阿尔金山巴什考供地区斜长角闪岩的岩石地球化学和Sm-Nd,Ar同位素特征

阿尔金山地区巴什考供以北、阿尔金山北缘断裂以南为一套变质程度达角闪岩相的片岩、大理岩夹少量斜长角闪岩。地球化学研究表明 ,这些斜长角闪岩原岩为玄武质成分 ,具有拉班玄武岩的特点。斜长角闪岩全岩Sm -Nd同位素等时线年龄为 1185± 130 (2σ)Ma ,其INd=0 .5 114 0 ,εNd(t) =+5 .8± 0 .6 ,表明原岩形成于中元古代晚期 ,源自亏损地幔。斜长角闪岩中角闪石4 0 Ar - 39Ar同位素分析显示变质作用发生在 6 12± 5 .8Ma之前 ,进一步表明其原岩应该形成于前寒武纪。这些年龄的确定 ,为探讨阿尔金山地区中晚元古代的古构造格局提供了重要的证据     

大别核部杂岩中斜长角闪岩的地球化学特征及其地质意义

大别核部杂岩单元中斜长角闪岩的地球化学特征对于认识大别核部杂岩单元的特征及归属有着十分重要的意义。本文对大别核部杂岩单元中斜长角闪岩的岩石地球化学特征及Sm-Nd 同位素特征进行了较系统研究。斜长角闪岩的 Nd亏损地幔模式年龄(t_(DM))有3个不连续年龄段,它们分别为2.50～2.92Ga(平均2.71Ga);1.79～2.47Ga(平均2.14Ga);1.07～1.57Ga(平均1.38Ga)。模式年龄为中元古代、古元古代的斜长角闪岩的等时线年龄分别为1444±180Ma、2220±210Ma,其模式年龄与等时线年龄在误差范围内一致。表明至少模式年龄为元古宙的斜长角门岩的t_(DM)可代表其原岩的近似形成年龄,从而证明大别核部杂岩单元中存在着古元古代、中元古代两期自亏损地幔分异的基性火山岩变质形成的斜长角闪岩。而模式年龄为新太古代的斜长角闪岩,其模式年龄能否代表其形成年龄还需要进一步研究。各期斜长角闪岩在地球化学特征上的差异表现得不明显。通过对其原岩性质研究表明:原岩主要为拉斑玄武岩,少数为钙碱性玄武岩。大别核部杂岩中斜长角闪岩原岩ε_(Nd)(t)反映出大别核部杂岩地区上地幔自古元古代到中元古代一直沿着亏损地幔 Nd 同位素的演化线演化发展,这种性质及演化趋势与扬子北缘及南秦岭早期上地幔 Nd 同位素性质及演化趋势十分     

大别山南部宿松杂岩的U-Pb锆石和Ar-Ar角闪石年龄及其地质意义

大别造山带南部宿松杂岩中花岗片麻岩和斜长角闪岩的U-Pb锆石年龄和Ar/Ar角闪石年龄测定结果表明,二长花岗片麻岩的形成年龄为2018±73Ma和2010±38Ma,白云斜长片麻岩的形成年龄为741±7Ma,宿松杂岩经过228Ma左右的变质作用。这些结果表明大别山南缘存在较大规模的古元古代花岗质结晶基底,广泛分布在宿松杂岩中的花岗片麻岩和由花岗片麻岩强烈剪切变形而成的白云斜长片麻岩、白云钠长石英片岩形成于新元古代,不整合覆于二长花岗片麻岩之上并被新元古代花岗片麻岩侵入的变质沉积岩形成于中元古代晚期-新元古代早期。由此得出,宿松杂岩主要由古元古代二长花岗片麻岩、中新元古代变质沉积岩和新元古代变质花岗岩和变质基性岩组成,因而也是扬子板块的俯冲陆壳基底的一部分。     

内蒙古锡林格勒杂岩的地球化学研究:从Rodinia聚合到古亚洲洋闭合后碰撞造山的历史记录

内蒙古东部出露的锡林格勒杂岩主要由中元古代原岩为火成岩的黑云母片麻岩和斜长角闪岩透镜体组成。片麻岩显示轻稀土元素富集的中等分异特征 ,具明显的Eu负异常 ,其不相容元素特征与平均地壳类似但相对亏损Ba和Sr。斜长角闪岩构成一条Sm -Nd等时线 ,其年龄值为12 0 2± 6 5Ma ,εNd(1.2 0Ga)值为 6 .8。角闪岩的亏损地幔模式年龄 (tDM,1.2 6～ 1.32Ga)与其Sm -Nd同位素等时线年龄接近。角闪岩的Rb -Sr同位素等时线年龄为 393± 14Ma ,其87Sr/ 86 Sr初始比值为 0 .70 379± 0 .0 0 0 0 7,此Rb -Sr等时线年龄与本区出露的篮片岩Ar-Ar年龄 (～ 383Ma)一致 ,记录了中亚造山带东南部洋壳俯冲结束后由大陆碰撞造山引起的变质作用事件。黑云母片麻岩的Rb -Sr同位素等时线年龄为 2 79.5± 6 .4Ma ,87Sr/ 86 Sr初始比值为 0 .70 85 1± 0 .0 0 0 10 ,此Rb -Sr等时线年龄与本区广泛分布的早二叠世火山岩的Rb -Sr等时线年龄 (～ 2 77± 15Ma)一致 ,因此可能是由大规模岩浆活动诱发的变质作用的记录。锡林格勒杂岩因此不仅记录了Rodinia超大陆聚合的地质事件 ,并且通过对比研究本地区蛇绿岩和晚古生代岩浆岩的演化历史 ,可以恢复从Ro dinia超大陆聚合 (～ 1.2 0Ga)到古亚洲洋关闭 (～ 4 30Ma)、大陆碰撞造山 (～ 39     

锡林浩特杂岩中斜长角闪岩锆石U-Pb年代学及Hf同位素研究

锡林浩特杂岩是一套经历强变形变质作用的变质岩,主要由黑云斜长片麻岩、角闪斜长片麻岩、斜长角闪片麻岩及变粒岩夹透镜状或脉状斜长角闪岩组成。查明其形成年龄、变质年龄对深入认识中亚造山带的形成演化具有重要意义。本次研究对锡林浩特杂岩中斜长角闪岩进行了SHRIMP锆石U-Pb测年和LA-MC-ICP-MS锆石Hf同位素组成分析,给出了锆石SHRIMP U-Pb的加权平均年龄为(316±4)Ma,该年龄代表斜长角闪岩的原岩形成年龄,表明锡林浩特杂岩不是前寒武纪地质体。通过锆石Hf同位素分析,εHf(t)值主要为正值(+4.1～+17.0),揭示其物源可能来自亏损地幔或壳幔混合。根据亏损地幔和古老地壳的锆石Hf同位素进行两端元的混合计算,得到斜长角闪岩原岩岩浆的源区以幔源增生组分为主体(经过计算壳幔混合比例大约1∶2)。部分锆石的模式年龄在1.8～2.5 Ga之间,表明斜长角闪岩的原岩在形成过程中有古元古代地壳物质的加入,通过兴蒙造山带和锡林浩特杂岩中斜长角闪岩的Hf模式年龄对比可知,物源可能来自兴蒙造山带内部。基于Hf同位素的两端元混合计算表明该区在晚古生代存在地壳增生。根据野外观察和室内岩石特征分析,该套杂岩可能是一套经历强变形与变质作用的晚古生代火山-沉积建造。     

内蒙古狼山地区晚太古代变质杂岩特征探讨

狼山位于内蒙古中部巴彦淖尔盟,在狼山主峰出露一套角闪岩相变质杂岩,它主要由角闪斜长片麻岩、黑云斜长片麻岩、斜长角闪岩、角闪岩、黑云变粒岩、黑云石英片岩组成,局部夹磁铁石英岩。其原岩以中、基性火山岩为主,顶部则为变粘土质碎屑岩。这套变质杂岩,至少经历了两期混合岩化作用,它与狼山南、北坡中元古代狼山群有明显的差异,作者对其中黑云斜长片麻岩测得sm—Nd等时线年龄为2735 Ma,证明其时代应为晚太古代。从变质杂岩地层层序、岩石化学、微量元素特征来看,它与绿岩带有许多相似之处。狼山主峰变质杂岩是该区的结晶基底,中元古代狼山群中的层控多金属矿床,就是在该基底上发育的裂陷槽中形成的。结晶基底自身的岩石中,Cu、Pb、Zn、Au等元素含量均较高,亦具有一定的找矿前景。     

康滇地轴冕宁杂岩的Sm-Nd同位素地质年代学初步研究

通过冕宁杂岩的稀土元素、微量元素及Sm—Nd同位素组成分析发现：杂岩核部二辉片麻岩微量元素以Th富集为特征，而典型的太古代灰色片麻岩则为Th亏损；分布于杂岩边部的英云闪长质片麻岩及花岗质片麻岩与灰色片麻岩宏观特征相似，且有Th，Nb亏损，但强不相容元素强烈富集，配分型式强烈右倾，也有别于太古代灰色片麻岩。两类岩石的Nd模式年龄均小于2000Ma，推测该杂岩的部分岩石原岩(二辉片麻岩及斜长角闪岩)形成时代可能为早元古代晚期，它们在晋宁期强烈的构造岩浆活动中发生角闪岩相变质。岩石的Nd模式年龄(2008Ma～766Ma)显示该区在元古代有较大规模的地壳增长，基底岩石的形成时代有别于扬子地台周边地区。     

石鼓群的划分及变质特征探讨

石鼓群位于云南西北部,面积约1 600km2,为甘孜一理塘板块的结晶基底.据现有资料,分为古元古代黎明岩群、中元古代新主岩群、新元古代巨甸岩群.黎明岩群为云母石英片岩、云母片岩,夹斜长片麻岩、斜长角闪岩.泥质岩石中具铁铝榴石、十字石、蓝晶石组合,基性岩中具铁铝榴石、普通角闪石组合,为中压低角闪岩相.黎明岩群后期抬升减压,叠加低压低角闪岩相变质,新生红柱石,部分原生蓝晶石退变成红柱石.于侵入其中的斜长角闪岩中获得Nd同位素模式年龄1 369.8Ma和1 343.8Ma,绿泥石英片岩中获得1 896.6Ma和2 161MaNd同位素模式年龄,故将黎明岩群时代置于古元古代.新主岩群分哈吉洛岩组和路西岩组,岩性为云母石英片岩、云母片岩、大理岩夹片麻岩及斜长角闪岩,部分岩石具糜棱岩化.哈吉洛岩组为低压低角闪岩相,具红柱石、十字石、铁铝榴石组合,路西岩组为高绿片岩相.于侵入新主岩群中的变质变形花岗质岩脉中获得锆石铅同位素年龄811 ±2Ma、820±1Ma、823±1Ma,故将新主岩群时代置于中元古代.巨甸岩群分陇巴岩组和塔城岩组,岩性为千枚岩、板岩,夹一层变质杏仁状玄武岩,为低绿片岩相.     

东阿拉善地块前寒武纪变质基底中晚古生代变质杂岩:来自波罗斯坦庙杂岩LA-ICP-MS锆石U-Pb定年的新证据

波罗斯坦庙杂岩是东阿拉善地块典型的中-高级变质杂岩之一,它的深入研究对进一步认识阿拉善地块起源、形成与演化过程具有十分重要的科学意义.通过对波罗斯坦庙杂岩中石英闪长质片麻岩、斜长角闪岩与花岗伟晶岩的野外观察、岩石学与锆石U-Pb定年发现,波罗斯坦庙杂岩中石英闪长质片麻岩、斜长角闪岩与花岗伟晶岩的岩浆锆石加权平均年龄分别为284±2 Ma、278±3 Ma,276±2 Ma、271±3 Ma与242±7 Ma,该组年龄被解释为其原岩成岩时代.石英闪长质片麻岩与斜长角闪岩中变质锆石加权平均年龄分别为274±6 Ma、272±5 Ma与269±3 Ma、268±2 Ma,代表它们遭受了晚古生代变质作用的时间.综合以上分析与前人研究资料,初步认为以往曾被认为是新太古代-古元古代的波罗斯坦庙杂岩,实际上可能是一个古元古代-晚古生代中-高级变质杂岩,并遭受了280~260 Ma角闪岩相变质作用,指示它们曾被卷入到中亚造山带晚古生代造山作用过程.      

湘东北古元古代连云山杂岩初步研究

连云山杂岩是经区域高绿片岩相—角闪岩相变质、混合岩化及热接触变质作用而形成的变质岩系，其变质矿物组合为St+Sill+Cr+Hb+Ab+Bi+Ms+Pl+Qz。其Sm—Nd全岩等时线年龄分别为1 960±5 Ma，1 905±25 Ma，其原岩组合及地球化学特征表明其构造盆地为活动大陆边缘—岛弧环境，代表了扬子陆块东南缘古元古代结晶基底。     

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