Regional conductance map of Andaman and Nicobar region

To image the electrical conductivity distribution, fluxgate magnetometers are operated at five sites in Andaman and Nicobar region. Transfer functions are estimated for the period range 8–128 min, from nighttime transient geomagnetic variations, using robust regression analysis. The observed induction arrows in Andaman Islands are found to point towards east despite deep sea located towards its west. This indicates that fore-arc basin (Andaman–Nicobar deep) is more conducting than the region of outer non-volcanic Island arc.Thin sheet model requires the conductance of 10,000–35,000 S (with increase conductivity towards the south) for explaining the observed induction pattern. The observed induction pattern at Andaman–Nicobar stations can be explained in terms of high conducting Cretaceous–Tertiary sediments filling the Andaman–Nicobar deep. High conductivity over Invisible bank has been attributed to the partial melts/volatile fluids derived from the subducting Indian plate that are intruding into the eastern margin of fore-arc basin through the West Andaman Fault (WAF).The induction pattern at Great Nicobar station (Campbell Bay) may be related to the highly conducting sediments filling the Mergui basin along with mafic intrusions. Also crustal transition occurs below the Mergui Terrace at the Malayan coast contributing to the enhanced conductivity anomaly.     

组合球形岩溶的中梯视电阻率异常特征

岩溶是水工电法的主要研究目标之一。为探明地下岩溶的发育与分布,对较为复杂的组合球形岩溶地质体,建立了计算其视电阻率的物理数学模型,并采用等效视电阻率迭代法计算沿测线水平方向及垂直测线水平方向上组合球形岩溶的中梯装置的ρｓ值。重点分析了不同组合模式的中梯ρｓ曲线形态特征,并讨论了μ２值变化,测量电极距ＭＮ大小对组合球形岩溶地质体中梯ρｓ异常的影响规律。得出中梯ρｓ曲线对沿测线水平方向的组合球形岩溶地质体分辨能力最强,而对垂直测线水平方向以及铅垂方向的组合球形岩溶地质体,中梯ρｓ曲线无法分辨;μ２值的变化既影响中梯ρｓ曲线异常幅度,也影响其形态;当两个组合球形岩溶地质体之间的距离ΔＸ与ＭＮ之比ΔＸ／ＭＮ≤１／３时,ρｓ曲线会发生畸变,直接影响分辨能力,并会导致错误的解释结果。故ΔＸ／ＭＮ值必须大于１／３,在保证观测精度的前提下,ＭＮ越小越好      

Research progress and prospect of snow avalanche disaster prevention and control北大核心CSCD

Snow avalanches are a major natural hazard in the cryosphere. It seriously threatens transportation corridors, energy transmission and communication lines, mining and touristic areas in the cold mountainous regions and often causes the destruction of infrastructure and human casualties, hindering the sustainable development of society and economy in mountainous areas. Under climate change and the expansion of human activities to alpine mountains, more population and infrastructure will expose to the risk of avalanches. In order to ensure the sustainable development in mountainous areas, the demand for the prevention and management of avalanche disasters is increasing. Based on the review of the main avalanche research progress in China since 1960 and the avalanche research results all over the world, this paper summarized the progress on the influencing factors and regional distribution of avalanche activities, avalanche formation and movement mechanism, avalanche monitoring and early warning, avalanche risk assessment and engineering prevention, as well as the frontier problems and scientific difficulties that need to be studied. In addition, the impact of climate change on avalanche activities and the interaction between human activities and avalanche activities are discussed. By looking forward to the future needs of avalanche disaster prevention and reduction, including the countermeasures, the research on avalanche in China is promoted. © 2022 by the Author(s).     

TECTONIC TRANSFER ON THE EASTERN EDGE OF PAMIR

TECTONIC TRANSFER ON THE EASTERN EDGE OF PAMIR     

基于显著性图像与纹理特征的遥感影像云检测

遥感影像云检测是遥感影像处理中非常关键的环节,准确识别影像含云区域能够提升影像的利用价值.根据遥感影像的成像特点,将阈值法和纹理特征结合实现云和下垫面的分割.首先将影像从RGB(red-green-blue)空间转化为HSI(hue-saturation-intensity)空间,进而构建影像的显著性图像,利用Otsu...     

Cobalt zoning in microscopic pyrite from Kamoto,Republic of the Congo (Kinshasa)

The Kamoto deposit consists of two stratiform orebodies separated by a barren sedimentary unit. It is a copper and cobalt deposit, the main features of which are summarized in the first part of the paper. Above the upper orebody, dolostone beds are found, where pyrite is the only sulfide mineral. This pyrite was investigated with the help of a microprobe: all idiomorphic grains were found to be surrounded by a well-defined rim, where the cobalt content reaches 4%; framboidal grains were also found to be heterogeneous with respect to cobalt. The distribution of nickel and copper is described. These observations afford one more evidence that post-depositional events played an important role in the Mine Series of Katanga, especially with regard to heavy metals geochemistry.

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Resume Le gisement de Kamoto est constitué de deux corps minéralisés stratiformes séparés par une unité sédimentaire stérile. C'est un gisement de cuivre et de cobalt dont les principales caractéristiques sont brièvement résumées. Audessus du corps minéralisé supérieur, on trouve des couches de dolomie, où la pyrite est le seul sulfure présent. Cette pyrite a été étudiée à l'aide d'une microsonde: tous les grains idiomorphes y sont entourés d'une bordure bien nette, où la teneur en cobalt atteint 4%; les grains d'apparence framboïdale sont également hétérogènes au point de vue de leur teneur en cobalt. La distribution du nickel et du cuivre est décrite. Ces observations apportent um témoignage supplémentaire de l'importance des événements postérieurs au dépôt dans la «Série des Mines» katangaise, tout spécialement en ce qui concerne la géochimie des métaux lourds. Elles démontrent que le «système» constitué par la roche sédimentaire est resté ouvert pendant un certain temps après la sédimentation.

     

Evaluation of the spatial changes in seagrass cover in the lagoons of Lakshadweep islands,India, using IRS LISS III satellite images

A study was conducted in Lakshadweep islands to determine the feasibility of using Indian Remote Sensing (IRS) satellites for detecting changes in the seagrass from other coastal features. IRS ID and IRS P6 LISS III having spatial resolution of 23.5 m with lower cost compared to all other contemporary satellites with the same spatial resolution have not been widely used for monitoring the changes in seagrass cover. In this context, the present study attempted to explore the effectiveness of LISS III data for mapping seagrasses and to inform the international community about the usefulness of these low-cost imageries for coastal resource monitoring. Supervised classification and change detection studies found a significant decrease in seagrass cover of 73.03 ha in the Lakshadweep group of islands. An overall accuracy of 67.5% was obtained for the change maps, and seagrass cover and its changes vary at different islands.     

Effects of the oophagous bivalve Acesta oophaga on the morphology and fecundity of its deep‐sea tubeworm host,Lamellibrachia luymesi

The deep‐sea bivalve Acesta oophaga lives attached to the anterior end of the vestimentiferan tubeworm, Lamellibrachia luymesi, at cold methane seeps. The bivalve is found almost exclusively on female tubeworms, where it consumes the lipid‐rich eggs of L. luymesi that are spawned year round (Biological Bulletin, 209, 2005, 87). It is apparent that A. oophaga benefits directly from this close association, but the consequences for the tubeworm host may be more complicated than just a simple predator–prey interaction. Since A. oophaga completely surrounds the tube opening and plume of the worm, it is likely that its presence would limit oxygen uptake by L. luymesi, thereby inhibiting worm growth and reproduction. We hypothesized that occupied tubeworms would compensate for this by growing larger plumes for oxygen uptake. To explore the effects of bivalve presence/absence on female tubeworms, several morphological features, including body size, plume length, tube diameter, and tube segment length, as well as instantaneous fecundity, were compared. Results suggest that the mere presence of A. oophaga has a significant impact on the morphology of its host worm, as all measures of worm size, except for tube segment length, were significantly greater with clams present. Additionally, instantaneous fecundity was 3.5 times higher in occupied worms, implying that tubeworms are not oxygen‐deprived or energy limited as a result of bivalve presence. Our findings suggest that the association between these two deep‐sea organisms may be a more complex form of symbiosis than the simple predator–prey relationship, as previously thought.