4.1 Ga old detrital zircon in western Tibet of China

4.1 Ga old detrital zircon was found by SHRIMP U-Pb dating for quartz schist from Buring County in western Tibet, Southwest China. This is the oldest zircon U-Pb age found in China so far. The detrital zircon is a zircon of magmatic origin because its Th/ U ratios are 0.76 to 0.86. Two dates older than 4.0 Ga were measured only in one grain. U-Pb ages of 35 measured spots in 24 zircons can be subdivided into 6 groups, corresponding to at least 6 episodes of magmatic activity in the target area. The present results provide an important geochronological constraint on the geological evolution of Qinghai-Tibet Plateau.     

海拉尔盆地乌尔逊凹陷油气成藏期次分析

目的研究海拉尔盆地乌尔逊凹陷油气成藏期次。方法圈闭形成时期、烃源岩生排烃史、储层自生伊利石测年和包裹体均一温度法。结果海拉尔盆地乌尔逊凹陷油气成藏期主要分为两个大的阶段:第一阶段油气成藏时期大约在距今120~90 Ma,相当于伊敏组沉积时期,是海拉尔盆地乌尔逊凹陷最主要的成藏时期。油气大规模注入储层时期应该在105~90 Ma,相当于伊敏组二三段沉积时期,此时期为烃源岩大量生排烃时期,油气运移动力充足,有利于油气运移并聚集成藏;第二阶段为青元岗组沉积至今。青元岗组沉积以来,发生过近东西向的挤压反转,使已形成的油气藏重新调整,同时,二次生成的油气继续注入成藏。结论乌尔逊凹陷油气成藏时期研究取得新的认识,对于盆地下一步勘探具有重要的指导意义。     

SHRIMP U-Pb zircon dating for the dacite of the Sangxiu Formation in the central segment of Tethyan Himalaya and its implications

The Tethyan Himalaya is located between the In-dus-Yarlung Zangbo suture zone to the north and HigherHimalayan crystallines to the south, paleogeographicallybelonging to the northern margin of “Greater India”. TheSangxiu Formation is used to define a series of specialstrata with rich volcanic interbeds, and is only distributedto the southeast of Yangzuoyong Co within 200 km×50 km along the eastern part of central Tethyan Hima-laya[1]. Based on overlapped relationships of strata andfos…     

Effect of dead carbon on the ^14C dating of the speleothem

Based on the comparison of dating results among high-precision TIMS U-series and AMS ^14C as well as the published ^14C dating results and their band counting ages(i.e. calendar ages), this paper discusses the effect of dead carbon on the speleothem ^14C dating. The result shows that the fraction of incorporated dead carbon during the formation of speleothem varies. The change in the fraction of dead carbon would result in big deviation in the ^14C age of the speleothem. It is indispensable to take the dead carbon into consideration when dating the speleothem using the ^14C method or studying the atmospheric ^14C concentration during the past with the speleothem.     

U-series dating of Zhangkou Cave in Yiliang,Yunnan Province:Evidence for human activities in China during 40—100 ka

The cultural deposits at pits T1 and T2 in Zhangkou Cave are intercalated with several flowstone layers. U-series dates show that the capping and 2rid flowstone layers are Holocene of age. The 4th and 5th flowstone layers are ca. 55 and 110 ka old respectively. The lithic artifacts bracketed by them provide unequivocal evidence for hominid presence during this time interval. The ““temporal gap““ of hominid fossil, widely quoted as in support of the out-of-Africa hypothesis, is most probably an artifact due to systematic errors of dating techniques. The infillings under 6th flowstone layer date to ＞300 ka, much older than the previous estimate at 15 ka based on classical 14C dating of fossil bones, providing one more example of the limited reliability of this chronometer. With rich relics and favorable conditions for precise dating, this site is promising for further multidisciplinary studies to address issues concerning recent human evolution in China.     

Zircon SHRIMP dating of granite from Qaidamshan, NW China

Zircon SHRIMP dating from Qaidamshan granite shows that the granite age is 446 Ma, similar to that of eclogite in the UHP belt. We think that both granite and eclogite may be formed at different stages during tectonic evolution of this area. Together with other studies we suggested that the collision of ocean and continent plates may occur at the early Caledonian in this area, forming the eclogite, and the collision of continent and continent plates at the late Caledonian, forming the Qaidamshan granite with the zircon SHRIMP age of 446 Ma.     

Scheelite Sm-Nd dating and quartz Ar-Ar dating for Woxi Au-Sb-W deposit,western Hunan

SinceFryeretal.[1](1984)firstdatedthehydrother-maldepositusingtheSm-Ndisotopemethod,thisisotopesystematicshasbeenwidelyappliedinthegeochro-nologicalstudyforhydrothermalmineralization.Inrecentyears,manyhydrothermalmineralssuchasfluorite[2—7],tourmaline[8,9],wolframite[5,10,11]andcalcite[12,13]havebeensuccessfullydatedusingtheSm-Ndgeochronometer.ScheeliteisoneofCa-bearingminerals,andrareearthelements(REE)areincorporatedinscheelitebysubstitu-tionatCa2+structuralstiesinminerallattices;moreove…     

Lower boundary age of the Nanhua System and the Gucheng glacial stage: Evidence from SHRIMPⅡ dating

After the disintegration of the pro-Sinian System, the choice of the stratotype section of the newly established Nanhua System and determination of its lower boundary age have been one of the most important problems in Neoproterozoic stratigraphy[1—3]. In the Yangtze Gorge area in Yichang of Hubei Province where the standard section of the pro-Sinian System is located, the newly established Nanhua System consists only of the Nantuo formation (tillite) and the Liantuo Formation with tuf-…     

内蒙古大苏计斑岩型钼矿赋矿岩体的锆石U-Pb年龄与地球化学特征研究

为研究内蒙古大苏计斑岩型钼矿床赋矿岩体的形成年龄、地球化学特征及构造背景, 对3种岩体(石英斑岩、花岗斑岩和正长花岗岩)的样品进行锆石U-Pb定年和主量元素、微量元素分析。结果显示, 石英斑岩、正长花岗岩和花岗斑岩分别形成于231, 227和225 Ma, 为印支期产物。3种岩体属于高钾钙碱性−钾玄质系列, 为高分异的I型花岗岩。岩石组合特征与区域地质背景揭示, 大苏计地区在印支期处于伸展环境, 软流圈上涌导致不同深度的地壳发生部分熔融作用, 产生与大苏计斑岩型钼矿成矿相关的母岩浆。这些母岩浆向上运移过程中萃取前中生代形成的矿源层中的成矿元素, 并在结晶分异过程中不断地富集钼元素, 当岩浆挥发分达到过饱和时发生流体相与熔体相的分离, 钼进入流体相。岩浆热液沿裂隙充填, 在演化过程中发生沸腾作用, 导致大量钼和石英沉淀, 形成大苏计钼矿床。     

Single-zircon dating of Precambrian strata in the west sector of the northern Qilian Mountains and its geological significance

Single_zircon evaporation method was employed in the present study to determine the age of the iron_bearing rock series in Precambrian strata in the western sector of the northern Qilian Mountains. Three zircon ages from the diabase of the Aoyougou ophiolite previously put into Upper Lithologic Formation of the Zhulongguan Group are (1 840±2), (1 783±2) and (1 784±2) Ma respectively, whereas the zircon ages from the welded breccias in the Zhulongguan Group are (733±7), (738±4) and (604±6) Ma respectively. These results show that they should belong to the bottom of the middle Proterozoic and the upper part of upper Proterozoic respectively.