Diachronous exhumation of HP-LT metamorphic rocks from southwestern Alps: evidence from fission-track analysis

International audienceNew fission-track ages on zircon and apatite (ZFT and AFT) from the southwestern alpine paleo-accretionary wedge document a contrasting cooling history from east to west. In the eclogitic Monviso ophiolites, the ZFT ages are 19.6 +/- 0.8 Ma and the AFT ages are 8.6 +/- 1.7 Ma. In the HT-blueschist eastern Queyras, ZFT ages range from 27.0 +/- 1.5 Ma to 21.7 +/- 1.6 Ma and AFT ages from 14.2 +/- 2.0 to 9.4 +/- 1.1 Ma. In the LT-blueschist western Queyras, ZFT ages are between 94.7 +/- 3.1 Ma and 63.1 +/- 2.9 Ma and AFT ages are between 22.2 +/- 1.6 and 22.6 +/- 1.5 Ma. The Chenaillet ophiolite yields ages of 118.1 +/- 3.7 Ma on ZFT and of 67.9 +/- 8.5 Ma on AFT. These new FT data combined with petrological and geochronological constraints record a diachronous exhumation in the paleo-accretionary wedge during subduction and collision

Denudation of the Côte d'Ivoire-Ghana transform margin from apatite fission tracks.

Apatite fission track analysis of samples from the shoulder (marginal ridge) of the Côte d'Ivoire-Ghana transform continental margin reveal a cooling of the margin between 85 and 65 Ma for the central and eastern parts of the ridge. All samples were heated in situ during sedimentary burial with a temperature >120 °C, except for two samples located in the eastern part which were heated between 105 and 120 °C. For the first time, age/depth diagram along a transform margin shows a shape involving erosion starting at the bottom of the continental slope, then stepping backwards towards the edge of the slope. This retrogressive erosion can result from the deepening of the lithospheric plate sliding along the transform margin, from thick continental crust to thin continental crust, and finally to oceanic crust. This process could be at the origin of the shoulder uplift by flexural response to the important crustal discharge (>2 km)

Late Miocene – Recent exhumation of the central Himalaya and recycling in the foreland basin assessed by apatite fission-track thermochronology of Siwalik sediments, Nepal

International audienceThermochronological analysis of detrital sediments derived from the erosion of mountain belts and contained in the sedimentary basins surrounding them allows reconstructing the long-term exhumation history of the sediment source areas. The effective closure temperature of the thermochronological system analysed determines the spatial and temporal resolution of the analysis through the duration of the lag time between closure of the system during exhumation and its deposition in the sedimentary basin. Here we report apatite fission-track (AFT) data from 31 detrital samples collected from Miocene to Pliocene stratigraphic sections of the Siwalik Group in western and central Nepal, as well as three samples from modern river sediments from the same area, that complement detrital zircon fission-track (ZFT) and U-Pb data from the same samples presented in a companion paper. Samples from the upper part of the stratigraphic sections are unreset and retain a signal of source-area exhumation; they show spatial variations in source-area exhumation rates that are not picked up by the higher-temperature systems. More deeply buried samples have been partially reset within the Siwalik basin and provide constraints on the thermal and kinematic history of the fold-and-thrust belt itself. The results suggest that peak source-area exhumation rates have been constant at ~1.8 km Myr-1 over the last ~7 Ma in central Nepal, whereas they ranged between 1 and ~1.5 km Myr-1 in western Nepal over the same time interval; these spatial variations may be explained by either a tectonic or climatic control on exhumation rates, or possibly a combination of the two. Increasing lag times within the uppermost part of the sections suggest an increasing component of apatites that have been recycled within the Siwalik belt and are corroborated by AFT ages of modern river sediment downstream as well as the record of the distal Bengal Fan. The most deeply buried and most strongly annealed samples record onset of exhumation of the frontal Siwaliks along the Himalayan frontal thrust at ~2 Ma and continuous shortening at rates comparable to the present-day shortening rates from at least 0.3 Ma onward

Вплив різних видів анестезіологічного забезпечення на неспецифічну ланку імунітету вагітних під час кесарева розтину

Компоненты хирургической операции – операционная травма, стресс, общая анестезия, кровопотеря, антибактериальная – терапия приводят к снижению защиты иммунной системы и развитию вторичной иммунной недостаточности. В результате операционно-анестезиологического стресса в организме больного возникает состояние иммунодепрессии, которое необходимо нивелировать путем выбора анестетиков, минимально угнетающих иммунные реакции. Такой подход дает возможность разработать и внедрить в клиническую практику оптимальные методы анестезии у беременных. Проведенное исследование показало, что операционный стресс негативно влияет на неспецифический иммунитет беременных. В зависимости от вида анестезии проявления негативного влияния будет различным. Установлено, что спинальная анестезия сопровождается минимальным влиянием на фагоцитарную активность лейкоцитов, а общая анестезия имеет депрессивное влияние, которое сопровождается более пяти дней.Components surgery . surgical trauma, stress, general anesthesia, blood loss, antibiotic . therapy leads to a decrease in defense of the immune system and the development of secondary immune deficiency. As a result of operational and anesthetic stress in the patient.s body a state of immunosuppression, which is necessary to level by selecting the anesthetic minimally depressing the immune response. This approach provides an opportunity to develop and introduce into clinical practice the best methods of anesthesia in pregnant women. The study showed that operational stress affects the nonspecific immunity of pregnant women. Depending on the type of anesthesia, manifestations of the negative impact will be different. Established that spinal anesthesia with a minimum influence on the phagocytic activity of leukocytes and general anesthesia has a depressive effect which is accompanied by more than five days

Miocene to Recent exhumation of the central Himalaya determined from combined detrital zircon fission-track and U/Pb analysis of Siwalik sediments, western Nepal

International audienceFission-track (FT) analysis of detrital zircon from synorogenic sediment is a well established tool to examine the cooling and exhumation history of convergent mountain belts, but has so far not been used to determine the long-term evolution of the central Himalaya. This study presents FT analysis of detrital zircon from 22 sandstone and modern sediment samples that were collected along three stratigraphic sections within the Miocene to Pliocene Siwalik Group, and from modern rivers, in western and central Nepal. The results provide evidence for widespread cooling in the Nepalese Himalaya at about 16.0 ± 1.4 Ma, and continuous exhumation at a rate of about 1.4 ± 0.2 km/Myr thereafter. The ~16 Ma cooling is likely related to a combination of tectonic and erosional activity, including movement on the Main Central thrust and Southern Tibetan Detachment system, as well as emplacement of the Ramgarh thrust on Lesser Himalayan sedimentary and meta-sedimentary units. The continuous exhumation signal following the ~16 Ma cooling event is seen in connection with ongoing tectonic uplift, river incision, and erosion of lower Lesser Himalayan rocks exposed below the MCT and Higher Himalayan rocks in the hanging wall of the MCT, controlled by orographic precipitation and crustal extrusion. Provenance analysis, to distinguish between Higher Himalayan and Lesser Himalayan zircon sources, is based on double dating of individual zircons with the FT and U/Pb methods. Zircons with pre-Himalayan FT cooling ages may be derived from either non-metamorphic parts of the Tethyan sedimentary succession or Higher Himalayan protolith that formerly covered the Dadeldhura and Ramgarh thrust sheets, but that have been removed by erosion. Both the Higher and Lesser Himalaya appear to be sources for the zircons that record either ~16 Ma cooling or the continuous exhumation afterwards

Diachronous late-stage exhumation across the western Alpine arc: constraints from 2 apatite fission-track thermochronology between the Pelvoux and Dora–Maira Massifs

International audienceWe present new apatite fission-track (AFT) data from the central western Alps that confirm the 10 synchronicity and high cooling rates during Latest Miocene–Pliocene final exhumation of the External 11 Crystalline Massifs but also provide evidence for diachronous Neogene evolution along and across the internal 12 arc. To the SE of the Pelvoux Massif, across the front of the internal arc (Penninic Frontal Thrust), the jump 13 in AFT ages (c. 22 Ma) and in final cooling rates is significantly larger than further north. This difference 14 results from reversal of movement along a major Oligocene thrust. In its hanging wall, the western 15 Brianc ̧onnais Zone provides a mean AFT age of c. 27 Ma, which is older than further north. Early cooling in 16 the southern Brianc ̧onnais Zone would result from rapid erosion of the compressional fan structure built 17 during the Oligocene. Across the entire Brianc ̧onnais and Pie ́mont nappe stack, with the exception of the 18 Dora–Maira Massif, AFT ages young eastward and span the entire Miocene, a period during which this 19 structure underwent extension. Further north a reverse gradient with ages younging northwestward has been 20 described, prompting the question of the asymmetry of the internal western Alpine arc during its late-stage 21 tectonic and morphological evolution

DATATION PAR TRACES DE FISSION ET ÉTUDE DE PROVENANCE D'ARTEFACTS EN OBSIDIENNE DES SITES ARCHÉOLOGIQUES DE LA TOLITA (Equateur) ET INGUAPI (Colombie)

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Cenozoic denudation of Corsica in response to Ligurian and Tyrrhenian extension: results from apatite fission-track thermochronology.

The Island of Corsica (France) occupies a unique position in the Western Mediterranean, since it has recorded both the Cenozoic Alpine orogenic history of the area as well as subsequent extensional collapse and oceanic basin formation. We present 41 new apatite fission track (AFT) ages and 23 measurements of track length distributions from Corsica, in order to elucidate its Cenozoic thermal and morphological evolution. AFT ages vary from 10.5±0.8 Ma to 53.8±4.1 Ma and form a clear spatial pattern: oldest ages are encountered in the south-west of the island, with a broad band of ages between 20 and 30 Ma running across the mountainous central area and ages <20 Ma confined to the eastern half of the island. Samples along the western and north-western coasts record km-scale erosional denudation linked to rifting in the Ligurian-Provençal Basin, whereas samples from close to the extensionally inverted Alpine deformation front record a later cooling phase related to Tyrrhenian extension. The eastward-younging pattern of AFT ages suggests the migration of a ‘wave' of erosional denudation from west to east across the island, apparently controlled by the migrating locus of extension. Our AFT data therefore support models of Mediterranean extension controlled by slab roll-back

Fission track thermochronology of the Beni Bousera peridotite massif (Internal, Rif, Marocco) and the exhumation of ultramafic rocks in the Gibraltar Arc

International audienceThe Beni Bousera peridotite massif and its metamorphic surrounding rocks have been analyzed by the fission track (FT) method. The aim was to determine the cooling and uplift history of these mantle and associated crustal rocks after the last major metamorphic event that dates back to the Lower Miocene–Upper Oligocene time (∼22–24 Ma). The zircon FT analyses give an average cooling—i.e., below 320 °C—age of ∼19.5 Ma. In addition, the apatite FT data give an average cooling—i.e., below 110 °C—age of ∼15.5 Ma. Taking into account the thermal properties of the different thermochronological systems used in this work, we have estimated a rate of cooling close to 50 °C/Ma. This cooling rate constrains a denudation rate of about ∼2 mm year−1 from 20 to 15 Ma. These results are similar to those determined in the Ronda peridotite massif of the Betic Cordilleras documenting that some ultrabasic massifs of the internal zones of the two segments of the Gibraltar Arc have a similar evolution. However, Burdigalian sediments occur along the Betic segment (Alozaina area, western Betic segment) unconformably overlying peridotite. At this site, ultramafic rock was exposed to weathering at ages ranging from 20.43 to 15.97 Ma. Since the Beni Bousera peridotite was still at depth until 15.5 Ma, we infer that no simple age projection from massif to massif is possible along the Gibraltar Arc. Moreover, the confined fission track lengths data reveal that a light warming (∼100 °C) has reheated the massif during the Late Miocene before the Pliocene–Quaternary tectonic uplift