Zircon Hf isotope perspective on the origin of granitic rocks from eastern Bavaria, SW Bohemian Massif     

Wolfgang Siebel  Fukun Chen 《International Journal of Earth Sciences》2010,99(5):993-1005

The petrogenetic potential of in situ laser ablation Hf isotope data from melt precipitated zircons was explored through the analyses of about 700 individual crystals derived from about 20 different granitic intrusions covering the Variscan basement segment of eastern Bavaria, SE Germany. In combination with geochemical features, four major suites of granitic rocks can be distinguished: (1) NE Bavarian redwitzites (52–57 wt% SiO₂, intrusion ages around 323 Ma) have chondritic εHf(t) values (+0.8 to –0.4). The redwitzites are hybrid rocks and the Hf data are permissive of mixing of a mantle progenitor and crustal melts. (2) Various intermediate rock types (dioritic dyke, granodiorite, palite, 59–63 wt% SiO₂, 334–320 Ma) from the Bavarian Forest yield negative εHf(t) values between –3.4 and –5.1. These values which apparently contradict a mantle contribution fingerprint an enriched (metasomatized) mantle component that was mixed with crustal material. (3) Voluminous, major crust forming granites sensu stricto (67–75 wt% SiO₂, 328–298 Ma) are characterized by a range in εHf(t) values from –0.5 to –5.6. Different crustal sources and/or modification of crustal melts by various input of juvenile material can explain this variation. (4) Post-plutonic (c. 299 Ma) porphyritic dykes of dacitic composition (64–67 wt% SiO₂) from the southern Bavarian Forest have chondritic εHf(t) values (+0.6 to –1.1) and display large intergrain Hf isotope variation. The dykes form a separate petrogenetic group and the Hf data suggest that the zircons crystallized when a pristine mantle-derived parental melt was modified by infiltration of crustal material. The zircon Hf data form a largely coherent positive array with the whole-rock Nd data and both systems yield similar two-stage depleted mantle model ages (1.1–1.7 Ga).  相似文献   

云南宁洱地震引发地质灾害效应初步分析          下载免费PDF全文

张红兵  崔建文  张能  杨迎冬 《水文地质工程地质》2010,37(5):46-49

2007年6月3日云南省宁洱县发生M s=6.4地震,云南省地震局21个台站获取了本次地震的加速度记录,为研究宁洱地震引发地质灾害效应奠定了良好的基础。对本次地震引发次生地质灾害调查结合地震的加速度监测数据分析得出:地震产生的垂直加速度和水平加速度都能引发地质灾害;地震引发的地质灾害分布与地震所产生的加速度主要作用方向正相关;崩塌、滑坡的主滑方向与最大水平加速度方向基本一致。  相似文献   

Breaking Criteria for Regular Waves on Gentle Slopes     

李玉成  崔丽芳  于洋  滕斌 《中国海洋工程》1999,(4)

Nelson pointed out that the wave breaking criterion(H/d)_b for gentle slopes(i<1/100),inwhich H is the wave height and d is the water depth at the breaking point,is smaller than that for beachslopes of i>1/100),i.e.,the value of(H/d)_b for gentle slopes may be smaller than 0.6.Goda indicatedthat the wave breaking criterion given by himself is a result based on theoretical study,so it should be alsocorrect and can be used for gentle beaches,i.e.,the value of(H/d)_b for gentle slopes may be still largerthan 0.7.By use of high order nonlinear wave theory,this problem is analyzed in this study and the reasonwhy there is a large difference between different studies is explained.Moreover,the bottom energy loss dur-ing wave propagation is considered and the critical slope for the absence of wave breaking is also analyzed.  相似文献   

利用二维恒虚警进行非均匀噪声背景下的目标检测     

桂任舟 《武汉大学学报(信息科学版)》2012,37(3):354-357

针对高频地波雷达中的非均匀噪声环境及各种干扰源时变的特点,提出构建一种时变白化滤波器。先对非均匀噪声环境进行白化处理,然后在一维恒虚警的基础上,采用一种基于多普勒频率和距离的二维恒虚警处理算法。实验结果表明,利用时变白化滤波进行处理后,再在距离和多普勒频率维同时进行恒虚警检测,可以得到较好的检测结果。  相似文献   

Common Pb of UHP metamorphic rocks from the CCSD project (100–5000 m) suggesting decoupling between the slices within subducting continental crust and multiple thin slab exhumation     

Shuguang Li  Chenxiang Wang  Feng Dong  Zhenhui Hou  Qiuli Li  Yican Liu  Fang Huang  Fukun Chen 《Tectonophysics》2009,475(2):308-317

In order to understand the vertical structure of the Dabie–Sulu ultrahigh-pressure metamorphic (UHPM) belt, common Pb isotopic compositions of omphacites in eclogites and feldspars in gneisses from the Chinese Continental Scientific Drilling (CCSD) project (100–5000 m) have been investigated in this study. Samples from 0 to 800 m (unit 1) in the drilling core have moderately high radiogenic Pb isotopes with small variations of ²⁰⁶Pb/²⁰⁴Pb (16.82–17.38), ²⁰⁷Pb/²⁰⁴Pb (15.37–15.49), and ²⁰⁸Pb/²⁰⁴Pb (37.21–37.72), indicating either high µ (²³⁸U/²⁰⁴Pb) or high initial Pb isotope ratios of their protoliths. In contrast, the samples from 1600 to 2040 m (unit 3) and most of samples from 3200 to 5000 m (unit 5) have moderately or very unradiogenic Pb (unit 3: ²⁰⁶Pb/²⁰⁴Pb from 16.05 to 16.46, ²⁰⁷Pb/²⁰⁴Pb from 15.22 to 15.29, and ²⁰⁸Pb/²⁰⁴Pb from 36.68 to 37.48; unit 5: ²⁰⁶Pb/²⁰⁴Pb from 15.52 to 15.69, ²⁰⁷Pb/²⁰⁴Pb from 15.15 to 15.27, and ²⁰⁸Pb/²⁰⁴Pb from 36.48 to 37.20), indicating either low µ or low initial Pb isotope ratios of their protoliths. Pb isotopes of samples from 800 to 1600 m (unit 2) and from 2040 to 3200 m (unit 4) in the drilling core with abundant ductile shear zones are intermediate between those of units 1 and 3 or 5 and display larger variations. Pb isotopes combined with the published oxygen isotope data of the CCSD samples reveal the original positions of the five units before the Triassic continental subduction. Units 1, 3, and 5 as three UHPM rock slabs could be derived from the subducted upper continental crust, upper–middle continental crust and lower–middle continental crust, respectively. The ductile shearing zones in units 2 and 4 could be the interfaces where the detachment and decoupling took place between the upper, upper–middle and lower–middle continental crusts. The detachment between the upper slab and subducting continental lithosphere probably occurred during continental subduction, and the upper slab (unit 1) was uplifted to a shallow depth along the detachment surface by thrusting. Units 3 and 5 may be detached later from the subducted middle and lower crust and uplifted to a shallow level underneath unit 1. The low δ¹⁸O values (? 4.0 to ? 7.4‰) [Xiao, Y.-L., Zhang, Z.-M., Hoefs, J., Kerkhof, A., 2006. Ultrahigh-pressure Metamorphic Rocks from the Chinese Continental Drilling Project-II Oxygen Isotope and Fluid Inclusion Distributions through Vertical Sections. Contribution Mineral Petrology 152, 443–458.; Zhang, Z.-M., Xiao, Y.-L., Zhao, X.-D., Shi, C., 2006. Fluid-rock interaction during the continental deep subduction: oxygen isotopic profile of the main hole of the CCSD project. Acta Petrologica Sinica 22 (7), 1941–1951.] in units 2 and 4 suggest that the detachment interfaces could be developed along an ancient fault zones which were the channels of meteoric water activity during the Neoproterozoic.  相似文献   

Geochronological framework and Pb, Sr isotope geochemistry of the Qingchengzi Pb–Zn–Ag–Au orefield, Northeastern China     

Gang Yu  Jiangfeng Chen  Chunji Xue  Yuchuan Chen  Fukun Chen  Xiaoyue Du 《Ore Geology Reviews》2009,35(3-4):367-382

The Qingchengzi orefield in northeastern China, is a concentration of several Pb–Zn, Ag, and Au ore deposits. A combination of geochronological and Pb, Sr isotopic investigations was conducted. Zircon SHRIMP U–Pb ages of 225.3 ± 1.8 Ma and 184.5 ± 1.6 Ma were obtained for the Xinling and Yaojiagou granites, respectively. By step-dissolution Rb–Sr dating, ages of 221 ± 12 Ma and 138.7 ± 4.1 Ma were obtained for the sphalerite of the Zhenzigou Zn–Pb deposit and pyrargyrite of the Ag ore in the Gaojiabaozi Ag deposit, respectively. Pb isotopic ratios of the Ag ore at Gaojiabaozi (²⁰⁶Pb/²⁰⁴Pb = 18.38 to 18.53) are higher than those of the Pb–Zn ores (²⁰⁶Pb/²⁰⁴Pb = 17.66 to 17.96; Chen et al. [Chen, J.F., Yu, G., Xue, C.J., Qian, H., He, J.F., Xing, Z., Zhang, X., 2005. Pb isotope geochemistry of lead, zinc, gold and silver deposit clustered region, Liaodong rift zone, northeastern China. Science in China Series D 48, 467–476.]). Triassic granites show low Pb isotopic ratios (²⁰⁶Pb/²⁰⁴Pb = 17.12 to 17.41, ²⁰⁷Pb/²⁰⁴Pb = 15.47 to 15.54, ²⁰⁸Pb/²⁰⁴Pb = 37.51 to 37.89) and metamorphic rocks of the Liaohe Group have high ratios (²⁰⁶Pb/²⁰⁴Pb = 18.20 to 24.28 and 18.32 to 20.06, ²⁰⁷Pb/²⁰⁴Pb = 15.69 to 16.44 and 15.66 to 15.98, ²⁰⁸Pb/²⁰⁴Pb = 37.29 to 38.61 and 38.69 to 40.00 for the marble of the Dashiqiao Formation and schist of the Gaixian Formation, respectively).Magmatic activities at Qingchengzi and in adjacent regions took place in three stages, and each contained several magmatic pulses: ca. 220 to 225 Ma and 211 to 216 Ma in the Triassic; 179 to 185 Ma, 163 to 168 Ma, 155 Ma and 149 Ma in the Jurassic, as well as ca. 140 to 130 Ma in the Early Cretaceous. The Triassic magmatism was part of the Triassic magmatic belt along the northern margin of the North China Craton produced in a post-collisional extensional setting, and granites in it formed by crustal melting induced by mantle magma. The Jurassic and Early Cretaceous magmatism was related to the lithospheric delamination in eastern China. The Triassic is the most important metallogenic stage at Qingchengzi. The Pb–Zn deposits, the Pb–Zn–Ag ore at Gaojiabaozi, and the gold deposits were all formed in this stage. They are temporally and spatially associated with the Triassic magmatic activity. Mineralization is very weak in the Jurassic. Ag ore at Gaojiabaozi was formed in the Early Cretaceous, which is suggested by the young Rb–Sr isochron age, field relations, and significantly different Pb isotopic ratios between the Pb–Zn–Ag and Ag ores. Pb isotopic compositions of the Pb–Zn ores suggest binary mixing for the source of the deposits. The magmatic end-member is the Triassic granites and the other metamorphic rocks of the Liaohe Group. Slightly different proportions of the two end-members, or an involvement of materials from hidden Cretaceous granites with slightly different Pb isotopic ratios, is postulated to interpret the difference of Pb isotopic compositions between the Pb–Zn–(Ag) and Ag ores. Sr isotopic ratios support this conclusion. At the western part of the Qingchengzi orefield, hydrothermal fluid driven by the heat provided by the now exposed Triassic granites deposited ore-forming materials in the low and middle horizons of the marbles of the Dashiqiao Formation near the intrusions to form mesothermal Zn–Pb deposits. In the eastern part, hydrothermal fluids associated with deep, hidden Triassic intrusions moved upward along a regional fault over a long distance and then deposited the ore-forming materials to form epithermal Au and Pb–Zn–Ag ores. Young magmatic activities are all represented by dykes across the entire orefield, suggesting that the corresponding main intrusion bodies are situated in the deep part of the crust. Among these, only intrusions with age of ca. 140 Ma might have released sufficient amounts of fluid to be responsible for the formation of the Ag ore at Gaojiabaozi.Our age results support previous conclusions that sphalerite can provide a reliable Rb–Sr age as long as the fluid inclusion phase is effectively separated from the “sulfide” phase. Our work suggests that the separation can be achieved by a step-resolution technique. Moreover, we suggest that pyrargyrite is a promising mineral for Rb–Sr isochron dating.  相似文献   

2007年淮河流域暴雨期间大气环流特征分析   总被引：6，自引：3，他引：3  

桂海林  周兵  金荣花 《气象》2010,36(8):8-18

利用NCAR/NCEP再分析资料及国家气象信息中心30年气候平均降水资料,通过动力诊断与分析手段研究了2007年6—7月发生在我国淮河流域的暴雨。结果表明,淮河流域的环流垂直结构和降水有着非常好的对应关系。暴雨期间,鄂霍茨克海阻高与乌拉尔山阻高这种双阻高形势对于淮河流域的持续降水提供了很好的条件;南亚高压高层(200 hPa)基本为正散度区,低层(850 hPa)为负散度区,上下层强烈的抽吸结构对暴雨的发生也是非常有利的条件,同时,在淮河暴雨期问,南亚高压(200 hPa)与500 hPa西太平洋副热带高压有着相向而行的移动路径;位涡对于分析冷空气的活动,有着比较清晰的意义,暴雨发生前,有明显的正位涡异常从高纬度向低纬度伸展。大气非绝热加热分析结果显示,视热源和视水汽汇两者的高值中心与相应时段暴雨中心位置一致。  相似文献   

酒泉地区风能资源开发优势度分析   总被引：10，自引：4，他引：6       下载免费PDF全文

邓国卫  高晓清  惠小英  桂俊祥  汪宁渤  刘建彪 《高原气象》2010,29(6):1634-1640

运用新一代中尺度模式WRF对酒泉部分地区进行了风场的数值模拟。结果表明,WRF模式对复杂地形条件下的风场具有较好的模拟能力,也能较好地模拟出地形对风速的影响。在此基础上,结合GIS技术在空间信息处理方面的优势,综合考虑各种地理要素的影响,对酒泉地区风能资源进行精细化研究,分析风能资源开发的优势度,发现(1)研究区域具有非常丰富的风能资源,较丰富区以上地区的面积将近达到研究区域的一半;(2)丰富风能资源区与该地区的地形有很好的对应关系,主要处于有地形狭口效应的区域;(3)最有利于风能资源开发的区域在玉门镇以南至昌马,这一片区域的地形平坦,风能资源丰富,又是戈壁,非常适合建设大型风力发电场。这些显示了酒泉地区风能资源开发的优势度分布,能为风电场的选址提供参考。  相似文献   

基于深度学习的低剂量CT成像算法研究进展     

韩泽芳  上官宏  张雄  韩兴隆  桂志国  崔学英  张鹏程 《CT理论与应用研究》2022,31(1):117-134

计算机断层扫描成像(CT)技术具有成像速度快分辨率高的优点,广泛应用于医学临床诊断中.然而,提高剂量辐射会引发人体组织器官受损,降低剂量又会造成成像质量严重下降.为解决上述矛盾,在确保成像质量满足临床诊断需求的条件下,研究如何最大程度地降低X射线辐射对人体造成的伤害,己成为低剂量CT成像技术的研究热点.近年来,在人工智...  相似文献   

Analysis of Working Condition in Key Steps of Weather Modification     

Hu Zhihua  Qiu Shengchun  Cao Fukun 《山西气象》2008,(4)

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