United States

We present a high-resolution investigation of the Ivrea Geophysical Body (IGB) at intra-crustal scales in the Western Alps. The IGB is a sliver of Adriatic lower lithosphere, located at anomalously shallow depths, and presenting positive gravity and fast seismic anomalies. Despite comprehensive information from previous studies, structural questions persist on the IGB and on its structural relation with the Ivrea-Verbano zone (IVZ), which exposes lower-to-middle crustal composition outcrops at the surface. Therefore, we measured 207 new gravity data points, obtaining a coverage of ca.1 point every 4-to-9 km2 across the IVZ, and we installed 10 broadband seismic stations (IvreaArray) along the linear West-East profile of Val Sesia, operated for 27 months. We compiled a surface rock-density map and used it to define the density-dependent terrain-corrected “Niggli” gravity anomaly to properly model the IGB density structure at depth. We modelled the IGB as a 3D, single density-contrast interface, obtaining 400 kg∙m-3 as optimal density contrast and a 20-km wide protruding structure, as shallow as 1 ±1 km below sea level. The seismic data was then used to constrain the IGB shape along the 2D Val Sesia cross-section by means of a joint inversion of seismic receiver functions and gravity anomaly data. This has confirmed the marked density contrast and shallow segments reaching 1 to 3 km depth below sea level, and provide agreement with the rock’s physical properties (ρ, vS) and the geological structures observed at the surface. These results are now published (doi:10.1093/gji/ggaa263 and doi:10.3389/feart.2021.671412).

SGI 2021

New constraints on the Ivrea Geophysical Body at intra-crustal scales: a combination of gravimetry with passive seismology and rock’s physical properties

**Attenzione, gli orari riportati nel PROGRAMMA (icona calendario) si riferiscono al fuso orario locale dell’utente. Il fuso orario ufficiale del Congresso è Central European Time (CET).**

L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


**Please note, times listed in the SCHEDULE tab (calendar icon) reflect YOUR LOCAL TIME ZONE. The main timezone for this conference will be Central European Summer Time.**

The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


Welcome to the SGI2021 virtual conference.  In order to access the conference and content, [please register for the meeting here](https://www.geoscienze.org/trieste2021/index.php/registrazioni/registrati)

Please register for the SGI conference to join the event.

Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

technical paper

Northeastern Italy is an area characterized by an active tectonic regime with a convergence rate of about 2 mm/yr due to the NNW motion of the Adria plate and its counterclockwise rotation with respect to Eurasia.  The N-S shortening is accommodated by the Southeastern Alps and the External Dinarides, mainly dominated by active thrust-and-fold systems and strike-slip faults (D’Agostino et al., 2005; Serpelloni et al., 2016). In the present study, we exploited the potential of geodetic data to extract information about the surface deformation in response to active tectonics.   We used a Multi-Temporal InSAR approach called Stanford Method for Persistent Scatterers (StaMPS). The technique, based on the detection of coherent and temporally stable pixels in a stack of single-master differential interferograms, allows obtaining mean ground velocity maps. We used Sentinel-1 SAR images acquired in ascending and descending orbits, spanning 2015-2019 temporal interval, as inputs for SNAP2StaMPS and StaMPS software (Foumelis et al., 2018; Hooper et al., 2012). After the PSI processing, we applied spatial-temporal filters and we performed some post-processing operations to obtain reliable PS candidates. We also performed a calibration by using Adria-fixed GNSS velocities to remove orbital ramps and residual atmospheric contributions. Finally, we obtained Line-Of-Sight calibrated mean ground velocity maps for ascending and descending tracks and, after the decomposition, East-West and vertical velocity maps. According to the results, we identify some deformation patterns, potentially related to active tectonics. Towards the Alps, we notice a positive vertical signal reaching about 2 mm/yr. In contrast, the East-West map shows deformation patterns with 1-2 mm/yr rate on the northeastern sector and on the Friulian pedemountain and plain areas. The analysis and the modeling of these signals will clarify the relationship with active tectonics in the study area.

Displacement rate measurement in Northeastern Italy by using PS-InSAR and GNSS data

The Apennines and Dinarides-Hellenides orogens share the same foreland in Apulia (Southern Italy), and in its submerged southeastern continuation in correspondence of the Salento offshore. In this last setting, the two thrust belt fronts of the opposite and converging orogens become very close (up to 150 km) giving rise, in this area, to one of the largest lithospheric anticlines in the world. Through the interpretation of seismic reflection profiles from CROP and ViDEPI projects, the interference between the Hellenides foreland basin and the southern Apennines one on the Apulian swell have been investigated. The results allow to unravel the tectono-sedimentary evolution of the southern segment of the Adria Plate, subducting both toward W-SW and E-NE and producing the two foredeeps that interfere during Quaternary. The deposits of the Hellenides foreland basin migrated towards W-SW at least from the Oligocene due to the E-NEward flexure of the Adria Plate in the northeastern part of the Ionian sea (i.e., on the area of the future Apulian swell). The same area, arching, was involved in the eastward roll-back of Adria Plate at least from the early Pleistocene, and the sedimentary wedge of the south Apennines foreland basin migrated towards E-NE beginning to occupy by the outermost part of the Hellenides foreland basin. From late Early and Middle Pleistocene the area coinciding with the culmination of the arc, where the two opposite foreland basin were interfering, began to uplift during arching, forming the Apulian swell. Starting from this moment, the Apulian swell became a threshold for sediments coming from the two opposite orogens, and two different narrow depocenters, well separated from each other, represent today the Apennines and Hellenides foredeeps, respectively.

Interference between Apennines and Hellenides foreland basins around the Apulian swell (Italy and Greece)

Slovenia and Italy share a number of cross-border active faults. Cross-border faults include the continuation of the Dinaric fault system into Friuli and the continuation of the Adriatic foreland thrust system into the SE Friuli plain and south Alpine thrusts (e.g., Moulin et al., 2016; Atanackov et al., 2021). Seismotectonic characterization, past earthquake activity, and seismic hazard assessment require a holistic approach, encompassing entire faults and fault systems. Constraining past seismicity and linking historic events with causative faults has proven exceedingly difficult (e.g., Bavec et al., 2013; Patricelli & Poli, 2020; Grützner et al., 2021). This is a challenge across various fields of geology, as faults produce a variety of geological expressions, crossing different settings: marine – Gulf of Trieste, alluvial plain in Friuli, Karst and Slovenian Istria. The need for significantly improved cross-border harmonization has been obvious in most recent efforts, including HIKE, ESHM20, and the new seismic hazard map of Slovenia. We will discuss open questions and challenges in joint characterization of cross-border faults and open an invitation for collaboration in future work.

Cross-border challenges in active fault definitions across the Slovenia-Italy border

The northernmost edge of the convergent margin between Eurasia and the Adria microplate is in the area of transition between Eastern Alps and External Dinarides. This area is the most seismically active area of the Alps, and several destructive earthquakes hit this region in historical times. The stress and strain tensor inversions from the focal mechanisms show a complex stress field with a resulting heterogeneous deformation pattern. Here, we present NAC (Northern Adria Crust): a 3D model of the geophysical crustal properties in this area (Magrin, Rossi, 2020). NAC has been built by critically choosing and integrating all available information about the depth of the main interfaces and the physical properties of the crust. We started from a VP dataset, and we converted it in VS and density by using empirical relations, tuned through the comparison with the available data from local tomographic inversion, and considering the lithologies of the area. Uncertainties and reliability of the model are quantified, taking into account the data quality and the interpolation procedure. NAC has two versions, with a different structure of the Moho: the first version considers one continuous surface for the whole area, while the second one implies three separate surfaces for the Adria microplate, Eurasia, and the Pannonian fragment. The differences between the two models are minimal, but the available data better sustain the solution of the fragmented crust. For its characteristics of multiparametric information and resolution, NAC can be precious for any purpose and use, where a detailed knowledge of the crustal structure of this area is required. Moreover, it is easy to improve NAC, including new data on structures or crustal properties. In the last years, new information on the crustal structures became available (e.g., Stipčević et al., 2020; Sadeghi-Bagherabadi et al., 2021). We compare NAC to some of them, in order to discuss its strengths,  limitations, and possible developments.

Deriving a new crustal model of Northern Adria: the Northern Adria Crust (NAC) model

The European Marine Observation and Data Network (EMODnet) is a Project aimed at the collection and harmonization in European Seas of existing data, to be represented on digital maps freely available through a dedicated portal (www.emodnet.eu), in order to facilitate their exchange and re-use. It is subdivided into thematic Lots concerning Bathymetry, Geology, Biology, Chemistry, Physics, Seabed Habitats and Human activities. Each Lot is carried out by a consortium of Institutions collating data for its thematic portal also by means of machine to machine communication. The Geology Lot (www.emodnet-geology.eu) is realized by a Consortium of European Geological Surveys. Information includes data at multiple scale on seafloor sediments grainsize, sedimentation rates, Quaternary geology, pre-Quaternary geology and stratigraphy, coastal behaviour, geological events, mineral resources, submerged landscapes. Metadata and available information collected during the Project are displayed on the Portal. The spatial data, organized in layers, are represented by the geometric primitives lines, points and polygons and the alphanumeric data are stored in harmonized and comprehensive databases, which can be consulted online through Attribute tables. Within the Project a subgroup of Geological Surveys of circum-Adriatic countries (Slovenia, Croatia, Montenegro, Albania and Italy) has been established in order to work together and provide already harmonized products to the Project. Elaboration has been carried out concerning pre-Quaternary units, as required by the Project, as well as pre-Pliocene units, considered by common agreement more meaningful in the Adriatic setting. In addition, other features to be represented were taken into account within the task “Geological events and probabilities”, coordinated by the Geological Survey of Italy – ISPRA. They include submarine landslides, earthquakes, volcanic centres, tsunamis, fluid emissions and Quaternary tectonics. However, the best achievement of the Adriatic group was the realization of a map of sediment grainsize at 1:250,000 scale, obtained thanks to the collaboration of CNR-ISMAR as well. Products elaborated for the entire Adriatic Sea highlight the continuity of geological units, as shown by the map of pre-Quaternary deposits, contribute to understand the geological evolution, as is the case of the map of pre-Pliocene deposits, and to outline sedimentary dynamics, as evidenced by the map of seafloor sediments. Moreover, collation of data across national boundaries allows to analyse in their entirety specific features, such as submarine landslides.

Harmonization of geological data in the Adriatic Sea

The morphology of back-arc basins is tightly linked to the dynamics of their associated subduction zone. Back-arc basins often present multiple spreading centres that form one after the other (e.g. Mariana subduction zone), propagate and rotate (e.g., Lau Basin) following trench retreat. In some cases, rift jumps can create continental fragments or microcontinents (e.g., Coral Sea, Central Mediterranean, Scotia Sea). The Tyrrhenian back-arc basin, in particular, is characterized by the presence of multiple sub-basins and a discontinuous production of new oceanic crust. Moreover, geophysical data show that the basin seafloor is partly made of exhumed serpentinized mantle and local intrusion of magma bodies. All these features reveal a picture of a back-arc basin that is much more complex than that of seafloor spreading at mid-ocean ridges. Importantly, the processes controlling rift jumps and mantle exhumation are still not fully understood, but they are certainly related to the dynamics of subduction and mantle flow. In this work, we show how episodic trench retreat shapes the morphology of back-arc basins and can produce rift jumps. We use the finite element code ASPECT to model the rifting of continental lithosphere in 2D with boundary conditions that simulate the asymmetric type of extension caused by the trench retreat. We perform a parametric study in which we systematically vary the duration of different extensional phases, simulating episodes of trench retreat. Our results show that when extension is continuous, continental break-up occurs and a spreading centre similar to a mid-ocean ridge develops. On the other hand, in models with multiple extensional phases, ridge jumps consistently occur and are often associated with mantle exhumation between the old and the new spreading ridge. This is in good agreement with what observed in Tyrrhenian basin. Timing and length of ridge jumps may depend on rheological properties of the lithosphere, but, importantly, we show that the resulting back-arc basin morphology is controlled by the duration of the different stages of extension.

Ridge jumps and mantle exhumation in the Tyrrhenian back-arc basin

Understanding the evolution and dynamics of the circum-Mediterranean orogens pass through the definition of the deep structure of the crust and upper mantle. Seismological data are the most often used to define the thermal and compositional heterogeneities of the earth. For the broad Alpine belt, there are still many open questions on active processes and on the interaction between adjacent segments of orogens that necessitate high resolution images. In this study, we emphasize some controversial aspects and unknown points from existing tomographic and receiver function models that revealed peculiar processes of delamination/subduction in the Alps and Apennines. We will also focus on data coming from the AlpArray initiative, a huge temporary seismological experiment done in past years, which results are decisive for the definition of the Alps deep structure. In our approach, we investigate Vp and Vp/Vs 3D models that more directly yield to discriminate the origin of mantle anomalies. A very comprehensive dataset of earthquakes recorded by more than 1300 stations during the experiment have been analyzed furnishing precious information. We derive some new aspects of the mantle structure in the central Mediterranean area and discuss some new idea base on the reconnaissance of low velocity and high attenuation portion of the upper mantle.

A look at the deep structure and dynamic of the circum-Mediterranean orogens

Back-arc regions are usually punctuated by pulses of tectonic deformation, lasting for few tens of millions of years. Yet, the origin of those short-lived deformation episodes is disputed. Based on an extensive dataset which compiling structural, stratigraphic, geochemical, and geochronological data from Iran, we propose a kinematic reconstruction of the Central Neotethys since 100Ma. We show that the back-arc region of the central Neotethys subduction zone was affected by alternating pulses of extension and compression, which are linked to episodes of trench retreat and advance, respectively. To back up these observations and investigate the causes of such a trench behavior, we run 2D numerical models exploring (i) the dynamics of subduction into a viscously stratified mantle, and (ii) the deep slab deformation induced by mineral phase changes at the mantle transition zone. Our results indicate that episodes of trench retreat and trench advance emerge spontaneously by slab folding and penetration into the mantle transition zone. Eventually, the results of our physical model guide our interpretation of the Central Neotethys subduction history. We propose a coupled mantle–surface tectonic evolution model of the Central Neotethys slab that reconciles back-arc deformation and short-lived pulses of upper-plate vertical motion in a unique, dynamically self-consistent model of deep mantle subduction.

Slab folding and surface deformation in the Iran mobile beltSlab folding and surface deformation in the Iran mobile belt

The subduction of Neotethys oceanic crust beneath Iranian plate along the southern margin of Eurasia during Mesozoic to Cenozoic resulted in the formation of diffused and prolonged arc magmatism, associated with numerous porphyry/epithermal system (PES) deposits. The PES deposits began during Eocene and show a climax during Miocene times, diachronoulsy distributed from northwest to southwest along the convergent margin during progress of the collisional tectonics. Their space distribution is heterogeneous and show concentrations in zones characterized by occurrence of long-lived and stationary magmatic activity, which are located along major, inherited structural weak zones. There, amphibole-dominated fractionation within the lower crustal magma chambers provided metal- and water-enriched residues, which are the source of the productive magmas. Productive magmas correlates with young TDMNd ages (younger than 0.7 Ga) and 87Sr/86Sr(i) isotopic ratios ranging from 0.704 to 0.706. We propose that the formation of PES deposits is essentially related to a sequence of several processes, among which the most important are: 1) crustal thickening, due both to magma underplating and collisional shortening; 2) continental lithosphere delamination; 3) partial melting of the enriched arc root; 4) magma upwelling facilitated by the presence of crustal weak zones and 4) emplacement of long-lived magma chambers.

A petrotectonic model for the Cenozoic porphyry/epithermal mineralizations along the Iranian tectono-magmatic belt

Orogenic plateaus represent the most spectacular consequence of continental collisions in orogenic belts. The mechanisms related to the growth of an orogenic plateau are still debated and can be the result of multiple tectonic phases and changes in collisional dynamics between the involved plates. In the last decades, the study of landscapes and landforms experienced a significative growth providing new advanced numerical models to relate surface deformation, topographic evolution and plate dynamics. In the Mediterranean area, the Central Anatolian Plateau represents a good example of how different mantle and crustal processes can be involved in building a plateau. The study of the topographic features alongside the plateau margins, such as drainage systems and marine terraces, revealed significantly different uplift histories and mechanisms characterizing the northern and the southern margins. While the northern margin of the plateau experienced vertical uplift from 11Ma ca to the present that can be associated with the transpression along the Northern Anatolian Fault, the southern margin records a fast uplift phase during Pleistocene, causing 1500 km of vertical uplift in about 600.000 years, which has been related to the break-off of the subducting African plate. In our work, we present a summary of how the numerical modeling of the evolution of drainage systems and marine terraces provided significant insights on the uplift history and the topographic evolution of the Central Anatolian Plateau margins, and how these results are linked to the geodynamical processes involving the Anatolian plate boundaries.

Downloads

Next from SGI 2021

Displacement rate measurement in Northeastern Italy by using PS-InSAR and GNSS data

Similar lecture

Exhumation of the HP eclogites from the Acatlán Complex (south Mexico): new insights from retrogressive microstructures

.css-70qvj9{display:-webkit-box;display:-webkit-flex;display:-ms-flexbox;display:flex;-webkit-align-items:center;-webkit-box-align:center;-ms-flex-align:center;align-items:center;}Downloads

Next from SGI 2021

Displacement rate measurement in Northeastern Italy by using PS-InSAR and GNSS data

Similar lecture

Exhumation of the HP eclogites from the Acatlán Complex (south Mexico): new insights from retrogressive microstructures

Downloads