湘中长安组碎屑锆石LA-ICP-MS U-Pb年龄及其地质意义

我国南方扬子板块是国际上新元古代冰期地层最具代表性的地区之一,冰期地层出露广泛,为国内外学者所关注.对扬子地块东南缘湘中大乘山地区长安组二段底部的凝灰质板岩中所获得的碎屑锆石的U-Pb LA-ICP-MS同位素年代分析研究结果显示,长安组碎屑锆石年龄主要为831 ～ 720 Ma,少数为新元古早期1005 ～ 842Ma,含有少量古元古—中元古的2500 ～ 1933 Ma的锆石.长安组较年轻的两组锆石加权年龄为769 Ma(2σ,n=9,MSWD=11.3)和828 Ma(2σ,n=16,MSWD=7.9),最小年龄720.2±12 Ma(206Pb/238U表面年龄).长安组碎屑锆石的U-Pb年代学表明,该地层最早形成时代＜770 Ma,那么长安冰期的启动年龄应不大于770 Ma.组成碎屑锆石年龄谱中最大碎屑锆石群体的年龄组构750～830Ma为华南在新元古代时期的生长和再造时代,可能与Rodinia超大陆的裂解有关.古元古代2500 ～ 1933 Ma年龄信息在长安组碎屑锆石的出现,则暗示了湘中大乘山地区或扬子东南缘的一次地壳再造事件.     

南秦岭勉略构造带略阳三岔子地区金家河千枚岩沉积物源分析：碎屑锆石U-Pb年代学证据

南秦岭勉略构造带略阳三岔子地区发育一套灰灰黑色含碳绢云石英千枚岩和灰白色绢云石英千枚岩夹灰黑色含砾绢云千枚岩、白云质灰岩、硅质岩以及碳硅质板岩的岩石组合。为探讨其形成时代及沉积物源,笔者对其中的含砾绢云白云质石英千枚岩、绢云白云质石英千枚岩进行岩石学及LA-ICP-MS碎屑锆石U-Pb年代学研究。所获得的碎屑锆石年龄可以分为3组:新元古代年龄组(678～966Ma),该段有明显峰值,峰值年龄分别为781Ma、865Ma;中元古代年龄组(1 122～1 432Ma);古元古代-太古代年龄组(1 944～2 824Ma)。2件变质碎屑岩的碎屑锆石最小年龄组分别为678～736Ma(平均年龄为725Ma)、771～775Ma(平均年龄为773Ma)。综合研究认为该沉积地层沉积时代不早于南华纪,其沉积物源主要为勉略构造带内、碧口微地块、扬子地块西北缘汉南米仓山杂岩新元古代岩浆岩,其沉积事件对应于新元古带中晚期(800 Ma～)勉略构造带及扬子地块西北缘后碰撞裂解阶段。     

武当地块与扬子陆核区新元古代早期沉积岩碎屑锆石U-Pb年代学对比及其地质意义

系统收集并总结了武当地块与扬子陆核区(崆岭地区)已发表的新元古代沉积岩中碎屑锆石的U-Pb年代学数据,对二者的相互关系进行分析,并讨论了扬子克拉通北缘新元古代时期的构造演化过程及特征。对前人发表的年代学数据进行的统计和对比结果表明,武当地块沉积岩中碎屑锆石年龄谱记录了~710Ma和~2.5Ga的年龄峰值,同时缺乏3.0Ga年龄的锆石,表明其沉积物质来源可能并非扬子陆核区,其在新元古代之前可能作为一个独立的微陆块与扬子陆核区(崆岭地区)分离开来,二者于新元古代中期发生碰撞拼合而成为一个整体。     

华南双桥山群和河上镇群凝灰岩中的锆石SHRIMP U-Pb年龄—对江南新元古代造山带演化的制约

通过西澳科庭大学离子探针中心的远程测试,在双桥山群横涌组和安乐林组斑脱岩中获得大量锆石,其SHRIMP U-Pb加权平均年龄为831Ma±5Ma(横涌组)、829Ma±5Ma(安乐林组),在河上镇群上墅组中获得加权平均年龄767Ma±5Ma.锆石SHRIMP U-Pb年龄表明华南地区广为发育的双桥山群应归入新元古界,该年龄为标定双桥山群在地层柱中的位置提供了准确的年代学依据.     

华南双桥山群和河上镇群凝灰岩中的锆石SHRIMP U-Pb年龄—对江南新元古代造山带演化的制约

通过西澳科庭大学离子探针中心的远程测试,在双桥山群横涌组和安乐林组斑脱岩中获得大量锆石,其SHRIMP U-Pb加权平均年龄为831 Ma±5 Ma(横涌组)、829 Ma±5 Ma（安乐林组）,在河上镇群上墅组中获得加权平均年龄767 Ma±5 Ma。锆石SHRIMP U-Pb年龄表明华南地区广为发育的双桥山群应归入新元古界,该年龄为标定双桥山群在地层柱中的位置提供了准确的年代学依据。     

赣东北景德镇双桥山群火山碎屑凝灰岩锆石U-Pb年龄及Hf同位素特征

为探讨赣东北景德镇地区双桥山群的沉积时代与物质来源,对该区双桥山群安乐林组地层中发育的一套变火山碎屑凝灰岩夹层进行了年代学、地球化学及锆石Lu-Hf同位素研究。结果显示,该套火山碎屑凝灰岩的岩性主要为英安岩、安山岩,凝灰岩的LA-ICP-MS锆石U-Pb年龄为(809±2)Ma,表明该套岩石形成于新元古代。凝灰岩锆石的Hf同位素组成变化范围较广,其中二阶模式年龄为1426~2313 Ma,主要集中于1.7~2.3 Ga之间,其ε_(Hf)(t)均为负值-2.6~-16.5,t_(DM2)模式年龄远大于U-Pb年龄,表明该组岩石的岩浆来源于元古代地壳物质的再循环。     

扬子西缘新元古代中期裂谷作用:来自年代学与沉积学的新证据

华南新元古代沉积盆地演化与Rodinia超大陆裂解存在紧密联系,但仍缺乏精细刻画.对扬子西缘澄江组开展了系统的碎屑锆石年代学和沉积学研究.澄江组砂岩的碎屑锆石U-Pb年龄主要为新元古代（870~780 Ma）,少数为前新元古代（2 850~1 010 Ma）,最显著的峰值为820 Ma,最年轻一组碎屑锆石206Pb/238U年龄加权平均值为804.5±5.4 Ma.结合已发表年龄数据,将澄江组沉积时限进一步限定为800~720 Ma.物源分析揭示澄江组的新元古代碎屑锆石剥蚀自邻近的新元古代岩浆岩,而前新元古代锆石可能来自于邻近新元古代岩体的剥蚀或地层的沉积再循环.扬子西缘新元古代中期沉积盆地具有由冲积扇相逐渐过渡为前扇三角洲相的沉积演化序列,最终形成了具有裂谷充填特征的“楔状地层”.这种沉积超覆演化过程在整个华南新元古代裂谷系普遍存在,指示在800 Ma左右华南全面进入裂谷盆地成熟阶段.      

扬子地块西南缘大红山群石榴白云母-长石石英片岩的白云母40Ar-39Ar定年及其地质意义

大红山群是扬子地块西南缘出露的古元古代结晶基底,主要经历了绿片岩相-低角闪岩相变质作用.本研究对大红山群老厂河组变质中酸性岩和变质沉积岩——石榴白云母-长石石英片岩中的白云母进行了40Ar-39Ar测年,得到三个样品的坪年龄和40Ar/39Ar等时线年龄结果较统一,坪年龄代表的变质年龄分别为837.7±4.2Ma、839.6±4.2Ma和844.2±4.2Ma.变质沉积岩和变质中酸性岩的变质时代类似,均介于837～845Ma.大红山群变质基性岩中变质锆石的U-Pb定年年龄为849±12Ma(杨红等,2012),40Ar-39Ar测年数据与锆石定年数据相结合,说明大红山群古元古代结晶基底中的火山岩和沉积岩均在新元古代经历了同期变质作用,其主期低角闪岩相变质作用发生于新元古代837～850Ma.结合前人发表的扬子西缘～750Ma的变质年龄,扬子西缘从北向南的区域变质作用时限可扩展到750 ～850Ma.此外,扬子西缘存在750～850Ma的岩浆事件,本文研究结果说明,扬子地块西缘在新元古代不仅发生了大规模岩浆作用,也发生了750～850Ma的区域变质作用,扬子西缘存在新元古代的岩浆-变质事件.岩浆事件与变质事件之间可能存在相关性,即新元古代岩浆作用引起了扬子西缘的区域动力热流变质作用.     

扬子板块北缘花山群沉积时代及其对Rodinia超大陆裂解的制约

出露于扬子板块北缘大洪山地区的花山群自下而上由一套以砾岩为主的粗碎屑沉积和一套以砂质板岩为主的细碎屑沉积组成,伴随有拉斑玄武质岩浆活动。花山群整体变质程度不高,形成构造环境复杂,对其构造属性及其与区内所谓的花山"蛇绿混杂岩"的时空关系一直存有争议,它们对新元古代Rodinia超大陆在扬子板块北缘的汇聚-裂解响应具有重要的制约意义。笔者在花山群六房咀组下部细砂岩中采集玄武质熔结凝灰岩夹层样品1件,碎屑岩样品2件,在上覆地层南华系莲沱组采集碎屑岩样品1件;对玄武质熔结凝灰岩进行了SHRIMP锆石U-Pb同位素测年,对碎屑岩样品进行了LA-MC-ICPMS锆石U-Pb同位素测年。获得玄武质熔结凝灰岩锆石U-Pb年龄814.7±7.3 Ma;花山群的碎屑锆石U-Pb年龄谱存在三个明显的峰值:~900 Ma、~2050Ma和~2650 Ma,最显著峰值为~2650 Ma,上覆莲沱组碎屑岩年龄谱的三个峰值为:~900 Ma、~2050 Ma和~2500 Ma,最显著峰值为~2050Ma,三件碎屑岩样品均与扬子板块的碎屑锆石U-Pb年龄统计峰值一致。花山群的碎屑源区可能包括下伏中元古代打鼓石群、太古宙鱼洞子杂岩以及崆岭杂岩。结合前人年代学研究资料和区域构造成果分析,花山群沉积时代应为820~815Ma,形成于伸展构造背景,与花山"蛇绿混杂岩"不是同期同构造背景的产物;花山"蛇绿混杂岩"与花山群沉积建造依次反映了扬子板块北缘由挤压构造背景向伸展构造背景的转换过程。花山群中的碎屑沉积物与基性火山岩、火山碎屑岩属于裂解背景下形成的同时代沉积-火山建造;结合前人在扬子板块周缘发现的大量约820 Ma酸性—基性岩浆活动记录以及同时代(820~800 Ma)的沉积地层,推测花山群形成于Rodinia超大陆裂解背景之下,与超级地幔柱活动有关。     

南秦岭佛坪地区地层格架与物源分析:变质沉积岩中碎屑锆石LA-ICP-MS U-Pb定年提供的制约

南秦岭佛坪地区位于东西秦岭交汇部位,以前寒武纪基底穹状隆升为主要特征,因其特殊的构造位置和变质变形特征而受到广泛关注。为了更好地揭示南秦岭构造带的性质及其在秦岭造山带构造演化中的作用,本文对佛坪地区的前寒武纪基底和沉积盖层进行了系统的碎屑锆石LA-ICP-MS U-Pb年代学研究。佛坪穹隆核部前寒武纪基底中碎屑锆石主要年龄峰值为600~820Ma、2021Ma和2467Ma,其中3个样品给出最年轻的年龄区间约为615~728Ma,沉积时代不早于新元古代,另外1个样品给出的最年轻的年龄峰值为1113Ma,沉积时代不早于中元古代,否定了关于认为其为太古代或古元古代的变质结晶基底的认识,其碎屑物质可能来源于南秦岭构造带和扬子陆块北缘。佛坪穹隆上覆盖层和外围南侧盖层给出了相似的年龄图谱,主要年龄峰值为410～450Ma、650～880Ma和910～950Ma,其中最年轻的年龄区间为344～416Ma,表明其沉积时代晚于泥盆纪,碎屑物质来源为北秦岭构造带和南秦岭构造带。上述研究结果表明,南秦岭构造带(前寒武纪基底)于新元古代已增生为扬子陆块北缘的重要组成部分,于晚古生代(泥盆纪)紧邻华北-北秦岭构造带南缘,并共同为南秦岭大面积的泥盆纪盆地提供碎屑物质。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)     

GEOCHEMISTRY

正20142002 Wei Hualing(Institute of Geophysical and Geochemical Exploration,Chinese Academy of Geological Sciences,Langfang065000,China);Zhou Guohua Element Content and Mineral Compositions in Different Sizes of Soil in Tongling Area,Anhui Province(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(11),2013,p.1861