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971.
西域陆块的建立及其地质意义 总被引:1,自引:0,他引:1
综合地质学、地球化学、地球物理学及深部构造等方面的资料,对“西域陆块”双重基底-结晶基底(Ar3Pt1)与褶皱基底(Pt2-3)、盖层(NhZ),上下冰碛层,陆块边界等方面进行了初步探讨。西域陆块由塔里木、柴达木、中天山、敦煌、中-北祁连山、阿拉善等微陆块组成.它既不同于华北陆块(北型),也有别于扬子陆块(南型)。但又具有华北与扬子陆块的某些特征,早古生代期间发育北西西向沟孤盆构造系以及中新生代与青藏高原隆升相伴产生的大型复合坳陷含油气盆地。暗示其很可能是中国西北部一个独立的构造单元。 相似文献
972.
Zhiyong Zhang Wenbin Liangshu Shu Jinglin Wan Wei Yang Jinbao Su Bihai Zheng 《Gondwana Research》2009,16(2):182
The Precambrian Aksu blueschist is located in the northwestern margin of the Tarim Block, NW China. In recent decades, many studies were carried out with focus on the metamorphic age. However, a complete understanding of the evolution of the Tarim Block requires the cooling history of the Precambrian metamorphic rocks and the time–temperature paths as determined by low-temperature thermochronometry. Therefore, apatite fission track (AFT) technique was applied on the Precambrian Aksu blueschist to reveal the thermo–tectonic evolution of the north Tarim basement. All of the six blueschist samples analysed in this study yielded AFT ages spanning 107.5–62.5 Ma, much younger than the blueschist facies metamorphic age of Neoproterozoic, and confined track lengths are between 10.46 and 12.12 µm. Based on regional stratigraphic sequences, the AFT thermal history modeling as well as previous chronological results, the thermo–tectonic evolution of the Aksu blueschist can be roughly reconstructed with four stages: (1) the Precambrain Aksu blueschist exhumed to the surface soon after its formation. Erosion during the Early Sinian is indicated by the lack of sedimentation until the Late Sinian; (2) the Late Sinian strata are continuous, while the Middle–Upper Silurian and the Lower–Middle Carboniferous strata are absent. The total thickness of the Late Sinian and Paleozoic strata probably reached 10,000 m and resulted in the total annealing and thermal resetting of AFT ages; (3) the AFT ages in the Cretaceous are related with the widespread uplift in Tian Shan and its adjacent regions that restarted the AFT clock during the Late Mesozoic. These reflect a distant effect of the collision of the Lhasa terrane with Eurasia in the Late Jurassic–Early Cretaceous; and (4) sediments of Cenozoic are documented in the Aksu area. The Aksu blueschist was heated to partial annealing zone with the overlying Cenozoic sediments. During Miocene time, the Aksu blueschist was re-exhumed which was probably a distant response to the ongoing India–Eurasia convergence. 相似文献
973.
针对2007年7月29~30日发生在山西省垣曲县的特大暴雨天气过程, 利用实况资料、 自动站资料以及GMS红外卫星云图, 计算了地形性垂直速度、 切变涡度、 散度、 能量, 并分析了其分布及演变特征, 对前期500 hPa高度和温度进行了合成分析, 结果表明: (1)前期500 hPa阻塞高压和切断低压的形成和长期维持, 使得冷空气在山西上空堆积, 形成强烈的高空冷涌; 同时, 副热带高压的稳定加强、 维持为暴雨提供了能量积累和水汽来源, 致使山西出现大范围降水和区域暴雨天气。(2)K-H不稳定的形成和维持, 是导致中尺度切变线上小尺度涡旋维持、 加强, 并产生强风暴雨的重要原因。(3)垣曲县特殊的地形, 使得其附近流场发生变化, 不仅使地形性垂直上升运动加强、 维持, 而且也使得水汽不断向云内卷入, 延长了暴雨云团在其上空的停留时间; 同时通过云物理作用, 使得已经凝结的水分高效率地下降, 从而增加降水量; 喇叭口地形的收缩作用也加强了迎风坡的辐合上升运动。 相似文献
974.
Abdelrahman M. Abdelgawad Kunio Watanabe Shinji Takeuchi Takashi Mizuno 《Engineering Geology》2009,108(1-2):76-85
The aim of this paper was to explore new factors that might be reasons for the occurrence of fluoride-rich groundwater in the area around a construction site. During the construction of two deep shafts of the Mizunami Underground Research Laboratory (MIU) in Mizunami city, central Japan, a large quantity of groundwater with high fluoride concentration was charged into the shafts. Chemical investigation carried out during the excavation revealed that fluoride concentrations in the area around the MIU site greatly exceeded those prescribed by Japanese standards. Therefore, the origin of fluoride ion was experimentally investigated. Samples were collected from the core of a deep borehole drilled in the study area. The weathering - and alteration levels of the collected granites varied greatly. Granitic powders were used to measure fluoride content in the granitic rock mass. The fluoride content ranged between 200 and 1300 mg/kg. The powders were reacted with purified water for 80 days. The results of water–rock interaction showed granitic rock to be one of the main sources of fluoride-rich groundwater in Mizunami area. Fluoride concentrations in these solutions that were shaken for 80 days varied between 2 and 7 mg/l. This change may have occurred as a result of the spatial distribution of fluoride ions in the granite mass as evidenced by mineralogical analysis of fluoride content in several specimens. X-ray powder diffraction analysis of the rock before- and after the water–rock interaction tests manifested that the presence of fluorite mineral was relatively small compared to other minerals. The degree of weathering and alteration might be an additional factor causing dissolution of fluoride-rich minerals. However, it was difficult to interpret the change in fluorite composition by X-ray diffraction analysis. 相似文献
975.
The distribution of As in a variety of sample materials was studied at different scales, from continental to local, combining published data sets with the aim of delineating the impact and relative importance of geogenic vs. anthropogenic As sources. Geochemical mapping of As with a variety of sample materials demonstrates that variation is high at all scales (local to continental) – from sample densities of 400 sites per km2 to 1 site per 5000 km2. Different processes govern the As distribution at different scales. A high sample density is needed to reliably detect mineralisation or contamination in soil samples. In both cases the impact on the much larger geochemical background variation is limited to a local scale. Distribution patterns in geochemical maps on the sub-continental to continental scale are dominated by natural variation. Given that the geochemical background is characterised by a high variation at all scales, it appears impossible to establish a reliable single value for “good soil quality” or a “natural background concentration” for As for any sizeable area, e.g., for Europe. For such a differentiation, geochemical maps at a variety of scales are needed. 相似文献
976.
Aleksandra Šajnović Ksenija Stojanović Branimir Jovančićević Anatoly Golovko 《Environmental Geology》2009,56(8):1629-1641
Sediments from the Valjevo-Mionica Basin of Neogene age were investigated in this study using different geochemical methods.
The results of the inorganic part analyses suggest that during genesis of the sediments, the contents of Na2O, B and As changed the most, which indicates that genesis of the investigated sediments was followed by climate changes and
volcanic activity. The quantity of other macro- and microelements did not vary significantly. Investigations of the organic
substance showed that it is native organic matter, which has been preserved to a significant extent, formed predominantly
of algal precursor organisms, which provided good quality, deposited under reducing conditions and that it is at a low maturity
level. As it has been established that genesis of the investigated sediments was mostly affected by an arid climate with more
intensive salinity, the aim of this study, was also to identify the processes which were the most affected by the change in
salinity, as well as biomarkers which are the most sensitive to this change. The results led to the conclusion that the salinity
increase in the depositional environment had a primary effect on the preservation of the organic substance and the formation
of the mineral searlesite. In addition, it was noticed that besides the Sq/nC26 ratio, the parameters nC17/nC27, CPI and Ph/nC18, are also significantly sensitive to salinity change in a depositional environment in case of immature organic substance
deposited under reducing conditions. 相似文献
977.
Geographical distribution of arsenic in sediments within the Rio Conchos Basin,Mexico 总被引:1,自引:0,他引:1
Melida Gutierrez M. Teresa Alarcón-Herrera Lucy M. Camacho 《Environmental Geology》2009,57(4):929-935
Arsenic (As) content of sediments from the Rio Conchos and Rio San Pedro in northern Mexico were measured to determine if
this toxic metalloid had accumulated to unsafe levels to humans and aquatic life. The spatial distribution of As in each of
the six clusters of river and arroyo sediments was analyzed to determine variations with respect to background levels and
to infer about potential As sources and sinks. In the northern part of the study area, background concentrations varied little
throughout the area and concentrations in river sediments were close to background levels. In the southern part, however,
the content of As in arroyo sediment contained a wider range of values and anomalous concentrations. The latter could be traced
in part to the presence of mine tailings. As concentrations were below the limit in all studied river stretches and thus do
not pose an immediate threat to the river environment, but As content in reservoir sediments exceeded the guideline values.
Reservoirs seem to act as a sink for As, warranting closer observation and monitoring. 相似文献
978.
南海神狐海域X区块天然气水合物的控制因素 总被引:5,自引:4,他引:1
为了探讨南海神狐海域X区块天然气水合物的控制因素,开展了高分辨地震资料精细解释和天然气水合物地震相研究。结果显示,X区块存在3条主控断层和众多滑塌断层;预测的稳定带内水合物呈多层分布,稳定带底部水合物层厚度较大、连续性较好。结合地震反射特征和可能的气源讨论初步认为,X区块天然气水合物的成藏模式主要有两种类型:在断裂或滑塌构造发育区,水合物的气源以热解成因气为主,水合物呈多层分布;在构造平缓地区,水合物的气源以生物成因气为主,水合物呈单层分布,且主要分布在似海底反射(BSR)之上一个狭窄的范围内。 相似文献
979.
980.
Rio Marina mining district (Elba Island) is characterised by hematite + pyrite ore association and was exploited for iron till 1981, leaving waste rock dumps of several millions m3. The effect of open pit mining activity in this site is to produce acid mine drainage (AMD) processes leading to environmental pollution, testified by all the sampled waters (Giove stream, drainage channels, superficial pools and settling basin) which have pH values ranging from 2.08 to 3.35 and heavy metal concentrations that reach 903.16 mg/l for Fe, 45.02 mg/l for Mn, 10.08 mg/l for Zn and 1.75 mg/l for Cu. In the present work a space and time related approach to geochemical hazard evaluation was applied. The geochemical hazard is mainly related to high heavy metal concentration, acid mine drainage processes development and topographic setting. As all these parameters are related in space, hazard evaluation was performed by geostatistical methods. Fifty-four earth material samples (residual soils, waste rocks or debris materials) were collected in a central aligned 100 m mesh square grid. These were analysed for major elements by XRF, for Cu, Pb, Zn by ICP-AES and for AMD potential following the AMIRA procedure. The concentration of heavy metals was compared with Italian law limits. The overlap of Cu, Pb and Zn content maps show that at least one of these heavy metals exceed law limits in all the area. The AMD test results show that more than 50% of samples have a positive NAPP (Net Acid Producing Potential) that could reach 258.9 kg H2SO4/t. According to the obtained data, three main geochemical hazard classes were established and their distribution in the mining area was assessed. About 51% of the mining area surface belongs to the major hazard class, where AMD process occurs, about 49% belongs to an intermediate hazard class, where AMD process could occur only if certain conditions are met. Finally, the persistence of the AMD process in the Rio Marina area was evaluated on the basis of yearly rainfall, mining waters pH and NAPP values. A complete leaching of the first 0.25 m of the earth materials can retain the current environmental conditions for several centuries. 相似文献