Aegean extension began during Eocene-Oligocene times and led to the thinning of the upper plate into a retreating slab system. The style of extension during the Miocene remains controversial, with a majority of studies arguing for extension accommodated by low-angle extensional brittle-ductile faults, called detachments. In other hands, the present-day active seismic faults in the Aegean Sea are only high-angle normal faults and dextral strike-slips. We aim to constrain and date the style of faulting in central Greece by combining analysis of 19 offshore seismic lines with onshore structural observations on Syros Island and LA-ICP-MS U-Pb dating of calcite sampled in two major fault zones of Syros (Palos and Fabrika faults). Three main sets of faults have been identified in the Central Cyclades: NW-SE trending normal faults, NNW-SSE oblique (sinistral)-normal faults, and NNE-SSW trending dextral strike-slip faults. High-angle normal faults define regularly spaced horsts and grabens, suggesting a wide rifting-type of extension. Dextral strike-slip faults occur at Syros, mainly offshore, and are kinematically compatible with normal faults. U-Pb dating of calcite crystallizing in normal fault planes at Syros yields ages at c.a. 10 Ma for high-angle normal faults activity. On these bases, we propose that wide rifting with high-angle normal faults accommodated Aegean extension when trench retreat accelerated in the middle to late Miocene. At this time, dextral strike-slip faults formed as a response of the onset of Anatolia lateral extrusion.
Abstract The present‐day Aegean tectonic configuration is marked by the interplay between Hellenic slab rollback and Anatolian extrusion, explaining the formation of extensional basins and dextral strike‐slip faults. We aim to constrain middle Miocene activity of dextral strike‐slip and normal faults in Central Greece with structural analysis and low‐temperature data. We show that onshore middle Miocene basins are controlled by both NW‐striking normal faults and NE‐striking dextral strike‐slip faults. E‐striking normal faults developed during the Plio‐Quaternary inside pre‐existing NW‐striking fault zones. Stress tensor calculations show that in the middle Miocene, NW‐striking normal faults and NE‐striking dextral faults are compatible, confirming their coeval activity. In contrast, the Plio‐Quaternary stress tensor suggests an almost N‐S radial extension, which is not compatible with NE‐striking dextral faults in Central Greece. Apatite fission‐track data additionally constrain middle Miocene local cooling near NW‐striking normal faults. They also support a difference in the amount of exhumation between Central Greece and the Cyclades, likely accommodated by the Pelagonian dextral strike‐slip fault. We propose that in the middle Miocene, the co‐existence of dextral strike‐slip and normal faults is associated with an almost N‐S extension related to trench retreat and an E‐W compression related to westward extrusion of Anatolia. The progressive trench curvature during rollback implies block rotation, accommodated by the Pelagonian fault, and subsequent normal fault and extensional stress rotation. During the Plio‐Quaternary, a change in extensional direction from NE‐SW to N‐S implies the formation of E‐striking normal faults inside NW‐striking fault zones, defining oblique rift systems.
Abstract. During gravitational collapse of orogenic systems or in hot extending back-arc systems, normal faulting is often associated with strike slip faulting whose origin remains enigmatic. The formation of major strike slip fault zones during subduction upper plate extension driven by slab-roll back can be related to slab tearing at depth. In the Aegean, where back-arc extension driven by southwest-ward migration of the Hellenic trench (slab rollback) has occurred since at least 30 Ma, the co-existence of normal faulting and a multiple strike-slip fault zones is observed since the onset of the westward extrusion of Anatolia, but before the onset of slab tearing that occurs in the Pliocene. Here we show how strike slip faults and normal faults can coexist in a hot deforming continental lithosphere. Our 3D numerical models with two deformation stages (initial pure extension followed by combined shortening and extension) can explain the Aegean tectonics. Several rifts form during the purely extensional stage that, during the second deformation stage, are either fully reactivated as strike-slip faults, or remain active but rimmed by dextral and sinistral strike-slip faults. This suggests that the extension driven by slab rollback and shortening driven by westward extrusion of Anatolia interact in space and time in the Aegean domain to create a complex tectonic pattern with coeval active normal faulting (e.g. Corinth and Evvia rifts) and dextral strike-slip faulting (e.g. the North Anatolian and Myrthes-Ikaria faults). These results show that strike slip faults in extending domain can be a sign of shortening at high angle to the extension direction.
Abstract. During gravitational collapse of orogenic systems or in hot extending back-arc systems, normal faulting is often associated with strike slip faulting whose origin remains enigmatic. The formation of major strike slip fault zones during subduction upper plate extension driven by slab-roll back can be related to slab tearing at depth. In the Aegean, where back-arc extension driven by southwest-ward migration of the Hellenic trench (slab rollback) has occurred since at least 30 Ma, the co-existence of normal faulting and a multiple strike-slip fault zones is observed since the onset of the westward extrusion of Anatolia, but before the onset of slab tearing that occurs in the Pliocene. Here we show how strike slip faults and normal faults can coexist in a hot deforming continental lithosphere. Our 3D numerical models with two deformation stages (initial pure extension followed by combined shortening and extension) can explain the Aegean tectonics. Several rifts form during the purely extensional stage that, during the second deformation stage, are either fully reactivated as strike-slip faults, or remain active but rimmed by dextral and sinistral strike-slip faults. This suggests that the extension driven by slab rollback and shortening driven by westward extrusion of Anatolia interact in space and time in the Aegean domain to create a complex tectonic pattern with coeval active normal faulting (e.g. Corinth and Evvia rifts) and dextral strike-slip faulting (e.g. the North Anatolian and Myrthes-Ikaria faults). These results show that strike slip faults in extending domain can be a sign of shortening at high angle to the extension direction.
La plaque Egeenne est un systeme geodynamique complexe marque depuis le Miocene, par l’interaction entre le recul de la fosse Hellenique et le debut de l’extrusion Anatolienne. Au Plio-Quaternaire, une torsion de la plaque plongeante a l’Ouest du domaine Egeen et la propagation vers l’Ouest de la Faille Nord Anatolienne, compliquent davantage le systeme. Les interactions entre ces phenomenes et leurs deformations presentent des zones d’ombre. Il existe notamment un large systeme de failles NE-SO dont le role et les caracteristiques sont encore peu etudies et qui ne sont pas incluses dans la geodynamique du systeme Egeen. Le but de cette these est de comprendre le role de ces decrochements NE-SO dans la tectonique Egeenne depuis 15 Ma et en particulier dans la region Eubee/Attique. Une caracterisation multi-echelle de la deformation de cette region a ete effectuee au travers de l’acquisition de nouvelles donnees de terrain, de traces de fission sur apatite, de fonctions recepteur et de modelisations numeriques lithospheriques 3D de la deformation. Les nouvelles donnees de terrain caracterisent une cinematique decrochante dextre sur la faille NE-SO Pelagonienne. Elle controle, avec les failles normales NO-SE, le depot de bassins Miocenes, suggerant une activite concomitante des failles normales et des decrochements a cette epoque. Nous proposons que la faille Pelagonienne accommode les rotations de blocs au Miocene. L’inversion des contraintes a partir des donnees de stries sur les failles montre une compatibilite des failles normales et decrochantes associee a une extension evoluant de N-S a NE-SO (durant la rotation des blocs) et une compression E-O. Au Plio-Quaternaire, une modification de la direction d’etirement induit la formation de nouvelles failles normales E-O se developpant a l’interieur des zones de failles NO-SE preexistantes, devenues senestres. Ces systemes de failles forment des rifts obliques et sont associes a une extension N-S radiale incompatible avec l’activite des failles NE-SO. Nous supposons que ce changement est lie a l’evolution de la torsion de la plaque plongeante. Les âges traces de fission sur apatite montrent une difference d’âge d’exhumation entre la Grece Centrale et les Cyclades. Nous proposons ainsi que la faille Pelagonienne accommode une extension differentielle au Miocene entre les Cyclades et la Grece Centrale, respectivement fortement et faiblement etirees a cette epoque. Des âges basse temperature Miocenes provenant des murs de failles normales NO-SE semblent confirmer leur activite au Miocene, concomitante de l’activite de la faille decrochante Pelagonienne. Nos nouvelles donnees de fonctions recepteur quantifient aussi une extension differentielle en caracterisant un Moho plus profond sous la Grece Centrale (26,5 km) que sous les Cyclades (25 km) et les Sporades (24,3 km). Une analyse du pendage et de la perturbation du signal sismique suggere que la transition entre la Grece Centrale et les Cyclades se produit dans une zone etroite, limitee par les failles NE-SO dextres Pelagonienne et Sud-Eubee. Entre la Grece Centrale et les Sporades, ce saut de Moho est accommode par une faille normale a fort pendage. L’extension differentielle est donc lateralement accommodee par ces failles crustales, mais aussi par la deformation interne des blocs qu’elles delimitent. Ces nouvelles donnees montrent l’importance des failles decrochantes dans la geodynamique Egeenne depuis le Miocene. Elles accommodent le raccourcissement E-O et definissent differents blocs qui tournent durant l’extension arriere-arc. Enfin, nos modeles 3D montrent qu’une extension et une compression horizontales et orthogonales a taux egaux causent la formation de decrochements dans une lithosphere continentale chaude. Ces modeles suggerent que l’activite contemporaine de l’extension, liee au recul de la fosse Hellenique, et de la compression, reliee a l’extrusion Anatolienne, peut expliquer la formation des decrochements en Egee.
<p>Aegean plate is marked since Eocene by widespread NE-SW extension induced by the African slab roll-back. In Miocene times, E-W shortening created by the westward Anatolian extrusion overlays the extension, with the formation of Miocene dextral strike slip faults in addition to normal faults. We propose to quantify the role of large dextral strike slip faults in accommodating Aegean extension, using receiver functions to image Moho geometry.</p><p>Aegean extension is particularly evidenced by a topographic difference between the emerged continental Greece and the submerged Cyclades. In this study we characterize the associated Moho geometry with a particular focus on the transition between these two domains. From a geological point of view, the transition between continental Greece and the Cyclades is marked by two dextral strike slip faults: the Pelagonian fault (onshore) and the South Evvia fault (offshore). Our objective is also to show a potential Moho signature of these strike slip faults. &#160;We processed receiver functions (RF) from the MEDUSA stations located in Attic and Evvia.</p><p>Our results show that the Moho is deeper beneath continental Greece (~27km) than beneath the Cyclades (~25km). A detailed azimuthal study of RF distribution shows a flat Moho underneath Continental Greece. The crustal thickness is also almost constant inside the Cyclades, as already suggested by previous studies. However, the transition between the Cyclades and Continental Greece is not continuous. These two crustal blocks are separated by the Pelagonian and the South Evvia strike slip faults in a narrow transition zone (~75km). In this zone (South Evvia/Attica), dip and strike of the Moho vary and suggest a crustal signature of the strike slip structures observed at the surface. These strike slip faults therefore accommodate in a narrow zone the inferred variations in crustal thicknesses between the Cyclades and Continental Greece.</p><p>Our data show that differences in topography between Continental Greece and the Cyclades are isostatically compensated, reflecting various amount of crustal thinning larger in the Cyclades than in Continental Greece. Inside these two crustal blocks, we imaged a flat Moho, suggesting a wide rift extension process associated with the formation of numerous Miocene and Plio-Quaternary basins. &#160;The dextral strike slip faults at the edges of the continental blocks (Continental Greece and Cyclades) accommodated the inferred variations in the amount of crustal thinning, suggesting that they act as continental transfer zones at crustal-scale during Miocene Aegean Extension.</p>
