Search results for "Tectonic"

Trench-parallel spreading ridge subduction and its consequences for the geological evolution of the overriding plate: Insights from analogue models a…

2018

A series of 3-D asthenospheric-scale analogue models have been conducted in the laboratory in order to simulate the arrival of a spreading ridge at the trench and understand its effect on plate kinematics, slab geometry, and on the deformation of the overriding plate. These models are made of a two-layered linearly viscous system simulating the lithosphere and asthenosphere. We reproduce the progressive decrease in thickness of the oceanic lithosphere at the trench. We measure plate kinematics, slab geometry and upper plate deformation. Our experiments reveal that the subduction of a thinning plate beneath a freely moving overriding continent favors a decrease of the subduction velocity and…

Polyphased mesozoic rifting from the Atlas to the north-west Africa paleomargin

2021

24 pages; International audience; Based on the interpretation of geological maps, seismic reflection and well data complemented with a bibliographic compilation and field work in the Rif, we investigate the factors that control the rift initiation, its development and the formation of oceanic crust in NW Africa. From SE to NW, we examine the Western Sahara Atlas, the Tendrara, the Guercif, and the Rif basins, to establish their geodynamic evolution in relation with the Mesozoic formation of the Central Atlantic and Maghrebian Tethys oceans, respectively. The Triassic extension was diffuse and developed over Lower Carboniferous horst-and-graben structures formed in the NW passive margin of G…

STOP 7: Madona-Trepe ice-marginal ridge at Smeceres sils, East-Latvian Lowland

2014

Fragmentation dynamics within shear bands--a model for aging tectonic faults?

2001

A numerical model for packing of fragmenting blocks in a shear band is introduced, and its dynamics is compared with that of a tectonic fault. The shear band undergoes a slow aging process in which the blocks are being grinded by the shear motion and the compression. The dynamics of the model have the same statistical characteristics as the seismic activity in faults. The characteristic magnitude distribution of earthquakes appears to result from frictional slips at small and medium magnitudes, and from fragmentation of blocks at the largest magnitudes. Aftershocks to large-magnitude earthquakes are local recombinations of the fragments before they reach a new quasi-static equilibrium. The …

The effects of age and emotional valence on recognition memory: An ex-Gaussian components analysis

2014

[EN] The aim of this work was to study the effects of valence and age on visual image recognition memory. The International Affective Picture System (IAPS) battery was used, and response time data were analyzed using analysis of variance, as well as an ex-Gaussian fit method. Older participants were slower and more variable in their reaction times. Response times were longer for negative valence pictures, however this was statistically significant only for young participants. This suggests that negative emotional valence has a strong effect on recognition memory in young but not in old participants. The tau parameter, often related to attention in the literature, was smaller for young than …

Hotspot distribution, gravity, mantle tomography: evidence for plumes

1999

Abstract Thermal convection is the motor of Earth dynamics and therefore is the link between plate motions, hotspots, seismic velocity variations in the mantle, and anomalies of the gravity field. Small scale mantle anomalies, such as plumes, do, however, generally escape detection by tomographic methods. It is attempted to approach the problem of detection in a somewhat statistical manner. Correlations are sought between spherical harmonic expansions of the fields under study: the hotspot distribution, mantle velocity variations, gravity, heat flow. Using spherical harmonic representations of global fields implies integration and averaging over the whole globe. Thus, although relationships…

Outgassing of Mantle Volatiles in Compressional Tectonic Regime Away From Volcanism: The Role of Continental Delamination

2019

In this study we discuss the occurrence of mantle-derived heat and volatiles (i.e., helium and CO 2 ) feeding hydrothermal systems in a seismically active margin between two convergent plates (African and European) without any signals of volcanism. The helium (He) isotopes clearly indicate a mantle-derived component in the outgassing volatiles. The estimated mantle-derived He fluxes are up to two to three orders of magnitude greater than those in a stable continental area. Such high He fluxes cannot be provided by a long-lasting diffusion, thereby implying a more efficient transport (i.e., advective transport through faults). He data coupled to heat-He relationship suggest the occurrence of…

Transfer of mantle derived fluids across the Calabrian-Peloritan arc: tectonic and geodynamic implications

2019

Mantle degassing occurs principally through active volcanic systems and young oceanic lithosphere. Tectonically active regions on the continental crust may additionally contribute a (poorly quantified) fraction of the deep CO2 budget. We studied volatiles in thermal manifestations along the seismically active Nebrodi-Peloritani chains (NE Sicily), to investigate the origin of thermalism and the sources of the outgassing fluids. The geological evolution of the area has been controlled by the interaction between the European and African plates and links the African Maghreb with the European Apennines. The collected samples exhibit 3He excess, supporting active outgassing of mantle-derived vol…

New Evidence of MIS 3 Relative Sea Level Changes from the Messina Strait, Calabria (Italy)

2021

Investigation of sea-level positions during the highly-dynamic Marine Isotope Stage 3 (MIS 3: 29–61 kyrs BP) proves difficult because: (i) in stable and subsiding areas, coeval coastal sediments are currently submerged at depths of few to several tens of meters below the present sea level

Preservation of modern and mis 5.5 erosional landforms and biological structures as sea level markers: A matter of luck?

2021

The Mediterranean Basin is characterized by a significant variability in tectonic behaviour, ranging from subsidence to uplifting. However, those coastal areas considered to be tectonically stable show coastal landforms at elevations consistent with eustatic and isostatic sea level change models. In particular, geomorphological indicators—such as tidal notches or shore platforms—are often used to define the tectonic stability of the Mediterranean coasts. We present the results of swim surveys in nine rocky coastal sectors in the central Mediterranean Sea using the Geoswim approach. The entire route was covered in 22 days for a total distance of 158.5 km. All surveyed sites are considered to…