The Triassic age for oceanic eclogites in the Dabie orogen: Entrainment of oceanic fragments in the continental subduction

Low-temperature and high-pressure eclogites with an oceanic affinity in the western part of the Dabie orogen have been investigated with combined Lu–Hf and U–Pb geochronology. These eclogites formed over a range of temperatures (482–565 °C and 1.9–2.2 GPa). Three eclogites, which were sampled from the Gaoqiao country, yielded Lu–Hf ages of 240.7 ± 1.2 Ma, 243.3 ± 4.1 Ma and 238.3 ± 1.2 Ma, with a corresponding lower-intercept U–Pb zircon age of 232 ± 26 Ma. Despite the well-preserved prograde major- and trace-element zoning in garnets, these Lu–Hf ages mostly reflect the high-pressure eclogite-facies metamorphism instead of representing the early phase of garnet growth due to the occurrence of omphacite inclusions from core to rim and the shell effect. An upper-intercept zircon U–Pb age of 765 ± 24 Ma is defined for the Gaoqiao eclogite, which is consistent with the weighted-mean age of 768 ± 21 Ma for the country gneiss. However, the gneiss has not been subjected to successive high-pressure metamorphism. The new Triassic ages are likely an estimate of the involvement of oceanic fragments in the continental subduction.     

Influences of overburden pressure and soil dilation on soil nail pull-out resistance

Soil nailing is the most popular technique for stabilizing newly formed and existing sub-standard slopes in Hong Kong because of its economic and technical advantages. The nail–soil interface shear resistance is an important parameter in design of soil nailed structures. A three-dimensional finite element model was established and used for simulating soil nail pull-out tests. The finite element model was verified by comparing simulated results with measured data. The agreement between the experimental and simulated results in terms of both average pull-out shear stress and stress variation was very good. Using this finite element model, a parametric study was carried out to study the influences of the overburden pressure and soil dilation angle on the soil nail pull-out resistance. The simulated peak pull-out resistance was not directly related to the overburden pressure, which was coincident with the observations in laboratory pull-out tests. The simulated pull-out resistance increased significantly with the increase in dilation angle of the shearing zone. This analysis indicated that the constrained dilatancy of the nail–soil interface and the soil surrounding the nail contributed a lot to the development of peak pull-out resistance.     

东海陆架盆地伸展率和压缩率及构造跃迁

东海陆架盆地位于欧亚板块的东南缘和西太平洋活动大陆边缘,本文选取了东海陆架盆地主要凹陷的17条地震剖面,采用平衡剖面技术,计算了主要凹陷新生代不同演化阶段的伸展率和压缩率。分析表明,东海陆架盆地构造演化总体由西向东跃迁。晚白垩世至晚古新世东海陆架盆地裂陷中心在西部坳陷带,始新世东迁至东部坳陷带,上新世东迁至东海陆架盆地东侧的冲绳海槽盆地。古新世中后期东海陆架盆地西部坳陷带北侧昆山凹陷反转;中新世东部坳陷带的西湖凹陷反转。东海陆架盆地西部坳陷带与东部坳陷带构造演化不同,证明了东海陆架盆地的东西分带。西部坳陷带北部的长江坳陷和南部的台北坳陷构造演化不同,东部坳陷带北部的西湖凹陷和南部的钓北凹陷构造演化不同,证明了东海陆架盆地的南北分块。     

Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies

The urban heat island (UHI), together with summertime heat waves, foster’s biophysical hazards such as heat stress, air pollution, and associated public health problems. Mitigation strategies such as increased vegetative cover and higher albedo surface materials have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently been investigated to better understand its heat island and related weather modifications. The objectives of this research were to (1) characterize temporal variations in the magnitude of UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under extremely high temperature conditions during Atlanta’s summer (June, July, and August) period, and (3) conduct theoretical numerical simulations to quantify the first-order effects of proposed mitigation strategies. Over the period 1984–2007, the climatological mean UHI magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71°C, respectively. There were statistically significant minimum temperature trends of 0.70°C per decade at Athens and −1.79°C per decade at Monticello while Atlanta’s minimum temperature remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the years spanning 1984–2007 and were exclusively summertime phenomena. The mean number of heat wave events in Atlanta during a given heat wave year was 1.83. On average, Atlanta heat waves lasted 14.18 days, although there was quite a bit of variability (standard deviation of 9.89). The mean maximum temperature during Atlanta’s heat waves was 35.85°C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta’s surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature. However, from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased vegetation seems to be a more likely choice for mitigating surface temperature.     

准噶尔盆地西北缘克百地区二叠系沉积特征及沉积模式

准噶尔盆地西北缘二叠系是重要的产油层和储集层,通过岩心观察、薄片分析,结合测井和录井资料,对西北缘克百断裂下盘二叠系砂砾岩的沉积环境和沉积特征进行了深入研究。研究表明,该区砂砾岩既有水上冲积扇沉积环境沉积的,也有水下扇三角洲前缘沉积环境形成的。前者主要为棕褐色、泥质杂基含量高、分选和磨圆差,储层物性相对较差;后者经过了稳定水流的淘洗,杂基含量少,钙质或沸石类胶结发育,分选性和磨圆度也较高,其物性条件也明显较好。并据此建立了研究区冲积扇与扇三角洲有机结合的沉积模式,该模式突出了湖岸线的重要性,同时模糊冲积扇与扇三角洲之间的界限。并对冲积扇与扇三角洲各亚相的岩性特征、沉积结构和沉积序列进行了归纳和总结,为该区寻找二叠系优质储层提供借鉴和思路。     

Clay minerals in the major Chinese coastal estuaries and their provenance implications

A sea-survey was carried out along the Chinese coast from the Bohai Sea to South China Sea, and 15 surficial samples were taken from major coastal estuaries, i.e., from north to south, the Yellow, abandoned Yellow, Yangtze, Qiantang, Ou, Min, Han, and Pearl River estuaries. On the basis of clay mineral analysis and published data collection, this paper discusses the characteristics of clay minerals of each coastal river and potentials of implications of sediment sources. The results show that the change of diagnostic clay minerals from smectite to kaolinite from the Yellow to the Pearl River estuaries is southward, as clearly shown by the ratios of smectite to chlorite (S/Ch) and kaolinite to illite (K/I). S/Ch decreases southward, while K/I moves reversely, implying change in climate setting from cool/dry to humid/hot with intensified weathering processes. Besides, these two indicators in the estuaries are also linked with the derivation of parent-rock of each river-basin and coastal hydrodynamics. The disproportional higher ratio of K/I in the Yellow and abandoned Yellow River estuaries is ascribed to their sediment sources with abundant loess component in the north-central China. The K/I decrease offshore from the Pearl River estuary is primarily due to hydrodynamic sorting. Therefore, the S/Ch and K/I of the present study comprehensively reflect the controls of climate, parent-rock, and sediment transport along the coast.     

Two-dimensional horizontal modeling of fine-sediment transport at the South Channel–North Passage of the partially mixed Changjiang River estuary,China

Tidal flow and fine-sediment transport at the South Channel–North Passage of the partially-mixed Changjiang River estuary were studied using a two-dimensional horizontal (2DH) numerical model. This 2DH model was achieved by depth-integrating the momentum and convection–diffusion equations. The Alternating Direction Implicit scheme was used to solve the governing equations. The iterative method was adopted for the calculation of convection and diffusion terms of momentum equation. Comparisons between calculated and measured results (tidal elevations and depth-averaged velocities) have shown reasonable agreement. Horizontal distributions of tidal current velocity and suspended sediment concentration were qualitatively consistent with observations. Those modeled results were analyzed to elucidate the mechanisms for the formation of the turbidity maximum and intratidal variations in fine-sediment transport processes.     

Temporal and spatial distribution characteristics of nutrients in Clarion-Clipperton Fracture Zone in the Pacific in 2017

This research investigated eight stations in Clarion-Clipperton Fracture Zone(CCFZ) in the eastern tropical Pacific in 2017 to study the spatial distribution characteristics of nutrients and chlorophyll a(Chl a) concentration,and compared nutrient concentrations and molar ratios with those of other investigations 20 years ago in the same area. The study found that dissolved inorganic nutrient(N, P and Si) concentrations were lowest in the upper layer, and increased from surface to some depths, t...     

Settlement Mode Analysis for An Immersed Tube Tunnel Considering A Nonuniform Foundation Under Tidal Load

Immersed tube tunnels are usually placed on soft soil layers in cross-sea tunnelling engineering. Owing to the influence of stratum conditions and slope design, the longitudinal distribution of substratum layers is generally uneven. Thus, the inhomogeneous deformation of the element-joint becomes the key factor in the failure of the immersed tube tunnel. Therefore, a corresponding calculation method for joint deformation is needed to explore the deformation law of immersed tube tunnels. By constructing a three-section immersed tube tunnel analysis model (TTM), the relationship between the two types of deformation of the immersed tube tunnel structure in a longitudinal nonuniform soft soil foundation is described, and the deformation characteristics of the immersed structure under different boundaries are discussed. Based on the mechanical behaviour of the joint and foundation, according to the Timoshenko beam on the Vlasov two-parameter foundation (VTM), considering the tidal cyclic load during the operation and maintenance period, an example analysis is given. Moreover, the deformation characteristics and development trend of the immersed tube tunnel under the influence of different soil layers are discussed. The obtained results have a certain guiding significance for the deformation calculation of immersed tube tunnels.

     

Efficient building facade structure extraction method using image-based laser point cloud

Facade structures from three-dimensional (3D) point cloud data (PCD) and two-dimensional (2D) optical images can provide significant information for 3D building modeling. However, a unified data model for integrating 2D imagery pixels and 3D PCD is absent in current methods, leading to a complex implementation process, large calculations, and inefficiency. An efficient facade structure extraction method for building facades is proposed in this study. Based on the conversion matrix, 2D image and 3D PCD information are merged to build an image-based laser point cloud (ILPC) data model first. Second, both the line segment detection and random sample consensus algorithms are improved according to the structure and characteristics of the ILPC data model. Finally, building facade structures are extracted and optimized. Facade structures can be extracted accurately and efficiently by the proposed method, which contains rich information support from the ILPC data model. The proposed method extracts fine building facade structures with accuracy over 0.68 in all experiments and recall up to 0.81, which are better than the Wang method. Extracted structures constitute valuable support for numerous fields, such as 3D building modeling and building information modeling construction.