Tectonics of the Syros blueschists (Cyclades, Greece): From subduction to Aegean extension

On Syros, high‐pressure metamorphism affects a lithological pile that is composed of, from base to top: (1) the Komito‐Vari granitic basement, (2) a margin sedimentary sequence that is predominantly made of marbles and schists (the Pyrgos and Kastri units), and (3) the Kambos metaophiolitic mélange. The tectonic history occurred in three main stages. During the first stage, in the mid‐Eocene, the Kambos oceanic unit was thrust southward on top of the sedimentary pile. Top‐to‐the‐south‐southwest ductile senses of shear are synchronous with prograde high‐pressure metamorphism and associated with this thrusting event. The second stage corresponds to a top‐to‐the‐northeast ductile shear that affects the whole metamorphic pile and is synchronous with the metamorphic retrogression from eclogite to greenschist facies. However, the Kambos oceanic unit remained partly undeformed, as shown by significant volumes containing undeformed lawsonite pseudomorphs. No major extensional detachment related to this exhumation event outcrops on the island. The localized semibrittle to brittle deformation of the third stage is associated with the postmetamorphic development of (1) a ramp‐flat extensional system at the island scale, whose southward minimum displacement is estimated at approximately 7 km, and (2) two sets of steeply dipping strike‐slip faults with a normal component, trending either east–west or around north–south, indicating that the mean stretching and shortening directions are trending NNE–SSW and ESE–WNW, respectively. This sequence of major tectonic events and their relationship to metamorphism are interpreted within the framework of the subduction of the Pindos Ocean and then of the Adria continental passive margin

The interaction between Aegean back-arc extension and Anatolia escape since Middle Miocene

International audienceThe Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Lithosphere-scale analogue models were employed to display that the overall pattern of Aegean extension requires not only the combination of trench retreat and Anatolia escape since middle Miocene but also the presence of an inherited lithosphere-scale mechanical discontinuity: the Vardar Suture Zone (VSZ). The reactivation in dextral shear of the eastern branch of the VSZ accommodates both the trench retreat (NS stretching) and the westward escape of Anatolia (EW shortening) in the Cyclades area since middle Miocene. Additionally, our model shows that the North Anatolian Fault (NAF) is a late structure in the evolution of the Aegean, initiated around 10 Ma after the onset of Anatolia escape. The displacement field at the surface of the model allows the identification of sub-domains, which result from strain partitioning instead of being "rigid microplates", directly comparable to the present-day displacement field (GPS) of the Aegean and western Anatolia. Our model provides a simple but powerful way to look at the dynamics of Aegean extension in two main stages. From middle Eocene to middle Miocene, extension was only driven by the southward retreat of the Hellenic trench at a rate lower than 1 cm*y− 1. Since middle Miocene, the combination of slab rollback with Anatolia westward escape resulted in a southwest direction of trench retreat, with an accelerating rate of up to 3 cm*y− 1

Deformation mechanisms in a continental rift up to mantle exhumation. Field evidence from the western Betics, Spain

International audienceThe identification of the structures and deformation patterns in magma-poor continental rifted margins is essential to characterize the processes of continental lithosphere necking. Brittle faults, often termed mantle detachments, are believed to play an essential role in the rifting processes that lead to mantle exhumation. However, ductile shear zones in the deep crust and mantle are rarely identified and their mechanical role remains to be established. The western Betics (Southern Spain) provides an exceptional exposure of a strongly thinned continental lithosphere, formed in a supra-subduction setting during Oligocene-Lower Miocene. A full section of the entire crust and the upper part of the mantle is investigated. Variations in crustal thickness are used to quantify crustal stretching that may reach values larger than 2000% where the ductile crust almost disappear, defining a stage of hyper-stretching. Opposite senses of shear top-to-W and top-to-E are observed in two extensional shear zones located close to the crust-mantle boundary and along the brittle-ductile transition in the crust, respectively. At locations where the ductile crust almost disappears, concordant top-to-E-NE senses of shear are observed in both upper crust and serpentinized mantle. Late high-angle normal faults with ages of ca. 21 Ma or older (40Ar/39Ar on white mica) crosscut the previously hyper-stretched domain, involving both crust and mantle in tilted blocks. The western Betics exemplifies, probably better than any previous field example, the changes in deformation processes that accommodate the progressive necking of a continental lithosphere. Three successive steps can be identified: i/a mid-crustal shear zone and a crust-mantle shear zone, acting synchronously but with opposite senses of shear, accommodate ductile crust thinning and ascent of subcontinental mantle; ii/hyper-stretching localizes in the neck, leading to an almost disappearance of the ductile crust and bringing the upper crust in contact with the subcontinental mantle, each of them with their already acquired opposite senses of shear; and iii/high-angle normal faulting, cutting through the Moho, with related block tilting, ends the full exhumation of the mantle in the zone of localized stretching. The presence of a high strength sub-Moho mantle is responsible for the change in sense of shear with depth. Whereas mantle exhumation in the western Betics occurred in a backarc setting, this deformation pattern controlled by a high-strength layer at the top of the lithosphere mantle makes it directly comparable to most passive margins whose formation lead to mantle exhumation. This unique field analogue has therefore a strong potential for the seismic interpretation of the so-called “hyper-extended margins”

Mechanisms of remanent optical alignment of dyes in a gel matrix

International audienceWe present the mechanisms of a remanent alignment of polarizable molecules dispersed in a solid silica gel matrix, when submitted to powerful, femtosecond, linearly polarized, optical pulses emitted from a dye laser. This alignment can be related to third-order nonlinearities of the dopants through an orientational optical Kerr effect. Its remanence results from the strong interactions the dopants share with their host matrix, particularly through hydrogen bonds. We expose here the detailed mechanism of this phenomenon, considering that such a rotation of large chromophores may not be compatible at first sight with subpicosecond pulse durations. Through several experiments, we show that this apparent contradiction is solved once analyzed, by the structure of the excitation pulses, which cannot be simply described as ''femtosecond pulses'', but consist of two temporal components--a femtosecond one and a nanosecond one--playing different but essential roles in the proces

Perylene and pyrromethene doped xerogels for solid state pulsed laser

International audienceHydrophobic photostable dye molecules such as perylenes or pyrromethenes were trapped in xerogel matrices. Using these new materials as solid-state dye lasers, we have demonstrated efficient laser operation. Slope efficiencies of up to 30% were obtained in the millijoule output-energy range. Tunabilities of up to 60 nm were observed, and more than 150,000 pulses were emitted by the same spot of a given sample when the laser was pumped at millijoule energy level

Toward millions of laser pulses using pyrromethene and perylene doped xerogels

International audienceSignificant improvements have been obtained for solid-state dye lasers with doped xerogels. By using longitudinal pumping with a frequency-doubled Q-switched Nd: YAG laser, we obtained as much as 86% slope efficiency and 5 3 105 pulses lifetime. Furthermore, newly prepared deoxygenated samples exhibited even greater lifetime

Upper Cretaceous exhumation of the western Rhodope Metamorphic Province (Chalkidiki Peninsula, northern Greece)

International audienceThe Vertiskos Unit of northern Greece is an elongated basement belt with a complex poly-metamorphic history. It extends from Greece (Chalkidiki peninsula), to the south, up to Serbia, in the north, and arguably represents the westernmost part of the Rhodope Metamorphic Province (northern Greece to southern Bulgaria). The Vertiskos Unit experienced a medium pressure lower amphibolite-facies metamorphic overprint during the Alpine Orogeny. The available medium-temperature geochronology implies that it remained at temperature of approximately 300°C (or slightly higher) during Lower Cretaceous. In order to constrain its post-Lower Cretaceous thermal history, until near-surface exposure, we applied apatite fission track analysis. The central ages obtained range from 68.5 ± 3.8 to 46.6 ± 3.6 Ma (uppermost Cretaceous to Middle Eocene) and mean track lengths between 13 and 13.5 μm. We applied two inverse thermal modeling approaches using either each sample independently (high degree of freedomin the thermal history, better data fit) or all samples together interpreting them as a vertical profile (simpler thermal history, worse data fit). Irrespective of the modeling approach, we conclude that the bulk thermal history of the Vertiskos Unit crosses the high-temperature limit of the apatite partial annealing zone by the uppermost Cretaceous and reaches near-surface conditions as early as lower/middle Eocene. These results contrast with the thermal history of the other domains of the Rhodope Metamorphic Province further east (namely the Southern Rhodope Core Complex and the Northern Rhodope Complex) and establish the Vertiskos basement complex as the oldest exhumed coherent basement fragment of the Rhodope Metamorphic Province and Greece

Neoadjuvant chemotherapy or primary surgery for stage III/IV ovarian cancer: contribution of diagnostic laparoscopy

<p>Abstract</p> <p>Background</p> <p>The aims of this retrospective study were to evaluate laparoscopic triage of patients with advanced ovarian cancer towards primary surgery or neoadjuvant chemotherapy, and to analyze outcome according to the treatment.</p> <p>Methods</p> <p>Between January 2001 and December 2006, 55 patients with stage III – IV ovarian cancer underwent diagnostic laparoscopy. Primary surgery was performed when complete cytoreduction was considered feasible, while the other patients received neoadjuvant chemotherapy (platinum-based combination with taxanes) and interval surgery. All the patients received adjuvant chemotherapy.</p> <p>Results</p> <p>Patients treated with neoadjuvant chemotherapy (n = 29) had a higher mean body mass index (P = 0.048), higher serum CA 125 levels (P = 0.026), and more metastases (P = 0.045) than patients treated with primary surgery (n = 26). In patients treated with primary surgery, complete cytoreduction and a residual tumour size ≤ 2 cm were obtained in respectively 54% and 77% of cases. Complete cytoreduction was achieved in respectively 100% and 33% of cases when primary surgery was performed by an oncologic gynaecologist and by a non-oncologic gynaecologist (P = 0.002). Interval surgery yielded complete cytoreduction and a residual tumour size ≤ 2 cm in respectively 73% and 85% of cases. With a median follow-up of 24 months (range 7 – 78 months), the survival rates after primary surgery and interval surgery were 61% and 66% respectively.</p> <p>Conclusion</p> <p>Diagnostic laparoscopy is useful for identifying patients with stage III/IV ovarian cancer who qualify for primary cytoreduction. Surgeon experience was a determining factor for the success of complete cytoreduction.</p

Reverse saturable absorption in solid xerogel matrices

International audienceAluminophthalocyanine (APC) and fullerene carbon 60 (C,) have been studied encaged in different silica matrices. The reverse saturable absorption properties of these doped xerogels have been compared to those of reference solutions of APC and C&,. We show that reverse saturable absorber molecules retain their properties even when they are enclosed in the pores of a solid xerogel matri