Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Analysis of short-term deformation along the southern part of Dead Sea Fault (DSF) provides a systematic view of kinematics this part of the continental transform. The southern DSF consists of two principal segments: the Wadi Araba and Jordan Valley faults. In addition to other regional continuous GPS data, this study uses new data from 25 survey sites and 4 continuous GPS stations in Jordan for improved near-field observations. Resulting velocities are reported with 1-sigma uncertainties ranging from 0.4-1.0 mm/yr. Application of elastic dislocation models yields estimates of slip rates for Wadi Araba and Jordan Valley faults are 4.9 +/- 0.4 mm/yr and 4.7 +/- 0.4 mm/yr, respectively. Modeling also suggests different depths of effective fault locking with 15 +/- 5 km and 8 +/- 5 km for the Wadi Araba and Jordan Valley faults, respectively. These slip rates are generally consistent with the upper end of the range of slip rates estimated from late Quaternary geology. Spatial variations in effective fault locking generally correspond with a heterogeneous mantle lithosphere. A similar observation can be observed along the southern San Andreas Fault, and this may reflect the influence of heterogeneity in the uppermost mantle on crustal faulting processes.
ISSN: 1525-2027

hal-00689031
https://hal.archives-ouvertes.fr/hal-00689031
DOI : 10.1029/2011GC003736

Éditeur(s) : HAL CCSD Techno-Press
Résumé : Fractures and faults riddle the Earth’s crust on all scales, and the deformation associated with them is presumed to have had significant effects on its petrological and structural evolution. However, despite the abundance of directly observable earthquake activity, unequivocal evidence for seismic slip rates along ancient faults is rare and usually related to frictional melting and the formation of pseudotachylites. We report novel microstructures from garnet crystals in the immediate vicinity of seismic slip planes that transected lower crustal granulites during intermediate-depth earthquakes in the Bergen Arcs area, western Norway, some 420 million years ago. Seismic loading caused massive dislocation formations and fragmentation of wall rock garnets. Microfracturing and the injection of sulfide melts occurred during an early stage of loading. Subsequent dilation caused pervasive transport of fluids into the garnets along a network of microfractures, dislocations, and subgrain and grain boundaries, leading to the growth of abundant mineral inclusions inside the fragmented garnets. Recrystallization by grain boundary migration closed most of the pores and fractures generated by the seismic event. This wall rock alteration represents the initial stages of an earthquake-triggered metamorphic transformation process that ultimately led to reworking of the lower crust on a regional scale.
ISSN: 2287-528X

hal-01553309
https://hal.archives-ouvertes.fr/hal-01553309
https://hal.archives-ouvertes.fr/hal-01553309/document
https://hal.archives-ouvertes.fr/hal-01553309/file/austrheim2017.pdf
DOI : 10.1126/sciadv.1602067

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present evidence that GPS velocity estimates of plate motions and fault slip rates agree to within uncertainties with geologic estimates during the most recent phase of the geologic evolution of the E Mediterranean region (post-Late Miocene). On this basis, we use the GPS differential velocities to estimate the timing of initiation of the principal structures in NW Turkey, the N Aegean Sea, and central Greece, including, the Marmara Sea, the Gulfs of Evia (GoE) and Corinth (GoC). and the Kephalonia Transform fault (KTF). We interpret these ages to indicate that the North Anatolian fault propagated across the N Aegean, opening the GoE and GoC and initiating the KTF, during the past 1-4 Ma. We further suggest that Aegean extension that was earlier more distributed across the Aegean Basin became focused on this new fault system allowing the southern Aegean and Peloponnisos to translate SW with little internal deformation, as observed today with GPS. This change in tectonic configuration may account for the clear geologic evidence for crustal thinning throughout the S Aegean in apparent contradiction with low present-day strain rates. We further show that the low present-day strain rate along the southern edge of the Aegean micro-plate requires substantial aseismic slip along the plate interface below Crete, consistent with the low level of historic, subduction-type earthquakes along this segment of the subduction zone.
ISSN: 0040-1951

hal-00512634
https://hal.archives-ouvertes.fr/hal-00512634
DOI : 10.1016/j.tecto.2009.05.027

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : International audience
Detailed seafloor mapping in the area east of Taiwan revealed trench-parallel stretching and folding of the Ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence. East of 122ø40'E, a steep accretionary wedge is elongated in an E-W direction. A major transcurrent right-lateral strike-slip fault accommodates the strain partitioning caused by an oblique convergence of 40 ø. A spectacular out-of-sequence thrust may be related to the subduction of a structural high lying in the axis of the N-S trending Gagua Ridge. This asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates. West of 122ø40'E, the low-taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the Ryukyu Arc. The bayonet shape of the southern Ryukyu Arc slope partly results from the recent (re)opening of the southern Okinawa Trough at a rate of about 2 to 4 cm/yr. Right-lateral shearing of the sedimentary forearc with respect to the nonlinear Ryukyu backstop generates trench-parallel extension in the forearc sediment sequence at dilational jogs and trench-parallel folding at compressive jogs. The Hoping Basin lies above a diffuse trench/trench/fault (TTF) or TFF unstable triple junction moving toward the south along a N-S transform zone which accommodates the southward drift of the Ryukyu Arc with respect to Eurasia.
ISSN: 0278-7407

hal-01261555
https://hal.archives-ouvertes.fr/hal-01261555
https://hal.archives-ouvertes.fr/hal-01261555/document
https://hal.archives-ouvertes.fr/hal-01261555/file/Lallemand_et_al-1999-Tectonics.pdf
DOI : 10.1029/1998TC900011

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : International audience
We surveyed the junction between the central and southern Philippine Trench and the Sangihe Trench near 6øN using swath bathymetry, gravity, and magnetics. These data, along with seismicity, allow us to discuss the genetic relations between these trenches and the forces acting on converging plates. Our final model favors the northern extension of the Halmahera Arc up to 8øN, with three segments offset left-laterally along NW-SE transform faults. Accretion of the northern segment to Mindanao Island 4 to 5 m.y. ago resulted in the failure within the Philippine Sea Plate east of the arc. Initiation of the Philippine Trench between 7øN and 10øN agrees with the maximum recorded depth of the Philippine Trench floor (10,000 m below sea-level) and Philippine Sea slab (200 km). South of 6øN (trench junction), another segment of the arc is being subducted beneath the Sangihe margin, while south of 3øN, the southern segment of the Halmahera Arc is still active. The rapid southward shallowing of the trench floor along the southern Philippine Trench, the type of faulting affecting both sides of the trench, the lack of significant interplate seismicity, and the concentration of the seismicity beneath the Miangas-Talaud Ridge are interpreted as a slowing down of the subduction along this branch of the Philippine Trench compared with the rest of the subduction zone. The Sangihe deformation front has been recognized up to 7øN but seems active only south of 6øN.
ISSN: 2169-9275

hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614
https://hal.archives-ouvertes.fr/hal-01261614/document
https://hal.archives-ouvertes.fr/hal-01261614/file/lallemandJGR1998.pdf

Éditeur(s) : Elsevier Sci Ltd
Résumé : The eastern Demerara Plateau offshore French Guiana was surveyed in 2003 during the GUYAPLAC cruise (multibeam bathymetry and acoustic imagery, 6-channel seismic reflection and 3.5 kHz echo-sounding). The data show the "post-transform" Cenozoic that the series located on the outer part of the plateau (below c. 2000 m) contain at least twelve stacked mass transport deposits (MTDs) that have recorded a history of large-scale slope failure, as well as two main normal fault sets that provide possible pathways for upward fluid migration through the series, reaching at high as the uppermost MTDs. Seabed data show that the area above the failures is characterized by circular-to-elongate (slope-parallel) depressions interpreted as fluid seeps (pockmarks), some of them have been modified by along slope currents. We suggest that the development of the MTDs to results from the combinaiton of the presence of fluid overpressure at depth the geometry of the margin's deep structure, in particular the existence of a 'free borderlateral border' on the outermost plateau. Our results also emphasise the role of stratigraphic decollements within the Cenozoic series.
Marine And Petroleum Geology (0264-8172) (Elsevier Sci Ltd), 2013-09 , Vol. 46 , P. 287-303

Droits : 2013 Elsevier Ltd. All rights reserved.
http://archimer.ifremer.fr/doc/00157/26850/25316.pdf
DOI:10.1016/j.marpetgeo.2013.06.010
http://archimer.ifremer.fr/doc/00157/26850/

Éditeur(s) : HAL CCSD AGU and the Geochemical Society
Résumé : International audience
Continental rifts and passive continental margins show fundamental along-axis segmentation patterns that have been attributed to one or a number of different processes: extensional fault geometry, variable stretching along strike, preexisting lithospheric compositional and structural heterogeneities, oblique rifting, and the presence or absence of eruptive volcanic centers. The length and width scales of the rift stage fault-bounded basin systems change during the late evolution of the new plate boundary, and the role of magmatism may increase as rifting progresses to continental rupture. Along obliquely spreading ridges, first-order mid-ocean ridge geometries originate during the synrift stage, indicating an intimate relationship between magma production and transform fault spacing and location. The Gulf of Aden rift is a young ocean basin in which the earliest synrift to breakup structures are well exposed onshore and covered by thin sediment layers offshore. This obliquely spreading rift is considered magma-poor and has several large-offset transforms that originated during late stage rifting and control the first-order axial segmentation of the spreading ridge. Widely spaced geophysical transects of passive margins that produce only isolated 2-D images of crust and uppermost mantle structure are inadequate for evaluation of competing rift evolution models. Using closely spaced new geophysical and geological observations from the Gulf of Aden we show that rift sectors between transforms have a large internal variability over short distances (∼10 km): the ocean-continent transition (OCT) evolves from a narrow magmatic transition to wider zones where continental mantle is probably exhumed. We suggest that this small-scale variability may be explained (1) by the distribution of volcanism and (2) by the along-strike differences in time-averaged extension rate of the oblique rift system. The volcanism may be associated with (1) the long-offset Alula-Fartak Fracture Zone, which may enhance magma production on its younger side, or (2) channeled flow from the Afar plume material along the newly formed OCT and the spreading ridge. Oblique extension and/or hot spot interactions may thereby have a significant control on the styles of rifting and continental breakup and on the evolution of many magma-poor margins.
ISSN: 1525-2027

hal-00504866
https://hal.archives-ouvertes.fr/hal-00504866
https://hal.archives-ouvertes.fr/hal-00504866/document
https://hal.archives-ouvertes.fr/hal-00504866/file/G3-Leroy_al-2010.pdf
DOI : 10.1029/2009GC002963

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H2O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO2 values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge.
ISSN: 0024-4937

insu-00213426
https://hal-insu.archives-ouvertes.fr/insu-00213426
DOI : 10.1016/j.lithos.2007.06.009

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
ISSN: 0956-540X

hal-00789114
https://hal.archives-ouvertes.fr/hal-00789114
DOI : 10.1093/gji/ggs085

Éditeur(s) : HAL CCSD
Résumé : International audience
In orogens, shortening is mainly accommodated by thrusts, which constitute preferential zones for fluid–rock interactions. Fluid flow, mass transfer, and mineralogical reactions taking place along thrusts have been intensely investigated, especially in sedimentary basins for petroleum and uranium research. This study combines petrological investigations, mineralogical quantifications, and geochemical characterizations with a wide range of analytical tools with the aim of defining the fluid properties (nature, origin, temperature, and redox) and fluid–host rock interactions (mass transfers, recrystallization mechanisms, and newly formed synkinematic mineralization) in the Pic-de-Port-Vieux thrust fault zone (Pyrenees, Spain). We demonstrate that two geochemically contrasted rocks have been transformed by fluid flow under low-grade metamorphism conditions during thrusting. The hanging-wall Triassic red pelite was locally bleached, while the footwall Cretaceous dolomitic limestone was mylonitized. The results suggest that thrusting was accompanied by a dynamic calcite recrystallization in the dolomitic limestone as well as by leaching of iron via destabilization of iron oxides and phyllosilicate crystallization in the pelite. Geochemical and physical changes highlighted in this study have strong implications on the understanding of the thrust behavior (tectonic and hydraulic), and improve our knowledge of fluid–rock interactions in open fluid systems in the crust.
Contributions to Mineralogy and Petrology

hal-01575548
https://hal-univ-fcomte.archives-ouvertes.fr/hal-01575548
DOI : 10.1007/s00410-017-1394-5

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We performed forward modelling of seismic anisotropy beneath a migrating strike-slip plate boundary to: (1) test if such a geodynamic context might explain teleseismic shear wave splitting data in the vicinity of the central part of the San Andreas Fault and (2) constrain the power of such data to unravel vertical and lateral variations in deformation patterns in the upper mantle. The modelling involves five steps: (1) thermomechanical modelling, using a finite-element code, of the deformation field, (2) viscoplastic self-consistent modelling of the resulting olivine and pyroxene crystal preferred orientations, (3) calculation of the elasticity tensors for different domains of the finite elements (FEs) model, (4) forward modelling of seismic wave propagation through the model using ray theory, finite-frequency theory and a full-wave approach and (5) performing splitting measurements on the synthetic seismograms. SKS splitting data in central California are best fitted by a model with a hotter geotherm within 60 km of the plate boundary accounting for the opening of an asthenospheric window due to the northward migration of the Mendocino Triple Junction. The westward motion of the plate boundary cannot however explain the rotation of fast polarization directions east of the San Andreas Fault in central California. Comparison between modelled and measured individual shear wave splitting also implies that the homogeneity of the two-layer models accounting for the observations in the vicinity of the San Andreas Fault indicates a sharp transition between lithospheric and asthenospheric deformations beneath this plate boundary. The ability of different synthetic approaches to localize horizontally and vertically the plate boundary-related deformation differs significantly. Splitting in ray theory synthetics closely follow variations in olivine crystallographic preferred orientations in the model. In contrast, splitting analysis on full-wave synthetics, which should be more representative of actual long-period SKS waves, results in smooth apparent lateral variations of anisotropy; the exact location and width of the plate boundary may only be retrieved by comparing fast-polarization profiles obtained using a multichannel analysis on waves with different periods.
ISSN: 0956-540X

hal-01236150
http://hal.univ-reunion.fr/hal-01236150
http://hal.univ-reunion.fr/hal-01236150/document
http://hal.univ-reunion.fr/hal-01236150/file/Bonnin_San_Andreas_modelling_GJI2012.pdf
DOI : 10.1111/j.1365-246X.2012.05650.x

Éditeur(s) : Geological Society of America
Résumé : A seismic-refraction study of the sedimentary structure of the South West African continental shelf was carried out between lat 17°S and 24°S using expendable sonobuoys. Striking differences exist both in the topography and sedimentary structure between the shelf north and south of the Walvis Ridge. South of the ridge, as far as lat 23°S, the shelf consists of a prograded series, whereas north of the ridge, at least as far as lat 17°S, east-trending canyons cut the shelf sedimentary cover. The steep northem scarp of Walvis Ridge can be traced eastward under the sediment of the continental margin. The southern flank of the ridge is buried under a thicker sedimentary cover and could only be traced eastward to long. 10°E on seismic-reflection records. This flank probably parallels the northern scarp under the continental margin. Two-dimensional structural models, built with the help of seismic-retlection and seismic-refraction results and based on the hypothesis of local isostatic equilibrium, account for the obsewed gravity profiles. A compensating root consists of light material (density 2.95 g/cm3) and reaches a depth of about 25 km. Gravity results also suggest that the Walvis Ridge does not constitute a superimposed load on the lithosphere; rather, the ridge and its underlying compensating mass were created at approximately the same time as the adjacent ocean basins. The creation of the two aseismic ridges of the South Atlantic - the Rio Grande Rise and Walvis Ridge - by a mantle hot spot and plume is accepted; this theory seems to explain most of the peculiar features of the Walvis Ridge. However, it is probable that the surface expression of the mantle hot spot was controlled by the presence of weak zones in the lithosphere such as transform faults. [NOT CONTROLLED OCR]
Geological Society of America Bulletin (Geological Society of America), 1975 , Vol. 86 , P. 1713-1724

Droits : Geological Society of America
http://archimer.ifremer.fr/doc/1975/publication-4978.pdf
http://archimer.ifremer.fr/doc/00000/4978/

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Our ability to decipher the mechanisms behind metamorphic transformation processes depends in a major way on the extent to which crystallographic and microstructural information is transferred from one stage to another. Within the Leka Ophiolite Complex in the Central Norwegian Caledonides, prograde olivine veins that formed by dehydration of serpentinite veins in dunites exhibit a characteristic distribution of microstructures: The outer part of the veins comprises coarse-grained olivine that forms an unusual, brick-like microstructure. The inner part of the veins, surrounding a central fault, is composed of fine-grained olivine. Where the fault movement included a dilational component, optically clear, equant olivine occurs in the centre. Electron backscatter diffraction mapping reveals that the vein olivine has inherited its crystallographic preferred orientation (CPO) from the olivine in the porphyroclastic host rock; however, misorientation is weaker and associated to different rotation axes. We propose that prograde olivine grew epitaxially on relics of mantle olivine and thereby acquired its CPO. Growth towards pre-existing microfractures along which serpentinisation had occurred led to straight grain boundaries and a brick-like microstructure in the veins. When dehydration embrittlement induced slip, a strong strain localisation on discrete fault planes prevented distortion of the CPO due to cataclastic deformation; grain size reduction did not significantly modify the olivine CPO. This illustrates how a CPO can be preserved though an entire metamorphic cycle, including hydration, dehydration, and deformation processes, and that the CPO and the microstructures (e.g. grain shape) of one phase do not necessarily record the same event.
ISSN: 0010-7999

hal-01622643
https://hal.archives-ouvertes.fr/hal-01622643
DOI : 10.1007/s00410-017-1378-5

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Alkali feldspar thermochronologic modeling with the 40Ar/39Ar method has generated marked advances in knowledge of the mechanisms for argon diffusion in feldspars. While the goal in many cases has been to extrapolate the observed and modeled argon behavior in feldspars to natural geological settings, scientific debate surrounding the true feasibility of such extrapolations and indeed, the validity of thermochronologic modeling in itself, have provided much impetus to improve laboratory techniques to test, and increase basic understanding of, argon diffusion. Two cornerstones for the debate over the feasibility of alkali feldspar thermochronology for modeling natural, geologic processes have been: 1. is volume diffusion the main mechanism for argon movement in feldspars? and 2. if volume diffusion is a viable mechanism, does argon then reside in discrete ‘domains' within the feldspar lattice? We describe a study of alkali feldspars from a profile through a well-controlled brittle fault zone in western Norway; the feldspars document argon loss during deformation and strongly suggest the existence of argon ‘domains' within the feldspars, at least during laboratory step heating. The progressive change in the character of argon diffusion is recognizable in the logr/ro diffusion data from the feldspars and is mimicked by physical changes observed optically in the feldspars through progressive degrees of brittle deformation. Modeling results indicate a reduction in size of the biggest domains and the appearance of smaller domains during the strongest stages of deformation. Whether or not this reveals the existence and the transformation of the domain structure in naturo is difficult to prove from our data alone, but interestingly, this behaviour corresponds directly to the physical (optical) appearance of more intense crack networks and subgrains in progressively more brecciated feldspars. Because the thermochronologic histories derived from modeling the feldspar data conform very well to the known tectonic history of the area, the feldspars appear to have successfully retained physical (optical and isotopic) records of episodic tectonic processes operating from ductile through lowtemperature brittle regimes in rocks with a Caledonian history overprinted by several later (younger) geologic events. However, because the ‘cold' brecciation is the last tectonothermal event recorded by these rocks, it is impossible to truly test for the existence of diffusion domains in naturo. Argon loss appears to have been effective only in the most highly brecciated (deformed) samples where the combination of the connected crack network, increased fluid flow and higher temperatures enhanced diffusion via fast diffusion pathways and thus, volume diffusion from the lattice. Only minor argon loss occurred in zones of lower brittle strain, although some development of cracks and brittle features is evident. Independent of the existence of diffusion domains, this study highlights the possible pitfalls when cooling histories are deduced from brecciated feldspars in which age and diffusion charateristics have been decoupled: while the geochronological memory has survived and is identical to that of nonbrecciated feldspars (suggesting no loss and minor effects of deformation), the diffusion characteristics have been completely transposed by brecciation and the appearance of new domains. Modeling feldspars with these latter characteristics would effectively utilise a new feldspar diffusion structure with an ‘old' (relict) age memory.
ISSN: 0016-7037

hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283
https://hal.archives-ouvertes.fr/hal-00198283/document
https://hal.archives-ouvertes.fr/hal-00198283/file/KsparBreccia_Arnaud_Eide_GCA_2000.pdf

Éditeur(s) : HAL CCSD
Résumé : International audience
Two opposing visions of the Aegean backarc tectonics implicitly contain contrasting images of the rheological behaviour of the lihosphere, supported by different sets of observations. The propagation of the NAF and extension in the Corinth Rift suggest a strongly localising rheology whereas the formation of MCC in the Cyclades and the Rhodope suggests instead a more viscous behaviour. This paradox was the seminal question addressed by the ANR-EGEO programme (2007-2010) that leads to the following conclusions: (1) The exhumation of the Cycladic MCC's is accommodated by the N-dipping North Cycladic Detachment System (NCDS) that partly reworks the Vardar suture and at the base by a series of thrusts, including the basal contact of the Cycladic Blueschists (CBS) over the Cycladic Basement (CB). The activity of LANF is due to the reactivation of pre-existing discontinuities such as thrusts or earlier detachments and much less to the interaction with granitic plutons. (2) Exhumation in the Cyclades has proceeded in two stages: (a) Eocene syn-orogenic exhumation within the subduction lower/upperplate interface while the post-orogenic Rhodope MCC formed further north, (b) Oligo-Miocene post-orogenic extension in an MCC mode coeval with syn-orogenic exhumation in Crete and the Peloponnese. (3) Both stages were associated with slab retreat, as early as the Eocene with an acceleration at 30-35 Ma. (4) The localisation of the presently active steeply-dipping normal faults on the southern margin of the Corinth Rift may have been preceded by a partial reworking of thrusts and syn-orogenic detachments by shallow-dipping decollements. (5) The localisation of the NAF in the Marmara Sea region and the Northern Aegean Sea is now accurately dated between 5.3 and 5 Ma Ma using the erosion and deposition surfaces that mark the Messinian salinity Crisis and nannofossils ages. (6) The formation of MCCs in the Cyclades resulted in the draining of the low viscosity lower crust from the northern Aegean Sea and led to an easier coupling between upper mantle and upper crust, easing the localisation and propagation of the NAF. (7) A comparison between crustal and mantle finite strain suggests that mantle flow due to slab retreat controls the stretching of the crust. Our model involves progressive slab retreat and mantle flow below the overriding plate inducing the observed succession of tectonic episodes with a progressive localisation of extension due to several slab tearing events. There is no paradox in the tectonic history and rheological behaviour of the Aegean lithosphere but an evolution of the kinematic boundary conditions due to slab deformation at depth.
American Geophysical Union
San Francisco, United States

insu-00860518
https://hal-insu.archives-ouvertes.fr/insu-00860518
BIBCODE : 2010AGUFM.T13G..04J

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy P - Oxford Open Option A Oxford University Press (OUP)
Résumé : International audience
While the kinematics of Anatolia plate and the North Anatolian Fault System (NAFS) has been studied extensively, the slip rate and locking depth along the NAFS are usually assumed constant in the analyses due to the lack of sufficient data. This is also partly due to the reasonably good fit of Euler small circle and partly due to the lack of spatial resolution of observations to determine slip rates independently from locking depths. On the other hand, recent geodetic studies show a contrast for locking depth between Marmara and other parts of the NAFS, implying a non-uniform locking depth across the NAFS. In this study, we analyse new GPS data and homogenously combine available data sets covering the eastern part of the NAFS to form the most complete data set. In particular, we incorporate the first results of Turkish Real-Time Kinematic GPS Network (CORS-TR) into our data set. A detailed analysis of three profiles within the NAFS reveals an increase of locking depth in the middle profile to 19.1 ± 3.4 km from 11.9 ± 3.5 km in the easternmost profile while the slip rate is nearly constant (20–22 mm yr−1), which implies a variation of strain rate of ∼100 nanostrain yr−1. Assuming a constant locking depth throughout whole NAFS gives an average locking depth of 14.3 ± 1.7 km. Our best estimates of slip rates in block modelling which takes the variation of locking depths into account are in the range between 22.5 and 22.8 mm yr−1 over eastern part of the NAFS.
ISSN: 0956-540X

hal-01218392
https://hal.archives-ouvertes.fr/hal-01218392
DOI : 10.1093/gji/ggv274