Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Structural, metamorphic, and geochronologic work shows that the Ampelos/Dilek nappe of the Cycladic blueschist unit in the eastern Aegean constitutes a wedge of high-pressure rocks extruded during early stages of orogeny. The extrusion wedge formed during the incipient collision of the Anatolian microcontinent with Eurasia when subduction and deep underthrusting ceased and the Ampelos/Dilek nappe was thrust southward over the greenschist-facies Menderes nappes along its lower tectonic contact, the Cycladic-Menderes thrust, effectively cutting out a ∼30- to 40-km-thick section of crust. The upper contact of the Ampelos/Dilek extrusion wedge is the top-to-the-NE Selçuk normal shear zone, along which the Ampelos/Dilek nappe was exhumed by ∼30–40 km. Detailed Rb-Sr and 40Ar/39Ar dating of mylonites demonstrates that both shear zones operated between 42 and 32 Ma. There is no evidence for episodic motion during the ∼10 Myr life span of the shear zones, suggesting that both shear zones operated in a steady, nonepisodic fashion. Our data provide supporting evidence that simultaneous thrust-type and normal sense shearing can accomplish the early exhumation of deep-seated rocks
ISSN: 0278-7407

hal-00405013
https://hal.archives-ouvertes.fr/hal-00405013
DOI : 10.1029/2005TC001872

Éditeur(s) : HAL CCSD Geological Society
Résumé : International audience
We constrain the slip and cooling history of the Mykonos detachment footwall using thermochronometry. A U-Pb zircon age of 13.5 +/- 0.3 Ma dates intrusion of the Mykonos monzogranite. Ar-40/ Ar-39 homblende and biotite ages from the monzogranite are 12.7 +/- 0.6 Ma and 10.9 +/- 0.6 Ma, whereas zircon and apatite fission-track ages range from 13 +/- 0.8 Ma to 10.7 +/- 0.8 Ma and 12.5 +/- 2.2 Ma to 10.5 +/- 1.8 Ma. (U-Th)/He ages range from 13.6 +/- 0.6 Ma to 9.0 +/- 0.7 Ma for zircon and 11. +/- 10.5 Ma to 8.9 +/- 0.4 Ma for apatite. The ages in part overlap within 2 sigma errors and together with the long apatite fission-track lengths (>14 mu m) support rapid cooling at rates > 100 degrees C Ma(-1). The low-temperature thermochronometric ages decrease east-northeastwards in the direction of hanging-wall transport on the Mykonos detachment. Age-distance relationships show that the Mykonos detachment slipped at an average rate of 6.0 + 9.2/-2.4 km Ma(-1) c. 30 km of offset and c. 12 km of exhumation. This result indicates that Miocene low-angle normal faulting was not important for the exhumation of the Cycladic blueschist unit. The opening of the Aegean Sea basin in the Miocene was controlled by a few large-magnitude low-angle normal faults.
ISSN: 0016-7649

hal-00412177
https://hal.archives-ouvertes.fr/hal-00412177
DOI : 10.1144/0016-76492006-145

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Zircon and apatite fission track (ZFT and AFT) and (U-Th)/He, ;40;Ar/;39;Ar hornblende, and U-Pb zircon ages from the granites of Tinos Island in the Aegean Sea, Greece, suggest, together with published ZFT data, that there are three extensional detachments on Tinos. The Tinos granites crosscut the Tinos detachment. Cooling of the granites was controlled by the Livadi detachment, which occurs structurally above the Tinos detachment. Our U-Pb zircon age is 14.6 ± 0.2 Ma and two ;40;Ar/;39;Ar hornblende ages are 14.4 ± 0.4 and 13.7 ± 0.4 Ma. ZFT and AFT ages go from 14.4 ± 1.2 to 12.2 ± 1.0 Ma and 12.8 ± 2.4 to 11.9 ± 2.0 Ma. (U-Th)/He ages are from 10.4 ± 0.2 to 9.9 ± 0.2 Ma (zircon) and 11.9 ± 0.5 to 10.0 ± 0.3 Ma (apatite). All ages decrease northeastward in the direction of hanging wall transport on the Livadi detachment and age-distance relationships yield a slip rate of 2.6 (+3.3 / −1.0) km Ma;−1;. This rate is smaller than a published slip rate of 6.5 km Ma;−1; for the Vari detachment, which is another detachment structurally above the Tinos detachment. Because of the different rates and because published ZFT ages from the footwall of the Vari detachment are ∼10 Ma, we propose that the Vari detachment has to be distinguished from the older Livadi detachment. We discuss various models of how the extensional detachments may have evolved and prefer a scenario in which the Vari detachment cut down into the footwall of the Livadi detachment successively exhuming deeper structural units. The thermochronologic ages demonstrate the importance of quantitative data for constraining localization processes during extensional deformation.
ISSN: 0278-7407

hal-00407638
https://hal.archives-ouvertes.fr/hal-00407638
DOI : 10.1029/2006TC001969