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  • 1
    Electronic Resource
    Electronic Resource
    Seabeam and seismic reflection imaging of the tectonic regime of the Andean continental margin off Peru (4^oS to 10^oS)
    Amsterdam : Elsevier
    Earth and Planetary Science Letters 87 (1988), S. 111-126 
    Details
    ISSN: 0012-821X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0012-821X(88)90068-4
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    Paper (German National Licenses)
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  • 2
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    New and revised radiolarian biochronology for the sedimentary cover of ophiolites in the Lesser Caucasus (Armenia) (2010)
    In:  Geological Society Special Publication 340: 383-391.
    Details
    Publication Date: 2010-09-14
    Description: In order to improve our understanding of the palaeogeographic and geodynamic evolution of the Tethyan realms preserved in the Lesser Caucasus we here review the existing data for the sedimentary cover of ophiolites preserved in Armenia. Particular attention is given to those dated sedimentary rocks that are in direct genetic contact with ophiolitic lavas, as they provide constraints for submarine oceanic activity. The oldest available ages come from the Sevan-Akera suture zone that point to a Late Triassic oceanization. Data from both the Sevan and Vedi ophiolites provide evidence for Middle Jurassic (Bajocian) submarine activity, that continued until at least the Late Jurassic (Mid/Late Oxfordian to Late Kimmeridgian/Early Tithonian), as dated recently in Stepanavan and in this study for the Vedi ophiolite.
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  • 3
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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
    Publication Date: 2010-09-14
    Description: 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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  • 4
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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
    Publication Date: 2010-09-14
    Description: 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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  • 5
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    The effect of leaving groups on binding and reactivity in enzyme-free copying of DNA and RNA (2016)
    Oxford University Press
    Details
    Publication Date: 2016-07-09
    Description: The template-directed incorporation of nucleotides at the terminus of a growing primer is the basis of the transmission of genetic information. Nature uses polymerases-catalyzed reactions, but enzyme-free versions exist that employ nucleotides with organic leaving groups. The leaving group affects yields, but it was not clear whether inefficient extensions are due to poor binding, low reactivity toward the primer, or rapid hydrolysis. We have measured the binding of a total of 15 different activated nucleotides to DNA or RNA sequences. Further, we determined rate constants for the chemical step of primer extension involving methylimidazolides or oxyazabenzotriazolides of deoxynucleotides or ribonucleotides. Binding constants range from 10 to 〉500 mM and rate constants from 0.1 to 370 M –1 h –1 . For aminoterminal primers, a fast covalent step and slow hydrolysis are the main factors leading to high yields. For monomers with weakly pairing bases, the leaving group can improve binding significantly. A detailed mechanistic picture emerges that explains why some enzyme-free primer extensions occur in high yield, while others remain recalcitrant to copying without enzymatic catalysis. A combination of tight binding and rapid extension, coupled with slow hydrolysis induces efficient enzyme-free copying.
    Print ISSN: 0305-1048
    Electronic ISSN: 1362-4962
    Topics: Biology
    Published by Oxford University Press
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  • 6
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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
    Publication Date: 2015-12-25
    Description: 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
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 7
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    Geochemistry of the Eocene magmatic rocks from the Lesser Caucasus area (Armenia): evidence of a subduction geodynamic environment (2016)
    Geological Society (of London)
    Details
    Publication Date: 2016-02-05
    Description: This paper is focused on petrological and geochemical data obtained on a series of Middle and Upper Eocene magmatic rocks from the Lesser Caucasus of Armenia in order to elucidate magma sources and geodynamic processes. Middle–Upper Eocene magmatism is present in two main zones: the Amasia–Sevan–Hakari suture zone (ASHSZ) and the so-called South Armenian Microplate (SAM). Volcanic rocks from both places range from basalt to rhyolite and mostly display a calc-alkaline character. Trace element patterns from the SAM and ASHSZ samples show mobile-elements enrichment (Rb, Ba, Th) together with strong negative high field strength elements (Nb, Ta, Hf, Zr) anomalies. The (La/Sm) N ratio yields very close values for both areas. Conversely, the (La/Yb) N ratio is, on average, significantly higher for SAM than for ASHSZ, suggesting the presence of residual garnet at the source of the SAM volcanic rocks. Nevertheless, trace elements suggest partial melting from phlogopite- and amphibole-bearing spinel lherzolitic mantle sources. Neodymium and strontium isotopes yield Nd (40Ma) and 87 Sr/ 86 Sr (40Ma) ratios ranging, respectively, from –0.3 to +6.6 and from 0.70314 to 0.70531 for SAM samples, and from +3.4 to +6.8 and from 0.70393 to 0.70433 for ASHSZ samples. Initial Pb/Pb isotopic ratios yield close values for both areas but with slightly higher and more homogeneous 207 Pb/ 204 Pb and 208 Pb/ 204 Pb ratios for SAM samples. Such features concur with a more pronounced slab-component contribution in the frontal part of the volcanic belt, that is, in the SAM domain. No significant crustal contamination has been detected in the studied Eocene magmatic rocks from both the ASHSZ and SAM. Considering geodynamic and geochemical constraints, we propose that this magmatism is connected with a north-dipping Southern Neotethys subduction, in an extensional (back-arc) environment of orogenic belts. The Arabia–Eurasia collision and the closure of the Neotethys Ocean may have occurred after this magmatic event.
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 8
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    Progressive orocline formation in the Eastern Pontides-Lesser Caucasus (2015)
    Geological Society (of London)
    Details
    Publication Date: 2015-10-29
    Description: The Eastern Pontides–Lesser Caucasus fold–thrust belt displays a peculiar northwards arc-shaped geometry that was defined as an orocline in earlier studies. The Lesser Caucasus was affected by two main tectonic events that could have caused orocline formation: (1) Paleocene–Eocene collision of the South Armenian Block with Eurasia; and (2) Oligocene–Miocene Arabia–Eurasia collision. We tested the hypothesis that the Lesser Caucasus is an orocline and aimed to time the formation of this orocline. To determine the vertical axis rotations, 37 sites were sampled for palaeomagnetism in rocks of Upper Cretaceous–Miocene age in Georgia and Armenia. In addition, we compiled a review of c. 100 available datasets. A strike test was applied to the remaining datasets, which were divided into four chronological sub-sets, leading us to conclude that the Eastern Pontides–Lesser Caucasus fold–thrust belt forms a progressive orocline. We concluded that: (1) some pre-existing curvature must have been present before the Late Cretaceous; (2) the orocline acquired part of its curvature after the Paleocene and before the Middle Eocene as a result of South Armenian Block–Eurasia collision; and (3) about 50% of the curvature formed after the Eocene and probably before the Late Miocene, probably as a result of Arabia–Eurasia collision. Supplementary material: Results from rock magnetic experiments, reversal and fold tests and equal area projections of the characteristic remanent magnetizations for each site, as well as biostratigraphic ages and a table with palaeomagnetic results from the literature review (with assigned numbers referred to in the text) are available at http://www.geolsoc.org.uk/SUP18852 .
    Print ISSN: 0305-8719
    Electronic ISSN: 2041-4927
    Topics: Geosciences
    Published by Geological Society (of London)
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  • 9
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    Radiolarian biostratigraphic constraints for latest Jurassic-earliest Cretaceous submarine volcanic activity in the Tethyan oceanic realm of the Sevan ophiolite (Armenia) (2012)
    Societe Geologique de France (SGF)
    Details
    Publication Date: 2012-09-01
    Description: Biostratigraphic constraints for the sedimentary cover of the ophiolites preserved in Armenia are of key importance for the palaeogeographic and geodynamic reconstruction of the greater area between Eurasia and the South-Armenian block, which is a micro-continent of Gondwanian origin. We present here radiolarian data obtained from radiolarites that are intercalated in a sequence of mafic volcanic rocks on the northern flank of the Dali valley (east of Lake Sevan), which is considered to be part of the Sevan ophiolite. Mafic sills and dykes with well-preserved igneous textures are probably part of the same sequence. The pseudomorphosis of primary phases indicates that the igneous rocks are strongly affected by alteration in the greenschist facies condition. The plagiogranites that are present in this locality appear to be intrusive into the mafic sequence. The radiolarian assemblages extracted from radiolarian cherts intercalated in the mafic volcanic rocks are dated as latest Tithonian-Late Valanginian; they contain metric rounded blocks of oolitic limestones with crinoid fragments, suggesting that these shallow water limestones slid during the Jurassic/Cretaceous transition into a rugged oceanic floor in which radiolarian ooze accumulated.
    Print ISSN: 0037-9409
    Electronic ISSN: 0037-9409
    Topics: Geosciences
    Published by Societe Geologique de France (SGF)
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  • 10
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    Geological history of ophiolites in the Lesser Caucasus and correlation with the Izmir-Ankara-Erzincan suture zone: insights from radiolarian biochronology (2012)
    Societe Geologique de France (SGF)
    Details
    Publication Date: 2012-09-01
    Description: Three distinct radiolarian assemblages were obtained in this study; two of them were extracted from large blocks of radiolarites included in a mélange NW of Lake Sevan (Dzknaget). The latest Tithonian-Late Valanginian assemblage comes from a coherent sequence of 6–7 m-thick radiolarites with intercalations of lavas and rounded blocks of shallow-water limestones. The Late Barremian-Early Aptian assemblage found in the second block allows correlation with radiolarites dated recently in Karabagh. A third radiolarian assemblage comes from Vedi and establishes that radiolarian ooze was accumulated in the Tethyan realm of the Lesser Caucasus until at least the middle Albian. A synthesis of all available micropaleontological (radiolarian) and geochronological ages for the ophiolites present in Armenia and Karabagh points to the following scenario for their geological evolution: the initial phase of oceanic floor spreading was under way during the Late Triassic (Carnian) or even slightly before; the bulk of oceanic lithosphere preserved today in the Lesser Caucasus was formed during the Jurassic; evidence for subaerial volcanic activity is recorded in tuffite intercalations in the Middle-Upper Jurassic radiolarian cherts; an oceanic volcanic plateau was formed during the Late Barremian-Aptian (or possibly even before) while the obduction of ophiolites took place during the Coniacian-Santonian. The geological history of ophiolites in the Lesser Caucasus shares a number of similarities with the Izmir-Ankara-Erzincan suture zone (i.e. initiation of ocean spreading during the Carnian, obduction after the Cenomanian), but there are also some differences especially with respect to the timing of the oceanic plateau emplacement.
    Print ISSN: 0037-9409
    Electronic ISSN: 0037-9409
    Topics: Geosciences
    Published by Societe Geologique de France (SGF)
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