On the dynamics of the Adria plate: a natural laboratory for multiple subduction systems (AdriaLab)
Descrizione
Subduction can occur on both sides of a single plate (outward-dipping double subduction, ODS), leading to the closure of an oceanic basin and the collision of the overriding plates. Recent advances in geodynamic modelling have shown that adjacent subductions interact each other through mantle influencing the slab kinematics and, consequently, the rate of trench migration and plate deformation. These studies have provided fundamental insights into the processes at work in these systems; yet the ODS remains mostly a theoretical model and the dynamics and driving mechanisms controlling its development are poorly constrained. The Central Mediterranean is one of the few settings where the Tertiary and Quaternary dynamics of ODS can be investigated. Here, the Adria plate is deformed and consumed by subduction and collisional processes along the peri-Adriatic mountain belts, two of which with opposite polarity (Apennines and Dinarides). Thus, Adria is a natural laboratory (AdriaLab) where a geodynamic model of a double subduction zone can be tested using geological and geophysical constraints. To unravel the dynamic processes of the Adria ODS, we propose a cross-disciplinary, multi-scale study that merges advanced methodologies in seismology, geophysics, coastal and marine morphotectonic, structural geology, palaeomagnetism, geodesy and geodynamics. We focus on two transects extending from the central Apennines and the southern Apennines-Calabrian Arc to the Dinarides. The project consists of three work packages (WP). The high-quality seismological data, recently made available by the AlpArray initiative and the new data from the AdriaArray network, will provide insights into the crust-mantle structure beneath Adria and surrounding regions (WP1). Newly acquired paleomagnetic data, geophysical data, geodetic measurements and geological constraints will be used to reconstruct the architecture and kinematics of the Adria plate, along key transects, from Tertiary to Present (WP2). The state-of-the-art analogue and numerical geodynamic modelling (WP3) will be implemented through the input of WP1 and WP2 to understand the dynamics of the Adria plate in the framework of its complex plate-tectonic setting. Results will have an important social impact on seismic risk assessment because the investigated transects partly extend over densely populated areas prone to several earthquake related geohazards (e.g., tsunami and landslide).
Finalità
The multi-disciplinary approach is expected to produce for the first time a fully data-driven geodynamic model along two transects crossing the Adria plate and will disclose unsolved geodynamic issues that apply to other convergence zones, such as 1) the role of mantle dynamics and plate interactions in controlling plate deformation and motion, 2) the causes and mechanisms of lateral slab tearing and break-off and their effect on orogenic processes, and 3) the style and scale of mantle convection and their space-time evolution.
This proposal aims to unravel the dynamic processes that shaped the Adria plate by addressing the questions listed in the previous section. We propose a cross-disciplinary project merging advanced methodologies in seismology, geophysics, coastal and marine morphotectonic, structural geology, palaeomagnetism, geodesy and geodynamics to achieve this goal. Objectives of this project are 1) improving the knowledge of the crust-mantle structure and its current physical conditions beneath key sectors of Adria by means of studies exploiting recently acquired seismological data in the frame of two pan-european initiatives, 2) reconstructing the Tertiary to Recent kinematics of Adria along key transects using reflection seismics with different resolution/penetration, modelling and interpretation of paleomagnetic data, structural, stratigraphic and geodetic data, and 3) understanding the evolution and the dynamics of Adria in the framework of its complex plate-tectonic setting through a joint transformative numerical and analogue modelling effort. Each objective is associated with distinct work packages (WP). To maximise the results, all Research Units will actively participate in each WP, whose objectives, tasks and research methods are detailed below.
WP1: REGIONAL-SCALE SEISMIC STRUCTURE AND PHYSICAL PROPERTIES OF THE CRUST-MANTLE SYSTEM
WP2: 3D KINEMATICS OF THE ADRIA PLATE FROM TERTIARY TO PRESENT
WP3: GEODYNAMIC EVOLUTION OF THE ADRIA PLATE: PAST AND PRESENT
Risultati attesi
The WP activities outlined above are finalised toward the same goal: unveiling the dynamics processes beneath and at both sides of the Adria plate. All of them are intimately connected and built to ensure a strong synergy: each activity of a given WP will benefit from and provide constraints to the activities of the other WPs. WP1 will constrain the shallow and deep structure beneath and at both sides of Adria, providing information relative to the present-day geometry of the different slab segments, mantle upwelling, and the current thermal and compositional structure of the crust-upper mantle. WP2 will focus on getting new seismic, geological, morphotectonic, geodetic and paleomagnetic data that will be integrated with paleogeographic constraints to reconstruct the architecture and kinematics of the Adria plate from Tertiary to Present. WP3 will focus on understanding the underlying geodynamic processes through numeric and analogue models accounting for constraints provided by the other two WPs. While the results from each WP will bring specific advancements in knowledge, the integration of the different contributions will lead to a new understanding of the dynamics of the Adria plate, contributing to fundamental aspects related to the surface expression of mantle dynamic processes. Adria will become a natural laboratory where we will iteratively test geodynamic and tectonic models against geological and geophysical data. Specifically, our new cross-disciplinary approach will allow elaborating the first multi-disciplinary, fully data-driven geodynamic model for Adria. Moreover, our approach could be used as a protocol in geodynamic studies addressing the evolution of plates characterised by multiple subduction zones.
We expect that our results will disclose relevant scientific questions whether Adria plate deformation and motion are dominated by plate interactions or by mantle dynamics or both, how lateral slab tears and/or vertical break-off affected past and present-day dynamics, what are the causes of the along-strike changes in the overall architecture of the northern Adria margin, what is the style and scale of mantle convection in the central Mediterranean, and how plates evolved with time.
Results will be published in international journals, while thematic sessions at the annual EGU-AGU meetings will be proposed to stimulate the dissemination of results. Also, project results will be consultable on a dedicated open access website (see Section 3.2).
Stato dell’arte
The descent of oceanic lithosphere into the mantle generates dynamic pressure and mantle flow around the slab that, in the case of multiple, adjacent subduction zones, may perturb the slab kinematics (e.g. Kiraly et al., 2017; Holt et al., 2017). Geodynamic models have investigated the interaction between slabs in double subduction systems, showing how trench and subduction velocity are controlled by interacting subductions (e.g. Holt et al., 2018). These studies have also shown that double subduction systems may provide essential information on the slab–mantle coupling. Despite the relevant progress on modelling, there are still very few cases where predictions can be tested against geologic data. The Central Mediterranean offers the opportunity to investigate the interaction between nearby subduction zones. The Adria plate is locked along three sides by accretionary belts as the Apennines to the west, the Dinarides-Hellenides to the east and the Alps to the north.
Since the late Cretaceous the growth of these orogens has reduced the size of Adria by more than 70% through subduction and underthrusting processes. Thus, Adria represents an ideal test site to unravel the connection between multiple subduction zones and between mantle flow and upper crustal deformation at convergent margins. The deep structure of Adria has been illuminated by regional tomography studies (e.g. Wortel and Spakman, 2000; Piromallo and Morelli, 2003; El‐Sharkawy et al., 2020) that detected several seismically active to inactive slab segments plunging outward beneath the Alps, the North Apennines, Calabria and the Central Dinarides-Hellenides (e.g. Faccenna et al., 2014). However, the detailed 3D geometry of these slab segments and their gaps remain unsolved, hampering our ability to perform quantitative modelling of plate deformation. Specifically, the 50-200 km depth range, crucial for understanding tectonic processes, is ill constrained (Kaestle et al., 2020). In the Dinarides, this is due mainly to the absence of modern high-resolution crustal-to-lithospheric scale geophysics. Similarly, its convergent history, which was probably punctuated by discrete episodes of deformation and lithosphere consumption (e.g. Handy et al., 2015; 2019), needs more quantitative constraints. This complex and undefined pattern of subducting panels in space and time raises essential questions: what is the geometry, extent, and nature of subducted lithosphere along the Adria plate margins? What is the polarity of subducted slabs? How did slab gaps affect past and present-day dynamics?
Adria has been considered a promontory of Africa for most of the Meso-Cenozoic, as documented by fauna exchanges and paleomagnetic data (e.g. Muttoni et al., 2001; Zarcone et al., 2010). Nonetheless, geodesy shows that Adria has attained an independent motion (Battaglia et al., 2004) and is internally deforming (D’Agostino et al., 2008). This implies that during the Neogene, Adria separated from Africa. The location of this new plate boundary is still unclear. Furthermore, internal deformation is accommodated by a poorly understood system of diffuse deformation zones. Currently, Adria is moving to the NE with respect to Eurasia, with increasing velocities moving southward. This differential motion creates large-scale plate tearing, differential subduction mechanics and active strike-slip and transpressional faulting at the transition between Adria and Dinarides. Fundamental questions about the long- and short-term kinematics of the Adria plate are: why does Adria move towards the NE? When did it become independent of Africa? Where is the boundary between Adria and Africa? Why and how is it interior deforming?
The large-scale plate motion, the occurrence of multiple subducting slabs and related mantle dynamics control the kinematics of Adria. The anisotropy pattern from SKS shear wave splitting fast directions indicates a trench parallel, NW-SE orientation beneath the Apennines, turning to N-S beneath the Apennines foreland, and progressively to SW-NE along the Dinarides. The interpretation and model of the anisotropy signal are still elusive due to the limited coverage and resolution in seismic images on the eastern side of Adria, leaving one main question still unanswered: is there a correspondence between crustal and mantle deformation? This overview shows that Adria is a natural laboratory where complex interactions among subducting plate, overriding plates and mantle can be studied. Understanding the Adria motion and internal deformation requires a multi-disciplinary approach integrating deep mantle and crustal-scale data to build a geodynamic, physically consistent model. Thanks to ongoing European initiatives providing unprecedented seismic and geodetic data through a great collaborative effort, this is now timely and feasible.
Riferimento: PRIN 2022 PNRR – Codice progetto: 2022XZ3W22 – CUP: F53D23002260006
Investimento totale del progetto: 309787 €
Partner/proponente: Università degli Studi di CATANIA, Istituto Nazionale Geofisica e Vulcanologia
Coordinatore dell’UdR Università degli Studi Roma Tre: Claudio Faccenna
