藏北羌塘中部冈玛日——桃形错蓝片岩的发现

位于藏北羌塘中部的冈玛日-桃形错地区首次发现含典型蓝闪石的蓝片岩。蓝片岩是由蓝闪石、铁蓝闪石、青铝闪石、多硅白云母、阳起石、黝帘石、绿帘石、方解石、榍石、金红石等矿物组成,变质温压条件为400℃±和7kbar±,属于高压变质作用。这是一条高压变质带,推测它可能向东与滇西的澜沧江高压变质带相连。冈玛日-桃形错地区含典型蓝闪石的蓝片岩的发现对羌塘陆块的重新认识以及冈瓦纳大陆与劳亚大陆的板块边界及晚古生代古特提斯洋的闭合,具有重要的大地构造意义。     

澜沧江杂岩带小黑江-上允地区蓝片岩的成因及变质演化

通过对澜沧江杂岩带小黑江-上允地区蓝片岩的岩相学、地球化学、成因矿物学以及相平衡模拟的综合研究,阐述蓝片岩的原岩以及变质演化过程。地球化学分析结果显示,蓝片岩具有一致的稀土元素配分模式,具弱Eu正或负异常,稀土元素和微量元素特征与OIB相似,其原岩可能为OIB型玄武岩。详细矿物学研究表明,本区蓝片岩记录了俯冲峰期蓝片岩相变质和峰期后绿片岩相变质两个变质阶段,其矿物组合分别为蓝闪石+钠长石+多硅白云母+绿泥石+绿帘石和蓝闪石+钠长石±阳起石+绿泥石+绿帘石。通过Na_2O-Ca O-Fe O-MgO-Al_2O_3-SiO_2-H_2O-O体系相平衡计算,得到两个阶段的压力范围分别约为0.95 GPa和0.40 GPa。     

宽坪群区域变质作用特征

宽坪群沿华北地台南缘呈近东西向展布,是北秦岭构造带中元古界以云母石英片岩、绿片岩和石英大理岩为主体的一套中浅变质岩系。原岩分别为类复理石沉积、拉斑玄武岩和浅海相富硅、镁碳酸盐岩。因主要经受中晚元古期中压区域动力热流变质作用,形成自南向北递增变质带,即低绿片岩相—高绿片岩相—低角闪岩相。低绿片岩相包括绿泥石带和黑云母带。高绿片岩相和低角闪岩相分别由铁铝榴石带和十字石—蓝晶石带构成。各变质带在贫钙和富钙岩石的主要矿物组合是:绿泥石带Ser+Chl+Qz,Ac+Ab+Chl+Qz;黑云母带Bi+Ms+Chl+Pl+Qz,Ab+Ac+Ep+Chl+Bi+Qz;铁铝榴石带Ala+Bi+Ms+Pl+Qz,Hb+Bi+Pl+Qz;十字石—蓝晶石带Bi+Ald+Ser+Ds+Ms+Qz。宽坪群原岩建造反映其形成于平行大陆边缘的海槽内,因处于两个一级构造单元的接合部位,可能具有板块边界性质。地慢上升热流和应力变形是引起区域变质作用的主要因素。     

内蒙古北部苏尼特左旗蓝片岩岩石学和年代学研究

在苏尼特左旗以南地区的中古生代造山带的混杂岩带内发现了以岩块形式出现的蓝片岩,其矿物组合为斜长石+阳起石+蓝闪石+绿帘石+榍石。蓝片岩化学成分说明由基性火山岩变质而成。矿物化学分析表明,蓝片岩中角闪石可分为钙质、钙钠质和钠质3类。钙质闪石均为阳起石,钙钠质闪石为蓝透闪石和冻蓝闪石,钠质闪石为蓝闪石和青铝闪石及少量镁钠闪石。利用Na(M₄)和Al^Ⅳ的含量推测本区钙质、钙钠质和钠质3类闪石的压力从0.3～0.7Gpa,表明蓝片岩相变质作用的压力约为0.7GPa。用化学反应限定蓝片岩的形成温度为200～375℃左右。⁴⁰Ar³⁹Ar同位素年代学测定蓝闪石的等时线年龄为383±13Ma(1δ)。这些结果进一步证实沿贺根山—苏尼特左旗南是一条中古生代的缝合线,其俯冲—碰撞的标志即为混杂岩带以及其中的蓝片岩。     

滇西澜沧变质带中白云母的研究及其地质意义

本文以滇西澜沧变质带中最为广泛分布的造岩矿物——白云母为对象,详细研究和分析了其成分、多型类型及b_0值等,探讨了白云母的发育规律。研究结果表明,本带中绝大多数白云母为多硅白云母,且为3T+2M_1型,与蓝闪石共生的则以3T多硅白云母为主。此外,澜沧变质带经历了蓝闪石片岩亚相的高压变质作用,与古特提斯构造演化密切相关,并可与世界著名的高压带对比。     

中国蓝闪石片岩带的一般特征及其分布

蓝闪石片岩相可依据其温度划分为蓝闪石-硬柱石和蓝闪石-绿片岩相区,并与一些变质相组成不同相系。中国蓝闪石片岩带根据其平均温度-压力梯度和构造地质环境可分为:(1)元古代克拉通内蓝闪石片岩带;(2)加里东期克拉通内裂谷型蓝闪石片岩带;(3)古生代中国陆台北缘蓝闪石片岩带;(4)中新生代与俯冲作用有关的蓝闪石片岩带。蓝闪石变质作用的形成和演化与构造地质环境有关。中国蓝闪石片岩带大部分形成于硅铝壳环境,从陆壳开始裂开,直至出现洋壳。这一演化与地壳内热流变化格局有关,形成机理不属于均变论的观点。     

滇西澜沧变质带中白云母的研究及其地质意义

本文以滇西澜沧变质带中最为广泛分布的造岩矿物—白云母为对象，详细研究和 分析了其成分、多型类型及ba值等，探讨了白云母的发育规律。研究结果表明，本带中绝大多数白云母为多硅白云母，且为3T+2M,型，与蓝闪石共生的则以3T多硅白云母为主。此外，斓沧变质 带经历了蓝闪石片岩亚相的高压变质作用，与古特提斯构造演化密切相突，并可与世界著名的高 压带对比。     

藏北羌塘中部绒玛地区蓝片岩岩石学、矿物学和40Ar/39Ar年代学

藏北羌塘中部沿龙木错-双湖-线出露一条低温高压变质带,目前已有多处蓝片岩的报道.然而,除冈玛错地区产有典型的蓝闪石外,多数地区并没有典型蓝闪石的报道.绒玛蓝片岩位于羌塘中部高压变质带的中段,是该带中规模最大、保存最好的蓝片岩,对蓝片岩进行了详细的岩石学和矿物学研究,钠质角闪石主要为蓝闪石、青铝闪石、钠闪石和镁钠闪石.对蓝片岩中蓝闪石和多硅白云母进行了40Ar/39Ar定年,获得了227.3±3.8Ma和215±1.5Ma的坪年龄,分别代表蓝片岩快速俯冲消减和俯冲作用结束开始折返抬升的时代.绒玛蓝片岩岩石学、矿物学和40Ar/39Ar年代学研究为羌塘中部高压变质带的研究提供了新的资料.     

青藏高原羌塘高压变质带的特征及其构造意义

羌塘高压变质带分布于龙木错-双湖板块缝合带的南侧．西起红脊山．经片石山、蓝岭、角木查尕日、纳若．到双湖以东的才多茶卡,长约500km。向东已经延伸到巴青以北和昌都的吉塘地区,再向南进入滇西与澜沧江蓝片岩带共同构成一条断续延伸近2000km的高压变质带。羌塘高压变质带主要由蓝片岩和榴辉岩构成,蓝闪石片岩中蓝闪石和多硅白云母同位素定年结果为223-215Ma,榴辉岩的变质年龄为243-217Ma。估算蓝片岩的变质温度为410-460℃,变质压力为0．67-0．75GPa：榴辉岩相的变质作用温度不超过5000C,压力为1．56-2．35GPa。羌塘高压变质岩定年研究结果确定龙木错-双湖板块缝合带最终碰撞闭合发生在晚三叠世早期。羌塘高压变质带是冈瓦纳与欧亚大陆汇聚事件的重要记录。     

西藏羌塘中部才多茶卡蓝闪石40Ar/39Ar年代学及地质意义

本文报道了藏北羌塘中部才多茶卡地区晚三叠世蓝闪石片岩及蓝闪石矿物的新发现及地质意义。通过对才多茶卡构造混杂岩地质剖面的实测,在剖面第6层灰绿色变基性火山岩(绿片岩)中新发现以产蓝闪石类矿物为特征的中—高压变质岩系——蓝闪石片岩。对蓝闪石片岩的岩石学和矿物学特征进行了详细室内研究。从蓝闪石片岩中挑选出蓝闪石单矿物进行了40Ar/39Ar同位素年龄测定,结果表明,蓝闪石单矿物的坪年龄值为209±4Ma,等时线年龄值为216±4Ma,坪年龄与等时线年龄基本一致,属于晚三叠世诺利期,这与区域上羌塘中部发育的红脊山—双湖蓝闪石片岩的中—高压变质事件相吻合。由于蓝闪石类矿物的产出具有特殊的构造机制和地质意义,因此双湖以东的才多茶卡地区蓝闪石片岩的新发现及蓝闪石矿物的40Ar/39Ar同位素年代学研究进一步补充和丰富了青藏高原腹地羌塘中部龙木错-双湖构造混杂岩带的物质组成和同位素年代学信息,同时也为解决羌塘地区"龙木错-双湖构造混杂岩带是否向东延伸"等重大基础性地质问题,提供了新的重要资料。研究资料表明,羌塘中部自西向东从冈玛错、红脊山、绒马,经嘎尔错到才多茶卡地区,沿构造线方向断续分布的长达600km的含蓝闪石片岩的中—高压变质岩系,都是龙木错-双湖构造混杂岩带印支期构造活动事件的产物。     

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