11 research outputs found
Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer-Bassit ophiolites: insights from Ar-40-Ar-39 geochronology
No full textOpen-Ended, N-Doped Carbon Nanotube-Graphene Hybrid Nanostructures as High-Performance Catalyst Support
No full textA hierarchical N-doped carbon nanotube-graphene hybrid nanostructure (NCNT-GHN), in which the graphene layers are distributed inside the CNT inner cavities, was designed to efficiently support noble metal (e.g., PtRu) nanoparticles. Well-dispersed PtRu nanoparticles with diameters of 2-4 nm were immobilized onto these NCNT-GHN supports by a low-temperature chemical reduction method without any pretreatment. Compared to conventional CNTs and commercial catalysts. a much better catalytic performance was achieved by a synergistic effect of the hierarchical structure (graphene-CNT hybrid) and electronic modulation (N-doping) during the methanol electrooxidation reaction. Improved single-cell performances with long-term stability are also demonstrated using NCNT-GHN as catalyst support.Chemistry, MultidisciplinaryChemistry, PhysicalNanoscience & NanotechnologyMaterials Science, MultidisciplinaryPhysics, AppliedPhysics, Condensed MatterSCI(E)EI50ARTICLE5999-10062
Detrital chrome spinel evidence for a Neotethyan intra-oceanic island arc collision with India in the Paleocene
No full textMagmatism associated with Gondwanaland rifting and neo-tethyan oceanic basin development: Evidence from the Mamonia Complex, SW Cyprus
No full textVolcanic and intrusive rocks of the Dhiarizos Group, occurring within the Mamonia Complex of SW Cyprus, comprise mainly tholeiitic basalts, ocean island tholeiites (OIT) and other alkalic varieties, with minor alkaline lamprophyre intrusive rocks. These rocks were highly tectonized and dismembered during the collision with the Troodos Oceanic lithosphere. Trace element data for the most primitive mafic igneous rock samples suggest that the tholeiitic basalts are derived from a depleted mantle source whereas the OIT and the alkalic basalts originated from variable degrees of partial melting of a spinel peridotite mantle. Alkaline lamprophyres are products f a small degree of partial melting of a deep-seated garnet lherzolite. The bulk of the tholeiites and alkalic varieties are Late Triassic in age and are interpreted as having formed during Neo-Tethyan sea-floor spreading and associated seamount volcanism. Amphibole separates from a lamprophyre intrusion have 40Ar- 39Ar ages of 140.7 ± 0.4 Ma. In this paper, we report for the first time an Early Cretaceous alkaline lamprophyric magmatism, which is probably associated with a renewed episode of Gondwanaland rifting. These results show that the development of the Neo-Tethyan oceanic basin in the Eastern Mediterranean was largely controlled by a two-phase rifting-drifting process.link_to_subscribed_fulltex
A correction to petrogenesis of latest miocene-quaternary continental intraplate volcanism along the Northern dead sea fault system (Al Ghab-Homs volcanic field), Western Syria: Evidence for lithosphere-asthenosphere interaction
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Timing of subduction zone metamorphism during the formation and emplacement of Troodos and Baer-Bassit ophiolites: Insights from 40Ar-39Ar geochronology
No full textThe Troodos ophiolite in Cyprus and Baer-Bassit ophiolite in Syria together form part of the Tethyan ophiolite belt. They were generated in a supra-subduction zone setting in Late Cretaceous times. As with many of the ophiolite occurrences in this belt, the sequences are closely associated with tectonic 'coloured mélange' zones, which contain, among a variety of lithologies, metre- to kilometre-size blocks of metamorphic rocks. Precise 40Ar-39Ar laser step-heating experiments performed on four amphibolites from SW Cyprus and six from NW Syria, yield plateau ages ranging from 75.7 ± 0.3 Ma to 88.9 ± 0.8 Ma in Cyprus and 71.7 ± 0.5 to 88.4 ± 0.4 Ma in Syria. The older limits of these time spans are coeval with the age of the formation of the associated ophiolites. Unlike other metamorphic sole rocks which seem to form in relatively short time spans, these metamorphic rocks found in Cyprus and Syria are interpreted to have formed in Late Cretaceous times by accretion below the overriding Troodos and Baer-Bassit crust for a period of 15-18 Ma. The metamorphic complexes were exhumed by extension and crustal thinning associated with subduction roll-back and the rotation of the overriding plate until the cessation of subduction in Maastrichtian times. In Cyprus, the exhumed metamorphic complex was incorporated into an accretionary prism constructed primarily of the collapsed Mamonia passive margin sequence intercalated with rocks of the Troodos ophiolite during plate collision in the Maastrichtian. Concomitantly, in Syria, the Baer-Bassit ophiolite and subcreted metamorphic complex were emplaced onto the Arabian passive margin and fragmented into blocks and knockers, forming the Baer-Bassit mélange.link_to_subscribed_fulltex
Probing the basement of southern Tibet : evidence from crustal xenoliths entrained in a Miocene ultrapotassic dyke
Full text linkA variety of felsic and mafic granulites and ultramafic rocks occur as xenoliths within a 12.7 Ma ultrapotassic dyke intruding Xigaze flysch immediately to the north of the Yarlung-Tsangpo suture zone in southern Tibet. Garnet-clinopyroxene-plagioclase-quartz thermobarometry on mafic granulite xenoliths gives temperatures of 1130-1330 °C and pressures between 22 and 26 kbar indicating equilibration in the high-pressure and ultrahigh-temperature granulite field and defining a geotherm of c. 16 °C km-1. Ultramafic xenoliths consist mainly of hornblende and biotite, probably of restitic crustal rather than mantle origin, and attained peak metamorphic conditions of 920-1130 °C and 17-24 kbar, whereas felsic granulites equilibrated at 870-900 °C at an inferred pressure of 17 kbar. In situ U-(Th)-Pb laser ablation inductively coupled plasma mass spectrometry dating of zircons shows that protoliths may include Proterozoic basement rocks, Late Cretaceous calc-alkaline tonalites of the Gangdese batholith root and/or remnants of a Neo-Tethyan oceanic arc. Certain zircons from a felsic granulite and an ultramafic xenolith have mean 206Pb/238U ages of 16.8 ± 0.9 Ma and 15.6 ± 0.6 Ma, respectively, and monazites from a micaceous xenolith yielded a mean 208Pb/232Th age of 14.4 ± 0.4 Ma. These results show that the southern Tibet basement reached a thickness of c. 80 km by 17-14 Ma at the latest and has remained unchanged until the present day. © 2009 Geological Society of London
Regions in the <i>ϵ</i><sub>1</sub>-|<i>ϵ</i><sub>2</sub>| parameter space where the spectral amplitudes could be calculated with an accuracy better than 1%, according to analysis presented in [26].
No full textIn the dark shaded region the Stewart-Lyth (SL) approximation [22], as well as all other approximations are supposedly sufficiently accurate. Second-order corrections, as calculated by Stewart and Gong (SG) [46], extend that region to the light shaded region. The constant horizon approximation at order n (chn), and the growing horizon approximation at order n (ghn), do well below the thick line. The rays indicate where the corresponding higher order corrections are necessary. The thick line itself is the condition ϵ1|ϵ2| A/100%)/ΔN, with ΔN = 10 and A = 1%. We study these approximations and others, and find that our models defy these analyses. Figure and caption adapted with author permission from [26].</p
Petrogenesis of latest miocene-quaternary continental intraplate volcanism along the northern Dead Sea Fault System (Al Ghab-Homs volcanic field), western Syria: Evidence for lithosphere-asthenosphere interaction
No full textLate Miocene to Quaternary intraplate basaltic volcanism in the Al Ghab and Homs regions, northwestern Syria (the Al Ghab volcanic group and the Homs volcanic group), occurred roughly synchronously with the propagation of the Dead Sea Fault System in these regions. Petrographic evidence as well as major and trace element variations suggest that the basalts have undergone varying amounts of crystal fractionation of olivine ± clinopyroxene ± spinel, with feldspar fractionation only in the most evolved samples. The major and trace element chemistry and Nd-Sr-Pb isotopic variations of the basalts reflect both mantle source heterogeneity and relatively minor crustal contamination. Semi-quantitative assimilation-fractional crystallization modelling suggests that some samples may reflect assimilation of no more than 6% of upper continental crust, probably with Late Proterozoic Arabian Shield characteristics. Amongst the least crustally contaminated and relatively primitive samples, basanites are characterized by marked depletion of K, Rb and Zr relative to other neighbouring incompatible elements on primitive mantle normalized trace element diagrams. This, together with their low SiO 2 and high TiO 2 and Dy/Yb, is consistent with magma genesis involving a large proportion of garnet-bearing hornblendite or similar amphibole-rich metasomatic veins. Associated alkali and tholeiitic basalts with the higher SiO 2, lower TiO 2, less negative K, Rb and Zr anomalies, and moderately high Dy/Yb are consistent with melt extraction from a largely peridotitic mantle source. It is suggested that the compositional spectrum from basanite via alkali basalt to tholeiitic basalt can be explained by increasing degrees of metasomatic vein-wall-rock interaction, plus asthenospheric melt assimilation. In agreement with this is the identification of three distinct isotopic and chemical characteristics within the spectrum of mafic lavas, each of which can be referred to a unique mantle source (metasomatic vein, lithospheric wall-rock peridotite mantle and asthenospheric peridotite mantle). A decrease in eruption volume and increase in Si-undersaturation of the lavas from south (Homs) to north (Al Ghab) along the northern Dead Sea Fault System from latest Miocene to Quaternary times suggest a diminishing thermal perturbation and increasing importance of the amphibole-rich veins in magma genesis over time. It is proposed that the genesis of the oldest lavas reflects the arrival of asthenospheric melts beneath the Homs region, which with assimilation of lithospheric metasomatic veins and their wall-rocks produced the parental magmas of the Homs volcanic group. Subsequently, upwelling asthenospheric material could have been channelled northwards at the base of the lithosphere, presumably related to the northward propagation of the Dead Sea Fault System in the Pliocene. Cooling of this channelled asthenospheric material, which did not penetrate the lithosphere during this later period of magma genesis, provided the minimal thermal perturbation necessary for melting of amphibole-rich metasomatic veins and wall-rock peridotite within the lithosphere. © The Author 2011. Published by Oxford University Press.link_to_subscribed_fulltex
U-Pb zircon ages for Yarlung Tsangpo suture zone ophiolites, southwestern Tibet and their tectonic implications
No full textOphiolite complexes preserved along the Yarlung Tsangpo suture zone (YTSZ) and obducted onto the northern continental margin of India in southern Tibet represent the remnants of the once extensive Permian-Mesozoic Neo-Tethyan Ocean that separated India from Asia. Complete ophiolite successions are preserved near Xigaze, whereas the rest of the belt is essentially represented by mantle rocks with subordinate disrupted lower crustal rocks. U-Pb zircon LA-MC-ICP-MS geochronology on two gabbro samples from the Luobusa ophiolite yielded concordant data with mean 206Pb/238U ages of 149.9 ± 1.4 (2σ) Ma and 150.0 ± 5.0 Ma. These ages are in contrast to a younger age of 131.8 ± 1.0 Ma obtained from a pegmatitic gabbro in Xigaze. Five U-Pb zircon TIMS ages from gabbroic samples in the western portion of the ophiolite belt reveal that the Dangxiong ophiolite formed between 126.7 ± 0.4 Ma and 123.4 ± 0.8 Ma. Zircons from the Jungbwa ophiolite have similar ages of 123.4 ± 0.8 Ma and 123.9 ± 0.9 Ma. A single zircon analysed from a gabbro in Kiogar has an age of 159.7 ± 0.5 Ma. Geochronological data reported here show YTSZ ophiolites formed in association with intra-oceanic subduction zone systems and are related a significant tectonic episode within the Tethyan Ocean during Late Jurassic to Early to mid Cretaceous times. © 2013 International Association for Gondwana Research
