Éditeur(s) : HAL CCSD
Résumé : International audience
Field trip Guidebook, CorseAlp 2011 Meeting of Geology

hal-00604006
https://hal.archives-ouvertes.fr/hal-00604006

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We review the geodynamic evolution of the Aegea-Anatolia region and discuss strain localisation there over geological times. From Late Eocene to Present, crustal deformation in the Aegean backarc has localised progressively during slab retreat. Extension started with the formation of the Rhodope Metamorphic Core Complex (Eocene) and migrated to the Cyclades and the northern Menderes massif (Oligocene and Miocene), accommodated by crustal-scale detachments and a first series of core complexes (MCCs). Extension then localised in Western Turkey, the Corinth Rift and the external Hellenic arc after Messinian times, while the North Anatolian Fault penetrated the Aegean Sea. Through time the direction and style of extension have not changed significantly except in terms of localisation. The contributions of progressive slab retreat and tearing, basal drag, extrusion tectonics and tectonic inheritance are discussed and we favour a model (1) where slab retreat is the main driving engine, (2) successive slab tearing episodes are the main causes of this stepwise strain localisation and (3) the inherited heterogeneity of the crust is a major factor for localising detachments. The continental crust has an inherited strong heterogeneity and crustal-scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation. The dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate. Successive slab ruptures from the Middle Miocene to the Late Miocene have isolated a narrow stripe of lithosphere, still attached to the African lithosphere below Crete. The formation of the North Anatolian Fault is partly a consequence of this evolution. The extrusion of Anatolia and the Aegean extension are partly driven from below (asthenospheric flow) and from above (extrusion of a lid of rigid crust).
ISSN: 0040-1951

insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950
https://hal-insu.archives-ouvertes.fr/insu-00715950/document
https://hal-insu.archives-ouvertes.fr/insu-00715950/file/Jolivet-Aegean_Tectonophysics-2012.pdf
DOI : 10.1016/j.tecto.2012.06.011

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Although subducting slabs undergo a bending deformation that resists tectonic plate motions, the magnitude of this resistance is not known because of poor constraints on slab strength. However, because slab bending slows the relatively rapid motions of oceanic plates, observed plate motions constrain the importance of bending. We estimated the slab pull force and the bending resistance globally for 207 subduction zone transects using new measurements of the bending curvature determined from slab seismicity. Predicting plate motions Using a global mantle flow model, we constrain the viscosity of the bending slab to be at most similar to 300 times more viscous than the upper mantle: stronger slabs are intolerably slowed by the bending deformation. Weaker slabs, however, cannot transmit a pull force sufficient to explain rapid trenchward plate motions unless slabs stretch faster than seismically observed rates of similar to 10(-15) s(-1). The constrained bending viscosity (similar to 2 x 10(23) Pa s) is larger than previous estimates that yielded similar or larger bending resistance (here similar to 25% of forces). This apparent discrepancy occurs because slabs bend more gently than previously thought, with an average radius of curvature of 390 km that permits subduction Of Strong slabs. This gentle bending may ultimately permit plate tectonics on Earth.
ISSN: 0012-821X

hal-00412383
https://hal.archives-ouvertes.fr/hal-00412383
DOI : 10.1016/j.epsl.2008.05.009

Éditeur(s) : HAL CCSD Elsevier
Résumé : The motion of oceanic plates is commonly related to the subduction of cold and dense oceanic material into the mantle. These models predict plate velocities from subduction velocities but the trench motion is not directly included in the computation. Here, using a recent compilation of a global data set, we found that the motion of trenches (either advancing or retreating with respect to upper plates) scales with their corresponding subducting plates motion. Based on simple experimental tests, we found that subduction of strong slabs inside the upper mantle correctly predicts these kinematic relationships. We deduce that the motion of the trenches represent the surface manifestation of the resistance encountered by the subducting lithosphere to bend and penetrate within the upper mantle.
ISSN: 0012-821X

hal-00407200
https://hal.archives-ouvertes.fr/hal-00407200
DOI : 10.1016/j.epsl.2007.02.016

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Recent global kinematic studies reveal that most of the trenches roll back but a significant number of them advance toward the upper plate. Those advancing trenches are mostly located in the Western Pacific and correspond to the subduction of very old, Mesozoic oceanic lithosphere. While retreating trenches are commonly explained by the slab pull action of the descending lithosphere, the origin of advancing trenches is still debated. Since this relationship is dependent upon the adopted reference frame, we select region where geological studies show the variability of trench migration style with time. The Izu-Bonin-Mariana (IBM) region represents a key example. The detailed reconstruction of the trench migration of the IBM subducting system reveals that after a long episode of asymmetric rollback, the IBM trench recently started advancing. We propose that this change from retreating to advancing trench mode results from the subduction of progressively older and stiffer lithospheric material. We test this hypothesis by means of two-dimensional (2-D) numerical models, reproducing the effects of the lithospheric aging during subduction. The result of our numerical tests shows that the entrance of old and stiff lithosphere forces the trench to advance because the increasing stiffness of the slab prevents the slab to unbend once it has subducted. We adapt this physical result to the IBM evolution, showing that the switch from trench retreat to trench advance can reconcile the shape of IBM slab as previously suggested. Finally we discuss the possibility that the subduction of the Cretaceous lithosphere might have triggered the change of the motion of the Pacific plate around 5 Ma.
ISSN: 0012-821X

hal-00455988
https://hal.archives-ouvertes.fr/hal-00455988
DOI : 10.1016/j.epsl.2009.09.042

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Based on global earthquake catalogs, the hypocenters, nodal planes, and seismic moments of worldwide subduction plate interface earthquakes were extracted for the period between 1900 and 2007. Assuming that the seismogenic zone coincides with the distribution of 5.5 <= M < 7 earthquakes, the subduction interface seismogenic zones were mapped for 80% of the trench systems and characterized with geometrical and mechanical parameters. Using this database, correlations were isolated between significant parameters to identify cause-effect relationships. Empirical laws obtained in previous studies were revisited in light of this more complete, accurate, and uniform description of the subduction interface seismogenic zone. The seismogenic zone was usually found to end in a fore-arc mantle, rather than at a Moho depth. The subduction velocity was the first-order controlling parameter for variations in the physical characteristics of plate interfaces, determining both the geometry and mechanical behavior. As such, the fast subduction zones and cold slabs were associated with large and steep plate interfaces, which, in turn, had large seismic rates. The subduction velocity could not account for the potential earthquake magnitude diversity that was observed along the trenches. Events with M-w >= 8.5 preferentially occurred in the vicinity of slab edges, where the upper plate was continental and the back-arc strain was neutral. This observation was interpreted in terms of compressive normal stresses along the plate interface. Large lateral ruptures should be promoted in neutral subduction zones due to moderate compressive stresses along the plate interface that allow the rupture to propagate laterally.
ISSN: 1525-2027

hal-00617681
https://hal.archives-ouvertes.fr/hal-00617681
https://hal.archives-ouvertes.fr/hal-00617681/document
https://hal.archives-ouvertes.fr/hal-00617681/file/heuretG32011.pdf
DOI : 10.1029/2010GC003230