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1.
胶东型金矿具有独特的成矿特征和成因机制,不同于国际已知金矿类型。为了深化认识控制矿床形成、变化和保存的地质要素及成矿过程,本文综合分析了胶东半岛晚中生代岩浆作用、构造活动和成矿特征及其构造背景,提出该区深部岩浆活动与地壳快速隆升及浅部变质核杂岩、张性断层、断陷盆地等伸展构造,共同控制了以Au为主的矿床成矿系列及成矿演化过程,谓之热隆-伸展成矿系统。阐明了晚中生代岩浆演化过程中的元素变化规律,发现了金矿化蚀变带中的低Ba、Sr含量异常及早白垩世胶东地壳中金丰度的显著变化,揭示了壳幔物质混合和伟德山型花岗岩岩浆活动对金成矿的贡献。认为这一成矿系统形成于古太平洋板块俯冲后撤的后俯冲伸展环境,由于软流圈上涌导致岩石圈地幔性质由富集向亏损转化,从而引起岩浆岩地球化学特征变化,地球化学元素重新调整,幔源含金流体与由重熔下地壳析出的壳源含金流体混合形成富金流体库,并产生贫金花岗岩。大规模岩浆活动为成矿元素的活化、迁移提供了热动力条件,上地壳伸展产生的断裂构造则为成矿元素聚集提供了良好空间。热隆-伸展成矿系统是中国东部晚中生代重要的成矿系统。  相似文献   
2.
川东褶皱带作为华南板块中部的“侏罗山式”褶皱,开始形成于晚古生代.自白垩纪晚期开始,受太平洋板块和印度板块对欧亚大陆挤压的影响,这一构造带乃至华南板块中部又叠加了新的构造变形.但是,目前对于川东褶皱带白垩纪以来的构造演化缺乏足够的认识.位于川东褶皱带东侧、雪峰造山带西麓的沅麻盆地形成于早白垩世.晚白垩世以来,沅麻盆地与川东褶皱带处于同一构造应力场中,因此对盆地内早白垩世红层的古地磁研究对于解释川东褶皱带中生代晚期以来的构造演化有着重要的意义.该研究在沅麻盆地早白垩世红层中开展的古地磁学研究获得了可靠的原生剩磁分量:Ds=15.6°,Is=42.9°,k=118.6,α95=2.6°,表明沅麻盆地自早白垩世以来发生了4.1°±3.0°的顺时针构造转动.对川东褶皱带周缘白垩纪古地磁数据所揭示的地壳旋转变形,与断裂和褶皱轴组成的构造线迹变化之间的线性相关性分析,表明川东褶皱带位于齐岳山断裂带东南侧的部分,受印度板块-欧亚大陆、太平洋板块-华南板块间的挤压作用,自晚白垩世以来累积了约50~93 km的右旋错断量.  相似文献   
3.
In this study we present the results from field work in northern Vietnam regarding the occurrence of the warty newt species Paramesotriton deloustali and P. guangxiensis in disturbed and undisturbed habitats and the presence of parasitic water mites of the genus Hygrobates (sg. Lurchibates) (Acari, Hydrachnidia). We report the first evidence of mite parasitism in P. guangxiensis and analyze differences in the infestation rates between both Paramesotriton species and habitat qualities. Furthermore we present the first indication of the detrimental effects of these parasite-host interactions.Our preliminary assessment seems to support the sensitivity of P. guangxiensis to habitat disturbances, as the average number of captured newts per stream was twice as high in undisturbed habitats as in disturbed ones.Until now a very specific parasite-host association was supposed between water mite and newt species. However, our results show the first evidence of a water mite species of the subgenus Lurchibates (Hygrobates forcipifer) parasitizing more than one host species, in this case not only P. deloustali (already known) but also P. guangxiensis (new record). The overall infestation rate was 27 % for P. deloustali and 71 % for P. guangxiensis, from which 100 % and 77 % of the mite-incidence occurred in undisturbed habitats, respectively. Furthermore the parasite load of the newts was clearly higher in prime quality streams: the parasite load in undisturbed habitats was very similar between P. deloustali (19.64 mites per newt) and P. guangxiensis (20.13 mites per newt), however it was significantly lower for P. guangxiensis in disturbed habitats (8.86 mites per newt). Future research should bring more detail on these parasite host associations, especially on the effect of parasitism on the newts. Warty newts are already threatened due to their shrinking natural habitat and overharvesting. We report the first concerns that mite parasitism might be a critical additional stress factor in undisturbed habitats.  相似文献   
4.
Soil resources in parts of Tanzania are rapidly being depleted by increased rates of soil erosion and downstream sediment transport, threatening ecosystem health, water and livelihood security in the region. However, incomplete understanding to what effect the dynamics of soil erosion and sediment transport are responding to land-use changes and climatic variability are hindering the actions needed to future-proof Tanzanian land-use practices. Complementary environmental diagnostic tools were applied to reconstruct the rates and sources of sedimentation over time in three Tanzanian river systems that have experienced changing land use and climatic conditions. Detailed historical analysis of sediment deposits revealed drastic changes in sediment yield and source contributions. Quantitative sedimentation reconstruction using radionuclide dating showed a 20-fold increase in sediment yield over the past 120 years. The observed dramatic increase in sediment yield is most likely driven by increasing land-use pressures. Deforestation, cropland expansion and increasing grazing pressures resulted into accelerating rates of sheet erosion. A regime shift after years of progressive soil degradation and convergence of surface flows resulted into a highly incised landscape, where high amounts of eroded soil from throughout the catchment are rapidly transported downstream by strongly connected ephemeral drainage networks. By integrating complementary spatial and temporal evidence bases, this study demonstrated links between land-use change, increased soil erosion and downstream sedimentation. Such evidence can guide stakeholders and policy makers in the design of targeted management interventions to safeguard future soil health and water quality.  相似文献   
5.
Amik Lake or, historically, Lake of Antioch, was a large freshwater body in the lower Orontes River basin (Hatay Province, Turkey) that was drained in the 1940s–1970s. Several endemic animal species were described from this lake, including the freshwater mussel Anodonta pseudodopsis Locard, 1883 (Bivalvia: Unionidae) characterized by a large rounded shell covered by a peculiar yellow or yellowish-brown periostracum. Molecular analyses of topotypes of this nominal taxon collected from the former lake’s tributaries in the Amik Plain indicate that it is an intra-specific lineage of the widespread Anodonta anatina (Linnaeus, 1758) based on the mitochondrial COI and 16S rRNA, and the nuclear 28S rRNA gene fragments. Geometric morphometric analyses using the lectotype and topotypes of Anodonta pseudodopsis support our DNA-based hypothesis on the status of this nominal taxon. A new synonymy is provided as follows: Anodonta anatina = Anodonta pseudodopsis syn. nov. The syntype of Anodonta pseudodopsis SMF 5129 “See von Antiochia” (Senckenberg Research Institute and Natural History Museum, Frankfurt, Germany) is designated here to be the lectotype of this nominal taxon. Finally, we conclude that Anodonta anatina range covers the Orontes River basin in Turkey and Syria and the Nahr al-Kabir al-Shamali River in the Latakia Governorate of Syria. This intraspecific lineage of Anodonta anatina and other freshwater mussels of the Middle East are highly threatened due to multiple anthropogenic impacts and must be a focus of international conservation efforts. The Karasu River in eastern Turkey hosts viable populations of all freshwater mussel species of the Orontes’s fauna and can be considered one of the most important water bodies for the conservation of these imperiled animals in the region.  相似文献   
6.
Wildfire significantly alters the hydrologic properties of a burned area, leading to increases in overland flow, erosion, and the potential for runoff-generated debris flows. The initiation of debris flows in recently burned areas is well characterized by rainfall intensity-duration (ID) thresholds. However, there is currently a paucity of data quantifying the rainfall intensities required to trigger post-wildfire debris flows, which limits our understanding of how and why rainfall ID thresholds vary in different climatic and geologic settings. In this study, we monitored debris-flow activity following the Pinal Fire in central Arizona, which differs from both a climatic and hydrogeomorphic perspective from other regions in the western United States where ID thresholds for post-wildfire debris flows are well established, namely the Transverse Ranges of southern California. Since the peak rainfall intensity within a rainstorm may exceed the rainfall intensity required to trigger a debris flow, the development of robust rainfall ID thresholds requires knowledge of the timing of debris flows within rainstorms. Existing post-wildfire debris-flow studies in Arizona only constrain the peak rainfall intensity within debris-flow-producing storms, which may far exceed the intensity that actually triggered the observed debris flow. In this study, we used pressure transducers within five burned drainage basins to constrain the timing of debris flows within rainstorms. Rainfall ID thresholds derived here from triggering rainfall intensities are, on average, 22 mm h−1 lower than ID thresholds derived under the assumption that the triggering intensity is equal to the maximum rainfall intensity recorded during a rainstorm. We then use a hydrologic model to demonstrate that the magnitude of the 15-min rainfall ID threshold at the Pinal Fire site is associated with the rainfall intensity required to exceed a recently proposed dimensionless discharge threshold for debris-flow initiation. Model results further suggest that previously observed differences in regional ID thresholds between Arizona and the San Gabriel Mountains of southern California may be attributed, in large part, to differences in the hydraulic properties of burned soils. © 2019 John Wiley & Sons, Ltd.  相似文献   
7.
Using rain-gauge-observation daily precipitation data from the Global Historical Climatology Network (V3.25) and the Chinese Surface Daily Climate Dataset (V3.0), this study investigates the fidelity of the AHPRODITE dataset in representing extreme precipitation, in terms of the extreme precipitation threshold value, occurrence number, probability of detection, and extremal dependence index during the cool (October to April) and warm (May to September) seasons in Central Asia during 1961–90. The distribution of extreme precipitation is characterized by large extreme precipitation threshold values and high occurrence numbers over the mountainous areas. The APHRODITE dataset is highly correlated with the gauge-observation precipitation data and can reproduce the spatial distributions of the extreme precipitation threshold value and total occurrence number. However, APHRODITE generally underestimates the extreme precipitation threshold values, while it overestimates the total numbers of extreme precipitation events, particularly over the mountainous areas. These biases can be attributed to the overestimation of light rainfall and the underestimation of heavy rainfall induced by the rainfall distribution–based interpolation. Such deficits are more evident for the warm season than the cool season, and thus the biases are more pronounced in the warm season than in the cool season. The probability of detection and extremal dependence index reveal that APHRODITE has a good capability of detecting extreme precipitation, particularly in the cool season.  相似文献   
8.
We compare the ability of coupled global climate models from the phases 5 and 6 of the Coupled Model Intercomparison Project(CMIP5 and CMIP6, respectively) in simulating the temperature and precipitation climatology and interannual variability over China for the period 1961–2005 and the climatological East Asian monsoon for the period1979–2005. All 92 models are able to simulate the geographical distribution of the above variables reasonably well.Compared with earlier CMIP5 models, current CMIP6 models have nationally weaker cold biases, a similar nationwide overestimation of precipitation and a weaker underestimation of the southeast–northwest precipitation gradient, a comparable overestimation of the spatial variability of the interannual variability, and a similar underestimation of the strength of winter monsoon over northern Asia. Pairwise comparison indicates that models have improved from CMIP5 to CMIP6 for climatological temperature and precipitation and winter monsoon but display little improvement for the interannual temperature and precipitation variability and summer monsoon. The ability of models relates to their horizontal resolutions in certain aspects. Both the multi-model arithmetic mean and median display similar skills and outperform most of the individual models in all considered aspects.  相似文献   
9.
沈世伟  吴飞  甘霖  姜满 《探矿工程》2021,48(1):120-128
对不同初始饱和度红砂岩冻融循环前后进行物理及力学试验研究,探讨初始饱和度对红砂岩冻融损伤的影响。本文设定红砂岩试样初始饱和度为20%、40%、60%、80%、100%,冻融次数设定为20次,对冻融前后试样分别测定质量、纵波波速以及进行单轴压缩试验。试验结果表明:1)冻融后不同初始饱和度红砂岩的物理性质发生变化,纵波波速降低、质量减小,但变化程度不同;2)随饱和度的增大,试样经冻融后峰值强度和弹性模量均呈降低趋势,但只有饱和度大于60%时,降低趋势较明显。本文研究为寒区隧道及地下工程建设以及岩土地质灾害监测与治理提供理论依据和试验基础。  相似文献   
10.
人类活动和自然因素共同但有区别的作用引起了长江口及邻近海域富营养化,造成夏季底层水体低氧现象加剧,成为近海生态健康恶化的重要征兆。本文梳理了国内外学者在该海域低氧研究中获得的重要认识,分析了底层水体溶解氧的潮周期尺度、事件尺度和年际尺度的变化特征,重点从层化与物质输运角度,介绍了长江冲淡水、台湾暖流、海洋锋面、风和潮等过程影响底层水体中氧气消耗或补充的机制,揭示了本海域主要低氧现象分别位于长江口和浙江近海的特征,对比了两处低氧区形成与演变的异同机制。目前,对低氧形成机制的定性认识和多尺度变化特征的了解已经有较好的基础,未来需要从多学科交叉角度加强现场试验和定量研究,掌握低氧的长期演变趋势,研发底层水体低氧的预测预警技术,支撑我国河口近海的生态预警监测工作。  相似文献   
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