Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
New estimates of trench migration rates allow us to address the dynamics of trench migration and back-arc strain. We show that trench migration is primarily controlled by the subducting plate velocity V-sub, which largely depends on its age at the trench. Using the hot and weak arc to back-arc region as a strain sensor, we define neutral arcs characterized by the absence of significant strain, meaning places where the forces (slab pull, bending, and anchoring) almost balance along the interface between the plates. We show that neutral subduction zones satisfy the kinematic relation between trench and subducting plate absolute motions: V-t = 0.5V(sub) - 2.3 (in cm a(-1)) in the HS3 reference frame. Deformation occurs when the velocity combination deviates from kinematic equilibrium. Balancing the torque components of the forces acting at the trench indicates that stiff (old) subducting plates facilitate trench advance by resisting bending.
ISSN: 0278-7407

hal-00411731
https://hal.archives-ouvertes.fr/hal-00411731
https://hal.archives-ouvertes.fr/hal-00411731/document
https://hal.archives-ouvertes.fr/hal-00411731/file/Lallemand2008-Tectonics.pdf
DOI : 10.1029/2007TC002212

Éditeur(s) : HAL CCSD Elsevier
Résumé : Upper mantle flow beneath the French Massif Central is investigated using teleseismic shear wave splitting induced by seismic anisotropy. About 25 three component stations (short period, intermediate and broad-band) were installed during the period 1998-1999 in the southern Massif Central, from the Clermont Ferrand volcanic area to the Mediterranean sea. Teleseismic shear waves (SKS, SKKS and PKS) were used to determine the splitting parameters: the fast polarization direction and the delay time. Delay times ranging between 0.7 and 1.5 s have been observed at most of the sites. The azimuths of the fast split shear waves trend homogeneously NW-SE in the southern Massif Central suggesting a homogeneous mantle flow beneath this area. The observed NW-SE direction differs from the N100°E Pyrenean anisotropy further South. It does not appear to be correlated to Hercynian structures nor to the present-day motion of the plate but is well correlated to the Tertiary extension direction. We propose that the opening of the western Mediterranean induced by the rotation of the Corsica-Sardinia lithospheric bloc and the roll-back to the SE of the Tethys slab may have generated a large asthenospheric mantle flow beneath the southern Massif Central and a deflection of the up going plume centered beneath the northern Massif Central toward the SE.
ISSN: 0012-821X

insu-00150214
https://hal-insu.archives-ouvertes.fr/insu-00150214
https://hal-insu.archives-ouvertes.fr/insu-00150214/document
https://hal-insu.archives-ouvertes.fr/insu-00150214/file/Barruol_Granet_EPSL2002_hal.pdf
DOI : 10.1016/S0012-821X(02)00752-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Located on the margin of the west Alboran basin, the Gibraltar Arc (Betic-Rif mountain belt) displays post-Pliocene vertical movements evidenced by uplifted marine sedimentary basins and marine terraces. Quantification of vertical movements is an important clue to understand the origin of present-day relief generation in the Betic-Rif mountain chain together with the causes of the Messinian Salinity Crisis. In this paper, we present the results of a pluridisciplinary study combining an analysis of low temperature thermochronology and Pliocene basins evolution to constrain the exhumation history and surface uplift of internals units of the Rif belt (Northern Morocco). The mean (U-Th)/He apatite ages obtained from 11 samples are comprised between 14.1 and 17.8 Ma and display a wide dispersion, which could be explained by a great variability of apatite chemistries in the analyzed samples. No correlations between altitude and age have been found along altitudinal profile suggesting a rapid exhumation during this period. Thermal modeling using our (U-Th)/He apatite ages and geochronological data previously obtained in the same area (40Ar/39Ar and K/Ar data on biotite, zircon and apatite fission track) allow us to propose a cooling history. The rocks suffered a rapid cooling at 60-100 °C/Ma between 22.5 and 19 Ma, then cooled to temperatures around 40 °C between 19 and 18 Ma. They were re-heated at around 110 °C between 18 and 15 Ma then rapidly cooled and exhumed to reach the surface temperature at around 13 Ma. The re-heating could be related to a renewal in thrusting and burying of the inner zones. Between 15 and 13 Ma the cooling resumed at a rate of 50 °C/Ma indicating an exhumation rate of 0.8 mm/y considering an average 40 °C/km geothermal gradient. This exhumation may be linked to the extension in the Alboran Sea. Otherwise biostratigraphic and sedimentological analysis of Pliocene basins of the internal Rif provided informations on the more recent events and vertical movements. Pliocene deposits of the Rifian coast represent the passive infilling of palaeo-rias between 5.33 and 3.8 Ma. The whole coastal area was uplifted at slow average rates (0.01-0.03 mm/y) in relation with a northeastward tilting of 0.2-0.3° since the Lower-Pliocene. A late Pliocene to present extensional tectonics associated to uplift has been identified all along the coastal ranges of the Internal Zone of the Rif chain. This extension was coeval with the major late Pliocene to Pleistocene extensional episode of the Alboran Sea and appears to be still active nowadays. No significant late Messinian uplift was evidenced, thus calling into question the geodynamic models relating the closure of the marine gateways and the MSC to slab roll back.
ISSN: 0264-3707

hal-01053531
https://hal.archives-ouvertes.fr/hal-01053531
DOI : 10.1016/j.jog.2014.01.006