SHRIMP U-Pb zircon age of tuff at the bottom of the Lower Cambrian Niutitang Formation,Zunyi, South China

A SHRIMP U-Pb zircon geochronology study of the tuff at the bottom of the Lower Cambrian Niutitang Formation at Songlin, Zunyi, South China yielded a mean ^206Pb/^238U age of 518±5 Ma. It is significantly younger than the Re-Os ages of 537--542 Ma for the overlying polymetallic Ni-Mo-PGE-rich layer in the basal Niutitang Formation at Songlin, suggesting that the Re-Os ages might represent that of the original magma chamber for the Ni-Mo-PGE-rich layer rather than the formation age of the strata. The intra-basinal stratigraphic correlation also implies that the absolute age of the Chengjiang biota should be younger than 518±5 Ma. Our new result, together with the SHRIMP U-Pb zircon age for the K-bentonite in the Zhongyicun member of the Zhujiaqing Formation at the Meishucun section, Yunnan Province, provides a temporal constraint for the Lower Cambrian of the Yangtze Platform in South China.     

Grenvillian orogeny in the Southern Cathaysia Block: Constraints from U-Pb ages and Lu-Hf isotopes in zircon from metamorphic basement

Metamorphic basement rocks in the Cathaysia Block are composed mainly of meta-sediments with different ages. New zircon U-Pb geochronological results from the meta-sedimentary rocks exposed in the Zengcheng and Hezi areas, southern Cathaysia Block, show that they consist dominantly of early Neoproterozoic （1.0-0.9 Ga） materials with minor Paleo- to Mesoproterozoic and late Neoproterozoic （0.8-0.6 Ga） components, suggesting that the detritus mostly come from a Grenvillian orogen. The youngest detrital zircon ages place a constraint on the deposition time of these sediments in Late Neoproterozoic. Zircon Hf isotopic compositions indicate that the Grenvillian zircons were derived from the reworking of Mesoproterozoic arc magmatic rocks and Paleoproterozoic continental crust, implying an arc-continent collisional setting. Single-peak age spectra and the presence of abundant euhedral Grenvillian zircons suggest that the sedimentary provenance is not far away from the sample location. Thus, the Grenvillian orogen probably preexisted along the southern margin of the Cathaysia Block, or very close to the south. Similarity in the ages of Grenvillian orogeny and the influence of the assembly of Gondwana in South China with India and East Antarctic are discussed, with suggestion that South China was more likely linked with the India-East Antarctica continents in Early Neoproterozoic rather than between western Laurentia and eastern Australia.     

天然锆石中铀的浸出实验

在90℃条件下的酸一碱性系列溶液中,对澳大利亚锆石和海南锆石进行了铀的浸出实验,浸出周期为30d。经拉曼光谱分析表明试验锆石没有发生变生现象。试验结果表明：经过3d的U浸出试验,就可检测到U的浸出,且U的浸出量均随反应时间的增加而增加,U元素在强酸、强碱性溶液中的浸出量均大于弱酸、弱碱性溶液,强酸溶液中的浸出量最大。     

锆石阴极发光和U-Pb年龄特征研究

根据锆石阴极发光和微区U-Pb定年的年龄结果,表明皖南新元古代花岗闪长岩中包含三类不同成因的锆石,即:同岩浆锆石、简单结构继承锆石和继承锆石核。同岩浆锆石能够反映岩体的形成时代与侵位条件,继承锆石反映岩浆岩的物质源区和岩浆形成条件。通过各岩体锆石样品的不同成因锆石分析研究,得出皖南新元古代各花岗闪长岩体具有相似的形成过程,但来自于不同的岩浆房,岩浆形成深度和侵位条件不同,与其形成于弧陆碰撞带的构造环境是一致的。     

大民屯凹陷油气充注史研究

油气充注历史的研究一直是石油地质学和油藏地球化学的重点和难点,而近年来流体定年技术的兴起为人们解决油气充注期次和时间提供了定量分析手段.利用伊利石K-Ar定年技术和流体包裹体均一温度分别研究了大民屯凹陷油气充注史.前者确定出的主充注期略晚于后者的分析结果.结合生烃史模拟资料认为:伊利石K-Ar定年结果可能更精确,但其样品挑选难度大,且只能用于砂岩油藏成藏史分析.而流体包裹体均一温度可用于碎屑岩和非碎屑岩油藏成藏史的分析.大民屯凹陷下第三系和太古界潜山油藏主充注时期为沙一二—东营早期,其中北部安福屯洼陷成藏期(沙一二期)略早于南部荣胜堡洼陷(东营早期).     

西藏洞中拉铅锌矿床石英斑岩锆石U-Pb年代学研究

探讨西藏洞中拉铅锌矿区的石英斑岩岩体归属.通过详细的地质填图,并采用LAICPMS锆石U-Pb法年龄测定技术,对石英斑岩进行年代学研究.通过石英斑岩样品中单颗粒锆石22个样品点的分析,得到其206 Pb/238U的加权平均年龄为126.9±1.1 Ma,MSWD=0.96.这一结果否认了这套岩石单元属于始新世林子宗群帕...     

热分析方法测定α粒子径迹密度及其在地质定年中的应用

将热分析法测定α粒子径迹密度应用于地质定年.用中子活化分析的方法测量了安徽马鞍山磷灰石样品中~(238)U、~(232)Th和~(147)Sm的含量.另外以Dorango磷灰石作为参考标准,用热分析方法测量了样品中α粒子的径迹含量,最后经计算得到安徽马鞍山磷灰石样品的地质年代为3.63×10~7 a.与其他地质资料比较,认为其地质年龄在3000万年左右是可信的.     

滇西小龙潭矿区始新世岩浆岩的成因及其地质意义

云南省宾川县小龙潭矿区是一个大型斑岩型铜多金属矿床,铜矿体主要产于斑岩体及其外围接触带,矿化与斑岩体密切相关。对矿区主要侵入岩开展全岩地球化学、锆石LA-ICPMS U-Pb年代学和Hf同位素研究,获得含矿二长斑岩的~(206)Pb/~(238)U加权平均年龄为(35.98±0.16)Ma,属于始新世岩浆活动的产物。斑岩体SiO_2质量分数变化较大(64.81%~69.6%),高钾(4.36%~10.95%)和碱(Na_2O+K_2O8%),A/CNK为0.99~1.36,属高钾的碱性—过碱性、准铝质—过铝质斑岩;富集大离子亲石元素(K、Rb、Ba、Sr等)、亏损高场强元素(Ta、Nb、P、Ti等),富集轻稀土元素、亏损重稀土元素;虽被划入富碱侵入岩及A型花岗岩,但具C型埃达克岩地球化学特征。斑岩体锆石ε_(Hf)(t)值为-26.93~1.66,地壳模式年龄为1 009~4141 Ma,显示斑岩体来源于下地壳物质的部分熔融,并有幔源物质的加入。结合区域演化特征,认为小龙潭斑岩体形成于造山期后的拉张环境,陆陆碰撞挤压后应力松弛,岩浆沿断裂及次级断裂上侵,进而形成铜多金属矿床。     

Age and genesis of the Myanmar jadeite: Constraints from U-Pb ages and Hf isotopes of zircon inclusions

Myanmar jadeite (jadeitite) is well known for its economical value and distinctive tectonic locality within the collisional belt between India and Eurasian plates. However, it is less studied for its genesis and geodynamic implications due to precipitous topography, adverse weather and local military conflicts in the area. By means of combined ICP-MS and LA-MC-ICPMS techniques, we have carried out in-situ trace elements, U-Pb and Lu-Hf isotopes for zircon inclusions in a piece of jadeite gem sample. CL imaging suggests that the zircons are metasomatic in origin, and contain mineral inclusions of jadeite and omphacite. Seventy-five analyses on 16 grains of the zircons yield a U-Pb age of 158 ± 2 Ma. The Myanmar zircons differ from other types in that they have no significant Eu anomalies despite high HREE concentrations. Measured ¹⁷⁶Hf/¹⁷⁷Hf ratios range from 0.282976 to 0.283122, with an average value of 0.283066 ± 7; ε_Hf(t) value of 13.8 ± 0.3 (n=75). These results indicate that the Myanmar jadeite was formed in the Late Jurassic, probably by interaction of fluid released from subducted oceanic slab with mantle wedge. Therefore, its formation has no genetic relationship to the continental collision between Indian and Euroasian plates. Supported by National Natural Science Foundation of China (Grant No. 40673039) and the Science Plan Foundation of Guangdong (Grant No. 2007B031200005)     

新甘交界北山地区大泉断裂走滑特征及ESR测年证据

卫星图片显示穿过大泉断裂的水系有被左行扭曲的特征,结合野外断层面上擦痕、断裂带中劈理观测统计和室内对断层岩显微构造的分析,确定了大泉断裂是以左行为主的走滑断裂带。对断层泥的ESR年代学测定,确定了大泉断裂开始活动时间为早更新世1.2～1.5Ma,其分支断层的活动时间在晚更新世300ka左右。大泉断裂活动时间与青藏高原在上新世末-早更新世初开始强烈隆升时间一致,表明大泉断裂的形成与青藏高原的隆升过程密切相关,是晚新生代印度和欧亚两大板块持续碰撞挤压和青藏高原隆升的远程效应。