滇西临沧岩基源区物质定量摸拟

在中国西南和东南亚领域内存在一条南北延伸的花岗岩岩基带,滇西的临沧岩体(LG)和平和街岩体(PMG)是这一巨型同碰撞岩基带最北段的二个岩体,出露面积共约11000平方公里。具壳源(S型)花岗岩许多特征。根据Sr、Nd同位素的上陆壳一下陆壳两端员混合摸拟,这两个岩体的源区岩石相当于由70—80％上陆壳物质加上20—30％的下陆壳物质构成的混合物。根据Rb、Sr、Rb/Sr等微量元素和微量元素对比值在部分熔融中的行为,计算了这一源区物质约30—35％的部分熔融形成当时的平和街和临沧岩体的初始岩浆。     

吉南地区古元古代双岔巨斑状花岗岩成因及其构造意义:岩石学、年代学、地球化学和Sr-Nd-Hf同位素证据

双岔岩体位于华北克拉通东部陆块辽吉活动带内,岩性主要为巨斑状石榴石黑云母二长花岗岩。LA-ICP-MS锆石U-Pb年代学研究表明该岩体形成于1890±21Ma。岩石A/CNK1.1属于强过铝质岩石,CaO/Na2O0.3,微量元素显示Nb、Ta、Sr、Ti、P的亏损,指示与弧岩浆的亲缘性。全岩同位素特征是:εNd(t)=-4.7~-4.1,ISr值介于0.7050~0.7110,εHf(t)值变化范围为-3.5~2.2,与~2.17Ga条痕状花岗岩和变粒岩-浅粒岩在1890Ma时的同位素组成大致吻合,指示其源岩应主要为成熟度较低的变质砂岩,主要源区为条痕状花岗岩和变粒岩-浅粒岩。双岔花岗岩具有较低的SiO 2含量(71%),较高的FeO T+MgO+TiO 2含量(除SC-1外都大于4%),较低的Sr/Y和(La/Yb)N比值及较高的Rb/Sr比值以及明显的Eu负异常,说明源岩可能有部分变质玄武岩卷入。Nd同位素模拟结果显示双岔巨斑状花岗岩的源岩中可有20%~30%的变质玄武岩。部分样品的Rb/Sr、Rb/Ba比值特征与泥质原岩相似,显示源区也有少量的泥质岩。岩石低的Al2O3/TiO 2比值及变质熔融残余的石榴石和夕线石,说明岩浆形成于高温中压环境,上涌的软流圈加热地壳使源岩发生部分熔融,是辽吉活动带由挤压向伸展转换的产物,标志着辽吉带古元古代造山作用的结束。     

淡色花岗岩的岩石学和地球化学特征及其成因

淡色花岗岩(leucogranite)是一类高铝高硅碱的酸性侵入岩,主要地球化学特征是:SiO2≥72%,Al2O3≥14%,Na2O+K2O~8.5%,富Rb,亏损Th、Ba、Sr,稀土总量较一般花岗岩低(∑REE=(40~120)×10-6),且表现为中等分异的轻稀土弱富集型,一般具有Eu负异常;Sr-Nd-Pb-O同位素指示其岩浆明显的陆壳来源。淡色花岗岩主要发育于陆壳(俯冲)碰撞加厚带,由逆冲折返的俯冲板片变沉积岩部分经过脱水熔融产生。淡色花岗岩可划分为三种不同的岩石类型:(1)二云母型淡色花岗岩,由变泥质岩(或变硬砂岩)在中地壳水平经黑云母(和/或白云母)脱水熔融产生;(2)电气石型淡色花岗岩,由变泥质岩在较低温度下经白云母脱水熔融产生;(3)石榴子石型淡色花岗岩,由长英质下地壳经黑云母脱水熔融产生。源区残留独居石、磷灰石等富REE矿物是淡色花岗岩亏损REE、Th等元素的原因。源岩为变泥质岩及源区残留钾长石是淡色花岗岩亏损Sr、Ba的主要原因。     

藏南冲巴淡色花岗岩的地球化学特征、成因机制及其构造动力学意义

冲巴淡色花岗岩位于大喜马拉雅淡色花岗岩带的东部,岩石地球化学研究结果显示,其具有高的SiO2(73.87%~74.95%)、Al2O3(14.20%~14.74%)和K2O(4.44%~4.89%),高的K2O/Na2O比值(1.19~1.42)和A/CNK比值(1.18~1.22),富集Rb、Th和U,亏损Ba、Nb、Sr和Zr,具有强烈的负Eu异常(δEu=0.27~0.37),属于高钾钙碱性过铝质S型花岗岩。冲巴淡色花岗岩具有较高的Rb/Sr比值(2.6~8.6),低的CaO/Na2O比值(0.18~0.20),指示源区可能为泥质岩区,(87 Sr/86 Sr)i和εNd(t)值分别为0.763 199~0.778 799和-16.7~-16.3,与大喜马拉雅结晶杂岩(GHC)中变泥质岩一致,表明其来自GHC变泥质岩的部分熔融。淡色花岗岩具有高的(87Sr/86Sr)i而低的Sr含量,且随着Ba含量增加,Rb/Sr比值降低。这些特征表明,冲巴淡色花岗岩是无水条件下变泥质岩发生白云母脱水熔融的产物,部分熔融可能与STDS伸展拆离导致的构造减压密切相关。     

西藏南部岗巴—定日地区花岗岩地球化学特征及其构造环境

通过对出露于西藏南部岗巴—定日地区花岗岩体的地球化学研究表明,岩石中SiO2,Al2O3,Na2O和FeO,MgO等的含量均高,贫CaO和Fe2O3;w(SiO2)介于71.40%～73.06%,A/CNK在1.17～1.34之间,为铝和硅过饱和类型的强过铝质花岗岩。岩石的稀土元素总量(ΣREE)为56.80×10-6～89.12×10-6,(La/Yb)N=6.30～18.26,(La/Sm)N=2.62～3.40,ΣLREE/ΣHREE=2.41～4.66;稀土元素配分曲线呈右倾型,具有弱的负铕异常。Nb,Ti等高场强元素具有明显的亏损,而Rb,U,La,Nd,Hf,Eu,Y等大离子亲石元素具有明显的正异常。岩石的87Sr/86Sr初始比值较高,87Sr/86Sr为(0.738 71～0.751 12)。综合研究认为,本区花岗岩的成因为陆壳部分熔融作用形成的,属陆壳改造型强过铝质花岗岩。本区花岗岩岩浆源区岩石成分主要为砂屑岩,其次为泥质岩,是上地壳部分熔融作用的结果。岩石的微量元素标准化曲线图、岩石地R1-R2图解、Rb-(Yb+Ta)和Rb-(Nb+Yb)图解均显示本区岩体形成于同碰撞构造环境的花岗岩,具有同碰撞岩浆活动的特征,是喜马拉雅早期印度板块与冈底斯板块的俯冲碰撞导致的地壳增厚,上地壳部分熔融的产物;为形成于同碰撞构造环境的花岗岩。     

三江造山带义敦岛弧中段格聂（南）花岗岩体地球化学特征及地质意义

夹持于甘孜—理塘结合带与金沙江结合带之间的义敦弧岩浆岩带上发育了3条纵贯南北的造山花岗岩带,其中:中带形成了由20余个岩体组成的雀而山—格聂花岗岩带和相关的银、锌、铅-锌多金属矿床。本文对格聂(南)花岗岩体进行研究,发现其岩石类型为花岗闪长岩、二长花岗岩和钾长花岗岩三类,以二长花岗岩为主体。锆石LA-ICP-MS U-Pb定年结果表明格聂花岗岩的成岩年龄为89.9±3.6Ma。地球化学研究表明,岩石中主量元素化学成分具有富硅、富铝、低钠高钾的特征,为典型的S型花岗岩。铝饱和指数ASI1,指示岩浆源自地壳;(CaO)%/(Na2O)%值等于0.1左右,表明源岩为大陆地壳沉积岩区的泥质岩。稀土总量均值228.83×10-6,稀土配分曲线呈略右倾近直线海鸥型,与地壳熔融型花岗岩形态一致。轻重稀土分馏不明显;铕出现明显负异常(δEu=0.13),显示岩浆分异结晶作用强烈。微量元素蛛网图上明显亏损大离子亲石元素Sr;富集高场强元素U。Rb/Sr平均比值14.97,表明格聂花岗岩的源岩为上部陆壳。结合Rb-(Y+Nb)图解、(Rb/30)-Hf-(Ta×3)图解、R1-R2变异图解,格聂南岩体形成于后碰撞造山环境,应是甘孜-理塘洋盆和金沙江洋盆闭合后,造山后伸展作用活动的产物。     

滇西“三江”地区临沧花岗岩基中三叠世碱长花岗岩的发现及其意义

在野外调研的基础上,对滇西“三江”地区临沧花岗岩基中勐库碱长花岗岩体的年代学、岩石学和地球化学开展了较系统的研究。结果显示,勐库岩体的锆石LA-ICP-MS U-Pb年龄为236.2±3.7 Ma,表明岩体应形成于中三叠世,而非前人认为的新生代。全岩主、微量元素,Sr同位素和锆石微量元素特征显示岩体属于S型花岗岩系列,来自于与临沧花岗岩基相类似的地壳沉积物源区的部分熔融,并经历了高程度的结晶分异作用。以勐库岩体为代表的碱长花岗岩与临沧花岗岩基形成时代一致,表明碱长花岗岩应为临沧花岗岩基的重要组成部分。除已报道的黑云母二长花岗岩类和黑云母花岗闪长岩类外,临沧花岗岩基还应包括较广泛分布的碱长花岗岩类。本文同时揭示,由于临沧花岗岩基中以勐库岩体为代表的碱长花岗岩并非早前认为的新生代岩体,“三江”南段特别是临沧地块前人划分的新生代岩体分布范围和规模可能需要重估。     

滇西“三江”地区临沧花岗岩基中三叠世碱长花岗岩的发现及其意义

在野外调研的基础上,对滇西"三江"地区临沧花岗岩基中勐库碱长花岗岩体的年代学、岩石学和地球化学开展了较系统的研究。结果显示,勐库岩体的锆石LA-ICP-MS U-Pb年龄为236.2±3.7 Ma,表明岩体应形成于中三叠世,而非前人认为的新生代。全岩主、微量元素,Sr同位素和锆石微量元素特征显示岩体属于S型花岗岩系列,来自于与临沧花岗岩基相类似的地壳沉积物源区的部分熔融,并经历了高程度的结晶分异作用。以勐库岩体为代表的碱长花岗岩与临沧花岗岩基形成时代一致,表明碱长花岗岩应为临沧花岗岩基的重要组成部分。除已报道的黑云母二长花岗岩类和黑云母花岗闪长岩类外,临沧花岗岩基还应包括较广泛分布的碱长花岗岩类。本文同时揭示,由于临沧花岗岩基中以勐库岩体为代表的碱长花岗岩并非早前认为的新生代岩体,"三江"南段特别是临沧地块前人划分的新生代岩体分布范围和规模可能需要重估。     

胶东半岛三佛山高Ba—Sr花岗岩成因

胶东半岛三佛山岩体是昆嵛山杂岩体的重要组成部分，其岩性主要由二长花岗岩组成，位于苏鲁超高压碰撞带与胶东陆块之间的缝合带中。岩石化学特点具高钾钙碱性岩石系列特征，岩体为准铝Ⅰ型花岗岩，并具有高Ba—Sr花岗岩的岩石地球化学特征，即高Ba、Sr含量，高Sr／Y、La／Yb、K／Rb值，低Y（〈13μg／g）、Yb（1．8μg／g）、Rb／Sr比值（平均为0．33），弱的Eu负异常，亏损Nb、P、Ti等高场强元素。根据该岩体岩石地球化学特征、包体岩石学特征，并结合前人对高Ba—sr花岗岩成因研究成果，笔者认为该岩体可能是幔源基性岩浆与地壳熔融的酸性端元混合而成。混合后的岩浆没有明显的长石和云母类矿物的结晶分异作用，混合岩浆最大温度在750-800℃左右。酸性岩浆的源区以石榴子石＋辉石＋角闪石＋斜长石的残留为特征。残留相物质组成特征暗示源区应位于壳幔边界，深度30km土，结合早期形成的昆嵛山二长花岗岩源区深度大于40km这一现象，表明胶东地区中生代岩石圈减薄作用在110Ma达到最大，地壳厚度恢复至正常厚度。     

新疆阿尔泰花岗岩类源区物质的定量模拟

对产出于阿尔泰、额尔齐斯、乌化古三条构造-岩浆带上的六个典型岩体进行了源区岩石化学组成和初始熔体部分熔融程度的定量模拟。模拟结果表明:六个岩体的ε_(Sr)~t值多介于0-120之间,源区岩石多为地幔物质与陆壳物质的混合源,地壳柱中成熟陆壳所占比例较少,反映了中亚型地洼区在地壳化学结构上的一个重要特征.从北往南,ε_(Sr)~t值与壳源锶所占百分率逐渐减小,反映了从地槽造山带核心部位往边缘部位往边缘部位,地壳柱中成熟陆壳所占比例逐渐减小。初始熔浆部分熔融程度温度、压力呈正消长关系。     

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