柴北缘构造带深部岩石的LA-ICP-MS锆石U-Pb年龄及微量元素研究:对全吉地块基底演化的启示

通过LA-ICP-MS方法对柴北缘全吉地块基底的斜长角闪岩和花岗闪长岩进行了锆石U-Pb年代学及锆石微区微量元素的研究。斜长角闪岩中的岩浆锆石上交点年龄为2 396±26 Ma,代表了锆石结晶的年龄,下交点为905±140 Ma,代表了锆石发生铅丢失事件的年龄。其岩浆锆石具有U/Yb较高(0.1~1),Hf值较低(10 000×10~(-6)),U值较低(150×10~(-6))的特点,显示其岩浆源区与富集地幔密切相关。在锆石微量元素判别图解中数据主要落在陆弧区和洋岛区,指示其形成的构造环境为弧后盆地。花岗闪长岩中岩浆锆石的加权平均年龄为484±21 Ma,岩浆锆石具有U/Yb较高(1)和U值较高(平均值为640×10~(-6))的特点,显示岩浆源区为典型陆壳。锆石微量元素判别图解显示其形成于陆弧。研究结果表明,全吉地块基底除前寒武纪岩石外,还包含早古生代的岩石组合。全吉地块基底内部岩石组合与形成时代的复杂性,与全吉地块经历的多次洋壳俯冲、陆陆碰撞密切相关。     

东准噶尔早泥盆世托让格库都克组火山岩SHRIMP锆石U-Pb测年及地质意义

新疆东准噶尔地区广泛分布晚古生代火山岩,对东准噶尔富蕴县一带托让格库都克组火山岩进行SHRIMP锆石U-Pb测年,获得锆石的~(206)Pb/~(238)U结晶年龄为(411.7±6)Ma,属早泥盆世。岩石地球化学分析表明,岩石具高钠(Na_2O为3.13%～6.67%)、富铝(Al_2O_3为15.04%～17.01%)及弱过铝质(A/NCK为1.16～1.58)特征,属钙碱性系列;稀土元素含量整体偏低,REE为79.54×10~(-6)～171.97×10~(-6),轻重稀土元素分馏不明显。富集Sr,Ce,Hf等元素,亏损Th,Sm等元素,属强不相容元素富集型,显示出源区的较富集性。结合区域构造演化,认为东准噶尔托让格库都克组火山岩形成于活动大陆边缘向北俯冲作用的火山弧环境。     

柴北缘构造带欧龙布鲁克地块西北缘辉长岩脉地球化学、年代学及Hf同位素特征

侵位于柴北缘构造带欧龙布鲁克地块西北缘达肯大坂岩群中的辉长岩脉岩石Al_2O_3、CaO含量较高,P_2O_5、TiO_2含量较低,属于钙碱性系列。稀土元素总量低(43.17×10-6～57.53×10~(-6)),LREE/HREE值为1.82～2.77,稀土元素配分曲线整体表现为右倾型。岩石Ti亏损,具高ThN/NbN值(3.75～8.03)和低Nb/La值(0.44～0.84)特征。辉长岩锆石的~(176Hf/~(177)Hf值介于0.282813～0.282979之间,ε_(Hf)(t)值为9.25～15.11,Hf模式年龄(T_(DM))分布在378～610Ma之间,平均494Ma。综合研究认为,辉长岩岩浆源区为软流圈地幔且后期可能受到壳源富集组分的混染。LA-ICP-MS锆石U-Pb定年结果表明,辉长岩脉形成于357±4Ma,即早石炭世。结合区域地质背景,认为早石炭世柴北缘仍处于后造山伸展的构造演化阶段,而辉长岩脉是后造山伸展阶段柴北缘造山带去根、软流圈地幔上涌作用形成的。     

内蒙古北山造山带百合山地区350 Ma石英闪长岩的成因及对红石山-百合山洋俯冲时限的制约

对内蒙古白山岩浆弧内百合山石英闪长岩进行了LA-ICP-MS锆石U-Pb测年、Hf同位素及岩石地球化学分析。结果显示,该岩体的形成年龄为350.8±1.5 Ma,岩浆锆石的ε_(Hf)(t)值在5.28～9.88之间,模式年龄为724～1018 Ma。地球化学数据显示,百合山石英闪长岩为一套I型钙碱性系列岩石,富碱(Na_2O+K_2O=6.03%～6.96%),富钠(Na_2O/K_2O2),较低的Mg~#(35.48～39.78)、Ni(2.06×10~(-6)～5.54×10~(-6))和Cr(2.11×10~(-6)～7.93×10~(-6))含量。相对富集轻稀土元素,重稀土分馏不明显,较低的(La/Yb)_N值(4.28～5.60),无明显Eu异常,相对富集Rb、K、U等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素等,地球化学成分表明,石英闪长岩具有俯冲带成因的特征。石英闪长岩的锆石U-Pb年龄和岩石成因证明了350 Ma石英闪长岩是晚古生代白山岩浆弧内首次发现的可以明确与红石山-百合山洋俯冲消减作用有关的最早的弧岩浆记录。表明红石山-百合山洋于约350 Ma之前就已经开始发生俯冲消减,比前人一般认为的俯冲开始的时间提前了22 Ma。     

东昆仑希望沟橄榄辉长岩的岩石成因：地球化学、锆石U-Pb年龄与Hf同位素制约

东昆仑古特提斯域镁铁-超镁铁质岩石的研究极为薄弱,文章报道了青海东昆仑东段希望沟橄榄辉长岩的岩相学、锆石U-Pb年代学、岩石地球化学及锆石Hf同位素资料,以确定该岩体的形成时代、岩石成因及构造环境,为东昆仑晚古生代—早中生代构造岩浆演化提供新的约束。岩石地球化学研究表明,希望沟橄榄辉长岩具有低SiO2(40.91%~42.14%)、低TiO2(0.29%~0.39%)、高MgO(28.18%~30.66%)、贫碱(K2O+Na2O=1.09%~1.36%)的特征,属亚碱性系列岩石,m/f比值介于5.03~5.39,属于铁质超基性岩类。岩石微量元素总体上富集大离子亲石元素(Rb、Th、U、K)和Pb,相对亏损高场强元素(Nb、P、Ti),ΣREE为28.17×10^-6~30.95×10^-6,(La/Yb)N为3.77~4.98,显示轻稀土富集的特征,δEu=0.80~0.95,具有弱的Eu负异常。利用LA-ICP-MS锆石U-Pb定年技术,获得橄榄辉长岩加权平均年龄为(264.9±1.2)Ma(n=26,MSWD=0.71),属中二叠世。锆石176Hf/177Hf比值为0.282709~0.283152,对应的εHf(t)=3.7~19.3,锆石单阶段Hf模式年龄TDM为135~753 Ma,平均为414 Ma,大于锆石U-Pb年龄。研究认为,橄榄辉长岩的岩浆源区主要为亏损地幔,可能有早期流体交代的岩石圈地幔组分的加入,并经历了地壳物质的混染。结合东昆仑区域构造演化,认为希望沟橄榄辉长岩是阿尼玛卿古特提斯洋俯冲阶段的产物,说明古特提斯洋在中二叠世已北向俯冲。     

内蒙古狼山地区早石炭世角闪辉长岩、花岗闪长岩的岩石成因及构造意义

内蒙古狼山山脉西侧分布有大面积的晚古生代岩浆岩,时代集中在早石炭世—晚二叠世,早石炭世角闪辉长岩、花岗闪长岩体出露于潮格温都尔镇西侧。角闪辉长岩体呈岩滴状产出,被花岗闪长岩体侵入,LA-ICP-MS锆石U-Pb年龄显示,角闪辉长岩的~(206)Pb/~(238)U加权平均年龄为329.0±2.3 Ma,花岗闪长岩的~(206)Pb/~(238)U加权平均年龄为331.1±0.9 Ma~330.0±4.2 Ma。花岗闪长岩暗色矿物以角闪石为主,富钠(Na2O=3.48%~4.46%),高钠钾比值(Na2O/K2O=1.03~2.39),钙碱性系列,P2O5-SiO_2之间存在较好的负相关性,岩石地球化学特征具Ⅰ型花岗岩的特点。Hf同位素及元素地球化学特征指示了角闪辉长岩及花岗闪长岩均来自于受地壳混染的亏损地幔,为同源岩浆演化的产物。角闪辉长岩及花岗闪长岩稀土元素配分型式一致,均为轻稀土元素富集,重稀土元素亏损,具弱的负Eu异常;角闪辉长岩富集Ba、Sr,亏损Nb、Ta、Zr、Hf;花岗闪长岩富集大离子亲石元素Rb、K、Pb、Sr,不同程度地亏损高场强元素Nb、Ta、P、Ti,总体反映了岩浆弧的地球化学特征。结合区域地质背景,早石炭世狼山地区侵入岩岩石组合为角闪辉长岩(闪长岩)+石英闪长岩+花岗闪长岩,认为狼山地区早石炭世处于大陆边缘弧构造背景。     

东昆仑阿克楚克塞地区辉长岩地球化学特征、锆石U-Pb年龄及其构造意义

东昆仑地区基性-超基性岩石的研究较薄弱,缺乏对东昆仑幔源岩浆活动及岩浆演化的整体认识。对阿克楚克塞辉长岩进行了地球化学、锆石U-Pb年代学及Hf同位素研究,结果显示,该岩石形成于晚三叠世早期(219.3±1.1Ma,MSWD=0.80);岩石SiO2含量为49.03%~57.26%,Mg#值为49~57,属于钙碱性系列岩石;稀土元素配分曲线为轻稀土元素富集的右倾型,富集大离子亲石元素Rb、Ba、K,相对亏损高场强元素Nb、Ta、Ti;εHf(t)=-1.81~3.25,锆石Hf模式年龄大于锆石结晶年龄。地球化学特征显示,阿克楚克塞辉长岩岩浆源区应为受俯冲板片流体交代的岩石圈地幔。结合区域构造背景分析,阿克楚克塞辉长岩形成于印支期造山后伸展的构造环境,继承了早期板片俯冲改造的地幔源区特征。     

内蒙古达茂旗黄花滩铜镍矿辉长岩LA-ICP-MS锆石U-Pb年龄、地球化学和Hf同位素特征

内蒙古达茂旗黄花滩铜镍矿位于华北克拉通北缘白云鄂博裂谷系,铜镍矿体产出于辉长岩体边缘与片麻岩的接触部位。利用LA-ICP-MS技术测得黄花滩铜镍矿辉长岩锆石~(206)Pb/~(238)U年龄为268.7±1.1 Ma(MSWD=0.44,n=32),限定黄花滩铜镍矿是中二叠世岩浆活动的产物。黄花滩矿区辉长岩具有高Al_2O_3(17.72%～19.81%)、偏碱性(K_2O+Na_2O=4.37%～5.09%)、低P_2O_5(0.28%～0.42%)、低Ti_2O(0.83%～1.21%)的特征,属钙碱性系列。岩石稀土元素总量为144×10~(-6)～167×10~(-6),富集轻稀土元素,(La/Yb)_N介于7.43～8.85之间,显弱负Eu异常(δEu=0.84～0.88),微量元素富集大离子亲石元素(Rb、Ba、K、Sr),亏损高场强元素(Nb、Ta、Ti)。锆石ε_(Hf)(t)变化范围为-17.69～-12.53(平均值为-15.21),二阶段"地壳"Hf模式年龄(t_(Hf2))介于2082～2411 Ma之间。地球化学特征表明,辉长岩源区为大量遭受地壳混染的岩石圈地幔,地壳物质很可能由色尔腾山群岩石部分熔融形成。结合区域构造演化,认为黄花滩辉长岩形成于造山后构造背景,为晚古生代伸展体制下幔源岩浆活动的产物。     

滇西南热水塘辉长岩形成时代、成因及古地理格局

滇西南澜沧江带的热水塘—龙洞河一带的沉积-岩浆岩组合被认为是反映昌宁-孟连洋开始俯冲阶段"弧前-弧-弧后"古地理格局的典型代表。本文对该体系中出露于热水塘一带的辉长岩进行了矿物学、岩石地球化学、年代学及锆石Hf同位素研究。热水塘辉长岩中单斜辉石组成为Fs16~18,Wo42~45,En38~42,Mg#Cpx=69~72。根据单斜辉石与岩浆间Fe-Mg分配关系计算,单斜辉石结晶时,其母岩浆的Mg#范围约为31~40,低于其全岩Mg#范围(约45~50),表明热水塘辉长岩全岩化学组成特征受到了矿物堆晶作用的影响。热水塘辉长岩全岩轻稀土元素弱富集,无明显Eu正异常,大离子亲石元素相对富集而高场强元素亏损。辉长岩的矿物学及岩石地球化学特征表明该岩体形成于火山弧构造背景,为火山弧玄武质岩浆经较高程度分异和斜长石分离结晶的产物。LA-ICP-MS锆石U-Pb测年结果显示辉长岩体形成于早二叠世早期(295 Ma±4 Ma),锆石Hf同位素分析显示其εHf(t)=7.5~14.0,平均为10.7,低于其结晶时的亏损地幔值。热水塘辉长岩的形成应与早二叠世早期昌宁-孟连洋在思茅地体西缘热水塘地区自西向东发生俯冲有关。     

北山造山带中部早古生代伸展构造体制：来自石板井辉长岩的年代学及地球化学证据

北山造山带位于华北板块、塔里木板块和哈萨克斯坦板块交汇部位。为了研究北山地区早古生代大地构造属性,基于1∶5万区域地质矿产调查,采用LA-ICP-MS锆石U-Pb同位素定年法对分布于石板井地区的辉长岩体进行了年龄测定和岩石地球化学测试。结果表明:辉长岩体锆石U-Pb年龄为498.9±2.4Ma,属晚寒武世。地球化学数据显示:岩石具有较低的SiO_2(40.39%~53.62%)和较高的Al_2O_3(12.56%~19.26%)、CaO(8.09%~10.93%)含量和Mg#值。稀土总量较高(∑REE=62.69×10~(-6)~250.62×10~(-6)),轻重稀土分异明显[(La/Yb)N=4.89~16.94],无明显Eu异常,δEu=0.82~1.28。岩石富集大离子亲石元素Rb、Ba、K等,亏损高场强元素Nb、Ta、P、Zr、Ti等。Rb/Nb-Rb/Zr、(Ce/Yb)N-(Yb)N、Zr-Y和Zr-Nb图解显示该岩体岩浆起源于过渡型岩石圈地幔的部分熔融,并且在上升侵位过程中发生明显的地壳混染。辉长岩体具有相对高的TiO2(0.65%~1.98%)、Nb(4.47×10~(-6)~18.56×10~(-6))、Ta(0.44×10~(-6)~1.86×10~(-6))、Zr(48.07×10~(-6)~386.86×10~(-6))、Hf(2.17×10~(-6)~21.23×10~(-6))含量,相近于板内玄武岩。此外,在辉长岩体南侧发育同期二长花岗岩,二者构成双峰式岩浆岩组合。综合上述特征,辉长岩产出构造背景为板内伸展构造体制,并推测在晚寒武世古亚洲洋未发生俯冲,仍处于扩张期。     

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