Asymmetric continental deformation during South Atlantic rifting along southern Brazil and Namibia     

《Gondwana Research》2017

Plate restoration of South America and Africa to their pre-breakup position faces the problem of gaps and overlaps between the continents, an issue commonly solved with implementing intra-plate deformation zones within South America. One of these zones is often positioned at the latitude of SE/S Brazil. However, geological evidence for the existence of a distinct zone in this region is lacking, which is why it remains controversial and is not included in all modeling studies. In order to solve this problem we present a study of multiple geological aspects of both parts of the margin, SE/S Brazil and its conjugate part NW Namibia at the time of continental breakup. Our study highlights pronounced differences between these regions with respect to Paraná-Etendeka lava distribution, magmatic dyke emplacement, basement reactivation, and fault patterns. In Namibia, faults and dykes reactivated the rift-parallel Neoproterozoic basement structure, whereas such reactivation was scarce in SE/S Brazil. Instead, most dykes, accompanied by small-scale grabens, are oriented margin-perpendicular along the margin from northern Uruguay to São Paulo. We propose that these differences are rooted in large-scale plate movement and suggest a clockwise rotation of southern South America away from a stable northern South America and Africa, in a similar way as proposed by others for a Patagonian continental section just prior to South Atlantic rifting. This rotation would produce margin-parallel extension in SE/S Brazil forming margin-perpendicular pathways for lava extrusion and leading to the asymmetric distribution of the Paraná-Etendeka lavas. NW Namibia instead remained relatively stable and was only influenced by extension due to rifting, hot spot activity, and mantle upwelling. Our study argues for significant margin-parallel extension in SE/S Brazil, however not confined to a single distinct deformation zone, but distributed across ~ 1000 km along the margin.  相似文献   

Post-collisional carbonatite-hosted rare earth element mineralization in the Hongcheon area,central Gyeonggi massif,Korea: Ion microprobe monazite U‐Th‐Pb geochronology and Nd‐Sr isotope geochemistry     

《Ore Geology Reviews》2016

The Hongcheon area in the central Gyeonggi massif is a unique carbonatite locality in South Korea. The age and petrogenesis of this uncommon rock type and associated rare earth element (REE) mineralization still remain uncertain. The NNE trending, 20–50 m wide and ~ 2 km long Fe-REE ore bodies are hosted within a swarm of carbonatite dykes intruding Precambrian basement gneisses. The intrusive nature of the dykes, fenite alteration halos, exsolution intergrowths of constituent minerals and stable isotope data in the literature collectively attest to the ore formation by crystallization of carbonatite magma. The carbonatites are composed primarily of dolomite, ankerite, siderite, magnetite, monazite, apatite, strontianite and pyrite with subordinate quartz, barite, columbite, fergusonite and calcite. The principal carrier phase of REEs is monazite. The REE contents of monazite vary narrowly (TREO = 66.1–69.4 wt.%) irrespective of the textural occurrence. Although the monazite shows a sample-to-sample variation in La/Nd ratio, the textural varieties from each rock sample are similar with respect to this ratio. Thorium contents in monazite are consistently low (average = ca. 2500 ppm) with unusually high (average = ca. 2200) Th/U ratios. Sensitive high-resolution ion microprobe (SHRIMP) dating of monazite yielded a weighted mean ²⁰⁸Pb/²³²Th age of 232.9 ± 1.6 Ma, which agrees with a weighted mean ²⁰⁶Pb/²³⁸U age of 227.2 ± 8.3 Ma within uncertainties. This age, coupled with comparable intrusion ages documented for kimberlites and monzonite-syenite-gabbro-mangerite suite from central Korea, demonstrates the occurrence of mantle-derived alkaline igneous activities and associated REE mineralization following the North and South China collision. The intrusion of the Hongcheon carbonatite and potassic or ultrapotassic suite in central Korea may have resulted from the post-collisional detachment of the subducted slab and consequent upwelling of hot asthenosphere and melting of the overriding lithospheric mantle. Initial Nd‐Sr isotopic ranges of the Hongcheon carbonatite (ε_Nd = ca. − 26, ⁸⁷Sr/⁸⁶Sr = 0.703–0.706) and previous trace element data deny a petrogenetic linkage with the coeval silicate magmas. The metasomatism in the lithospheric mantle source of the Hongcheon carbonatite must have occurred in the distant past (> 1.7 Ga) to generate significantly negative ε_Nd values.  相似文献   

Assessing the vegetation canopy influences on wind flow using wind tunnel experiments with artificial plants     

YOUNGJOO HONG  DONGYEOB KIM  SANGJUN IM 《Journal of Earth System Science》2016,125(3):499-506

Wind erosion causes serious problems and considerable threat in most regions of the world. Vegetation on the ground has an important role in controlling wind erosion by covering soil surface and absorbing wind momentum. A set of wind tunnel experiments was performed to quantitatively examine the effect of canopy structure on wind movement. Artificial plastic vegetations with different porosity and canopy shape were introduced as the model canopy. Normalized roughness length (Z ₀/H) and shear velocity ratio (R) were analyzed as a function of roughness density (λ). Experiments showed that Z ₀/H increases and R decreases as λ reaches a maximum value, λ _max, while the values of Z ₀/H and R showed little change with λ value beyond as λ _max.  相似文献   

A new species of the Late Cretaceous ‘sail-finned’ bony fish,Pentanogmius (Actinopterygii: Tselfatiiformes), from Texas,USA     

《Cretaceous Research》2016

Pentanogmius Taverne (Actinopterygii: Tselfatiiformes) is a Late Cretaceous bony fish. Here, the diagnosis for the genus is emended and a new species, P. fritschi sp. nov., described. The new species is based on a nearly complete skeleton from the Britton Formation (upper Cenomanian–lower Turonian) of the Eagle Ford Shale in Dallas County, Texas, USA. The skeleton measures about 1.7 m in total length and represents the sole Cenomanian–Turonian example of Pentanogmius in North America. The most peculiar aspect of this new species is the morphology of the dorsal fin in which its anterior one-third is elongate to form a ‘hook-shaped sail.’ Pentanogmius fritschi sp. nov. was likely an active swimmer in open ocean environments that possibly fed opportunistically on a variety of relatively small pelagic fishes and invertebrates. The present stratigraphic record and anatomical evidence indicate the following phylogenetic hypothesis among the three North American Pentanogmius species: [P. fritschi sp. nov. [P. evolutus + P. crieleyi]].  相似文献   

An efficient quasi-Newton approximation-based SORM to estimate the reliability of geotechnical problems     

《Computers and Geotechnics》2016

The first order reliability method (FORM) is efficient, but it has limited accuracy; the second order reliability method (SORM) provides greater accuracy, but with additional computational effort. In this study, a new method which integrates two quasi-Newton approximation algorithms is proposed to efficiently estimate the second order reliability of geotechnical problems with reasonable accuracy. In particular, the Hasofer–Lind–Rackwitz–Fiessler–Broyden–Fletcher–Goldfarb–Shanno (HLRF–BFGS) algorithm is applied to identify the design point on the limit state function (LSF), and consequently to compute the first order reliability index; whereas the Symmetric Rank-one (SR1) algorithm is nested within the HLRF–BFGS algorithm to compute good approximations, yet with a reduced computational effort, of the Hessian matrix required to compute second order reliabilities. Three typical geotechnical problems are employed to demonstrate the ability of the suggested procedure, and advantages of the proposed approach with respect to conventional alternatives are discussed. Results show that the proposed method is able to achieve the accuracy of conventional SORM, but with a reduced computational cost that is equal to the computational cost of HLRF–BFGS-based FORM.  相似文献   

Study of high temperature targets identification and temperature retrieval experimental model in SWIR remote sensing based Landsat8     

《International Journal of Applied Earth Observation and Geoinformation》2016

For surface features in short-wave infrared (SWIR, 1.3–3.0 μm) in remote sensing imagery, pixel values depict the total energy including reflection and emission. For surface features at normal temperature in SWIR band, emission energy can be ignored. While for surface features at high temperature in SWIR band, emission energy is equal to or even higher than the reflection energy. So remote sensing imagery of SWIR band can be used to separate emission and reflection energy as well as to realize temperature retrieval of high temperature targets. In this study, the seventh band (SWIR band) of Landsat8 OLI remote sensing imagery is used to perform the theoretical model research for temperature retrieval of high temperature targets. In the meantime, it is also used with the corresponding observation experiment of synchronization satellite to check the theoretical model. The result shows that the radiant flux density for mixed pixels with high temperature targets is higher than adjacent pixels without high temperature targets. Thus, the high temperature pixels can be identified in SWIR band. The retrieval results of temperature and fractional area for high temperature targets are consistent with reality. In the study, the result illustrates that it is effective to identify high temperature targets in remote sensing imagery of SWIR band and the model is appropriate for temperature retrieval use.  相似文献   

Recent advances in (soil moisture) triple collocation analysis     

《International Journal of Applied Earth Observation and Geoinformation》2016

To date, triple collocation (TC) analysis is one of the most important methods for the global-scale evaluation of remotely sensed soil moisture data sets. In this study we review existing implementations of soil moisture TC analysis as well as investigations of the assumptions underlying the method. Different notations that are used to formulate the TC problem are shown to be mathematically identical. While many studies have investigated issues related to possible violations of the underlying assumptions, only few TC modifications have been proposed to mitigate the impact of these violations. Moreover, assumptions, which are often understood as a limitation that is unique to TC analysis are shown to be common also to other conventional performance metrics. Noteworthy advances in TC analysis have been made in the way error estimates are being presented by moving from the investigation of absolute error variance estimates to the investigation of signal-to-noise ratio (SNR) metrics. Here we review existing error presentations and propose the combined investigation of the SNR (expressed in logarithmic units), the unscaled error variances, and the soil moisture sensitivities of the data sets as an optimal strategy for the evaluation of remotely-sensed soil moisture data sets.  相似文献   

Systematic Revision of Trilobites from the Middle Ordovician (Darriwilian) Klimoli Formation of the Zhuozishan Area, Inner Mongolia, China     

LEE Seung-Bae  LEE Dong-Chan  WOO Jusun  ZHANG Xingliang 《《地质学报》英文版》2016,90(6):1955-1975

New morphologic information permits systematic revision of trilobites from the Middle Ordovician Klimoli Formation of the Zhuozishan area, Ordos Basin, Inner Mongolia. The new assemblage is composed of 10 species of the Raphiophoridae, Nileidae, Asaphidae, and Telephinidae.? An asaphid, aff. Mioptychopyge lashachungensis (previously Paraptychopyge lashachungensis) displays an intermediate morphology between the Chinese nobiliasaphine genera Mioptychopyge and Zhenganites. The pygidial doublure is regarded as the most significant character to differentiate Symphysurus klimoliensis (previously Nileus klimoliensis) of the Nileidae from such closely allied taxa as Poronileus. A nileid, cf. Peraspis kujandensis displays typical nileid morphology, unlike the type species, Peraspis lineolata, which might turn out to be an asaphid. Ampyx gongwusuensis sp. nov. of the Raphiophoridae is the first record of the genus in the Zhuozishan area and reveals morphologic details that might be employed to resolve Ampyx taxonomy in China. Morphologic differences between A. gongwusuensis and Abulbaspis ordosensis might represent a case of sexual dimorphism.  相似文献   

Improved assessments of wave-induced fatigue for free spanning pipelines     

《Applied Ocean Research》2016

For subsea pipeline projects, the costs related to seabed correction and free span intervention are often considerable. Development of reliable methods for fatigue analyses of pipelines in free spans contributes to minimize costs without compromising pipeline integrity. Assessment of wave-induced fatigue damage on multi-span pipelines is investigated, and improved analysis methods are suggested in this paper. A time-domain (TD) algorithm is developed, which accounts for non-linear hydrodynamic loading and dynamic interaction between adjacent spans. The proposed TD approach is employed to evaluate linearized frequency-domain (FD) solutions from recognized design standards and to study the dynamic response of multi-span pipelines to direct wave loading. Differences between multi- and single-span analyses are described for the first time, and the common assumption that the main fatigue damage contribution comes from the fundamental mode is demonstrated not to hold for multi-spans. An improved FD solution capable of predicting multi-mode response is derived and demonstrated to give accurate fatigue life estimates for multi-span pipelines.  相似文献   

Axial friction response of full-scale pipes in soft clays     

《Applied Ocean Research》2016

The axial friction response of subsea pipelines in soft clays is a very important aspect for designers of subsea pipelines but the response is not well understood so far. There is a pressing need for the comprehension of the response. In this paper, model tests are performed using full-scale pipes coated with polyethylene (PE) to study the effects of the set-up period, the pipe diameter, the buried depth of the pipe, the shear strength of soft clays and the loading rate on the axial friction response of pipelines in soft clays. The variations of the axial friction coefficient are analyzed using the effective stress method based on model test results. The results show that the axial friction resistance increases with the increasing pipe diameter but the effect of the pipe diameter on the axial friction coefficient can be neglected. The ultimate axial resistance also increases with the increase of the buried depth of pipelines, the undrained shear strength of soft clays and the loading rate. The axial friction coefficient increases with the increasing loading rate. However, the axial friction coefficient decreases with the increasing buried depth. The method to determine the axial friction coefficient is developed by analyzing model test results, which considers the effects of the diameter, the buried depth, the undrained shear strength of soft clays and the loading rate. The study results not only extend the industry data base but also supply a basis to determine the axial friction coefficient of PE-coated pipes in soft clays for ocean engineering geological investigations.  相似文献