Tectonic evolution of the western Ordos Basin during the Palaeozoic-Mesozoic time as constrained by detrital zircon ages     

《International Geology Review》2012,54(4):461-480

ABSTRACT

The Ordos Basin has experienced a complicated tectonic evolution since the Palaeozoic. Its multi-stage evolution was closely related to the tectonic events that occurred along plate boundaries. The detrital zircon ages and crystallization age (CA)-deposition age (DA)/cumulative proportion curves obtained from Palaeozoic-Mesozoic strata from different tectonic units in and around the western Ordos Basin demonstrate that during the early Palaeozoic, the so-called Helan Aulacogen did not develop along the western Ordos Basin, the Alxa Block was an independent unit from the North China Craton, and the southern Ordos Basin was a foreland basin of the North Qinling Orogenic Belt. During the early Palaeozoic, the western Ordos Basin and its vicinity belonged to three different tectonic units (i.e. the North China Craton, the Alxa Block, and the North Qilian Orogenic Belt). At the end of the early Palaeozoic, the Alxa Block amalgamated with the Ordos Basin. From the Silurian to the Middle Devonian, the southern Alxa Block was a foreland basin of the North Qilian Orogenic Belt and underwent regional extension during the Late Devonian. During the late Palaeozoic, the western Ordos Basin and its vicinities were located in a back-arc extensional setting of the western Qinling Orogenic Belt. The southern part of the western Ordos Basin may have been a retro-arc foreland basin of the western Qinling Orogenic Belt during the Late Triassic, and the northern part of the western Ordos Basin experienced large-scale left-lateral strike-slip at the same time. The CA-DA/cumulative proportion curves can adequately explain the evolution of the western Ordos Basin during the Palaeozoic; however, the settings indicated by the CA-DA/cumulative proportion curves in intraplate evolutions are different from those proposed in other studies, which may be due to the number and distribution of samples and rapid lateral changes in sedimentary facies.  相似文献   

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张磊  顾勇为  归庆明  马朝忠 《大地测量与地球动力学》2007,27(2):99-102

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渭河干流典型断面非点源污染监测与负荷估算   总被引：5，自引：0，他引：5       下载免费PDF全文

李家科  李怀恩  沈冰  秦耀民  董雯 《水科学进展》2011,22(6):818-828

渭河水质在较大程度上受非点源污染的影响,因此,有必要对其负荷和比重进行研究。2009年至2010年,对渭河干流关中段咸阳和临潼断面进行了洪水期和非洪水期水质水量同步监测。根据监测结果及水文站实测流量资料,分别采用改进的水文分割法和平均浓度法对两断面的非点源污染负荷进行了计算,分析了非点源污染的特点。结果表明:渭河干流关中段主要污染物为COD、NH₃-N和TN,两断面洪水期间各指标的平均浓度基本都小于平时的平均浓度;各指标非洪水期浓度变化总体上小于洪水期浓度变化幅度,量级较大的洪水水质变化幅度相对较小;改进的水文分割法和已被检验并被广泛采用的平均浓度法计算结果符合良好。2009年(枯水年,P=68%)渭河咸阳和临潼站各指标非点源污染所占比例基本在20%～30%左右;2009年渭河干流咸阳-临潼河段污染以点源污染为主,构成比例在80%以上。对比2006年(枯水年,P=69%),2009年临潼站COD、NH₃-N和TN年点源负荷分别减少11937t、791t和29t,渭河点源治理取得一定成效;此外,临潼站这两年的污染构成比例基本相同。非点源污染在渭河水污染中占较大比重,其对渭河水质的影响不容忽视。  相似文献   

应用图像卷积运算提取城市范围   总被引：3，自引：0，他引：3  

穆晓东  刘慧平  王宏斌 《遥感学报》2011,15(6):1295-1307

通过一种卷积算法,从遥感分类数据中计算城市用地比例,并以该比例作为划分城市和非城市区的阈值,进而提取城市范围。方法构建了评价提取结果的指标体系,以确定卷积模板大小和阈值的选取。以北京为研究区,利用2007年SPOT 5多光谱影像分类数据,对方法的可行性进行了验证。结合统计数据中的建成区面积,采用504种模板和阈值组合进行提取试验,讨论了模板和阈值对提取结果的影响。最终选择(205, 51)的模板和阈值组合,对城市范围进行提取。研究结果表明：(1)该方法解决了遥感监测的城市用地分布区与城市范围存在差异的问题,为城市研究基础数据的准备提供了新的方法;(2)阈值过高或过低会造成城市范围的明显缩小或扩大;较小的模板不利于消除随机误差,较大的模板则会导致结果过于平滑;(3)对于SPOT 5多光谱影像分类数据,模板大小在193—205像元(约4 km²)、阈值接近50时,提取结果最好。  相似文献   

Use of biomarkers indices in a sediment core to evaluate potential pollution sources in a subtropical reservoir in Brazil   总被引：1，自引：0，他引：1  

Juan Sánez  Sandro Froehner  Filipe Falcão 《Chemie der Erde / Geochemistry》2013

The presence of PAHs, n-alkanes, pristane, and phytanes in core sediment from the Vossoroca reservoir (Parana, southern Brazil) was investigated. The total concentration of the 16 PAHs varied from 15.5 to 1646 μg kg⁻¹. Naphthalene was present in all layers (3.34–74.0 μg kg⁻¹). The most abundant and dominant n-alkanes were n-C₁₅ and n-C₃₆, with average concentrations of 198.1 ± 46.8 and 522.9 ± 167.7 μg kg⁻¹, respectively. Lighter n-alkanes were distributed more evenly through the layers and showed less variation, specially n-C₉, n-C₁₂, and n-C₁₈, with average concentrations of 14.6 ± 3.0, 31.6 ± 1.9, and 95.0 ± 5.2 μg kg⁻¹, respectively; heavier n-alkanes were more unevenly distributed.  相似文献   

贵州省喀斯特地貌分布面积及分布特征分析   总被引：6，自引：0，他引：6  

邓晓红  毕坤 《贵州地质》2004,21(3):191-193,177

对贵州省喀斯特地貌进行了特征分析,讨论了喀地貌类型及其与人口、经济、植被和河网密度等的关系。  相似文献   

Stable oxygen and hydrogen isotopes as indicators of lake water recharge and evaporation in the lakes of the Yinchuan Plain   总被引：2，自引：0，他引：2       下载免费PDF全文

Hui Qian  Jianhua Wu  Yahong Zhou  Peiyue Li 《水文研究》2014,28(10):3554-3562

The Yinchuan Plain has more than 2000 years of history of irrigation by diverting water from the Yellow River. Currently, the amount of water diverted from the Yellow River is about 21.7 times the water formed on the plain as a result of precipitation and inflow of groundwater. Under the intensive influence of irrigation, the plain changed from a desert into a rich and populous area, earning its name as ‘South China Beyond the Great Wall’, with lakes scattered across the Yinchuan Plain just as stars in the sky. In this research, 17 representative lakes were sampled to analyze and study ²H and ¹⁸O content; the results showed that lakes on the plain have undergone obvious non‐equilibrium evaporation. Recharges of the lakes can be divided into three types: recharge from the Yellow River, from groundwater and from both of these. The Craig–Gordon non‐equilibrium evaporation model for isotope fractionation was used to estimate the evaporation proportion of each lake. The results showed that evaporation from lakes on Yinchuan Plain is generally extensive under the dry climatic conditions. Most lakes have an evaporation proportion of over 25%, with the largest originating from Shahu lake and Gaomiaohu lake in the northern part of the plain, at 42.5% and 42.8%, respectively. The evaporation proportions calculated on the basis of ¹⁸O and ²H are very close to each other. This shows that the method used in this paper is feasible for estimating the evaporation proportions of lakes in areas with a heavy anthropogenic influence. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

基质胶结对土石混合体强度变形特性影响   总被引：1，自引：0，他引：1  

高玮  胡瑞林 《吉林大学学报(地球科学版)》2015,45(4):1164-1172

利用应变控制式静力三轴剪切仪,对具有不同胶结程度和含石量的土石混合体试样进行了固结不排水剪切试验;通过对制备的土石混合体试样的应力-应变关系、孔隙水压力变化、有效应力路径和抗剪强度指标等试验结果的对比分析,探讨了不同胶结程度土石混合体试样的差别及产生原因.试验结果表明:不同胶结程度土石混合体破坏方式可分为剪切带破坏和鼓肚变形破坏两种基本类型;胶结使得土石混合体应力应变关系和孔隙水压力变化与未胶结土石混合体差异明显,胶结作用对土石混合体的剪胀和软化特性影响显著.在块石软硬程度、形状及试样密实度相近的条件下,不论是否胶结或胶结程度如何,土石混合体有效内摩擦角φ'与无量纲粒度分布特征参数D₅₀WBP/D₆₀具有较好的线性相关性.试验结论为确定不同胶结程度土石混合体强度提供了参考.  相似文献   

基于载荷试验的土体回弹再压缩变形规律及计算方法     

李建民  滕延京 《岩土力学》2018,39(Z1):113-121

载荷试验成果多用于判断土的变形特性和求得土的变形模量、极限荷载等数据。借助卸荷比、回弹比率、再加荷比、再压缩比率等参数对载荷试验成果中的卸荷及再压缩段的变形特征进行分析,发现其发展变化规律与由固结压缩试验得到的规律一致,载荷试验的特点又恰好弥补了固结压缩试验的一些不足,将其成果应用于回弹再压缩变形的计算中是一种有益的探索性研究。结合工程实例,在固结压缩试验数据处理方法的基础上进行合理改进,将载荷试验成果应用于基坑开挖回弹变形与再压缩沉降的计算,计算结果与原有方法的计算结果、工程实测数据对比分析,验证了该种方法的有效性。现有载荷试验数据也有着明显的不足之处,结合变形计算需要,对载荷试验的试验方法提出了改进性意见,为进一步的研究指出了方向。  相似文献   

细粒硫酸钠盐渍土盐冻胀特性试验研究   总被引：1，自引：1，他引：0  

于天佑  吴亚平  司培国  张磊  孔令楠  蒲增钢 《冰川冻土》2019,41(2):407-210

为探究温度与硫酸钠含量对细粒硫酸钠盐渍土盐冻胀率及盐胀占比的影响,取兰州黄土作为素土人工配盐,用平衡公式进行理论推导,并设计了室内试验对其进行验证。结果表明：当压实度为92%、含水率为最优含水率16.8%时,随着含盐量的升高,细粒硫酸钠盐渍土的冻结温度随硫酸钠含量的增大而降低,且随着温度的降低,盐胀率的变化趋势与盐冻胀率基本一致。在冻结温度以下至-5 ℃盐胀发展速度最快,在-5 ℃以下盐胀率增长很小;在压实度为92%、含水率为最优含水率16.8%条件下,在硫酸钠含量不变时,温度越低,盐胀占比越大;温度不变时,硫酸钠含量越高,盐胀占比越大,在冻结温度以上盐胀占比为100%,但当温度降至-3~-4 ℃时盐胀占比降到50%,在-10 ℃以下盐胀占比基本保持不变。  相似文献