The structure of the lower crust at the Argentine continental margin, South Atlantic at 44°S

It is well established that the Argentine passive margin is of the rifted volcanic margin type. This classification is based primarily on the presence of a buried volcanic wedge beneath the continental slope, manifested by seismic data as a seaward dipping reflector sequence (SDRS). Here, we investigate the deep structure of the Argentine volcanic margin at 44°S over 200 km from the shelf to the deep oceanic Argentine Basin. We use wide-angle reflection/refraction seismic data to perform a joint travel time inversion for refracted and reflected travel times. The resulting P-wave velocity-depth model confirms the typical volcanic margin structure. An underplated body is resolved as distinctive high seismic velocity (v_p up to 7.5 km/s) feature in the lower crust in the prolongation of a seaward dipping reflector sequence. A remarkable result is that a second, isolated body of high seismic velocity (v_p up to 7.3 km/s) exists landward of the first high-velocity feature. The centres of both bodies are 60 km apart. The high-velocity lower-crustal bodies likely were emplaced during transient magmatic–volcanic events accompanying the late rifting and initial drifting stages. The lateral variability of the lower crust may be an expression of a multiple rifting process in the sense that the South Atlantic rift evolved by instantaneous breakup of longer continental margin segments. These segments are confined by transfer zones that acted as rift propagation barriers. A lower-crustal reflector was detected at 3 to 5 km above the modern Moho and probably represents the lower boundary of stretched continental crust. With this finding we suggest that the continent–ocean boundary is situated 70 km more seaward than in previous interpretations.     

Calculation of the CO2 Degassing during Contact Metamorphism and Its Geological Significance: The Model and Example from the Shuanshan Area of the South Tan–Lu Fault Belt

The paper studies CO2 degassing and controlling factors under the condition of contact metamorphism in the Shuangshan area, southern Tan-Lu fault belt and the method of calculating the amount of CO2 degassing. The results show that the amount of CO2 degassing is controlled by the characteristics of the country rocks, including the thermal conductivity, penetrability, porosity and connectivity. Compositions, size and depth of intrusive rock also have an important influence on CO2 degassing, i.e., they generated numerous cracks in the country rocks, and thus allowed the easy flow and accumulation of fluids. The amount of CO2 flux in contact metamorphism is calculated quantitatively based on the metamorphic reaction and time-integrated fluid flux. The value （0.729- 2.446×10^4 mol/cm^2） of CO2 flux suggests that CO2 was provided mainly by the contact metamorphic reaction. The generation and releasing of CO2 are positively correlated with the degree of metamorphism, and XCO2 in fluids gradually increases from dolomite zone to calcite zone, but in the zone of grossular, fluid flux is the largest and XCO2 sharply decreases due to involvement of magmatic water. This study presents evidence that a large amount of industrial-scale CO2 can be produced during contact metamorphism. On the basis of theoretical and practical studies, a cone model has been proposed to response CO2 degassing for the contact metamorphism, and it can be used to explore CO2 accumulations beyond the oil-gas basins. This model can also be applied to the study of inorganic genesis of CO2 accumulations.     

On the impossibility of the co-existence of monsoons and severe storm surges in the Bay of Bengal

The problem of storm surges is introduced briefly. The utility of passive microwave observations to study this phenomenon is pointed out. The reasons for the nonoccurrence of severe surges in the Bay of Bengal, during monsoon regimes, is discussed in this paper. It was demonstrated that the predominant reason for lack of severe surges over the Bay of Bengal coast is due to the absence of weak wind shear during monsoon seasons.Atmospheric Environment Service, Ice Center, Environment Canada, 373 Sussex Drive, Ottawa, Ontario, Canada K1A OH3.     

五台山早元古代碰撞造山带初步认识

五台山地区分布着复杂的变质杂岩。过去人们把这些变质岩作为地层分成群组段。龙泉关剪切构造岩的发现突破了这种传统观念。野外工作中发现所谓五台群主要包含了三个蛇绿混杂带;阜平群和恒山群的主要成分是灰片麻岩,它们构成两个太古代陆块的基底。五台地区的花岗岩类由代表弧环境的双花岗岩带的I型和S型花岗岩组成,它们与变质的钙碱性火山岩代表了古代的岩浆弧。滹沱群的豆村和东冶亚群以及过去划入阜平群和五台群的某些变沉积岩是阜平陆块被动大陆边缘的沉积。滹沱群的郭家寨亚群则是前陆盆地的磨拉石沉积。因此可以认为,这是一个由恒山仰冲陆块、北台-车厂弧和阜平俯冲陆块构成的碰撞造山带,碰撞时间大致是距今2050Ma。闭合的弧前大洋和弧后盆地形成了三条蛇绿混杂带。     

Response of rigid piles during passive dragging

This paper develops a three‐layer model and elastic solutions to capture nonlinear response of rigid, passive piles in sliding soil. Elastic solutions are obtained for an equivalent force per unit length p_s of the soil movement. They are repeated for a series of linearly increasing p_s (with depth) to yield the nonlinear response. The parameters underpinning the model are determined against pertinent numerical solutions and model tests on passive free‐head and capped piles. The solutions are presented in non‐dimensional charts and elaborated through three examples. The study reveals the following:

• On‐pile pressure in rotationally restrained, sliding layer reduces by a factor α, which resembles the p‐multiplier for a laterally loaded, capped pile, but for its increase with vertical loading (embankment surcharge), and stiffness of underlying stiff layer: α = 0.25 and 0.6 for a shallow, translating and rotating piles, respectively; α = 0.33–0.5 and 0.8–1.3 for a slide overlying a stiff layer concerning a uniform and a linearly increasing pressure, respectively; and α = 0.5–0.72 for moving clay under embankment loading.
• Ultimate state is well defined using the ratio of passive earth pressure coefficient over that of active earth pressure. The subgrade modulus for a large soil movement may be scaled from model tests.
• The normalised rotational stiffness is equal to 0.1–0.15 for the capped piles, which increases the pile displacement with depth.

The three‐layer model solutions well predict nonlinear response of capped piles subjected to passive loading, which may be used for pertinent design. Copyright © 2016 John Wiley & Sons, Ltd.     

Sedimentology,structure and age estimate of five continental slope submarine landslides,eastern Australia

Sedimentological and accelerator mass spectrometry (AMS) ¹⁴C data provide estimates of the structure and age of five submarine landslides (～0.4–3 km³) present on eastern Australia's continental slope between Noosa Heads and Yamba. Dating of the post-slide conformably deposited sediment indicates sediment accumulation rates between 0.017 m ka^–1 and 0.2 m ka^–1, which is consistent with previous estimates reported for this area. Boundary surfaces were identified in five continental slope cores at depths of 0.8 to 2.2 m below the present-day seafloor. Boundary surfaces present as a sharp colour-change across the surface, discernible but small increases in sediment stiffness, a slight increase in sediment bulk density of 0.1 g cm^–3, and distinct gaps in AMS ¹⁴C ages of at least 25 ka. Boundary surfaces are interpreted to represent a slide plane detachment surface but are not necessarily the only ones or even the major ones. Sub-bottom profiler records indicate that: (1) the youngest identifiable sediment reflectors upslope from three submarine landslides terminate on and are truncated by slide rupture surfaces; (2) there is no obvious evidence for a post-slide sediment layer draped over, or burying, slide ruptures or exposed slide detachment surfaces; and (3) the boundary surfaces identified within the cores are unlikely to be near-surface slide surfaces within an overall larger en masse dislocation. These findings suggest that these submarine landslides are geologically recent (<25 ka), and that the boundary surfaces are either: (a) an erosional features that developed after the landslide, in which case the boundary surface age provides a minimum age for the landslide; or (b) detachment surfaces from which slabs of near-surface sediment were removed during landsliding, in which case the age of the sediment above the boundary surface indicates the approximate age of landsliding. While an earthquake-triggering mechanism is favoured for the initiation of submarine landslides on the eastern Australian margin, further evidence is required to confirm this interpretation.     

Development of passive sampling devices for bioavailable contaminants of current and emerging concern: Waitemata Harbour case study

Bioavailable contaminant concentrations are an important component in assessing environmental effects as they directly affect ecosystem health. Shellfish contaminant monitoring programmes have traditionally filled this requirement but are being phased out in some jurisdictions. Passive sampling devices (PSDs) have the potential to replace shellfish monitoring; however, there are still knowledge gaps to address before this can occur. This study assessed the suitability of three different PSDs in providing the required information to replace shellfish monitoring. PSDs were deployed at three historic mussel monitoring sites with different levels of urban influence in the Waitemata Harbour, Auckland, New Zealand. Contaminants of interest were urban heavy metals, plus current and emerging organic contaminants. PSDs provided extremely low detection limits and, for some contaminants, very strong correlations to shellfish. PSDs can currently complement shellfish in monitoring, but it is premature to make conclusions as to the suitability of PSDs in replacing shellfish monitoring until more information is available.     

Passive Fathometry in Shallow Waters of the Indian Continental Shelf

The present study demonstrates the use of ambient noise for estimating the ocean depth in shallow waters of the Indian continental shelf. Ocean depth is estimated using a technique known as passive fathometer processing, which involves the correlation of surface-generated ambient noise with its reflection from the seabed. Ambient noise data collected using a vertical array from four locations (off Cochin, off Cuddalore, off Kakinada, and off Goa) along the Indian continental shelf were used for the study. The noise data recorded during windy conditions within the frequency band of 200–5000 Hz were used for analysis. Both conventional and adaptive beamforming techniques were applied for the passive estimation of the ocean depth. The estimated water column depth using the ambient noise measurement shows good agreement with the known depth from all the four locations. The advantages and limitations of the adaptive processing technique have also been discussed. The study clearly demonstrates the application of the surface-generated ambient noise in seabed image processing.     

基于GIS和RS的白龟山水库洪水淹没分析及其损失评估

随着GIS技术的发展,其在自然灾害中的应用越来越广泛,特别是在洪水淹没分析中的应用。本文基于GIS技术以及RS技术,以TM影像和DEM为数据源,分析平顶山市范围内白龟山水库淹没的范围,并对淹没损失做了初步的评估,为湖区周围土地的合理利用提供依据并为减灾预灾提供一定的支撑。