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  • 1
    Digitale Medien
    Digitale Medien
    Tectono-metamorphic evolution of the Karakorum Metamorphic complex (Dassu–Askole area, NE Pakistan): exhumation of mid-crustal HT–MP gneisses in a convergent context (2001)
    Oxford, UK : Blackwell Science Inc
    Journal of metamorphic geology 19 (2001), S. 0 
    Details
    ISSN: 1525-1314
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie
    Notizen: The South Karakorum margin, east of the Himalayan syntaxis, consist of an E–W elongated zone of young (10–3 Ma) high-grade metamorphic rocks (M2) and related migmatitic domes. This late tectono-metamorphic event post-dates the Palaeogene (55–37 Ma) phase of thickening of the belt featured by NW–SE structures and associated M1 amphibolite facies metamorphism (0.7 GPa, 700 °C). This M2 metamorphism is characterised by low-pressure, high-temperature conditions coeval with migmatite formation in response to a thermal increase of c. 150 °C compared to M1, culminating at a temperature of c. 770 °C and a pressure of 0.5–0.6 GPa. Rapid exhumation of migmatitic domes, at a rate of 5 mm yr−1, was accommodated by vertical extrusion, in the core of E–W crustal-scale folds. These crustal-scale folds formed in response to N–S syn-collisional shortening and were enhanced by thermal weakening of the migmatised continental crust.M2 metamorphism is spatially and temporarily associated with granitoids showing a mantle affinity, firmly suggesting that this could be the advective heat source for the granite and syenite generation and the subsequent migmatisation of the mid-crustal level. Such relationships between a mantle-related magmatism and a high-temperature metamorphism in a convergent shortening context are suggestive of the breakoff of the subducted Indian slab since 20 Ma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1046/j.0263-4929.2001.00342.x
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  • 2
    Digitale Medien
    Digitale Medien
    Alcaloides des feuilles de Voacanga thouarsii
    Amsterdam : Elsevier
    Phytochemistry 12 (1973), S. 2039-2042 
    Details
    ISSN: 0031-9422
    Schlagwort(e): Apocynaccae ; Voacanga thouarsii ; Yobtusine ; bis-indole alkaloids.
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/S0031-9422(00)91531-0
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  • 3
    Digitale Medien
    Digitale Medien
    Pharmacological Treatments That Affect CNS Activity: Serotonin (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 499 (1987), S. 0 
    Details
    ISSN: 1749-6632
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Allgemeine Naturwissenschaft
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1749-6632.1987.tb36219.x
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  • 4
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    40Ar/39Ar dating of synkinematic white mica: insights from fluid-rock reaction in low-grade shear zones (Mont Blanc Massif) and constraints on timing of deformation in the NW external Alps (2008)
    In:  Geological Society Special Publication 299: 293-315.
    Details
    Publikationsdatum: 2008-07-02
    Beschreibung: This paper highlights the use of synkinematic white mica, biotite and phlogopite for the dating of deformation in ductile shear zones within crystalline rocks under low-grade metamorphic conditions. The Mont Blanc shear zones range from 1 mm to 50 m in width and have localized intense fluid flow, resulting in substantial differences in mineralogy and whole-rock geochemistry. On the basis of their synkinematic alteration assemblages and geographic distribution within the Mont Blanc Massif, three main metamorphic zones are distinguished within the network of shear zones. These are: (i) epidote{+/-}white mica-bearing assemblages; (ii) chlorite-phlogopite-bearing assemblages; and (iii) white mica{+/-}biotite{+/-}calcite{+/-}actinolite{+/-}epidote- bearing assemblages. 40Ar/39Ar age spectra of biotite and phlogopite are complex, and reflect significant variations in chemical composition. In biotite, this is partly due to inheritance from precursor Variscan magmatic biotite. In contrast, new white mica grew at the expense of feldspar during Alpine deformation and its Ar spectra do not show any excess 40Ar. On the SE side of Mont Blanc, ages of shear zone phengites have a narrow range of 15.8-16.0{+/-}0.2 Ma, which is in the same age range as 40Ar/39Ar ages of minerals from kinematically related veins. The top-to-SE sense of shear is consistent with initiation of a Mont Blanc flower-structure within a dextral transpressional system by 16 Ma. On the NW side, mini-plateaux ages of 14.5{+/-}0.3 and 23.4{+/-}0.4 Ma are preserved in the same sample, suggesting the possibility of two phases of deformation. This is also supported by partly preserved ages of 18-36.6 Ma in biotites and phlogopites. Ages between 36 and 18 Ma might reflect ongoing top-to-NW thrusting, following Penninic Front activation, in a context of nappe stacking and crustal thickening. NW-directed thrusting on the NW side of Mont Blanc continued after 18 Ma, synchronous with SE-directed thrusting on the SE side of the massif. These divergent movements produced the overall pop-up geometry of the Mont Blanc Massif, which may correspond to a positive flower structure developed within a zone of regional dextral transpression extending SW from the Rhone valley into the Mont Blanc area.
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  • 5
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    Subductions, obduction and collision in the Lesser Caucasus (Armenia, Azerbaijan, Georgia), new insights (2010)
    In:  Geological Society Special Publication 340: 329-352.
    Details
    Publikationsdatum: 2010-09-14
    Beschreibung: In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the autochthonous South Armenian Block (SAB), a Gondwana-derived terrane; (2) the ophiolitic Sevan-Akera suture zone; and (3) the Eurasian plate. Based on our field work, new stratigraphical, petrological, geochemical and geochronological data combined with previous data we present new insights on the subduction, obduction and collision processes recorded in the Lesser Caucasus. Two subductions are clearly identified, one related to the Neotethys subduction beneath the Eurasian margin and one intra-oceanic (SSZ) responsible for the opening of a back-arc basin which corresponds to the ophiolites of the Lesser Caucasus. The obduction occurred during the Late Coniacian to Santonian and is responsible for the widespread ophiolitic nappe outcrop in front of the suture zone. Following the subduction of oceanic lithosphere remnants under Eurasia, the collision of the SAB with Eurasia started during the Paleocene, producing 1) folding of ophiolites, arc and Upper Cretaceous formations (Transcaucasus massif to Karabakh); 2) thrusting toward SW; and 3) a foreland basin in front of the belt. Upper-Middle Eocene series unconformably cover the three domains. From Eocene to Miocene as a result of the Arabian plate collision with the SAB to the South, southward propagation of shortening featured by folding and thrusting occurred all along the belt. These deformations are sealed by a thick sequence of unconformable Miocene to Quaternary clastic and volcanic rocks of debated origin.
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  • 6
    facet.materialart.
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    Geochemical variations and element transfer during shear-zone development and related episyenites at middle crust depths: insights from the Mont Blanc granite (French -- Italian Alps) (2007)
    In:  Geological Society Special Publication 245: 373-396.
    Details
    Publikationsdatum: 2007-10-08
    Beschreibung: This paper highlights the relationships between the formation of shear zones, associated quartz-rich veins and their quartz-depleted alteration haloes ( episyenites') that have formed in the Mont Blanc Massif during the Alpine orogeny. The shear zones are steeply dipping and formed late (18-13 Ma) during collisional orogeny, at mid-crustal depths (5 {+/-} 1 kbar, 400 {+/-} 50 {degrees}C) during uplift of the Mont Blanc Massif. Between the shear zones, nearly undeformed granite contains widely dispersed, subhorizontal veins with a quartz-dominant quartz + albite + chlorite + adularia assemblage. They do not intersect the shear zones and are surrounded by quartz-depleted alteration haloes up to several metres wide. The compositions of the shear zones and the vein-alteration haloes (episyenites) show substantial departures from the bulk composition of the host rock. Shear zones are characterized by greenschist facies assemblages (epidote-, chlorite- or K-white-micabearing assemblages). Each shear zone type is featured by a specific chemical change: depletions in K2O, and enrichments in Fe2O3 and CaO (epidote-); with depletions in CaO, Na2O, K2O and slight SiO2 enrichments (white mica-chlorite-); with depletions in SiO2, CaO, Na2O, K2O and enrichments in MgO (phlogopite-chlorite shear zones). Episyenites are characterized by chemically induced porosity enhancement due to dissolution of magmatic quartz and biotite, with subsequent partial infilling of pore spaces by quartz, chlorite, albite and adularia. The vein arrays have accommodated minor vertical stretching in the Mont Blanc Massif, probably at the same time as the adjacent shear zones were accommodating more substantial vertical stretching in the massif. Coupled quartz dissolution in the wallrock alteration haloes and quartz precipitation in veins could be interpreted to reflect local mass transfer between wallrock and veins during essentially closed-system behaviour in the relatively underformed granite domains between shear zones. In contrast, shear zones probably develop in opened systems due to their kilometric length.
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  • 7
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    Paraglacial gravitational deformations in the SW Alps: a review of field investigations, 10Be cosmogenic dating and physical modelling (2011)
    In:  Geological Society Special Publication 351: 11-25.
    Details
    Publikationsdatum: 2011-03-30
    Beschreibung: Catastrophic deep-seated landslides (DSL) are generally considered to be the result of large slope deformations also known as deep-seated gravitational slope deformation (DSGSD). This paper aims to build a synthesis of multiple studies made in the Tinée Valley (southern French Alps) to assess the geometrical, kinematical, mechanical and chronological relationships between these two gravitational processes.At the scale of the valley, data issued from geological, geomorphological and 10Be dating indicate a clear geometrical link between DSGSD and DSL occurring at the base of the slope and suggest that gravitational slope evolution began after the glacial retreat (13 ka BP). This is supported by the example of the well-documented La Clapière slope. A continuous evolution process is characterized geometrically and temporally from geomorphic observations and analogue modelling. Coupling structural, geomorphological, physical and chronological studies allowed us to propose a four-dimensional (4D) deformation model mechanically correlated with progressive failure concept. The validity and variability of this reference site are discussed at the valley scale (taking Isola and Le Pra slope deformation as examples).It allows a rough estimation of the state of slope deformation at the valley scale to be constructed and the slope evolution with time to be considered. This 4D model could then be considered as a reference for other deep-seated gravitational slope deformations in comparable Alpine valleys.
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  • 8
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    The Armenian Ophiolite: insights for Jurassic back-arc formation, Lower Cretaceous hot spot magmatism and Upper Cretaceous obduction over the South Armenian Block (2010)
    In:  Geological Society Special Publication 340: 353-382.
    Details
    Publikationsdatum: 2010-09-14
    Beschreibung: Similar geological, petrological, geochemical and age features are found in various Armenian ophiolitic massifs (Sevan, Stepanavan and Vedi). These data argue for the presence of a single large ophiolite unit obducted on the South Armenian Block (SAB). Lherzolite Ophiolite type rock assemblages evidence a Lower-Middle Jurassic slow-spreading rate. The lavas and gabbros have a hybrid geochemical composition intermediate between arc and Mid Ocean Ridge Basalt (MORB) signatures which suggest they were probably formed in a back-arc basin. This oceanic sequence is overlain by pillowed alkaline lavas emplaced in marine conditions. Their geochemical composition is similar to plateau-lavas. Finally, this thickened oceanic crust is overlain by Upper Cretaceous calc-alkaline lavas likely formed in a supra-subduction zone environment. The age of the ophiolite is constrained by 40Ar/39Ar dating experiments provided a magmatic crystallization age of 178.7{+/-}2.6 Ma, and further evidence of greenschist facies crystallization during hydrothermal alteration until c. 155 Ma. Thus, top-to-the-south obduction likely initiated along the margin of the back-arc domain, directly south of the Vedi oceanic crust, and was transported as a whole on the SAB in the Coniacian times (88-87 Ma). Final closure of the basin is Late Cretaceous in age (73-71 Ma) as dated by metamorphic rocks.
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  • 9
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    Thermochronology of the highest central Asian massifs (Khan Tengri - Pobedi, SE Kyrgyztan): Evidence for Late Miocene (ca. 8 Ma) reactivation of Permian faults and insights into building the Tian Shan (2020)
    Elsevier
    Details
    Publikationsdatum: 2020-09-01
    Print ISSN: 1367-9120
    Digitale ISSN: 1878-5786
    Thema: Geologie und Paläontologie
    Publiziert von Elsevier
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  • 10
    facet.materialart.
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    From seafloor spreading to obduction: Jurassic-Cretaceous evolution of the northern branch of the Neotethys in the Northeastern Anatolian and Lesser Caucasus regions (2015)
    Geological Society (of London)
    Details
    Publikationsdatum: 2015-12-25
    Beschreibung: We present arguments for an innovative tectonic set-up just prior to the Northern Neotethys obduction event in the NE Anatolian and Lesser Caucasus area. Along the Northern Neotethyan suture (the Ankara–Erzincan–Amasia–Sevan–Akera suture zone), relicts of the northern branch of the Neotethys oceanic domain outcrop as preserved unmetamorphosed slivers obducted over the northern edge of the South Armenian Block (SAB) and Taurides–Anatolides Platform (TAP) margins. Recent studies have shown that the ophiolitic bodies are formed of similar lithologies of Middle Jurassic age, all bearing mid-ocean ridge basalt chemical compositions enriched in large ion lithophile elements. This extensive database supports a model in which these ophiolites are derived from a single obducted nappe. This model is supported by the metamorphic pressure–temperature–time paths of the sole lithologies under the outcrops of the suture zone ophiolites. Palaeontological dating of sediment deposits directly under or sealing the obduction contact also support this model by temporally linking the emplacement of distant ophiolite outcrops. General emplacement during early Late Cretaceous time has been determined. A south-dipping subduction under the SAB shortly predating obduction has recently been proposed from the metamorphic and magmatic evolution preserved in the SAB crystalline basement, founding a model featuring opposite-direction subduction from at least late Middle Jurassic to Early Cretaceous times. The emplacement of alkaline pillow basalts directly on the oceanic crust is dated as Early to mid-Cretaceous. These dates argue the existence of abnormal mantle heat flows which may be responsible for a decrease in the density of the 80 Ma-old oceanic lithosphere prior to its obduction onto the SAB–TAP. We present a detailed review of recent data to further constrain the structural and geodynamic evolution of this sector and to define the tectonic set-up just prior to the obduction event.
    Print ISSN: 0305-8719
    Digitale ISSN: 2041-4927
    Thema: Geologie und Paläontologie
    Publiziert von Geological Society (of London)
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