Geochemical, Sr–Nd and zircon U–Pb–Hf isotopic studies of Late Carboniferous magmatism in the West Junggar, Xinjiang: Implications for ridge subduction?     

Hongyan Geng  Min Sun  Chao Yuan  Wenjiao Xiao  Weisheng Xian  Guochun Zhao  Lifei Zhang  Kenny Wong  Fuyuan Wu 《Chemical Geology》2009,266(3-4):373-398

Voluminous granitic intrusions are distributed in the West Junggar, NW China, and they can be classified as the dioritic rocks, charnockite and alkali-feldspar granite groups. The dioritic rocks (SiO₂ = 50.4–63.8 wt.%) are calc-alkaline and Mg enriched (average MgO = 4.54 wt.%, Mg^# = 0.39–0.64), with high Sr/Y ratios (average = 21.2), weak negative Eu (average Eu/Eu = 0.80) and pronounced negative Nb–Ta anomalies. Their Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7035–0.7042, ε_Nd(t) = 4.5–7.9, ε_Hf(t) = 14.1–14.5) show a depleted mantle-like signature. These features are compatible with adakites derived from partial melting of subducted oceanic crust that interacted with mantle materials. The charnockites (SiO₂ = 60.0–65.3 wt.%) show transitional geochemical characteristics from calc-alkaline to alkaline, with weak negative Eu (average Eu/Eu = 0.75) but pronounced negative Nb–Ta anomalies. Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7037–0.7039, ε_Nd(t) = 5.2–8.0, ε_Hf(t) = 13.9–14.7) also indicate a depleted source, suggesting melts from a hot, juvenile lower crust. Alkali-feldspar granites (SiO₂ = 70.0–78.4 wt.%) are alkali and Fe-enriched, and have distinct negative Eu and Nb–Ta anomalies (average Eu/Eu = 0.26), low Sr/Y ratios (average = 2.11), and depleted Sr–Nd and zircon Hf isotopic compositions ((⁸⁷Sr/⁸⁶Sr)_i = 0.7024–0.7045, ε_Nd(t) = 5.1–8.9, ε_Hf(t) = 13.7–14.2). These characteristics are also comparable with those of rocks derived from juvenile lower crust. Despite of the differences in petrology, geochemistry and possibly different origins, zircon ages indicate that these three groups of rocks were coevally emplaced at ~ 305 Ma.A ridge subduction model can account for the geochemical characteristics of these granitoids and coeval mafic rocks. As the “slab window” opened, upwelling asthenosphere provided enhanced heat flux and triggered voluminous magmatisms: partial melting of the subducting slab formed the dioritic rocks; partial melting of the hot juvenile lower crust produced charnockite and alkali-feldspar granite, and partial melting in the mantle wedge generated mafic rocks in the region. These results suggest that subduction was ongoing in the Late Carboniferous and, thus support that the accretion and collision in the Central Asian Orogenic Belt took place in North Xinjiang after 305 Ma, and possibly in the Permian.  相似文献   

Episodic crustal growth of North China as revealed by U-Pb age and Hf isotopes of detrital zircons from modern rivers   总被引：9，自引：0，他引：9  

Jie Yang  Shan Gao  Chen Chen  Honglin Yuan  Siwen Xie 《Geochimica et cosmochimica acta》2009,73(9):2660-2673

Clastic sedimentary rocks are samples of the exposed continental crust. In order to characterize the crustal growth history of North China and its possible regional variations, 479 concordant detrital zircons in three sand samples from the lower reach of the Yellow River (which drains the Tibet-Qinghai Plateau, the Western Qinling Orogen, the Qilian Orogen and the North China Craton) and two sand samples from the Luan River and the Yongding River (which run entirely within the North China Craton) were measured for U-Pb age and Lu-Hf isotopic compositions by excimer laser-ablation ICP-MS and MC-ICP-MS. Although regional variations exist, concordant detrital zircons from the Yellow River reveal three major age groups of 2.1-2.5 Ga, 1.6-2.0 Ga, and 150-500 Ma. Detrital zircons from the smaller Luan and Yongding Rivers show three broadly similar major age groups at 2.3-2.6 Ga, 1.6-2.0 Ga, and 140-350 Ma, but with narrower age ranges. Compared to the Luan and Yongding River zircons, the Yellow River zircons are characterized by a significant number of Neoproterozoic grains. Although Hf isotopic compositions show both juvenile crustal growth and crustal reworking for all age groups, much of the crustal growth of North China occurred in the Neoarchean and Mesoproterozoic. All three rivers are characterized by a common prominent group of Hf crust formation model ages at 2.4-2.9 Ga with a peak at 2.7-2.8 Ga. A less significant age group lies between 1.4 and 1.8 Ga for the Yellow River, and between 1.6 and 1.9 Ga for the Yongding River and Luan River. Crustal growth rates based on Hf continental crust formation model ages suggest 45% and 90% of the present crustal volume was formed by 2.5 Ga and 1.0 Ga, respectively, for the drainage area of the Yellow River. In comparison, 60% and 98% of the present crustal volume of the North China Craton was generated by 2.5 Ga and 1.0 Ga, respectively, for the Luan and Yongding Rivers. The 2.7-2.8 Ga age peak observed in all river samples agrees well with the coeval major peak for global crustal growth. However, the other suggested global peaks of crustal growth at 3.4 and 3.8 Ga are insignificant in North China. Taken together with our previous studies of the Yangtze Craton, which show insignificant crustal growth at 2.7-2.8 Ga, we suggest that these advocated worldwide crust formation peaks be re-examined and treated carefully. Our results also show that Phanerozoic zircons may have been derived from crustal sources separated from the mantle up to 2.0 Ga ago before the zircons crystallized, suggesting long-term preservation, reworking and recycling of the continental crust.  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   

纳米铁去除饮用水中As(Ⅲ)和As(Ⅴ)   总被引：3，自引：1，他引：2  

黄园英  秦臻  刘菲 《岩矿测试》2009,28(6):529-534

在好氧水体中,As(Ⅲ)比As(Ⅴ)更易迁移,而且在水处理过程中去除效率更低。在实验室合成制得BET比表面积为49.16 m2/g,直径范围为20~40 nm的纳米铁。通过批试验考察纳米铁对As(Ⅲ)和As(Ⅴ)去除能力及其反应动力学情况。结果表明,在pH为7,温度20℃时纳米铁能够快速地去除As(Ⅲ)和As(Ⅴ),在60 m in内,0.25 g纳米铁对起始浓度为968.6μg/L As(Ⅲ)和828.9μg/L As(Ⅴ)的去除率大于99.5%。反应遵循准一级反应动力学方程,标准化后的As(Ⅲ)和As(Ⅴ)比表面积速率常数kSA分别为1.30 mL/(m2.m in)和1.64 mL/(m2.m in)。由实验结果可知,具有高反应活性的纳米铁是用于含砷饮用水处理非常有效的吸附材料。  相似文献   

鄂尔多斯盆地侏罗纪西界分析   总被引：6，自引：1，他引：5  

张珂  邹和平  刘忠厚  马占武 《地质论评》2009,55(1):761-774

鄂尔多斯盆地西界,特别是其早—中侏罗世盆地西界,由于不同期次、不同性质的构造相互叠加而模糊不清,究竟是在贺兰山以西还是现在银川盆地以东的问题,至今尚无共识,极大地影响着矿产资源的评价和找矿战略的部署。本文在前人工作的基础上,通过针对性的野外工作,分析和筛分了不同时期的古构造,探讨了晚侏罗世和早—中侏罗世盆地的西界。文章认为,鄂尔多斯盆地西部巨大的近南北向挤压构造形成于晚侏罗世,而东西向的挤压构造则出现于晚三叠世。两期方向截然不同的挤压构造相互叠加,构成了鄂尔多斯盆地西部复杂的叠加构造和不规则的盆地西界。晚期挤压构造较为清晰,表现为近南北向的逆冲推覆构造带和纵贯盆地南北的“古脊梁”,使盆地西界退缩到桌子山东麓断裂、横山堡—磁窑堡断褶带以及马儿庄冲断裂和崆峒山断裂以东。早期挤压构造受后期构造的叠加改造,断断续续,时隐时现。近东西向挤压构造受古亚洲域的影响,是印支运动的产物,近南北向挤压构造转受滨太平洋域的作用,是燕山运动的表现。在古亚洲域向太平洋域转换过程中的早—中侏罗世,鄂尔多斯盆地西部出现了近东西向的拉张伸展,在盆地内部表现为近东西向隆起凹陷的古地形,使盆地西缘波状弯曲,而非平直,“银川古隆起”和“汝箕沟—鄂尔多斯盆地”两者并存,并不矛盾。早—中侏罗世盆地西界可能远至阿拉善地块。上述中生代构造又经新生代构造改造,变得更加复杂多样,甚至面目全非。如不注意构造筛分,中生代构造乃至盆地边界的研究就会被误导,从而得出错误结论。  相似文献   

松辽盆地深层侏罗系-下白垩统生物组合和沉积环境   总被引：5，自引：0，他引：5       下载免费PDF全文

万传彪  李延锋  薛云飞 《地质科学》2009,44(2):418-434

本文描述了松辽盆地探井揭露的深层地层序列及其所产的5个牛物门类化石组合特征.9个孢粉组合是Monosulcites-Cyathidites组合、Pinaceae-Cyathidites-Osmundaeidites组合、Classopollis-Piceites组合、Lophotriletes-Cicatricosisporites组合、Paleoconiferus-Lygodiumsporites组合、Cyathidites-Leiotriletes-Clavatipollenites组合、Cicatricosisporites-Leiotriletes-Polyporopollenites组合、Leiotriletes-Schizaeoisporites-Classopollis组合和Trilobosporites-Cyathidites-Tricolpollenites组合.3个藻类组合是Vesperopsis-Australisphaera组合、Balmula granorugosa组合和Vesperopsis zhaodongensis组合.2个介形类组合是Cypridea unicostata-Limnocypridesadscondida组合和Mongolocypris limpida-Paracandona planiuscula组合.4个植物组合是Elatocladus submanchurica-Ginkgoites orientalis组合、Acanthopteris gothani-Pterophyllum组合、Sphenopteris johnstrupii-Coniopteris nympharum组合和Platanus septentrionalis-Protophyllum undulaturn组合.3个大孢子组合是Minerisporites sp.组合、Ricinospora leavigata-Galamospora sp.组合和Arcellites组合.还介绍了叶肢介、轮藻、双壳类和鱼类化石的产出情况.结合同位素资料认为：大庆群时代为中侏罗世,火石岭组可能为贝里阿斯期,沙河子组为凡兰吟期-欧特里夫期,营城组为欧特里夫期-巴列姆期,登娄库组为巴列姆期-阿普第期早期,泉头组一-二段为阿普第-阿尔卑期,并对各组沉积环境进行了初步分析.  相似文献   

钻孔体应变仪在地震前兆观测中的理论和应用研究综述     

孙艺玫  查楠  任雪  张丽  毛佳宁 《防灾减灾学报》2021,37(4):69-74

一些地震发生前后,时常会观测到有别于正常地震波的前驱波信号,这些前驱波信号对于地震的预报和观测有重要的现实意义;钻孔应变观测是观测前驱波信号的重要手段,也是地震前兆观测与研究中不可或缺的主要技术,可以给出传统测震仪观测无法给出的信息;文章概述了当前钻孔体应变观测的原理和研究发展路径,并集中表述了其在实际预测中的重要研究成果;从研究实例上可以看出来,当前的钻孔应变观测结果和实际的地震发生状况存在一定的不确定性,回溯研究表明现在的观测结果还有很大的提升空间.  相似文献   

Understanding the dynamical-microphysical-electrical processes associated with severe thunderstorms over the Beijing metropolitan region     

Xiushu QIE  Shanfeng YUAN  Zhixiong CHEN  Dongfeng WANG  Dongxia LIU  Mengyu SUN  Zhuling SUN  Abhay SRIVASTAVA  Hongbo ZHANG  Jingyu LU  Hui XIAO  Yongheng BI  Liang FENG  Ye TIAN  Yan XU  Rubin JIANG  Mingyuan LIU  Xian XIAO  Shu DUAN  Debin SU  Chengyun SUN  Wenjing XU  Yijun ZHANG  Gaopeng LU  Da-Lin ZHANG  Yan YIN  Ye YU 《中国科学:地球科学(英文版)》2021,64(1):10-26

The Dynamical-microphysical-electrical Processes in Severe Thunderstorms and Lightning Hazards(STORM973)project conducted coordinated comprehensive field observations of thunderstorms in the Beijing metropolitan region(BMR)during the warm season from 2014 to 2018.The aim of the project was to understand how dynamical,microphysical and electrical processes interact in severe thunderstorms in the BMR,and how to assimilate lightning data in numerical weather prediction models to improve severe thunderstorm forecasts.The platforms used in the field campaign included the Beijing Lightning Network(BLNET,consisting of 16 stations),2 X-band dual linear polarimetric Doppler radars,and 4 laser raindrop spectrometers.The collaboration also made use of the China Meteorological Administration’s mesoscale meteorological observation network in the Beijing-Tianjin-Hebei region.Although diverse thunderstorm types were documented,it was found that squall lines and multicell storms were the two major categories of severe thunderstorms with frequent lightning activity and extreme rainfall or unexpected local short-duration heavy rainfall resulting in inundations in the central urban area,influenced by the terrain and environmental conditions.The flash density maximums were found in eastern Changping District,central and eastern Shunyi District,and the central urban area of Beijing,suggesting that the urban heat island effect has a crucial role in the intensification of thunderstorms over Beijing.In addition,the flash rate associated with super thunderstorms can reach hundreds of flashes per minute in the central city regions.The super(5%of the total),strong(35%),and weak(60%)thunderstorms contributed about 37%,56%,and 7%to the total flashes in the BMR,respectively.Owing to the close connection between lightning activity and the thermodynamic and microphysical characteristics of the thunderstorms,the lightning flash rate can be used as an indicator of severe weather events,such as hail and short-duration heavy rainfall.Lightning data can also be assimilated into numerical weather prediction models to help improve the forecasting of severe convection and precipitation at the cloud-resolved scale,through adjusting or correcting the thermodynamic and microphysical parameters of the model.  相似文献   

Quasi-waveform seismic tomography of crustal structures in the capital circle region of China     

Xueyuan HUANG  Dinghui YANG  Ping TONG  Yuan GAO  Yutao SHI  Hao WU 《中国科学:地球科学(英文版)》2021,64(1):110-126

Seismic tomography is one of the main tools to explore the interior of the earth.In this study,the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital region of China.3-D highresolution V_P,V_S and the Poisson’s ratio models are generated by inverting 29839 direct P-and 29972 direct S-wave traveltimes selected from 3231 local earthquakes.The results reveal strong crustal heterogeneities.The velocity anomalies at shallow depths are well consistent with surface geologic structures.The relatively low-velocity anomaly layer in the middle crust may be the result of multiple phases of tectonic activity.Earthquakes generally occurred on the boundaries of high-and low-velocity and Poisson’s ratio anomalies.There are obvious low-velocity anomalies below the hypocenters of the Tangshan earthquake and the historical Sanhe-Pinggu earthquake,implying the existence of fluids.The similar velocity structures around the hypocenters of the two earthquakes indicate that the occurrences of the two earthquakes may be related to the same mechanism.The highresolution velocity models provide important observational constraints on the small-scale heterogeneities and dynamic mechanism of the crust in the capital region of China.  相似文献   

玉米大豆生长中后期遥感辨识的指示性特征研究     

沈宇  李强子  杜鑫  王红岩  张源 《遥感学报》2022,26(7):1410-1422

玉米和大豆是两种主要的粮食作物,及时准确地监测两者的种植面积对于产量预测和市场价格的制定具有重要的意义。利用遥感技术探究在生长季中后期能有效区分玉米和大豆的指示性特征集,为在不同实验区进行推广应用和提前玉米和大豆种植面积信息发布的时间提供技术支撑。文章以玉米和大豆为研究对象,以黑龙江和安徽省两个典型种植区为实验区,以高分一号影像为数据源,计算多种植被指数特征和两种纹理特征,同时利用特征优选方法评价特征间的相对重要性,并结合随机森林分类算法分析特征个数对精度的影响,得到不同试验区区分两者的最佳特征子集。随后根据不同实验区最佳特征子集的共同点和差异,遴选出对玉米和大豆中后期区分的遥感指示性识别特征集,并设计实验方案验证其有效性和稳定性。实验表明：在玉米和大豆生长中后期存在具有高效辨识两者的遥感特征集,能有效和稳定地增强两者的遥感识别能力;在不同实验区,基于特征优选方法可以选择出区分玉米和大豆的最佳分类特征子集,得到两者最优的识别效果,比仅仅使用原始波段特征的分类精度提升了近10个百分点,总体分类精度能够平均达到97%,Kappa系数0.96,玉米和大豆的单类分类精度平均超过95%;在不同的种植区,利用玉米和大豆的指示性特征集可以得到几乎与优选出的最佳特征子集同样的分类精度和制图效果,且具有稳定性和有效性,较最佳特征集更具推广使用意义。指示性特征集包含6种：植被指数中的比值植被指数（RVI）,差值植被指数（DVI）,转换型植被指数（TVI）,改进型叶绿素吸收比率指数（MCARI）和灰度共生矩阵（GLCM）纹理特征中的二阶矩（the Second Moment）和熵（Entropy）。  相似文献