Fabio Corbi

The surface tectonics of mantle lithosphere delamination following ocean lithosphere subduction: Insights from physical‐scaled analogue experiments

Many postulated lithospheric removal events occur in regions with an earlier history of subduction, but the relationship between the two processes has not been explored. In this work, we use physical-scaled analogue experiments to investigate the evolution from ocean lithosphere subduction to collision and possible delamination of the mantle lithosphere from the crust. We test how varying the magnitude of plate convergence alters the behavior of the subduction-delamination model. Our experiments show that a retreating ocean proplate can evolve to continental mantle lithosphere delamination. Negative surface topography is supported at the delamination hinge, and this migrates back with the peeling lithosphere. With high plate convergence, delamination is suppressed. Rather, the crust and mantle lithosphere split at the collision zone in a form of flake tectonics as oncoming procrust is accreted on top of the retroplate and the promantle lithosphere subducts below. Localized high topography develops at this zone of crustal accretion and thickening. The results suggest that delamination may be a continental continuation of plate retreat and that lithospheric removal is triggered by the transition from one process to another.

Vertical movements in the Ionian margin of the Sila Massif (Calabria, Italy)

Detailed geological-geomorphological investigations, carried out in the Ionian coastal belt between the Trionto River and the Colognati River, allowed us to set up a tectonic-sedimentary model of the northern flank of the Sila Massif during Pliocene-Pleistocene times. The study area is characterised by a distinct step-like topography displaying a well-preserved flight of coastal plain (alluvial/marine) terraces, arranged in five altimetric orders (T1 to T5). The deposition of sandy-clayey marine sediments of Middle Pliocene age ( CTSL Unit ) and beach sandstones grading upward to gray silty clays, referred to the Emilian-Sicilian ( Bisciglia Unit ) on the basis of micropaleontological analysis, has been related to a phase of subsidence, likely induced by the activity of E-W trending extensional faults. The Bisciglia Unit grades westward into conglomerates, sandstones and silty-clay sediments forming part of juxtaposed and superimposed deltaic (and subordinate alluvial/beach) deposits. A phase of subaerial landscape modelling, starting from the Middle Pleistocene, marks the end of subsidence and the onset of a rapid uplift which, interacting with eustatic sea-level changes, gave rise to the five orders of terraces. The uplift rate of the whole area, inferred by correlating the terrace surfaces with the paleoclimatic curve proposed by Bintanja et alii (2005), is 0.65 ± 0.1 mm yr −1 . However, the contemporaneous occurrence of extensional fault activity in the area induced variations in the uplift rates, which actually range between 0.52 and 0.88 mm yr _1 in relation to the distance from the fault trace. These data highlight the competing role of fault activity and regional uplift in controlling vertical movements and surface topography at the local scale.

Graben formation and dike arrest during the 2009 Harrat Lunayyir dike intrusion in Saudi Arabia: Insights from InSAR, stress calculations and analog experiments

Detailed spatial and temporal accounts of propagating dikes from crustal deformation data, including their interplay with faulting, are rare, leaving many questions about how this interplay affects graben formation and the arrest of dikes unanswered. Here we use interferometric synthetic aperture radar (InSAR) observations, stress calculations, and analog experiments to investigate the interaction between an intruding dike and normal faulting during the 2009 Harrat Lunayyir dike intrusion in western Saudi Arabia. We generated five displacement maps from InSAR data to unravel the temporal evolution of deformation covering the majority of the intrusion. We find that the observed surface displacements can be modeled by a ~2 m thick dike with an upper tip ~2 km below the surface on 16 May 2009, 4weeks after the onset of seismic unrest. In the following three days, the dike propagated to within ~1 km of the surface with graben-bounding normal faulting dominating the near-field deformation. The volume of the dike doubled between mid-May and mid-June. We carried out analog experiments that indicate that the wedge-shaped graben grew outward with the faulting style changing progressively from normal faulting to oblique. Coulomb failure stress change calculations show that the intruding dike caused two zones of shallow horizontal tension on both sides of the dike, producing two zones of fissuring and normal faulting at the surface. In return, the faulting provoked compression around the upper tip of the dike, holding back its vertical propagation.

Understanding the link between circumferential dikes and eruptive fissures around calderas based on numerical and analog models

Active calderas are seldom associated with circumferential eruptive fissures, but erodedmagmatic complexes reveal widespread circumferential dikes. This suggests that, while the conditions to emplace circumferential dikes are easily met, mechanismsmust prevent them from reaching the surface. We explain this discrepancy with experiments of air injection into gelatin shaped as a volcano with caldera. Analog dikes show variable deflection, depending on the competition between overpressure, Pe, and topographic unloading, Pl; when Pl/Pe=4.8–5.3, the dikes propagate orthogonal to the least compressive stress. Due to the unloading, they become circumferential and stall below the caldera rim; buoyancy is fundamental for the further rise and circumferential fissure development. Numerical models quantitatively constrain the stress orientation within the gelatin, explaining the observed circumferential dikes. Our results explain how dikes propagate below the rim of felsic and mafic calderas, but only in the latter they are prone to feed circumferential fissures.

Geomorphological Map of the Ionian Area between the Trionto and Colognati River Catchments (Calabria, Italy)

Abstract Please click here to download the map associated with this article. This paper describes a geomorphological map representing a sector of the Ionian coastal belt, located in north-eastern Calabria, between the catchments of the Trionto and Colognati Rivers. The landforms have been distinguished according to their origin into: a) structural and tectonic-controlled landforms; b) gravity-induced landforms; c) landforms formed by running water; d) coastal and transitional landforms; e) anthropic landforms, using as support a simplified topographic map on scale 1:20,000. The geomorphological map provides information about the long-term evolution of the landscape and identifies the geomorphic processes presently active. Therefore, the map could be used in developing land management and planning guidelines.

Unraveling Megathrust Seismicity

The majority of global seismicity originates at subduction zones, either within the converging plates or along the plate interface. In particular, events with Mw ≥ 8.0 usually occur at the subduction megathrust, which is the frictional interface between subducting and overriding plates. Consequently, seismicity at subduction megathrusts is responsible for most of the seismic energy globally released during the last century [Pacheco and Sykes, 1992]. Whats more, during the last decade giant megathrust earthquakes occurred at an increased rate with respect to the last century [Ammon et al., 2010], often revealing unexpected characteristics and resulting in catastrophic effects. Determining the controlling factors of these events would have fundamental implications for earthquake and tsunami hazard assessment.

How Subduction Interface Roughness Influences the Occurrence of Large Interplate Earthquakes

The role of seafloor roughness on the seismogenic behavior of subduction zones has been increasingly addressed over the past years, although their exact relationship remains unclear. Do subducting features like seamounts, fracture zones, or submarine ridges act as barriers, preventing ruptures from propagating, or do they initiate megathrust earthquakes instead? We address this question using a global approach, taking into account all oceanic subduction zones and a 117-year time window of megathrust earthquake recording. We first compile a global database, SubQuake, that provides the location of a rupture epicenter, the overall rupture area, and the region where the largest displacement occurs (the seismic asperity) for M W ≥ 7.5 subduction interplate earthquakes. With these data, we made a quantitative comparison with the seafloor roughness seaward of the trench, which is assumed to be a reasonable proxy for the subduction interface roughness. We compare the spatial occurrence of megathrust ruptures, seismic asperities, and epicenters, with two roughness parameters: the short-wavelength roughness R SW (12-20 km) and the long-wavelength roughness R LW (80-100 km). We observe that ruptures with M W ≥ 7.5 tend to occur preferentially on smooth subducting seafloor at long wavelengths, which is especially clear for the M W > 8.5 events. At both short and long wavelengths, seismic asperities show a more amplified relation with smooth seafloor than rupture segments in general. For the epicenter correlation, we see a slight difference in roughness signal, which suggests that there might be a physical relationship between rupture nucleation and subduction interface roughness. Plain Language Summary Subduction zones are regions on Earth where an oceanic plate dives below another plate. Earthquakes that occur along the contact between plates in such regions are among the largest and most destructive on Earth. To better understand where these large earthquakes are most likely to occur, we look at the effect of seafloor roughness. A rough seafloor is often characterized by many topographic features, such as seamounts or ridges, while a smooth seafloor is generally more flat. On a global scale, we compared the roughness of the incoming seafloor of the downgoing plate, with the occurrence of large earthquakes in each subduction zone. We find that the seafloor in front of large earthquakes is generally smoother than in areas where no large earthquakes have occurred. This is the clearest for very large earthquakes, with magnitudes larger than 8.5. Investigating which parameters play a role in the location of earthquakes helps us to understand where future earthquakes are more likely to occur.

Experimental Tectonics: Convergent Margins from a Lithosphere–Mantle Perspective

Experimental modeling is a methodology used for a wide range of scientific applications, including the study of tectonic processes. This contribution is devoted to provide an overview of laboratory models realized to understand the physics behind the behavior of convergent margins at the mantle scale, focusing on the overall process controlled by the lithosphere–mantle interaction.