lateral Variation ◽

Tectonic Structures ◽

Tauern Window ◽

Adriatic Plate ◽

Lateral Extrusion

Abstract. Neogene indentation of the Adriatic plate into Europe led to major modifications of the Alpine orogenic structures and style of deformation in the Eastern Alps. Especially, the offset of the Periadriatic Fault by the Northern Giudicarie Fault marks the initiation of strike-slip faulting and lateral extrusion of the Eastern Alps. Questions remain on the exact role of this fault zone in changes of the Alpine orogen at depth. This necessitates quantitative analysis of the shortening, kinematics and depth of decoupling underneath the Northern Giudicarie Fault and associated fold-and thrust belt in the Southern Alps. Tectonic balancing of a network of seven cross sections through the Giudicarie Belt parallel to the local shortening direction reveals that it comprises two kinematic domains with different amounts and partly overlapping ages of shortening. These two domains are delimitated by the NW-SE oriented strike-slip Trento-Cles – Schio-Vicenza fault system, cross-cutting the Southern Alpine orogenic front in the south and merging with the Northern Giudicarie Fault in the north. The SW kinematic domain (Val Trompia sector) accommodated at least ~18 km of Late Oligocene to Early Miocene shortening. Since the Middle Miocene, the SW kinematic domain experienced a minimum of ~12–22 km shortening, whereas the NE kinematic domain underwent at least ~25–35 km shortening. Together, these domains contributed to an estimated ~53–75 km of sinistral strike-slip motion along the Northern Giudicarie Fault, implying that (most of) the offset of the Periadriatic Fault is due to Late Oligocene to Neogene indentation of the Adriatic plate into the Eastern Alps. Moreover, the faults linking the Giudicarie Belt with the Northern Giudicarie Fault reach ~15–20 km depth, indicating a thick-skinned tectonic style of deformation. These fault detachments may also connect at depth with a lower crustal Adriatic wedge that protruded north of the Periadriatic Fault and was responsible for N-S shortening and eastward escape of deeply exhumed units in the Tauern Window. Finally, the east-west lateral variation of shortening indicates internal deformation and lateral variation in strength of the Adriatic indenter, related to Permian – Mesozoic tectonic structures and paleogeographic domains.

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The arc of the Western Alps : understanding its kinematics and formation mechanisms based on new structural and paleomagnetic datas, and thermo-mechanical modelling.

10.5194/egusphere-egu21-16529 ◽

2021 ◽

Author(s):

Quentin Brunsmann ◽

Claudio Rosenberg ◽

Nicolas Bellahsen ◽

Laetitia Le Pourhiet

Keyword(s):

Western Alps ◽

Strike Slip ◽

Rheological Parameters ◽

The South ◽

Adriatic Plate ◽

The North ◽

Field Evidence ◽

Internal Zone ◽

The Alps ◽

East West

The Alps have an overall East-West orientation, which changes radically in their western termination, where they rotate southward into a N-S strike, and then eastward into an E-W strike, forming the arc of the Western Alps. This arc is commonly inferred to have formed during collision, due to indentation of the Adriatic plate into the European continental margin. Several models attempted to provide a kinematic explanation for the formation of this arched, lateral end of the Alps. Indeed, the radial nature of the transport directions observed along the arc of the Western Alps cannot be explained by a classic convergence model. For more than 50 years the formation of this arc was been associated to westward-directed indentation of Adria, accommodated along East-West oriented strike-slip faults, a sinistral one in the South of the arc and a dextral one in the North. The dextral one correspond to the Insubric Fault. The sinistral strike-slip zone, inferred to be localized along the &#171;Stura corridor&#187; (Piedmont, Italy) would correspond to a displacement of 100 to 150 km according to palaeogeographical, and geometric analyses. However, field evidence is scarce and barely documented in the literature. Vertical axis rotations of the Adriatic indenter also inferred to be syn-collisional could have influenced the acquisition of the morphology of the arc. Paleomagnetic analyses carried out in the Internal Zone and in the Po plain suggest a southward increading amount of counter-clockwise rotation of the Adriatic plate and the Internal Zone, varying from 20&#176;-25&#176; in the North to nearly 120&#176; in the South. Dextral shear zones possibly accommodating this rotation in some conceptual models is observed in several places below the Penninic Front and affect the Argentera massif to the south. However, the measured displacement quantities do not appear to be equivalent to those induced by such rotations. The present study aims to constrain the kinematic evolution of the arc of the Western Alps through a multidisciplinary approach. The first aspect of this project is the structural analysis of the area (Stura corridor) inferred to accommodate large sinistral displacements allowing for the westward indentation of the Adriatic indenter. We discuss the general lack of field evidence supporting sinistral strike-slip movements, in contrast to large-scale compilation of structures suggesting the possible occurrence of such displacement. The second part consists of a palaeomagnetic study, in which new data are integred with a compilation of already existing data. This compilation shows that several parts of the arc in the External Zone did not suffer any Cenozoic rotations, hence suggesting that a proto-arc already axisted at the onset collision, as suggested by independent evidence of some paleogeographic reconstruction. Finally, 2D and 3D thermo-mechanical modeling in using the pTatin3D code is used to test which structural (geometrical), and rheological parameters affected the first-order morphology of the Western Alpin arc and its kinematics. The synthesis of these different approaches allows us to propose a new model explaining the kinematics and the mechanisms of formation of the Western Alps arc.

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European-Adriatic plate collision in teleseismic tomography of the Eastern Alps

10.5194/egusphere-egu21-10724 ◽

2021 ◽

Author(s):

Jaroslava Plomerova ◽

Helena Zlebcikova ◽

Gyorgy Hetenyi ◽

Ludek Vecsey ◽

Vladislav Babuska ◽

...

Keyword(s):

Body Wave ◽

Oceanic Lithosphere ◽

Eastern Alps ◽

Seismic Network ◽

Quality Data ◽

Seismic Velocities ◽

Teleseismic Tomography ◽

Adriatic Plate ◽

The Alps ◽

Mountain Belts

We present potential scenarios of the European and Adriatic plates&#8217; collision that formed the Alps and the neighbouring mountain belts. Our results are based on teleseismic body-wave data from the AlpArray-EASI complementary experiment (2014-2015, Het&#233;nyi et al., Tectonophysics 2018) and the AlpArray Seismic Network (Het&#233;nyi et al., Surv. Geophys. 2018).&#160; Tomography of seismic velocities in the upper mantle along a ca. 200 km broad and 540 km long north-south transect images steady southward thickening of the lithosphere beneath the Bohemian Massif&#160; and northward dipping East-Alpine lithospheric keel. Thanks to the dense spacing of the AlpArray Seismic Network stations and high-quality data, the high-resolution tomography resolves for the first time two sub-parallel down-going high-velocity heterogeneities beneath the Eastern Alps, instead of a single, thick anomaly. The southern heterogeneity, which we relate to the subducted Adriatic plate, is more distinct than the northern one, which loses its connection with the shallow parts. Moreover, amplitudes and size of this heterogeneity decrease in cross-sections perpendicular to the strike of the Alps when shifting towards the Central Alps. The presented collision scenarios consider the smaller northern heterogeneity as (1) a remnant of a delaminated early phase subduction of the European plate with the reversed polarity relative to that in the Western Alps, (2) a piece of continental and oceanic lithosphere together, or, (3) a fragment of a quite extended lithosphere margin foundering in a preceding phase of the Adriatic subduction.

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Tomographic Study of the Adriatic Plate

Pure and Applied Geophysics ◽

10.1007/s00024-004-2602-6 ◽

2005 ◽

Vol 162 (2) ◽

pp. 311-329 ◽

Cited By ~ 12

Author(s):

N. Venisti ◽

G. Calcagnile ◽

A. Pontevivo ◽

G.F. Panza

Keyword(s):

Adriatic Plate

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Kinematics and extent of the Liguro-Piemont Ocean

10.5194/egusphere-egu2020-11228 ◽

2020 ◽

Author(s):

Eline Le Breton ◽

Sascha Brune ◽

Kamil Ustaszewski ◽

Sabin Zahirovic ◽

Maria Seton ◽

...

Keyword(s):

Kinematic Model ◽

Proximal Part ◽

Upper Jurassic ◽

Western Mediterranean ◽

Continental Margins ◽

Geological Evidence ◽

Adriatic Plate ◽

Rifted Margins ◽

Oceanic Spreading ◽

Mountain Belts

Assessing the extent of a former ocean, of which only remnants are found in mountain belts, is challenging but crucial to understand subduction and exhumation processes. Here we present new constraints on the opening and width of the Liguro-Piemont (LP) Ocean (or Alpine Tethys) in Mesozoic time using plate kinematic reconstructions of the Western Mediterranean-Alpine area.Our kinematic model is based on a compilation of geological-geophysical data and published reconstructions of the opening of the Atlantic for the motion of Europe, Africa and Iberia, and of the Cenozoic deformation along fold-and-thrust belts (Alps, Apennines, Dinarides, Provence) and extensional basins (Liguro-Provencal Basin and Sicily Channel Rift Zone) for the motion of the Adriatic plate (Adria) and Sardinia-Corsica. For Jurassic and Cretaceous times, our main assumption is to avoid significant convergence or divergence between Adria and Africa and between Iberia and Sardinia-Corsica, as there is no geological evidence for such deformation. This implies in return strike-slip motion between southern France and Iberia-Sardinia-Corsica and within the Adriatic plate.Our model shows that the LP basin opened in three phases: (1) first a slow extensional phase of c. 4 mm/yr (full rate) in Lower-Middle Jurassic between 200-165 Ma, followed by (2) a faster (up to 1.5 cm/yr) oblique extension in Middle-Upper Jurassic between 165-154 Ma, which coincides with emplacement ages of gabbros and pillow-lavas, and (3) a final main extensional phase in Upper Jurassic between 154 and 145 Ma, with rates up to 2.3 cm/yr. At 145 Ma, Iberia starts to move relative to Europe and thus extension in the LP domain decreases rapidly till it ceases completely at about 130 Ma. We interpret the first phase as rifting of the proximal part of the continental margins (200-165 Ma) followed by hyper-extension and formation of the ocean-continent transition zone (165-154 Ma), and break-up and ultra-slow oceanic spreading during the final third phase (mainly 154-145 Ma). Along a NW-SE transect between Corsica and northern Adria, we estimate the width of the LP Ocean to a maximum of ~ 240 km (oceanic domain) and the extent of the whole rifted margins to ~ 500 km, subdivided into ~380 km for the proximal and necking zones, and ~120 km for the hyper-extended and ocean-continent transition zones. Our results are supported by high-resolution thermo-mechanical modelling of the rifting phase that, using our kinematic constraints, reproduces very well the geometry of the Adriatic margin, as obtained by published geological reconstructions of the Southern Alps.We test other kinematic scenarios for the motion of Sardinia-Corsica and for the opening of the Ionian Basin which would increase the obliquity of rifting and reduce even more the width of the extended domain. Therefore, our calculated extent of the LP Ocean constitutes a maximum estimate providing crucial constraints for geodynamic modelling and a better understanding of subduction processes during the Alpine Orogeny.&#160;

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The Gargano Promontory: a Neogene contractional belt within the Adriatic plate

Terra Nova ◽

10.1046/j.1365-3121.1999.00243.x ◽

1999 ◽

Vol 11 (4) ◽

pp. 168-173 ◽

Cited By ~ 42

Author(s):

Bertotti ◽

Casolari ◽

Picotti

Keyword(s):

Adriatic Plate ◽

Gargano Promontory

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Time for a change of paradigm for Alpine subduction?

10.5194/egusphere-egu21-11826 ◽

2021 ◽

Author(s):

Mark R. Handy ◽

Stefan M. Schmid ◽

Marcel Paffrath ◽

Wolfgang Friederich

Keyword(s):

Pannonian Basin ◽

Lower Boundary ◽

Eastern Alps ◽

P Wave ◽

Moho Depth ◽

Depth Interval ◽

Tauern Window ◽

Adriatic Plate ◽

Lateral Extrusion ◽

European Plate

The prevailing paradigm of mountain building in the Alps entails subduction of European continental lithosphere some 100km thick beneath the Adriatic plate. Based on recent results of AlpArray, we propose a new model that involves subduction and wholesale detachment of locally much thicker (200-240 km) European lithosphere. Our approach combines teleseismic P-wave tomography and existing Local Earthquake Tomography (LET) to image the Alpine slabs and their connections with the overlying orogenic crust at unprecedented resolution. The images call into question the simple notion that slabs comprise only seismically fast lithosphere and suggest that the mantle of the downgoing European plate is compositionally heterogeneous, containing both positive and negative seismic anomalies of up to 5%. We interpret these as compositional rather than thermal anomalies, inherited from the Paleozoic Variscan orogenic cycle and presently dipping beneath the Alpine orogenic front. In contrast to the European Plate, the lithosphere of the Adriatic Plate is thinner (100-120 km) and has a more poorly defined lower boundary approximately at the interface between positive and negative Vp anomalies.&#160;Horizontal and vertical tomographic slices reveal that beneath the Central and Western Alps, the downgoing European Plate dips steeply to the S and SE and is locally detached from the Alpine crust. However, in the Eastern Alps and Carpathians east of the central Tauern Window, the Alpine slab anomaly occupies the 150-400 km depth interval and dips steeply to the N-NE, having completely detached from the &#160;Alpine orogenic crust. This along-strike change coincides with an abrupt eastward decrease in Moho depth (Kind et al., this session), the Moho being underlain by a pronounced negative Vp anomaly reaching eastward into the Pannonian Basin area. This negative Vp anomaly is interpreted to represent hot upwelling asthenosphere that was instrumental in accommodating Neogene orogen-parallel lateral extrusion of the ALCAPA tectonic unit (upper plate crustal edifice of Alps and Carpathians) to the E.&#160; An Adriatic origin of the northward-dipping, detached slab segment beneath the Eastern Alps is unlikely since its imaged down-dip length (200-300 km) matches estimated Tertiary shortening in the Eastern Alps accommodated by south-dipping subduction of European lithosphere, whereas shortening in the south-vergent eastern Southern Alps is only &#8804; 70 km.&#160;A slab anomaly beneath the northernmost Dinarides, laterally adjoining the Eastern Alps, is missing. The slab anomaly beneath the northern Apennines, of Adriatic origin und dipping beneath the Tyrrhenian backarc, hangs subvertically and appears to be almost detached from the Apenninic orogenic crust. Except for its westernmost segment where it meets the Alpine slab, this slab is clearly separated from the latter by a broad extent of upwelling asthenosphere located south of the Alpine slabs beneath the Po Plain, i.e., just south of the Alpine subduction zone. Considered as a whole, the slabs beneath the Alpine chain are interpreted as attenuated, largely detached sheets of continental margin and Alpine Tethyan lithosphere that locally reach down to a slab graveyard in the Mantle Transition Zone (MTZ).

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