Time scale of an early to mid-Paleozoic orogenic cycle of the long-lived Central Asian Orogenic Belt, Inner Mongolia of China: Implications for continental growth   总被引：50，自引：0，他引：50  

Ping Jian  Dunyi Liu  Alfred Krner  Brian F. Windley  Yuruo Shi  Fuqin Zhang  Guanghai Shi  Laicheng Miao  Wei Zhang  Qi Zhang  Liqao Zhang  Jishun Ren 《Lithos》2008,101(3-4):233-259

We present a detailed, new time scale for an orogenic cycle (oceanic accretion–subduction–collision) that provides significant insights into Paleozoic continental growth processes in the southeastern segment of the long-lived Central Asian Orogenic Belt (CAOB). The most prominent tectonic feature in Inner Mongolia is the association of paired orogens. A southern orogen forms a typical arc-trench complex, in which a supra-subduction zone ophiolite records successive phases during its life cycle: birth (ca. 497–477 Ma), when the ocean floor of the ophiolite was formed; (2) youth (ca. 473–470 Ma), characterized by mantle wedge magmatism; (3) shortly after maturity (ca. 461–450 Ma), high-Mg adakite and adakite were produced by slab melting and subsequent interaction of the melt with the mantle wedge; (4) death, caused by subduction of a ridge crest (ca. 451–434 Ma) and by ridge collision with the ophiolite (ca. 428–423 Ma). The evolution of the magmatic arc exhibits three major coherent phases: arc volcanism (ca. 488–444 Ma); adakite plutonism (ca. 448–438 Ma) and collision (ca. 419–415 Ma) of the arc with a passive continental margin. The northern orogen, a product of ridge-trench interaction, evolved progressively from coeval generation of near-trench plutons (ca. 498–461 Ma) and juvenile arc crust (ca. 484–469 Ma), to ridge subduction (ca. 440–434 Ma), microcontinent accretion (ca. 430–420 Ma), and finally to forearc formation. The paired orogens followed a consistent progression from ocean floor subduction/arc formation (ca. 500–438 Ma), ridge subduction (ca. 451–434 Ma) to microcontinent accretion/collision (ca. 430–415 Ma); ridge subduction records the turning point that transformed oceanic lithosphere into continental crust. The recognition of this orogenic cycle followed by Permian–early Triassic terminal collision of the CAOB provides compelling evidence for episodic continental growth.  相似文献   

Possible chemical structures and biological precursors of different vitrinites in coal measure in Northwest China     

Dayong Liu  Ping'an Peng   《International Journal of Coal Geology》2008,75(4):204-212

Chemical structure of Jurassic vitrinites isolated from the coals in basins in NW China have been checked using solid state ¹³C NMR and flash pyrolysis-GC/MS. Study shows some Jurassic collodetrinites are rich in aliphatic products in pyrolysates, consisting with the high amount of methylene carbon in ¹³C NMR spectra. In contrast, pyrolysates of Jurassic collotelinites are rich in phenols and alkylbenzenes. Also one Pennsylvanian and one Permian vitrinite selected from the Ordos basin, NW China have been checked for comparison. The proportion of aliphatics is low in pyrolysates, and aliphatic carbon peak in ¹³C NMR spectrum of Permian vitrinite is mostly composed of gas-prone carbons compared with collodetrinites in those Jurassic basins. But both pyrolysis and ¹³C NMR data shows the Pennsylvanian vitrinite is not only gas-prone but also oil-prone. Relatively high proportion of long chain aliphatic structure of some Jurassic vitrinite in Junggar, Turpan-Hami basins may be due to the contribution of liptodetrinites, which may be included during the formation of vitrinites. And it seems that suberinite is the most possible precursor of long chain aliphatics in the structure of Jurassic collodetrinite.  相似文献   

华南寒武系年代地层系统的修订及相关问题   总被引：10，自引：3，他引：7  

彭善池 《地层学杂志》2008,32(3)

将早先提出的华南寒武系4统9阶的年代地层系统,修订成4统10阶,除王村阶的底界略高于全球鼓山阶(Drumian Stage)的底界外,其余界线都与目前的全球4统10阶的年代地层界线一致。新系统采纳了在我国华南建立的全球芙蓉统、排碧阶和古丈阶,在原桃源阶的上部另建"牛车河阶"。原王村阶和桃源阶的时限因这一修订有所缩减。全球鼓山阶的底界与台江阶上部的Ptychagnostus atavus带底界可以精确对比。滇东统包含晋宁阶和梅树村阶(狭义)两个年代地层单位,晋宁阶的底界采用全球寒武系的底界,梅树村阶的底界采用罗惠麟等1994年正式修订后的定义,即位于梅树村剖面的"B"点。梅树村阶的原始定义仅指梅树村剖面的磷块岩层(即现今的中谊村段),它的底界高于现在的以Tricophycus pedum首现定义的全球寒武系底界。  相似文献   

软玉子料的形状规律及其应用   总被引：2，自引：1，他引：1  

李平  李凌丽 《岩矿测试》2008,27(5):395-396

通过对软玉子料形状总结,发现子料多呈扁平状,其长宽比较小,磨圆好的子料形状可分为11类。这些特征可用于子料鉴别与特殊材料制作。  相似文献   

大型敞流坳陷湖盆浅水三角洲与湖盆中心砂体的形成与分布   总被引：34，自引：0，他引：34  

邹才能  赵文智  张兴阳  罗平  王岚  刘柳红  薛叔浩  袁选俊  朱如凯  陶士振 《地质学报》2008,82(6):813-825

大型敞流坳陷湖盆浅水三角洲及湖盆中心砂体已成为中国陆相盆地岩性油气藏最重要的勘探目标。通过对现代典型湖盆浅水三角洲的深入分析,结合我国中、新生代大型坳陷湖盆浅水三角洲及湖盆中心砂体的地质研究,取得以下主要进展与认识：①在分析浅水三角洲形成地质背景的基础上,按照供源体系、湖水深度及三角洲前缘倾斜坡度将湖盆三角洲分为9种成因结构类型;②建立了毯式浅水曲流河三角洲的沉积模式,指出末端分流河道及末端决口扇是浅水曲流河三角洲的典型微相类型;③分析了浅水三角洲砂体大面积分布的形成条件,指出敞流湖盆是湖盆中心浅水三角洲砂体发育的重要条件,敞流通道对湖盆中心砂体分布有重要控制作用;④湖盆中心发育河流、三角洲、湖流及密度底流砂体等牵引流成因砂体,也发育洪水浊积扇及滑塌浊积扇等重力流成因砂体;⑤大型浅水三角洲体系三级层序界面对岩性（成岩）圈闭的发育有重要控制作用,三角洲平原带层序界面上覆叠置砂体富集岩性油气藏,勘探潜力大。本文研究成果希对坳陷湖盆沉积学研究及岩性油气藏勘探能有推动作用。  相似文献   

Distribution of Cd,Pb, Zn and Cu and their chemical speciations in soils from a peri-smelter area in northeast China   总被引：2，自引：0，他引：2  

Ping Du  Nandong Xue  Li Liu  Fasheng Li 《Environmental Geology》2008,55(1):205-213

An exploratory study on soil contamination of heavy metals was carried out surrounding Huludao zinc smelter in Liaoning province, China. The distribution of total heavy metals and their chemical speciations were investigated. The correlations between heavy metal speciations and soil pH values in corresponding sites were also analyzed. In general, Cd, Zn, Pb, Cu and As presented a significant contamination in the area near the smelter, comparied with Environmental Quality Standards for Soils in China. The geoaccumulation index showed the degree of contamination: Cd > Zn > Pb > Cu > As. There was no obvious pollution of Cr and Ni in the studied area. The speciation analysis showed that the dominant fraction of Cd and Zn was the acid soluble fraction, and the second was the residual fraction. Pb was mostly associated with the residual fraction, which constituted more than 50% of total concentration in all samples. Cu in residual fraction accounted for a high percentage (40–80%) of total concentration, and the proportion of Cu in the oxidizable fraction is higher than that of other metals. The distribution pattern of Pb and Zn was obviously affected by soil pH. It seemed that Pb and Zn content in acid solution fraction increased with increasing soil pH values, while Cd content in acid soluble fraction accounted for more proportion in neutral and alkaline groups than acidic one. The fraction distribution patterns of Cu in three pH groups were very similar and independent of soil pH values. And the residual fraction of Cu took a predominant part (50%) of the total content.  相似文献   

Soil n-alkane δD vs. altitude gradients along Mount Gongga, China   总被引：1，自引：0，他引：1  

Guodong Jia  Kai Wei  Fajin Chen  Ping’an Peng 《Geochimica et cosmochimica acta》2008,72(21):5165-5174

The altitude effect on the isotopic composition of precipitation and its application to paleoelevation reconstruction using authigenic or pedogenic minerals have been intensively studied. However, there are still no studies on variations in biomarker δD along altitude transects to investigate its potential as a paleoelevation indicator, although it has been observed that δD of higher plant lipid may record changes in precipitation δD (δD_p). Here, we present δD values of higher plant-derived C₂₇, C₂₉, and C₃₁n-alkanes from surface soil along the eastern slope of Mount Gongga, China with great changes in physical variables and vegetation over a range from 1000 to 4000 m above sea level. The weighted-mean δD values of these n-alkanes (δD_wax) show significant linear correlations with predicted δD_p values (R² = 0.76) with an apparent isotopic enrichment (ε_wax-p) of −137 ± 9‰, indicating that soil δD_wax values track overall δD_p variation along the entire altitudinal transect. Leaf δD_wax is also highly correlated with mountain altitude by a significant quadratic relationship (R² = 0.80). Evapotranspiration is found declining with altitude, potentially lowering δD_wax values at higher elevations. However, this evapotranspiration effect is believed to be largely compensated by the opposing effect of vegetation changes, resulting in less varied ε_wax-p values over the slope transect. This study therefore confirms the potential of using leaf δD_wax to infer paleoelevations, and more generally, to infer the δD of precipitation.  相似文献   

Identification of sources and causes of leakage on a zoned earth dam in northern Taiwan: Hydrological and isotopic evidence   总被引：3，自引：0，他引：3  

Tsung-Ren Peng  Chung-Ho Wang 《Applied Geochemistry》2008,23(8):2438-2451

Seepage through an earth dam body must be regulated as a well–planned process, if it is not properly managed, the abnormal seepage may cause dam failure. This study employed stable isotopic and statistical methods to identify the source and cause of an abnormal leakage on the zoned earth dam of the Xin–Shan reservoir located in northern Taiwan. Water samples from the dam area over a 2-a period were collected and analyzed for their stable O and H isotope compositions. In addition, a 4-a period of hydrological data, including rainfall, reservoir level, well level, seepage of filter drainage and leakage, were statistically analyzed with a stepwise multiple regression approach. Both the stable isotopic and hydrological results indicate that the abnormal leakage on the dam shell comes from the filter drainage in the dam. The reason for abnormal leakage is due to unexpected and significant precipitation–sourced water flowing into the dam’s body. The dam filter fails to drain out the incoming water sufficiently, thus generating the abnormal seepage. In addition, the defect in the dam filter may also cause the drainage filter to drain off reservoir seepage inadequately. Therefore, it is suggested that checking the filter function and preventing excessive precipitation–sourced water from flowing into the dam are the two top priorities for the follow-up remedial strategy of the dam.  相似文献   

利用MC-ICPMS对水样中硼同位素比值的测定   总被引：2，自引：0，他引：2  

吕苑苑  许荣华  赵平  谢烈文  李禾 《地球化学》2008,37(1):1-8

采用Amberlite IRA-743硼特效树脂进行水溶液中硼的分离,对洗脱液温度、体积以及树脂动态交换容量等进行了实验.它的动态交换容量为4.2 mg/g,在室温条件下,用5 mL 2%HNO3可定量从树脂柱上洗脱被吸附的硼.采用Neptune型MC-ICPMS进行硼同位素组成的测定,1 μg/g浓度的硼标准溶液获得放大的信号强度约为0.7V,硼的化学分离过程有效避免了质量歧视效应.实验结果表明,MC-ICPMS对硼存在严重的记忆效应,通过采用5%HNO3-(1%HNO3 0.1%HF)-H2O-20%NH3H2O-H2O的交替清洗方法,可在约1 h内消除硼的记忆效应.在最佳仪器条件下,对含有250 ng硼的水样,可以快速测定硼的同位素组成,占δ11B测定的绝对偏差为0.4‰-0.5‰(SD).  相似文献   

延边东部五道沟岩群的单颗粒锆石SHRIMP U-Pb 年代学及其地质意义   总被引：1，自引：0，他引：1  

逄 伟孙景贵  门兰静陈 雷 陈 冬 常 艳 梁树能 张 朋 聂喜涛 《中国地质》2008,35(6):1178-1184

通过对延边地区东部五道沟岩群黑云阳起石片岩的单颗粒锆石SHRIMP U-Pb年龄测定.获得21个单点年龄,其中包括7组谐和年龄和1组不谐和年龄.谐和年龄分别为1347.8 Ma、844.8 Ma、340.2～313.7 Ma(平均值为323±23 Ma,N=4,MSWD=0.23,置信度=0.88)、292.9～288.3 Ma(平均值=291±25 Ma,N=3,MSWD=0.031.置信度=0.86)、279.2～266.2 Ma(平均值为279±28 Ma,N=4,MSWD=0.031,置信度=0.86)、127.4～124.2 Ma(206Pb/208U年龄平均值为126.5±3.7 Ma,N=5,MSWD=0.12;置信度=O.97)、116.1～106.3 Ma(平均值为115±39 Ma,N=2,MSWD=1.2置信度=0.27),不谐和年龄的下交点年龄为(451±120)Ma、上交点年龄为(1811±400)Ma(MSWD=7.2);这一结果表明:阳起石片岩的原岩主要是来自中元古代、新元古代和早古生代的碎屑物,指示五道沟群的沉积成岩作用发生在石炭世(323±23 Ma),变质作用发生在晚二叠世(291±25 Ma),之后在279.2～266.2 Ma、126.5～106.3 Ma先后受两次岩浆用和蚀变作用的改造.  相似文献