东昆仑造山带早中生代镁铁质岩墙群LA-ICP-MS锆石U-Pb定年、元素和Sr-Nd-Hf同位素地球化学

东昆仑造山带白日其利镁铁质岩墙群以苏长辉长岩为主,含少量含斑辉绿岩,LA-ICP-MS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为251±2Ma.岩石具有中等的Mg#(31～50)和高铝(16.25％～19.49％)的特征,整体属于钙碱性玄武岩系列岩石(Na2O+ K2O =2.75％～3.51％;FeOT/MgO=1.02～2.22);微量和稀土元素方面,岩石具有较低的稀土总量、轻稀土轻微富集和Eu正异常特征(ΣREE =52.16×10-6～99.81×10-6,(La/Yb)N =2.08～5.49,δEu=1.0～1.3),所有岩石富集LILE(如Rb、Ba和Pb等)而亏损HFSE(如Nb、Ta、P和Ti等),且具有显著不同于地壳的不相容元素组成(如Nb/Ta比值).岩墙具有富集的Sr-Nd同位素组成((87Sr/86 Sr)i=0.71103～0.71502,εNd(t)=-7.4～-3.6),具有相对集中且显著不同于地壳岩浆的Hf同位素组成(εHf(t)=-2.37～1.07).元素地球化学和同位素研究指示镁轶质岩浆起源于流体交代的富集地幔Ⅱ,并未受到显著的地壳混染.构造环境分析表明,岩石具有岛弧和洋中脊玄武岩双重特征.结合区域构造演化分析,我们认为,在晚二叠世-早三叠世时期,在俯冲环境下,板片流体交代使上覆地幔楔发生富集,形成富集地幔Ⅱ,随着该区伸展作用的加强,在早三叠世,进一步诱发了富集地幔的部分熔融并产生镁铁质岩浆,最终侵位结晶就形成了白日其利镁铁质岩墙群.     

内蒙古东乌珠穆沁旗早古生代辉长闪长岩年代学和地球化学特征及地质意义

东乌旗乌拉盖地区出露一套早古生代辉长闪长岩,为兴蒙造山带北缘二连-东乌旗早古生代岩浆岩带的组成部分。对该岩体进行了锆石U-Pb年龄、全岩地球化学及Sr-Nd-Hf同位素分析,探讨了岩石成因及其对兴蒙造山带北缘早古生代构造演化的启示。锆石LA-ICP-MS U-Pb定年显示岩体年龄为499.6±1.2 Ma,为二连-东乌旗地区出露的最古老侵入体。岩体具有中等的Si O2含量(51.60%~54.28%),富铝,贫铁、镁,全碱及钾含量较低,属钙碱性岩浆系列;富大离子亲石元素,亏损高场强元素,具有弱的Eu正异常(δEu=1.03~1.34),稀土元素配分型式呈平缓的右倾型。辉长闪长岩同位素组成比较亏损,(~(87)Sr/~(86)Sr)_i=0.704 5~0.704 7,εNd(t)=+2.71~+4.17,εHf(t)相对εNd(t)明显偏高,为+10.8~+18.7,存在Nd-Hf同位素解耦现象。年代学、岩石地球化学以及Sr-Nd-Hf同位素综合分析表明,乌拉盖辉长闪长岩是早古生代古亚洲洋沿苏左旗-锡林浩特一线向北俯冲的产物,岩体形成于俯冲作用的初始阶段,源区为受到俯冲物质交代的地幔楔,交代物质以板片熔体为主,流体交代为辅,无明显沉积物加入,后期由于弧后拉张、贺根山洋盆打开与主体岛弧带脱离,最终形成了与俯冲带彼此分隔的格局。     

大别-苏鲁地区晚中生代镁铁质岩地球化学对造山带岩石圈地幔性质的约束

来自大别-苏鲁地区晚中生代镁铁质岩石表现出类似于岛弧火山岩的富集大离子亲石元素(LILE)、轻稀土元素(LREE)和相对亏损高场强元素(HFSE)的微量元素地球化学特征,和高度富集的放射成因 Sr(I_(Sr)=0.7065～0.7090)和低放射成因 Nd(ε_(Nd)(t)=-19～-10)的同位素组成;同时它们显示出一定程度的 Nb/Ta 和 Zr/Hf 内部分馏特征,反映其地幔源区曾受到了相对富金红石和 CO_2的熔体交代作用。我们倾向认为深俯冲陆壳在俯冲或折返过程中发生部分熔融作用形成的熔体与地幔反应是形成大别-苏鲁地区造山带富集岩石圈地幔的重要机制。     

新疆东天山黄山岩体岩石地球化学特征与岩石成因

黄山岩体位于东天山北部的土墩-黄山-图拉尔根镁铁-超镁铁质岩带中段,受康古尔塔格-黄山韧性剪切带控制,主要由橄榄岩、橄榄二辉岩、辉石岩、辉长苏长岩、辉长岩以及辉长闪长岩组成.岩石化学组成属拉斑玄武岩系列,普遍富集大离子亲石元素(Rb,Ba,Sr),亏损高场强元素(Nb,Ta,Ti).岩体εNd(t)=+4.1～+9.2,除3件样品εSr(t)为+2.2,+12.5和+15.4,大部分εSr(t)=(-22.5～-4.5),Nd,Sr同位素组成基本属亏损型地幔特征;Pb同住素初始值(206Pb/204Pb)i=18.081～18.413,(207Pb/204Pb)i=15.441～15.513,(208Pb/204Pb)i=37.461 6～37.899,具有MORB亲和性.岩相学及岩石地球化学特征显示岩浆演化过程中主要发生了橄榄石、斜方辉石、单斜辉石和斜长石的分离结晶作用.岩浆演化晚期阶段发生了一定程度的同化混染作用,元素地球化学和Nd,Sr,Pb同位素体系证明,岩浆源区主体由软流圈地幔物质组成,同时也有一定量富集型岩石圈地幔组份加入.黄山岩体是岩石圈根部拆沉加热熔融和软流圈地幔上涌减压熔融的产物,这种地幔动力学机制应该对应于后碰撞伸展环境.     

东昆仑希望沟中二叠世辉长岩Sr-Nd-Lu-Hf同位素特征及其地质意义

东昆仑东段希望沟-哈陇休玛一带有多处镁铁-超镁铁质岩的出露,针对希望沟地区中二叠世辉长岩3块样品进行的全岩Sr-Nd同位素及锆石Lu-Hf同位素测试,结果表明:希望沟辉长岩87Sr/86Sr为0.707 445~0.707 676,(87Sr/86Sr)i值为0.707 045~0.707 297,高于现代深海拉斑玄武岩(0.702 0~0.703 5),143 Nd/144 Nd的初始计算值为0.512 476~0.512 543,εNd(t)值为-2.65^-1.34,Nd(t)值受蚀变影响较小,基本反映了其源区洋岛玄武岩的同位素特征;176 Lu/177 Hf在0.000 592~0.001 860间,εHf(t)在2.27~5.46间,一阶段Hf模式年龄为691Ma^816Ma,平均为758Ma,表明岩浆源区主要来源于亏损地幔并有少量壳源物质(如洋壳沉积物)的加入。结合区域构造演化特征,认为希望沟辉长岩源区主要为洋岛玄武岩,是东昆仑地区阿尼玛卿古特提斯洋向北俯冲的结果。     

塔里木盆地东南缘安南坝地区镁铁质麻粒岩的成因——来自地球化学及Sr-Nd-Pb同位素的制约

甘肃阿克塞县安南坝地区镁铁质麻粒岩呈脉状、透镜状赋存于新太古代米兰岩群和TTG片麻岩中。岩石主要由斜长石(Pl)+斜方辉石(Opx)+单斜辉石(Cpx)+角闪石(Amp)+磁铁矿(Mt)等组成。安南坝镁铁质麻粒岩中Ti、P、Nb、Ta、Th、Hf、Sr及REE等元素与Zr相关性较好,表明其在变质作用过程中保持基本稳定。地球化学数据显示其原岩属于拉斑玄武质岩系列,Si O_2、Ti O_2、Al_2O_3、P_2O_5含量相对较低,Ca O、Mg O含量相对较高。Mg~#值为41.52~43.09,低于原生玄武质岩石的Mg~#值,Fe_2O_3~T、Mg O、Ca O与Si O_2含量呈负相关性,指示原岩岩浆演化过程中可能发生了辉石、角闪石等镁铁质矿物的分异结晶作用。镁铁质麻粒岩∑REE较低,稀土元素配分模式为轻稀土元素弱富集、重稀土元素相对平坦的右倾型,Eu异常不明显(Eu/Eu~*=0.91~1.01)。岩石富集Rb、Ba、Sr等大离子亲石元素,亏损Nb、Ta、Zr、Ti等高场强元素,具有显生宙典型岛弧玄武质岩石的地球化学特征。Sr、Nd、Pb同位素组成显示镁铁质麻粒岩原岩源自富集地幔,并受到一定程度的地壳物质混染。构造环境分析表明安南坝镁铁质麻粒岩原岩形成于与俯冲有关的岛弧环境。在俯冲作用机制下,俯冲板片流体交代使地幔楔发生富集,形成富集地幔,随着(弧后)伸展作用的加强,进一步诱发富集地幔的部分熔融形成镁铁质岩浆,最终岩浆就位形成辉长岩或辉绿岩脉,后期在麻粒岩相变质作用条件下变质为镁铁质麻粒岩。     

东天山卡拉塔格地区镁铁质岩体年代学、岩石地球化学研究

东天山大南湖岛弧带北缘卡拉塔格地区发育一系列镁铁质岩体,出露面积1km2。岩体岩相较为单一,主要岩性有辉长岩、橄榄辉长岩、橄长岩、淡色辉长岩和辉绿岩。本文利用LA-ICP-MS测得2个辉长岩的锆石U-Pb年龄分别为282. 2±0. 6Ma和278. 3±0. 6Ma;与吐哈盆地玄武岩及东天山地区铜镍硫化物矿床时代一致。岩石地球化学显示相对低Fe、高Al、Ca、碱、Ti,富集Rb、Ba、Sr、K,亏损Th、Nb、Ta的特征。岩石的(~(87)Sr/~(86)Sr)_i=0. 70313～0. 70461,εNd(t)=+6. 22～+8. 64,(~(206)Pb/~(204)Pb)_i=17. 68～18. 103,(~(207)Pb/~(204)Pb)_i=15. 443～15. 536,(~(208)Pb/~(204)Pb)_i=37. 423～37. 801,表现出高Nd、低Sr、低Pb,且变化范围较窄的特征。综合研究表明,该地区镁铁质岩体的岩浆动力学背景为后碰撞伸展环境;岩浆源区为俯冲板片交代的岩石圈地幔,并被软流圈物质混染;同位素和微量元素模拟显示母岩浆在源区遭受了5%～15%的板片流体交代,在上升过程中遭受了5%的上地壳物质混染。卡拉塔格地区镁铁质岩体与东天山二叠纪镁铁-超镁铁质岩体和吐哈盆地玄武岩形成于同一构造岩浆系统,在剥蚀较浅的大南湖岛弧带具有形成铜镍硫化物矿床的潜力。     

内蒙古东乌旗北部早古生代火山岩年代学、地球化学特征及地质意义

内蒙古北部二连-东乌旗地区出露早古生代火山岩,为兴蒙造山带北缘构造-岩浆岩带的组成部分,对研究造山带早古生代构造格局及演化具有重要作用。本文对东乌旗北部早古生代中基性及酸性火山岩进行了锆石U-Pb年代学、岩石学、全岩地球化学及Sr-Nd-Hf同位素分析。定年结果显示,中基性火山岩成岩年龄为452±2Ma,酸性火山岩为430±20Ma,表明早古生代岩浆活动可延续至中志留世。地球化学组成上,中基性火山岩稀土总量中等,Eu异常不明显,富集Rb、Sr、Th、U等大离子亲石元素,亏损Nb、Ta等高场强元素,特征类似岛弧岩浆岩;酸性火山岩富集Th、U,Eu负异常显著,但Rb、Ba等大离子亲石元素富集程度不高,Nb、Ta等高场强元素亏损不明显,表现出板内岩浆特点。中基性和酸性火山岩均具有亏损的同位素组成:中基性火山岩ε_(Nd)(t)=+203～+267,ε_(Hf)(t)值介于+79～+145之间;酸性火山岩ε_(Nd)(t)=+494,ε_(Hf)(t)值为+99～+153。岩石学及地球化学分析表明,中基性火山岩为岛弧环境下遭受俯冲流体交代的地幔楔部分熔融产物,酸性火山岩则来源于新生基性下地壳熔融并具有板内岩浆特征,可能指示了俯冲的结束。结合前人资料,二连-东乌旗地区早古生代岩浆活动介于晚寒武-中志留世之间,形成时间及阶段性演化特征近似于苏尼特左旗-锡林浩特早古生代岩浆岩带,暗示两者可能具有成因联系,均为早古生代古亚洲洋向北俯冲的产物。     

延边小西南岔金铜矿区早白垩世英云闪长岩的岩石成因

锆石U-Pb测年结果表明小西南岔富金铜矿床矿区内的英云闪长岩形成于(112±1)Ma。该英云闪长岩富Na2O和Al2O3,高Sr、LREE(轻稀土元素),低Y、Yb和HREE(重稀土元素)(如Sr=369~774μg/g,(La/Yb)CN=7.5~17.5),具有类似于埃达克质岩石的元素地球化学特征。在同位素组成上具中等放射成因Sr((87Sr/86Sr)i=0.7044~0.7048)、Nd(εNd(t)=+0.5~+1.7)和Hf(εHf(t)=+5.4~+8.6,ΔεHf=2.3~4.2)同位素,高放射成因Pb((206Pb/204Pb)i=18.40~18.60;(207Pb/204Pb)i=15.56~18.60;(208Pb/204Pb)i=38.22~38.36)同位素的特点。结合区域构造背景以及古太平洋板块俯冲历史,笔者倾向认为该岩体可能是玄武质岩浆底侵下地壳部分熔融形成的,而非板片熔融形成的埃达克质岩浆,岩浆源区为石榴子石角闪岩相向角闪岩相过渡的岩石。该岩体侵位的晚古生代((257±3)Ma)镁铁质围岩的角闪石Ar-Ar坪年龄为(110.1±1.5)Ma,与英云闪长岩的侵位时间一致,暗示晚古生代镁铁质侵入岩经历的热液事件与英云闪长岩的侵位作用存在成因联系,区域金铜矿化可能为早白垩世岩浆热液作用下成矿物质富集而形成。     

新疆东准噶尔克拉麦里蛇绿岩地球化学：洋脊俯冲的产物

新疆东准噶尔克拉麦里蛇绿岩中的镁铁质岩兼具有洋中脊玄武岩(MORB)和岛弧拉斑玄武岩(IAB)的特征,岩石地球化学特征表现为轻稀土(LREE)亏损、平坦或略微富集,不同程度地亏损高场强元素(HFSE)而富集大离子亲石元素(LILE),成分上非常相似于受洋脊俯冲影响的 Chile Ridge 和 Cocos Ridge 玄武岩。可以认为其可能形成于受洋脊俯冲影响的岛弧或弧前扩张环境。相对较高的ε_(Nd)(t)(7.2～9.8)、低 Nb/Zr、Ta/Yb 比值,说明在洋脊俯冲的影响下,其源区可能存在有至少三种组分:弧下地幔、来自消减板片流体和俯冲沉积物、MORB 地幔。     

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