Fabio Speranza

The Dinaride-Albanide-Hellenides form a remarkably continuous chain facing the E margin of Adria and the Ionian oceanic basin. Paleogeography and nappe assemblage change significantly from Dinarides to Albano-Hellenides, as well as age and magnitude of nappe rotation synchronous with thrust emplacement since Miocene times. Although it is well-established that the external zones of the Albano-Hellenides underwent a ~40° post-Oligocene clockwise (CW) rotation relative to Africa/Adria, the rotation timing remains debated. Previous models mainly suggested either two Miocene and Plio–Pleistocene rotation episodes, or a single post mid-Miocene rotation accelerating along time. Uncertainties reflect the contribution from local thrust tectonics and/or strike-slip faults biasing the regional rotational trend. Here we present new paleomagnetic data from 41 sites in the continuous Eocene-Upper Pliocene sedimentary sequence of the Tragjasi thrust sheet (Ionian zone, SW Albania). Sampled layers lie on the backlimb of a 50 km-long anticline subparallel to the regional orogenic trend and away from major strike-slip faults. Twenty-eight sites yielded reliable paleomagnetic directions carried by magnetite. The dataset includes 15 normal, 11 reverse and 2 mixed-polarity sites, yielding positive fold and reversal tests. Eocene to Lower Pliocene sediments consistently record a 37°±9° CW rotation, demonstrating that rotation in the external Albanides began not earlier than the late Early Pliocene (~4 Ma). By assuming rigid orogen rotations, we get post-4 Ma displacements reaching ~100 km at Vlore and ~150 km in Crete, corresponding to trench-retreat rates of ~3 to ~4 cm/yr. We interpret this rapid, recent rotation as driven by enhanced Ionian slab pull, slab tearing beneath the Albanides, crust coupling across the Kefalonia-Lefkada Transform Fault, and ultimately westward propagation of the North Anatolian Fault. The boundary between Dinarides and Albano-Hellenides is traditionally acknowledged to occur along the Shkoder‐Peja transverse zone (SPTZ) of Northern Albania, characterized by a ∼100 km SW‐ward shift of the ophiolitic nappe front. The SPTZ has been variably interpreted as a paleogeographic inheritance, a dextral strike‐slip fault, the hinge of the clockwise (CW) rotating Albano‐Hellenides, and a Miocene normal fault. We studied the paleomagnetism of 23 Triassic‐Cretaceous sites from the Krasta‐Cukali and Albanian Alps domains, located both within and north of the SPTZ. We found both pre‐and post‐tilt paleomagnetic directions that consistently yielded a∼70° CW rotation with respect to Adria/Africa, except 9 sites from the Koman zone at the boundary with the ophiolitic nappe, which record a 38°±15° CW rotation. Thus, the well‐known regional CW rotation of the Albano‐Hellenides extends northward in the southern Dinarides, and the SPTZ is not a rotation boundary as previously assumed. The∼70° CW rotation is interpreted as the sum of a 30° rotation associated with Late Oligocene‐Aquitanian thrusting of the Krasta‐Cukali nappe over the Kruja zone, plus the 40° post-4 Ma rotation that we have now constrained in the external Ionian zone of Albania. We suggest that the SPTZ is the heritage of a Lower‐Middle Triassic transform fault of the Maliac Tethyan Ocean, later overprinted by the Lower Cretaceous obduction of the Vardar Ocean that rejuvenated Maliac Ocean since the Middle Jurassic.

The Aegean arc is the most prominent Mediterranean salient, characterized by significant paleomagnetic rotations along its limbs. Although it is well‐established that the external Ionian and Kruja zones of the Albano‐Hellenides underwent a ∼40° post‐Oligocene clockwise (CW) rotation relative to Africa/Adria, the rotation timing remains debated. Previous models mainly suggested either two (Miocene and Plio–Pleistocene) rotation episodes, or a single post mid‐Miocene rotation accelerating along time. Uncertainties reflect the contribution from local thrust tectonics and/or strike‐slip faults biasing the regional rotational trend. Here we present new paleomagnetic data from 41 sites located in the virtually continuous Eocene‐Early Pliocene sedimentary sequence of the Tragjasi thrust sheet (Ionian zone, SW Albania). Sampled layers lie on the backlimb of a 50 km‐long anticline subparallel to the regional orogenic trend and away from major strike‐slip faults. Twenty‐eight sites yielded reliable paleomagnetic directions carried by magnetite. The data set includes 15 normal, 11 reverse and 2 mixed‐polarity sites, yielding positive reversal and fold tests. Eocene to early Early Pliocene sediments consistently record a 35° ± 9° CW rotation, demonstrating that rotation in the external Albanides began not earlier than the late Early Pliocene (∼4 Ma). By assuming rigid orogen rotations, we get post‐4 Ma displacements reaching ∼100 km at Vlore and ∼150 km in Crete, corresponding to trench‐retreat rates of ∼3–4 cm/yr. We interpret this rapid, recent rotation as driven by enhanced Ionian slab pull, slab tearing beneath the Albanides, crust coupling across the Kefalonia‐Lefkada Fault, and ultimately westward propagation of the North Anatolian Fault.

The paleomagnetism of Miocene calc‐alkaline volcanics and sediments from Sardinia has firmly showed that the Corsica‐Sardinia microplate rotated 50°–60° counterclockwise (CCW) with respect to Europe between 21 and 15 Ma, during its drift from the Provencal margin. However, Permian to Eocene rocks from central‐south Sardinia revealed higher (up to 120°) CCW rotation values that implied contrasting kinematic models for pre‐Miocene times. Late Permian block rotations, a connection with the Brianconnais and closure of the Valais Ocean, and Oligocene assembly of two Sardinian sub‐microplates of Iberian and European affinity were advocated. In such frame, a total post‐Permian 60° CCW rotation of N Sardinia‐S Corsica was considered a first‐order constraint, given the solid database from Permian dykes and volcanics gathered there. Here we report on the paleomagnetism of 38 sites from Permian, Triassic, Jurassic, and Cretaceous sediments (and one ignimbrite) from Nurra (NW Sardinia). All sites are located on the same crustal sub‐block, thus are pivotal to constrain rotation timing. We find that Lower Triassic to Upper Cretaceous sediments consistently show a ∼90° CCW rotation, whereas Permian data reveal a ∼30° clockwise (CW) rotation occurring in the 290–250 Ma time window. We conclude that the Oligo‐Miocene CCW rotation of a Sardinia‐S Corsica area must be increased to a 90° value, of which 30° occurred before 21–15 Ma microplate drift. The Permian 30° CW rotation occurred 90–50 Myr earlier than Central Atlantic rifting episodes, eventually leading to Pangea breakup. Thus, it unquestionably testifies an intra‐Pangean microplate mobility significantly pre‐dating its fragmentation.

Correlation of ignimbrite units at polygenic calderas is mandatory for the reconstruction of caldera‐forming events and proper identification of their eruption dynamics. However, ignimbrites erupted at different times from the same caldera can display similarities in composition and lithology that can hamper proper correlation of outcrops across the caldera structure. Here, high‐resolution paleomagnetic and ⁴⁰ Ar/ ³⁹ Ar data are used along with stratigraphic evidence to address and resolve the relationships between two ignimbrites associated with the Latera caldera (Grotte di Castro and Onano Formations, Vulsini Volcanic District, Central Italy). These were characterized at 32 paleomagnetic sites and eleven ⁴⁰ Ar/ ³⁹ Ar sampling sites encompassing proximal and distal facies. Overall, the paleomagnetic directions of the two ignimbrites are statistically indistinguishable whereas single‐grain ⁴⁰ Ar/ ³⁹ Ar ages of sanidine and leucite crystals show systematic preservation of pre‐eruptive ages with sectorial variations closely controlled by eruption dynamics, yet with a neatly defined common juvenile (syn‐eruptive) age at 205 ka. The data show that the two ignimbrites are the product of a single event, here renamed the “Grotte di Castro‐Onano” eruption, representing the largest and latest caldera‐forming stage of the Latera system. The sectorial preservation of pre‐eruptive ⁴⁰ Ar/ ³⁹ Ar ages across the depositional sequence is interpreted to reflect the extraction processes with selective (re)mobilization of magma batches associated to piston collapse dynamics. Coupling paleomagnetism with ⁴⁰ Ar/ ³⁹ Ar dating is shown to be a key step in such cases for successful resolution of individual caldera‐forming events at the millennial scale.

The source of high‐intensity magnetic anomalies from (mostly Precambrian) lower crust of continent interiors has long been debated, as it requires speculative rocks yielding 2–6 A/m magnetization. We report on the magnetic and paleomagnetic investigation of the Ivrea‐Verbano Zone (IVZ), Western Alps, where metamorphic and intrusive lower crust rocks of Late Variscan‐Permian ages are exposed. We sampled 39 oriented sites along the Cannobina, Ossola, Strona, and Sesia valleys/sections. Low (0.27–2.1·10⁻³ SI) magnetic susceptibility (k) values were measured in metapelite‐metabasite metamorphic rocks from the Ossola and Strona valleys. There only two metabasite (one amphibolite and one granulite) out of 25 metamorphic sites containing pseudo‐single domain (PSD) magnetite yield 0.48–1.1·10⁻¹ SI k values that remain constant until 550°C heating. K of gabbros‐granodiorites from Sesia valley mimic low values from metamorphic rocks, whereas at Cannobina valley one gabbro and one mafic granulite display values comparable to the two strongly magnetic sites from Ossola/Strona valleys. Peridotite lenses at Balmuccia and Finero similarly yielded low (0.24–5.5·10⁻³ SI) k values, consistently with their low (Q < 1 values imply remanent magnetization subordinate to induced magnetization, (b) paleomagnetic directions from most magnetic sites are scattered, and (c) remanence is unstable at lower crust temperatures. We conclude that IVZ lower crust rocks could not yield magnetic anomalies generated by Precambrian lower crust from continent interiors, and similar conclusions might stand for other Variscan‐age lower crust sections. Scattered high‐intensity metabasites could be candidates, if their PSD magnetite‐rich mineralogy dominated Precambrian lower crust.

The Shkoder‐Peja transverse zone (SPTZ) of Northern Albania marks the boundary between the Dinarides and Albano‐Hellenides and is marked by a ∼100 km SW‐ward shift of the ophiolitic nappe front. The SPTZ has been variably interpreted as a paleogeographic inheritance, a dextral strike‐slip fault, the hinge of the clockwise (CW) rotating Albano‐Hellenides, and a Miocene normal fault. Here we report on the paleomagnetism of 23 Triassic‐Cretaceous sites from the Krasta‐Cukali and Albanian Alps domains, located both within and north of the SPTZ. Six sites yielded only a pre‐tilt magnetization, 14 sites were found to be remagnetized after late Eocene‐Aquitanian tilt, and 3 sites showed both pre‐ and post‐tilt magnetizations. Both pre‐ and post‐tilt paleomagnetic directions yielded a ∼70° CW rotation with respect to Adria/Africa, except 9 sites from the Koman zone at the boundary with the ophiolitic nappe, which record a 38° ± 15° CW rotation. Thus, the well‐known regional CW rotation of the Albano‐Hellenides extends northward in the southern Dinarides, and the SPTZ is not a rotation boundary as previously assumed. The ∼70° CW rotation is interpreted as the sum of a 30° rotation associated with Late Oligocene‐Aquitanian thrusting of the Krasta‐Cukali nappe over the Kruja zone, plus the 40° Miocene‐Pleistocene rotation well‐documented in the external Kruja and Ionian zones of Albania. We suggest that the SPTZ is the heritage of a Lower‐Middle Triassic transform fault of the Maliac Tethyan Ocean, later overprinted by the Lower Cretaceous obduction of the Vardar Ocean that rejuvenated Maliac since the Middle Jurassic.

During the last 20 kyr, the Etna volcano has been characterized by almost continuous summit eruptions and by less frequent—yet definitely more destructive—flank eruptions issuing at <1,000 m asl altitudes and reaching the Ionian Sea. The chronological framework of pre‐historic (pre‐2,750 yr BP) flank eruptions is supported only by few radiometric and paleomagnetic ages. Here we paleomagnetically investigated 15 Holocene lava flows from SE Etna lower slopes and dated 12 of them. Paleomagnetic dating at Etna relies on best method pre‐requisites: European location where reference geomagnetic models are well defined, and detailed stratigraphic evidence is available. We sampled 45 sites (450 oriented cores) from lavas loosely constrained in the 19,000–2,000 yr BP age window. Ten eruptions yielded a minimum 40% refinement with respect to initial age constraints, with four lava flows achieving refinement up to 90%. We obtained 620–1,398 yr (998 yr on average) dating accuracy for three flows bracketed in relatively short (1,398–1,644 yr) independent age constraints. By contrast, five flows characterized by longer 6,567–7,439 yr initial age windows yielded multiple age solutions. Finally, four lava flows with 1,644–6,567 yr‐long initial age windows were tightly dated with 120–680 yr age ranges. We conclude that at volcanoes where best paleomagnetic dating pre‐requisite are fulfilled, singular solutions are expected for 30% of the analyzed flows and, significant refinements for the others. Seven kyr seems to represent an independent age window threshold length to get or not significant dating refinements.

Calabria and the Peloritan Mts. of NE Sicily are exotic terranes predominantly formed by Hercynian rocks interrupting the Meso‐Cenozoic sediments exposed along Apennine‐Maghrebide chains. Dual‐polarity pre‐tilting magnetization direction retrieved from 5 Jurassic, 5 upper Cretaceous‐Eocene, and 4 upper Oligocene sedimentary sites from external‐intermediate Peloritan nappes yield 99° ± 12°, 131° ± 15°, and 138° ± 12° (respectively) clockwise (CW) rotations with respect to Europe. Upper Cretaceous‐Oligocene values are similar to the ∼130° CW late Miocene‐Early Pleistocene rotation previously documented on internal Maghrebian nappes of W Sicily. Jurassic data imply a ∼30° Early Cretaceous counterclockwise (CCW) rotation, similar for sign, magnitude, and timing to Iberia rotation, proving that the Peloritan crust was part of Greater Iberia before its <30 Ma fragmentation and dispersal. Furthermore, 20 Jurassic‐Oligocene sites yield post‐tilting overprint direction (later rotated up to 60° CW) that was acquired synchronous to late Miocene‐Pleistocene rotation. The Peloritan rotation is completely different from the 160° post‐late Jurassic CCW rotation documented on NE Calabria, and demonstrates that the two terranes underwent independent drift histories. Lack of a Sardinian rotation fingerprint (90° CCW between 30 and 15 Ma) suggests that the Peloritan terrane lied S of the Calabria‐Sardinia CCW rotating system, at the non‐rotational apex of an Oligocene‐early Miocene “Paleo Apennine‐Maghrebide Arc.” The Peloritan terrane was stacked onto the African margin and incorporated in the Maghrebian chain in mid Burdigalian (18–17 Ma). Afterward, it formed the S limb of the “Neo Apennine‐Maghrebide Arc,” and was passively carried on top of CW rotating Maghrebide nappes during late Miocene‐Early Pleistocene (12–1 Ma).

We present a multidisciplinary study based on Differential Scanning Calorimetry (DSC), paleomagnetic analysis, and numerical modeling to gain information on the timescales of syn‐ and post‐depositional ductile deformation of the strongly welded and rheomorphic Green Tuff ignimbrite (GT; Pantelleria, Italy). DSC measurements allow the determination of glass fictive temperatures (T_f; i.e., the parameter accounting for the cooling dependence of glass structure and properties). Using a T_f‐based geospeedometry procedure, we infer the cooling rate (q_c) experienced by the glassy phases in different lithofacies within the GT formation. Glass shards from the basal pumice fall deposit record a fast q_c of ∼10°C/s. In contrast, the ignimbrite body returns slow q_c values depending on the stratigraphic position and lithofacies (basal/upper vitrophyres, fiamme‐rich and rheomorphic layers), ranging from ∼10⁻² to ∼10⁻⁶ °C/s. Moreover, paleomagnetic analyses of the natural remanent magnetization of ignimbrite matrix and embedded lithic clasts indicate an emplacement temperature higher than 550–600°C. By integrating calorimetric and paleomagnetic datasets, we constrain a conductive cooling model, describing the ignimbrite's temperature‐time‐viscosity (T–t–η) evolution from the eruptive temperature to below T_f. Outcomes suggest that the upper and basal vitrophyres deformed and quenched over hours, indicating that the entire GT underwent intense syn‐depositional ductile deformation. Furthermore, the central body remained above T_f for a much longer timespan (>1 month), enabling post‐emplacement rheomorphic flow. Lastly, we discuss the critical role of mechanisms such as shear heating and retrograde solubility of volatiles, in locally controlling the rheological behavior of the GT.

It is unanimously acknowledged that the Corsica‐Sardinia microplate rotated counterclockwise (CCW) by 40–50° between 21 and 15 Ma, synchronous with Liguro‐Provençal Basin oceanic spreading. Conversely, 60–120° CCW rotations with respect to Europe from Sardinia (Permian dykes, volcanics and sediments, Mesozoic carbonates, and lower Eocene limestones) have been interpreted to be related to (a) late Permian intra‐Pangea shear events, (b) Aptian Iberia rotation, and (c) Eocene Valais Ocean closure. We report paleomagnetic data from 31 red‐bed sites from the mid‐late Eocene (45–32 Ma) Cixerri Fm. exposed in SW Sardinia. Characteristic paleomagnetic directions from 25 dual polarity sites (240 samples) define an 86 ± 7° CCW rotation. We suggest that a S Sardinia block located NE of Balearic Islands rotated 30° CCW during the 30–21 Ma Liguro‐Provençal rifting, and was decoupled from N Sardinia along the left‐lateral Nuoro fault. After 21 Ma, Corsica‐Sardinia underwent a drift‐related 60° CCW rotation as a whole. A re‐analysis of available paleomagnetic results shows that Permian data from N Sardinia‐Corsica align with European directions considering a 60° CCW rotation, whereas Permian and mid Jurassic data from S Sardinia match European directions only after considering a ∼35° CCW Iberia rotation besides the 90° post‐Eocene event. We suggest that S Sardinia was part of Iberia, and rotated CCW during both Aptian Iberia drift and Oligo‐Miocene Liguro‐Provençal opening. Our data, along with recent paleomagnetic results from Calabria, suggest that S Sardinia, Balearic Islands, Calabria, Peloritan, Kabylies, and Alboran were fragments of “Greater Iberia,” joined to Iberia before 30 Ma Liguro‐Provençal rifting.