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  • Articles  (477)
  • Geosciences  (477)
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  • Articles  (477)
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  • 1
    Electronic Resource
    Electronic Resource
    Determination of phase transition pressures of ZnTe under quasihydrostatic conditions (1993)
    Springer
    Pure and applied geophysics 141 (1993), S. 643-652 
    Details
    ISSN: 1420-9136
    Keywords: High pressure ; pressure calibration ; ZnTe ; synchrotron X-ray source ; DIA type cubic anvil apparatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Pressure behavior of ZnTe at room temperature was studied using an X-ray energy dispersive method on a DIA type cubic anvil apparatus (SAM-85) at NSLS-X17B1. By using powdered polyethylene, the sample and NaCl for a pressure scale were held under quasihydrostatic conditions, which were confirmed by X-ray diffraction method. Two high-pressure phase transitions were confirmed using X-ray powder diffraction simultaneously with electrical resistance measurements. The phase transition pressures under quasihydrostatic conditions were determined to be 9.6 GPa, at which the resistance increased, and 12.0 GPa, which was the midpoint of a large resistance decrease. Errors in the pressure determinations were estimated to be less than 0.2 GPa. These pressure values may depend on grain size and anisotropic stress effects on the calibrant. From X-ray observation of ZnTe, the bulk modulus of the zinc blende structure was calculated to beK 0=51(3) GPa andK 0 ′ =3.6(0.8), and the first transition at 9.6 GPa was found to have about 9% volume change. It was consistent with an anomaly in the pressure generating curves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00998350
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  • 2
    Electronic Resource
    Electronic Resource
    (ϖμ/ϖT) P of the lower mantle (1996)
    Springer
    Pure and applied geophysics 146 (1996), S. 533-549 
    Details
    ISSN: 1420-9136
    Keywords: Lower mantle ; seismic tomography ; thermoelasticiti ; composition models ; geodynamics ; shear modulus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We estimate (ϖμ/ϖT) P of the lower mantle at seismic frequencies using two distinct approaches by combining ambient laboratory measurements on lower mantle minerals with seismic data. In the first approach, an upper bound is estimated for |(ϖμ/ϖT) P | by comparing the shear modulus (μ) profile of PREM with laboratory room-temperature data of μ extrapolated to high pressures. The second approach employs a seismic tomography constraint (ϖ lnV S /ϖ lnV P ) P =1.8–2, which directly relates (ϖμ/ϖT) P with (ϖK S /ϖT) P . An average (ϖK S /ϖT) P can be obtained by comparing the well-established room-temperature compression data for lower mantle minerals with theK S profile of PREM along several possible adiabats. Both (ϖK S /ϖT) and (ϖμ/ϖT) depend on silicon content [or (Mg+Fe)/Sil of the model. For various compositions, the two approaches predict rather distinct (ϖμ/ϖT) P vs. (ϖK S /ϖT) P curves, which intersect at a composition similar to pyrolite with (ϖμ/ϖT) P =−0.02 to −0.035 and (ϖK S /ϖT) P =−0.015 to −0.020 GPa/K. The pure perovskite model, on the other hand, yields grossly inconsistent results using the two approaches. We conclude that both vertical and lateral variations in seismic velocities are consistent with variation due to pressure, temperature, and phase transformations of a uniform composition. Additional physical properties of a pyrolite lower mantle are further predicted. Lateral temperature variations are predicted to be about 100–250 K, and the ratio of (ϖ lnp/ϖ lnV S ) P around 0.13 and 0.26. All of these parameters increase slightly with depth if the ratio of (ϖ lnV S /ϖ lnV P ) P remains constant throughout the lower mantle. These predicted values are in excellent agreement with geodynamic analyses, in which the ratios (ϖ ln ϱ/ϖ lnV S ) P and (ϖ ϱ/ϖ lnV S ) P are free parameters arbitrarily adjusted to fit the tomography and geoid data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00874732
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  • 3
    Electronic Resource
    Electronic Resource
    Zircon U–Pb ages and tectonic implications of ‘Early Paleozoic’ granitoids at Yanbian, Jilin Province, northeast China (2004)
    Melbourne, Australia : Blackwell Science Pty
    The @island arc 13 (2004), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract  The Yanbian area is located in the eastern part of the Central Asian Orogenic Belt (CAOB) of China and is characterized by widespread Phanerozoic granitic intrusions. It was previously thought that the Yanbian granitoids were mainly emplaced in the Early Paleozoic (so-called ‘Caledonian’ granitoids), extending east–west along the northern margin of the North China craton. However, few of them have been precisely dated; therefore, five typical ‘Caledonian’ granitic intrusions (the Huangniling, Dakai, Mengshan, Gaoling and Bailiping batholiths) were selected for U–Pb zircon isotopic study. New-age data show that emplacement of these granitoids extended from the Late Paleozoic to Late Mesozoic (285–116 Ma). This indicates that no ‘Caledonian’ granitic belt exists along the northern margin of the North China craton. The granitoids can be subdivided into four episodes based on our new data: Early Permian (285 ± 9 Ma), Early Triassic (249–245 Ma), Jurassic (192–168 Ma) and Cretaceous (119–116 Ma). The 285 ± 9 Ma tonalite was most likely related to subduction of the Paleo-Asian Oceanic Plate beneath the North China craton, followed by Triassic (249–245 Ma) syn-collisional monzogranites, representing the collision of the CAOB orogenic collage with the North China craton and final closure of the Paleo-Asian Ocean. The Jurassic granitoids resulted from subduction of the Paleo-Pacific plate and subsequent collision of the Jiamusi–Khanka Massif with the existing continent, assembled in the Triassic. The Early Cretaceous granitoids formed in an extensional setting along the eastern Asian continental margin.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.2004.00442.x
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  • 4
    Electronic Resource
    Electronic Resource
    Separation of P- and S-wavefields from wide-angle multicomponent OBC data for a basalt model (2003)
    Oxford, UK : Blackwell Science Ltd
    Geophysical prospecting 51 (2003), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Wide-angle multicomponent ocean-bottom cable (OBC) data should further enhance sub-basalt imaging by using both compressional and converted shear wavefields. The first step in analysing multicomponent OBC data is to decompose the recorded wavefields into pure P- and pure S-wavefields, and extract the upgoing P- and S-waves. This paper presents a new scheme to separate P- and S-wavefields from wide-angle multicomponent OBC data in the τ–p domain. By considering plane-wave components with a known horizontal slowness, the P- and S-wavefields are separated into the directions of observed P- and S-wave oscillations using the horizontal and vertical components of the data. The upgoing P- and S-waves are then extracted from the separated P- and S-wavefields. The parameters used in the separation are the seismic wave velocities and the density at the receiver location, which can be estimated from the first reflection phase observed on the horizontal and vertical components. Numerical tests on synthetic data for a plane-layered model show good performance and demonstrate the accuracy of the scheme. Separation of wavefields from a basalt model is performed using synthetic wide-angle multicomponent OBC data. The results show that both near-offset and wide-angle reflections and conversions from within and below basalt layers are enhanced and clearly identified on the separated wavefields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.2003.00377.x
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  • 5
    Electronic Resource
    Electronic Resource
    Dislocation dissociation in CaGeO3 perovskite (1989)
    Springer
    Physics and chemistry of minerals 16 (1989), S. 630-633 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Dissociated dislocations have been observed for the first time by transmission electron microscopy in the perovskite-structure compound CaGeO3. Dislocations with Burgers vectors $$\left[ {1\bar 10} \right]$$ and [001] (in pseudo-cubic index) are dissociated into collinear partials on the (110) plane: $$\left[ {1\bar 10} \right] = {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {1\bar 10} \right] + {1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}\left[ {1\bar 10} \right]$$ and [001] = 1/2[001] + 1/2[001]. The partials react to form octagonal extended nodes. The stacking fault ribbons with displacement vector $$\left[ {1\bar 10} \right]$$ have a width of 350 A, which corresponds to a stacking fault energy of 35 erg/cm2 (or mJ/m2).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00223310
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  • 6
    Electronic Resource
    Electronic Resource
    Olivine as an in situ piezometer in high pressure apparatus (1988)
    Springer
    Physics and chemistry of minerals 15 (1988), S. 493-497 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The deviatoric stress produced in a large-volume, high-pressure apparatus of the girdle-anvil type has been estimated from the density of free dislocations induced in natural olivine single crystals (initial density of 2×106 cm−2). Experiments at maximum pressure P=40 kbar and temperature T=1050°C for t=1 h in NaCl cell assemblies and various P-T paths yield specimens whose dislocation densities are unchanged from this initial value, implying that the deviatoric stress was less than 140 bar. In BN cell assemblies, the recovered specimen from high P-T experiments exhibit much higher densities of dislocations (∼109 cm−2) which have been produced by steady-state plastic deformation of the olivine crystals under a deviatoric stress of ∼3 kbar. This value of deviatoric stress in BN has been corroborated by observations of the subgrain size and recrystallized grain size in specimens of longer run duration (3 h).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00311130
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  • 7
    Electronic Resource
    Electronic Resource
    Optical Absorption Spectra of (Mg, Fe)SiO3 Silicate Perovskites (1994)
    Springer
    Physics and chemistry of minerals 20 (1994), S. 478-482 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Electronic absorption spectra have been measured at room temperature and pressure for polycrystalline samples of (Mg, Fe)SiO3 silicate perovskites synthesized by multi-anvil device. One strong near-infrared band at about 7000 cm-1 and several weak bands in the visible region were found. The near-infrared band at 7000 cm-1 is assigned to a spin-allowed transition of Fe2+ at the 8–12 coordinated site in perovskite. However, definite assignments of the weak bands in the visible region are difficult because of their low intensities and the scattering effect at the gain boundaries. Crystal field calculations for Fe2+ at different sites in perovskite have been carried out based on the crystal structure data. The results agree with the assignment of Fe2+ to the 8–12 coordinated site in perovskite. Crystal field stabilization energy of Fe2+ with coordination number of 8 in perovskite is 3332 cm-1 which is small compared to the octahedral site of magnesiowüstite (4320 cm-1), another important lower-mantle mineral.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203217
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  • 8
    Electronic Resource
    Electronic Resource
    Electron microscopy study of domain structure due to phase transitions in natural perovskite (1993)
    Springer
    Physics and chemistry of minerals 20 (1993), S. 147-158 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Transmission electron microscopy on natural calcium metatitanate perovskite (dysanalyte) reveals the following twin laws in the orthorhombic (space group Pbnm) phase: reflection twins on the {110} and {112} planes, and 90° rotation twins about the [001] axis (referred to as [001]90° twin). Single crystals that were heattreated and quenched from above 1585 K exhibit a dramatic change in domain structure compared with the starting material and specimens quenched from T 〈 1470 K. Mutually perpendicular {110} and [001]90° twins are observed throughout the crystal, forming a cross-hatched domain texture. 1/2[001] antiphase domains, which are very rarely observed in the starting material, also become dominant in the crystal. This change in domain structure is interpreted as due to a structural phase transition in perovskite at a temperature below 1585 K. From the point symmetry elements that describe the twin laws and the translational elements that relate the antiphase domains, the most likely phase near 1585 K is tetragonal with space group P4/mbm. These results are consistent with high-temperature powder X-ray diffraction study. On the other hand, density of the {112} twins is increased significantly in the crystal quenched from 1673 K. Twin domains are either bound by mutually perpendicular {110} and (001) walls, or by {112} walls with {110} twin domains within the polygonal {112} domains. Both twin density variation and domain morphology suggest that the crystal may be cubic at this temperature. Microstructure of a single crystal deformed at 1273 K and 3.5 GPa (within the orthorhombic stability field) is morphologically quite distinct from that of the heat-treated specimens. Dislocations dominate the microstructure and often interact with twin domain boundaries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00200117
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  • 9
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    Data Analysis of Safety Assessment and Early Warning for Offshore Platform (2020)
    Coastal Education and Research Foundation
    Details
    Publication Date: 2020-07-10
    Print ISSN: 0749-0208
    Electronic ISSN: 1551-5036
    Topics: Geosciences
    Published by Coastal Education and Research Foundation
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  • 10
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    Early Cretaceous Xiuyan adakitic granitoids in the Liaodong Peninsula, east China: Petrogenesis and implications for lithospheric thinning of the North China Craton (2020)
    Canadian Science Publishing
    Details
    Publication Date: 2020-07-07
    Description: Mesozoic magmatic rocks are widely distributed in the North China Craton (NCC) and are crucial to understanding the timing, location, and geodynamic mechanisms of lithospheric thinning of the NCC. In this study, we report geochronological, petrogeochemical and Lu–Hf isotopic data for adakitic granitoids from different parts of Xiuyan pluton in the Liaodong Peninsula, aiming to constrain their magma sources, petrogenesis and tectonic implications. The adakites are metaluminous to weakly peraluminous and are classified as high-K calc-alkaline I-type granite with Early Cretaceous zircon U–Pb ages of 129–126 Ma. They exhibit adakite-like geochemical characteristics, such as high Sr content and low Yb and Y contents, coupled with high Sr/Y and no pronounced Eu anomalies. They are enriched in Rb, U and light rare-earth elements and are depleted in Ta, Nb, P, and Ti. The adakites from the eastern part of the pluton have low εHf(t) values (−8.5 to −4.0) with old TDM2 ages (1.57–1.31 Ga), indicating they were derived from the lower crust containing juvenile mantle-derived materials. In contrast, adakites from the northern part of the pluton have lower εHf(t) values (−19.7 to −16.6) with older TDM2 ages (2.21–2.03 Ga), indicating that they were derived mainly from an ancient crust. Our results show that both two adakitic magmas were derived from partial melting of delaminated lower crust. Their relatively high MgO, Ni contents and Mg# values indicate that the melts interacted with mantle peridotites. The lower crust delamination beneath the Liaodong Peninsula resulted from paleo-Pacific plate subduction during the Early Cretaceous, which resulted in thinning of Mesozoic crust in the Xiuyan area.
    Print ISSN: 0008-4077
    Electronic ISSN: 1480-3313
    Topics: Geosciences
    Published by Canadian Science Publishing
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