Comment on “Evidence for Mesoproterozoic collision,deep burial and rapid exhumation of garbenschiefer in the Namaqua Front,South Africa” by Valby Van Schijndel,David H. Cornell,Robert Anczkiewicz,Anders Scherstén,Geoscience Frontiers,Volume 11, Issue 2, Pages 511-531     

《地学前缘(英文版)》2020,11(5):1889-1894

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An improved analytical approach for simulating the lateral kinematic distress of deepwater offshore pipelines     

《Applied Ocean Research》2019

Offshore pipelines are critical infrastructures and any possible damage may have devastating financial and environmental consequences. Earthquake-related geohazards (such as strong ground motion, active seismic faults, submarine landslides and debris flows) consist crucial threats that an offshore pipeline has to overcome. The main aim of the current study is to examine analytically a seabed-laid offshore pipeline subjected to a lateral kinematic distress due to a submarine landslide or a debris flow. Extra emphasis is given on the impact of pipe-soil interaction on the pipe response, by the realistic representation of the soil resistance via a tri-linear model. Firstly, the proposed analytical model is validated with a numerical model utilizing the finite-element method. Subsequently, various combinations of soil parameters and loading conditions that affect the examined problem are investigated with realistic input data taken from the offshore section of the high-pressure natural-gas pipeline TAP (Trans Adriatic Pipeline) in the Adriatic Sea. Finally, useful conclusions are drawn regarding the applicability and the efficiency of the proposed approach.  相似文献   

Origin of K-rich diamond-forming immiscible melts and CO2 fluid via partial melting of carbonated pelites at a depth of 180–200 km     

《Gondwana Research》2019

Melt inclusions in kimberlitic and metamorphic diamonds worldwide range in composition from potassic aluminosilicate to alkali-rich carbonatitic and their low-temperature derivative, a saline high-density fluid (HDF). The discovery of CO₂ inclusions in diamonds containing eclogitic minerals are also essential. These melts and HDFs may be responsible for diamond formation and metasomatic alteration of mantle rocks since the late Archean to Phanerozoic. Although a genetic link between these melts and fluids was suggested, their origin is still highly uncertain. Here we present experimental results on melting phase relations in a carbonated pelite at 6 GPa and 900–1500 °C. We found that just below solidus K₂O enters potassium feldspar or K₂TiSi₃O₉ wadeite coexisting with clinopyroxene, garnet, kyanite, coesite, and dolomite. The potassium phases react with dolomite to produce garnet, kyanite, coesite, and potassic dolomitic melt, 40(K_0.90Na_0.10)₂CO₃·60Ca_0.55Mg_0.24Fe_0.21CO₃ + 1.9 mol% SiO₂ + 0.7 mol% TiO₂ + 1.4 mol% Al₂O₃ at the solidus established near 1000 °C. Molecular CO₂ liberates at 1100 °C. Potassic aluminosilicate melt appears in addition to carbonatite melt at 1200 °C. This melt contains (mol/wt%): SiO₂ = 57.0/52.4, TiO₂ = 1.8/2.3, Al₂O₃ = 8.5/13.0, FeO = 1.4/1.6, MgO = 1.9/1.2, CaO = 3.8/3.2, Na₂O = 3.2/3.0, K₂O = 10.5/15.2, CO₂ = 12.0/8.0, while carbonatite melt can be approximated as 24(K_0.81Na_0.19)₂CO₃·76Ca_0.59Mg_0.21Fe_0.20CO₃ + 3.0 mol% SiO₂ + 1.6 mol% TiO₂ + 1.4 mol% Al₂O₃. Both melts remain stable to at least 1500 °C coexisting with CO₂ fluid and residual eclogite assemblage consisting of K-rich omphacite (0.4–1.5 wt% K₂O), almandine-pyrope-grossular garnet, kyanite, and coesite. The obtained immiscible alkali‑carbonatitic and potassic aluminosilicate melts resemble compositions of melt inclusions in diamonds worldwide. Thus, these melts entrapped by diamonds could be derived by partial melting of the carbonated material of the continental crust subducted down to 180–200 km depths. Given the high solubility of chlorides and water in both carbonate and aluminosilicate melts inferred in previous experiments, the saline end-member, brine, could evolve from potassic carbonatitic and/or silicic melts by fractionation of Ca-Mg carbonates/eclogitic minerals and accumulation of alkalis, chlorine and water in the residual low-temperature supercritical fluid. Direct extraction from the hydrated marine sediments under conditions of cold subduction would be another possibility for the brine formation.  相似文献   

Benthic foraminiferal fauna and sediment provenance of Eocene syn-rift sequences in Taiwan: implication for onset of Asian epi-continental marginal seas off China coast     

Huang  Chi-Yue  Shao  Lei  Wang  Ming-Huei  Xue  Wei-Guang  Qiao  Pei-Jun  Cui  Yu-Chi  Hou  Yuan-Li 《Marine Geophysical Researches》2019,40(2):111-127

Marine Geophysical Research - Early Cenozoic rift basins developed commonly on the Mesozoic basement along the SE Asia Continent. However, Eocene–Oligocene sequences were only exposed widely...  相似文献   

Holocene permafrost history and cryostratigraphy in the High‐Arctic Adventdalen Valley,central Svalbard     

Stefanie Cable  Bo Elberling  Aart Kroon 《Boreas: An International Journal of Quaternary Research》2018,47(2):423-442

This paper presents the history and cryostratigraphy of the upper permafrost in the High‐Arctic Adventdalen Valley, central Svalbard. Nineteen frozen sediment cores, up to 10.7 m long, obtained at five periglacial landforms, were analysed for cryostructures, ice, carbon and solute contents, and grain‐size distribution, and were ¹⁴C‐ and OSL‐dated. Spatial variability in ice and carbon contents is closely related to the sedimentary history and mode of permafrost aggradation. In the valley bottom, saline epigenetic permafrost with pore ice down to depths of 10.7 m depth formed in deltaic sediments since the mid‐Holocene; cryopegs were encountered below 6 m. In the top 1 to 5 m, syngenetic and quasi‐syngenetic permafrost with microlenticular, lenticular, suspended and organic‐matrix cryostructures developed due to loess and alluvial sedimentation since the colder late Holocene, which resulted in the burial of organic material. At the transition between deltaic sediments and loess, massive ice bodies occurred. A pingo developed where the deltaic sediments reached the surface. On hillslopes, suspended cryostructure on solifluction sheets indicates quasi‐syngenetic permafrost aggradation; lobes, in contrast, were ice‐poor. Suspended cryostructure in eluvial deposits reflects epigenetic or quasi‐syngenetic permafrost formation on a weathered bedrock plateau. Landform‐scale spatial variations in ground ice and carbon relate to variations in slope, sedimentation rate, moisture conditions and stratigraphy. Although the study reveals close links between Holocene landscape evolution and permafrost history, our results emphasize a large uncertainty in using terrain surface indicators to infer ground‐ice contents and upscale from core to landform scale in mountainous permafrost landscapes.  相似文献   

Preface to Special Issue ‘Insights on the vertebrate paleontology of the Neuquén Group,Argentina’     

《Cretaceous Research》2018

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Correction to: Flood hazard assessment and mapping of River Swat using HEC-RAS 2D model and high-resolution 12-m TanDEM-X DEM (WorldDEM)     

Farooq  Muhammad  Shafique  Muhammad  Khattak  Muhammad Shahzad 《Natural Hazards》2019,97(2):493-493

Natural Hazards - The original article was updated and corrected due to numbering errors in Figure 8’s subfigures and the placement of some of the article’s other figures. Additional...  相似文献   

Two generations of Variscan garnet: Implications from a petrochronological study of a high-grade Avalonia-derived paragneiss from the Drosendorf unit,Bohemian Massif     

《Gondwana Research》2020

Garnets in metapelitic paragneisses from the southern Drosendorf unit in the Austrian part of the Bohemian Massif exhibit two episodes of growth during the Variscan orogeny, which can be distinguished on textural and chemical grounds. The first garnet (grt1) records evidence of high-grade metamorphism in the Late Devonian (Frasnian–Famennian), while the second garnet (grt2) formed by a second high-grade event in the Early Carboniferous (Visean). Both garnet generations contain abundant inclusions, of which monazite, rutile and crystallised melt droplets are particularly useful for reconstructing P–T–t conditions. The Late Devonian age (373 ± 9 Ma) for the first episode of garnet growth was obtained from chemical dating of monazite inclusions in grt1. Metamorphic conditions during the first episode of garnet growth are estimated to have been between 0.7 and 0.8 GPa at 680–700 °C and 0.95–1.10 GPa at 745–785 °C. There followed a phase of cooling and exhumation, after which the second garnet (grt2) were formed beginning under amphibolite facies conditions and continuing prograde to peak conditions of 0.95–1.10 GPa and 745–785 °C, which are similar to those of the first garnet forming event. Subsequently, the rocks experienced near isothermal decompression to 0.5–0.8 GPa. Chemical dating of both monazite inclusions in grt2 and the matrix provide a Visean age (343 ± 3 Ma).A study of detrital zircons in these paragneisses revealed zircon forming events at around 1.2, 1.5 and 1.8 Ga, suggesting an Avalonian provenance. The lack of zircons younger than 1 Ga and the presence of Cadomian metamorphic monazite relics (652 ± 15 Ma) indicates an Early Neoproterozoic deposition age for the sedimentary protolith likely. Our documentation of a Late Devonian high-grade metamorphic event in rocks derived from Avalonian corroborates tectonic models which assume that frontal parts of the Armorican terrane had already docked with Avalonia by this time.  相似文献   

Estimating average shock pressures recorded by impactite samples based on universal stage investigations of planar deformation features in quartz—Sources of error and recommendations          下载免费PDF全文

S. Holm-Alwmark  L. Ferrière  C. Alwmark  M. H. Poelchau 《Meteoritics & planetary science》2018,53(1):110-130

Planar deformation features (PDFs) in quartz are the most widely used indicator of shock metamorphism in terrestrial rocks. They can also be used for estimating average shock pressures that quartz-bearing rocks have been subjected to. Here we report on a number of observations and problems that we have encountered when performing universal stage measurements and crystallographically indexing of PDF orientations in quartz. These include a comparison between manual and automated methods of indexing PDFs, an evaluation of the new stereographic projection template, and observations regarding the PDF statistics related to the c-axis position and rhombohedral plane symmetry. We further discuss the implications that our findings have for shock barometry studies. Our study shows that the currently used stereographic projection template for indexing PDFs in quartz might induce an overestimation of rhombohedral planes with low Miller–Bravais indices. We suggest, based on a comparison of different shock barometry methods, that a unified method of assigning shock pressures to samples based on PDFs in quartz is necessary to allow comparison of data sets. This method needs to take into account not only the average number of PDF sets/grain but also the number of high Miller–Bravais index planes, both of which are important factors according to our study. Finally, we present a suggestion for such a method (which is valid for nonporous quartz-bearing rock types), which consists of assigning quartz grains into types (A–E) based on the PDF orientation pattern, and then calculation of a mean shock pressure for each sample.  相似文献   

Forearc ophiolite in Havana-Matanzas, Western Cuba: evidence from serpentinized mantle peridotite REE geochemistry and Cr-spinel composition     

LLANES CASTRO Angélica Isabel  PROENZA Joaquín Antonio  CRUZ GáMEZ Esther María 《《地质学报》英文版》2018,92(Z2):19-21

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