西准噶尔成矿带晚古生代花岗岩类岩浆活动及其构造意义

中亚造山带是晚古生代地壳显著生长与大规模成矿的重要地区。本文采集了中亚造山带西部的西准噶尔成矿带哈图-别鲁阿嘎希及其附近地区11个岩体共33件花岗岩类样品,对其开展了岩石地球化学与同位素示踪等研究,厘定了该地区晚古生代岩浆活动的特点与大地构造环境,并与哈萨克斯坦境内的巴尔喀什成矿带晚古生代岩浆活动进行了对比。研究表明,哈图地区晚石炭世花岗岩类主要为后碰撞伸展构造环境的A型花岗岩类,别鲁阿嘎希等地区存在洋内俯冲与岛弧环境的埃达克岩,显示了西准噶尔晚古生代构造环境时空变化的复杂性。该地区花岗岩类εNd(t)值较高(+4.62~+7.53)、εSr(t)值为(-57.61~+18.21),具有中亚造山带花岗岩类的共同特征,为古生代增生的新生陆壳,其源区与亏损地幔组分具有亲缘关系,这与巴尔喀什成矿带东段的花岗岩类具有一致性。花岗岩的~(206)Pb/~(204)Pb、~(207)Pb/~(204)Pb和~(208)Pb/~(204)Pb比值范围分别为18.2776~19.1677、15.5260~15.5796和38.2080~39.0821,为造山带花岗岩类。     

青藏高原中新生代花岗岩Sr、Nd同位素研究

青藏高原中新生代岩浆活动强烈，本文报道青藏高原西部中新生代代表性花岗岩的Sr，Nd同位素测定结果，结合前人已发表的东部地区花岗岩同位素资料，初步探讨了青藏高原地区中新生代花岗岩的Sr，Nd同位素组成、物质来源与成因。研究表明，分布于冈底斯地块北南边界(即冈底斯花岗岩北带和南带)与洋壳俯冲有关的燕山晚期花岗岩，具有低^87Sr／^86Sr初始值(小于0．706)、正εNd(t)值和年轻的t2DM模式年龄的特征，岩浆来源于俯冲洋壳的熔融；与陆-陆碰撞及碰撞后有关的冈底斯花岗岩^87Sr／^86Sr初始值变化大(0．706～0719)，而εNd(t)值和t2DM都在很小范围变化，Sr、Nd同位素组成似乎与时代、岩性无关，说明壳幔混合花岗岩的同位素源区长时期保持相对均一。无洋壳物质参与的通过陆内俯冲作用形成的喜马拉雅区花岗岩，具有高^87Sr/^86Sr初始值(大于0.720)、古老模式t2DM年龄(1792～2206Ma)和低εNd(t)值(-10．3～-16．3)特征，并与基底岩石的Sr，Nd组成一致，岩浆源区为壳源。由此说明花岗岩类及其岩石组合的形成主要取决于深部部分熔融物质的成分，不同火成岩组合的差异反映了青藏高原岩石圈组成和演化的不均一性。     

天山石炭-二叠纪后碰撞花岗岩的Nd、Sr、Pb同位素源区示踪

天山造山带不仅是中亚巨型造山带的组成部分，也是我国西部晚古生代岩浆活动的集中区，蕴含着丰富的古亚洲洋演化的复合地质信息。笔者以探索天山晚古生代花岗岩浆活动的物质来源为目标，采用Sr、Nd、Pb同位素地球化学方法，对该区不同构造单元中具有代表性的花岗岩体进行了全面系统的研究，发现天山不同构造单元中花岗岩Sr、Nd、Pb同位素特征具有明显差异。在与其围岩的同位素特征进行对比研究的基础上，提出了产于不同构造单元石炭-二叠纪花岗岩的可能源区。觉罗塔格石炭-二叠纪裂谷带的晚古生代花岗岩，具有最高的εNd(t)值和最低的(^87Sr／^86Sr)t值，如，以康古尔石英闪长岩为代表的二叠纪花岗岩的源岩可能是早期泥盆纪大南湖岛弧火山岩(新生地壳)；博格达地区的晚石炭-二叠纪花岗岩是早期基性火山岩，亦可能是底侵基性岩部分熔融的产物。中新元古代基底晚石炭-二叠纪裂谷带中花岗岩的源岩亦为同期基性火山岩，但在岩浆演化过程中受到古老基底地壳的混染，导致其εNd(t)值低于石炭-二叠纪裂谷带中花岗岩，而(^87Sr／^86Sr)t高于石炭-二叠纪裂谷带花岗岩。南天山东段和前寒武系微地块及其边缘中的晚古生代(含个别早古生代花岗岩)花岗岩分别是类似于库米什斜长角闪岩的古老地壳和西天山元古代古老地壳部分熔融的产物，因此它们均具有负的εNd(t)值和异常高的(^87Sr／^86Sr)t值。上述认识对于了解天山晚古生代区域岩石圈演化及深部过程具有重要意义。     

北山辉铜山泥盆纪钾长花岗岩锆石U-Pb年龄、 成因及构造意义

LA-ICP-MS锆石U-Pb定年结果表明,北山柳园地区辉铜山钾长花岗岩的形成年龄为397±3Ma (MSWD=1.1).地球化学特征显示为高钾钙碱性的高分异Ⅰ型花岗岩到A型花岗岩过渡的特征.其全岩εNd(t)值为-1.3～ +1.2,Nd模式年龄(tDM)为960 ～ 1530Ma;锆石εHf(t)值为-1.0～ +5.8,两阶段Hf模式年龄(tDM2)为1024～1455Ma.地质背景、地球化学和同位素综合分析显示,辉铜山岩体为造山后伸展拉张背景下,幔源岩浆底侵导致上覆年轻地壳(可能为洋壳、岛弧建造或增生楔物质)部分熔融形成的钙碱性花岗闪长质岩浆经进一步演化及结晶分异形成.北山南带地区早-中泥盆世花岗岩显示出高分异钙碱性Ⅰ型花岗岩、I-A型花岗岩和A型花岗岩的组合特征.因此,在397Ma左右,北山地区古生代岩浆已经从Ⅰ型或S型转化为I-A型特征,构造环境转化为后造山或同造山晚期的伸展环境.     

东昆仑造山带花岗岩类Pb-Sr-Nd-O同位素特征

本文报道了东昆仑造山带三叠纪辉长岩、花岗岩类及其包裹体的Pb、Sr、Nd和O同位素组成。东昆仑造山带花岗质岩石全岩和长石Pb同位素组成相差不大，具明显的造山带Pb同位素特征；Sr同位素初始值(ISr)变化于0．70144～0．70972之间，暗示幔源成因；εNd值变化于-4．49939～-9．19258之间，具壳源成因特点；Nd同位素模式年龄(tDM)在1．38～1．761Ga之间，与中元古代变质岩相当；O同位素组成变化范围7．8～9．5，表明花岗岩类成岩物质主要来自地壳。综合岩石的同位素组成，结合矿物学、岩石地球化学的研究，表明花岗岩浆主要起源于地壳，但与来自地幔的基性岩浆曾发生过混合作用，从而导致同位素组成趋于一致。     

中国阿尔泰造山带后造山喇嘛昭花岗岩体锆石SHRIMP年龄、成因及陆壳垂向生长意义

喇嘛昭岩体是阿尔泰造山带典型的后构造岩体,其时代问题一直没有解决。本次锆石SHRIMP定年给出 206Pb／238U年龄276±9Ma(MSWD=1．1),代表其形成年龄。这为阿尔泰后造山花岗岩和后造山作用提供了一个可靠的年代学证据。主量、微量元素地球化学特征显示该岩体具有I-A过渡的高钾钙碱性或高分异钙碱性花岗岩的特点。依据岩体构造特征、年代学、地球化学和地质背景综合分析,该岩体应为后造山岩体。该岩体Sr初始值变化于0．704-0．71659之间。εNd(T) 值为正值( 1．3- 2．8),模式年龄TDM-2为0．93-0．81Ga,与中亚造山带典型的高(正)εNd(T)值花岗岩相同。而且,其εNd (T)值略高于该地区同造山花岗岩。这说明,在具有陆壳基底的阿尔泰造山带后造山阶段,除了可能的俯冲下埋的年轻洋壳或岛弧物质外,可能有新的幔源物质参与了花岗岩的形成。这为中亚造山带后造山阶段陆壳垂向生长提供了一个证据。     

甘肃北山野马泉岩体同位素地球化学特征

Nd、Sr、Pb同位素研究结果揭示：甘肃北山野马泉岩体第Ⅰ、Ⅱ侵入阶段花岗岩类具有Ⅰ-型花岗岩的特征，(87Sr/86Sr)i=0.708~0.710，εNd=-2.229~-5.866，在207 Pb/204Pb-206Pb/204Pb构造模式图上其投影点落在造山带演化线附近，在εNd-εSr图解中，其投影点落人Ⅰ-型花岗岩类范围内，其成岩物质为壳幔混合来源。第Ⅲ侵人阶段的岩石成因类型为S-型，其(87Sr/86Sr)i=0.7149~0.7358, εNd＝-7.3750~-8.9556。该岩体形成的地球动力学环境是北山陆内碰撞造山带。     

吉林中部后倒木中侏罗世花岗质岩石的成因:对中亚造山带东部元古宙大陆地壳生长的启示

中亚造山带属于地球上最大的增生型造山带其中之一,中亚造山带东部正是我国东北地区,而该地区的地壳增长时间与地壳增长机制仍然有待于进一步深入的研究。本研究选取中亚造山带东部后倒木地区的花岗质岩石为研究对象,进行岩石学、岩石地球化学、同位素年代学等研究结合前人的研究成果,探讨其成因岩石学、构造背景以及对地壳增生的指示意义。通过同位素测年研究,发现后倒木地区的花岗岩类岩石就位于175～171Ma;全岩地球化学结果显示SiO_2含量为66.58%-76.73%,Al_2O_3含量为12.21%～16.03% MgO含量介于0.09%～2.07%之间,显示出高钾钙碱性特征;后倒木地区花岗岩类岩石富集大离子亲石元素,同时亏损高场强元素;Sr-Nd-Hf同位素显示:I_(Sr)值介于0.7063～0.7077之间,ε_(Nd)(t)值介于+2.38～+3.95之间具年轻的t_(DM2)年龄(639～768Ma),岩浆锆石ε_(Hf)(t)值介于+4.1～+9.0之间,同样具有年轻的二阶段模式年龄t_(DM2)(554～806Ma),揭示岩石重熔的下地壳物质可能是花岗岩类岩石的源区。综合研究表明,古太平洋板块俯冲导致区域下地壳熔融形成该类花岗质岩石,而模式年龄揭示新元古代为中亚造山带重要的地壳生长期。     

东天山东段同造山到后造山花岗岩幔源组分的递增及陆壳垂向生长意义——Sr、Nd同位素证据

显生宙陆壳垂向生长是一个新的值得进一步深入探索的课题。在已有的地质、地球化学研究基础上,本文报导了东天山东段矿物组成、成因类型相似的早古生代同造山花岗岩体和晚古生代-早中生代后造山花岗岩体新的Sr、Nd同位素测试结果,并进一步对比研究了它们的Sr、Nd同位素差异。前者I_(Sr)值较高(0.7087～0.7288),ε_(Nd)(t)值较低(-5.8～-15.8),模式年龄T_(DM)大(1.29～2.37Ga),显示以古老陆壳物质为主的物源特征;后者I_(Sr)低(0.7069～0.708),ε_(Nd)(t)值高(-3.8～ 0.3),T_(DM)较年轻(0.80～1.28Ga为主),显示混有较多的年轻幔源组分;同期的煌斑岩脉I_(Sr)为0.7080,ε_(Nd)(t)值为 4.3, T_(DM)为0.8 Ga。这些特征为探讨显生宙地壳垂向生长提供了良好实例。一般而言,显生宙高ε_(Nd)(t)值后造山花岗岩中的年轻幔源组分至少有3个可能的来源:(1)前造山(前寒武纪)底侵形成的年轻基性下地壳;(2)同造山水平增生的年轻地壳再循环;(3)后造山底侵的幔源岩浆。这3种来源分别揭示了3种陆壳生长方式和时限:前造山垂向生长;同造山水平生长;后造山垂向生长。通常,这3种情况仅仅依据地球化学特征不易鉴别;而通过花岗岩物源演变的对比研究有可能提供鉴别的线索。该区早古生代花岗岩以古老壳源为特点;而地点相同、矿物组成和地球化学相似、侵位深度相近的晚古生代-早中生代花岗岩幔源组分增多,并伴随有辉绿岩、煌斑岩侵入。这种新的年轻组分最可能与新底侵的幔源岩浆有关,它们随后造山花岗岩加入地壳,导致地壳垂向生长,这是造山后垂向生长的一种特征。该研究为中亚造山带后碰撞或后造山陆壳垂向生长的存在提供了一个证据。     

巴尔喀什成矿带晚古生代地壳增生与构造演化

巴尔喀什成矿带是中亚成矿域重要的晚古生代斑岩铜钼成矿带。巴尔喀什成矿带晚古生代花岗岩类(石炭-二叠纪)主要为高钾钙碱性系列,晚期出现钾玄岩系列岩石,主要为I型花岗岩类;石炭纪处在同碰撞和火山弧环境,二叠纪为后碰撞环境。分析表明,博尔雷属于经典的岛弧花岗岩区,科翁腊德、阿克斗卡和萨亚克属于埃达克岩(Adakite)区。巴尔喀什成矿带内花岗岩类εNd(t)值为(-5.87～+5.94),εSr(t)值为(-17.16～+51.10)。以巴尔喀什中央断裂为界,成矿带东、西分带,断裂两侧具有不同的地壳生长历史:断裂以东的萨亚克和阿克斗卡地区εNd(t)值较高,具有亏损地幔组分特征,为古生代增生的新生陆壳;以西的科翁腊德和博尔雷εNd(t)值较低,主要是壳幔岩浆混合的结果,反映了古老基底的存在,主要为新元古代增生地壳。成矿带花岗岩类206Pb/204Pb、207Pb/204Pb和208Pb/204Pb比值范围分别为18.3346～20.9929、15.5213～15.7321和38.2874～40.0209,为造山带花岗岩类,具有与天山、阿尔泰和准噶尔花岗岩类的亲缘性。     

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