昌宁－孟连结合带斜长角闪岩锆石U-Pb年龄、地球化学特征及其地质意义

昌宁-孟连结合带牛井山地区发育以构造岩片和透镜体形式产出的斜长角闪岩,其对于认识和恢复昌宁-孟连结合带特提斯演化历史具有重要意义。本研究对牛井山蛇绿混杂岩带内的斜长角闪岩进行了系统的岩石学、锆石U-Pb定年、Hf同位素及全岩地球化学研究。锆石CL图像揭示斜长角闪岩锆石为岩浆成因锆石。锆石U-Pb定年结果为272±1.2 Ma(MSWD=1.1,n=21),代表斜长角闪岩原岩时代。岩石地球化学分析表明,斜长角闪岩Si O2含量为51.83%~52.6%,全碱(Na2O+K2O)含量为3.33%~4.16%,Na2O/K2O比值为5.8~19.8,属于低钾拉斑玄武岩系列。微量元素结果表明斜长角闪岩具有N-MORB的地球化学特征。原岩恢复研究揭示斜长角闪岩的原岩为272±1.2 Ma的N-MORB型辉长岩。斜长角闪岩锆石初始(176Hf/177Hf)i值为0.282906~0.282956,对应的εHf(t)为10.7~12.5;单阶段亏损地幔Hf模式年龄tDM1为416~499 Ma(平均值为466Ma),明显老于原岩结晶时代。岩石地球化学特征和锆石Hf模式年龄揭示昌宁-孟连特提斯洋在272 Ma时具有一个长期亏损的地幔,地幔年龄为早古生代416~499 Ma。结合该带存在早古生代洋壳残余及洋壳俯冲成因埃达克岩的事实,我们认为昌宁-孟连带是一个连续演化的原-古特提斯洋,晚古生代272 Ma时还存在洋中脊扩张并产生具有N-MORB性质的洋壳。     

青藏高原古特提斯洋早石炭世弧后拉张:来自A型花岗岩的证据

本文报道了羌塘中部冈玛错钾长花岗岩的锆石U-Pb定年、岩石地球化学和锆石Hf同位素分析结果。钾长花岗岩中的锆石具岩浆生长环带,未见继承的老核,并且锆石Th/U比值大于0.5(0.58~1.05),显示出典型岩浆成因的锆石特征。锆石LA-ICP-MS定年结果为352.4±1.9Ma,表明其形成时代为早石炭世。钾长花岗岩富硅(Si O_2=74.17%~77.88%),低铝(Al2O3=10.50%~11.98%),贫镁(Mg O=0.23%~0.36%),富碱(Na_2O+K_2O=5.74%~7.24%),Na_2OK_2O,K_2O/Na_2O=0.53~0.71,A/CNK=0.87~1.06,富集轻稀土元素和Zr、Hf、Rb、Th和U等元素,亏损Sr、Eu、P和Ti等元素,10000Ga/Al=3.12~4.14,显示出A2型花岗岩的地球化学特征。钾长花岗岩中锆石的εHf(t)值和Hf同位素两阶段模式年龄分别变化于+4.40~+12.14和549~985Ma,显示出正的、不均一的同位素组成,可能形成于壳-幔混合作用,其中幔源端元应当是伸展环境下上涌的地幔岩浆,而壳源端元则可能是扬子板块新元古代的新生地壳部分熔融形成的长英质岩浆。结合区域地质资料,认为该花岗岩可能形成于古特提斯洋壳对羌北-昌都板块北向俯冲引起的陆缘弧后拉张环境。     

冈底斯中段碱长花岗岩锆石U-Pb-Hf同位素特征及地质意义

本文对冈底斯岩浆带中段谢通门塔玛地区碱长花岗岩进行了原位LA-ICP-MS锆石U-Pb定年和LA-MCICP-MS锆石Lu-Hf同位素分析。研究结果表明,采自该岩体不同部位的两件锆石U-Pb同位素加权平均年龄分别为(40.02±0.39)Ma和(40.65±0.32)Ma,具有几乎一致的地质年龄,即碱长花岗岩侵位结晶年龄为40 Ma左右。LA-MCICP-MS锆石Lu-Hf同位素研究显示,176Hf/177Hf比值在0.282633~0.282878,平均值为0.282765,计算所得的εHf(t)值介于-4.08~4.15,平均值为0.28,峰值在-1~+1之间;TDMC模式年龄在822~1373 Ma,平均值为1075 Ma,峰值年龄为1000~1200 Ma。其次,样品的εHf(t)值具有正负相间的特点,εHf(t)也相对较小,为典型的壳幔混染型,岩浆源区主要以古老地壳的熔融为主。综合研究表明,谢通门塔玛地区碱长花岗岩主要是由新特斯洋板片的断离,致使软流圈地幔上涌,引起拉萨地体地壳物质的熔融、再循环而形成的,在这个过程中有部分幔源物质的加入。     

藏北羌塘中部桃形湖蛇绿岩中钠长花岗岩——古特提斯洋壳消减的证据

本文报道了羌塘中部黑脊山钠长花岗岩的锆石U-Pb定年结果和岩石地球化学资料以及锆石Hf同位素成分。野外观察表明钠长花岗岩与桃形湖蛇绿岩为侵入接触关系。样品中的锆石晶型比较完整,具典型的岩浆生长环带,未见继承的老岩浆核,结合其Th/U比值（0.41~1.06）,表明为典型的岩浆成因。锆石LA-ICP-MS定年结果为351.2±1.9Ma,表明其形成时代为早石炭世。钠长花岗岩具有较高的SiO₂含量和很高的Na₂O/K₂O比值,为准铝质-弱过铝质岩石,属于钙碱性I型花岗岩;稀土元素配分模式显示为右倾的曲线,伴随较弱的正Eu异常;微量元素蛛网图上表现出Nb、Ta、Ti负异常和Rb、Th、U、K、Pb、Zr、Hf正异常,具有岛弧花岗岩的地球化学特征;样品在构造环境判别图解上投点均落入岛弧花岗岩区。样品中锆石的ε_Hf（t）值为+11.56~+14.46,二阶段Hf模式年龄为432~581Ma,显示出明显的幔源特征,说明其源岩可能为俯冲消减的玄武质洋壳。黑脊山钠长花岗岩的发现,表明羌塘中部的古特提洋在早石炭世已经进入岛弧消减阶段。     

滇西腾冲-梁河地块早白垩世岩浆作用

滇西腾冲-梁河地区分布有大量的花岗岩。本文对梁河地区二长花岗岩进行了锆石LA-ICPMS U-Pb测年和Hf同位素分析,研究表明,锆石具有清晰的韵律环带,其Th/U值为0.34～1.65,为典型的岩浆锆石;锆石U-Pb年龄显示,花岗岩有三个年龄峰值(139.6±2.3Ma、129.7±5.2 Ma和118.8±4.2 Ma),表明该区早白垩世经历了多期岩浆作用;εHf(t)值为-20.15～-30.65,tCDM为2458～3083Ma,暗示花岗岩源自古老地壳部分熔融。该区片麻岩中具有2503Ma的碎屑锆石年龄,据此推测可能存在新太古宙基底。上述研究说明,该区早白垩世花岗岩的形成可能与班公湖-怒江洋的俯冲作用有关。     

藏北羌塘果干加年山花岗闪长岩的锆石U-Pb定年和Hf同位素特征

报道了藏北羌塘中部果干加年山地区花岗闪长岩的锆石U-Pb定年结果和Hf同位素成分。花岗闪长岩的锆石U-Pb定年结果为(225.1±2.4)Ma,与该地区的高压变质带的形成时代一致。样品中锆石的εHf(t)值为-9.8~-17.6,地壳Hf模式年龄为1 874~2 372Ma,表明花岗闪长岩为古元古代地壳物质部分熔融的产物。结合区域地质资料,该花岗岩体可能形成于板块消减的火山弧构造环境,与羌塘地区古特提斯洋的晚三叠世俯冲消减有关。     

福建魁岐晶洞花岗岩锆石U-Pb年代学及其地球化学研究

魁岐晶洞花岗岩具有高Si、高碱、低Ca、富集大离子亲石元素和高场强元素的地球化学特征,为典型的A型花岗岩。LA-ICP-MS锆石U-Pb定年分析显示,魁岐小晶洞花岗岩的锆石U-Pb年龄在101.7±2Ma和97.3±0.77Ma之间,而大晶洞花岗岩的锆石U-Pb年龄在93.6±1.5Ma和92.0±1.3Ma之间,表明它们是晚白垩世早期岩浆活动的产物。锆石原位Hf同位素分析显示,大晶洞锆石的εHf(t)分别为+1.45和+1.21,锆石二阶段模式年龄平均值为1064Ma和1078Ma,说明该类岩石是幔源岩浆底侵导致下地壳熔融的结果。以上研究成果表明,魁岐晶洞A型花岗岩形成于库拉板块向欧亚板块俯冲,诱发其上的大陆岩石圈板块伸展的构造环境。因此,其原始岩浆是新元古代下地壳物质部分熔融的产物,并伴有地幔物质的加入。     

东昆仑小灶火软玉中热液锆石U-Pb年龄及Hf同位素特征:对成矿时代的制约

小灶火软玉矿床位于东昆仑造山带西段,同新疆和田玉处于昆仑山脉同一条成矿带上。该矿床软玉种类主要为青玉,其中透闪石含量达99%以上,为特殊的镁矽卡岩矿床。对该矿区青玉及其相关的黑云二长花岗岩进行了系统的LA-MC-ICP-MS锆石微量元素、U-Pb及Lu-Hf同位素研究。结果显示,黑云二长花岗岩中均为具典型韵律振荡环带的岩浆成因锆石,锆石U-Pb定年得到其成岩年龄为415.8±1.7 Ma;锆石ε_(Hf)(t)值为1.5~6.6,亏损地幔Hf模式年龄(tDM)为779~965 Ma,指示黑云二长花岗岩为东昆仑原特提斯造山带后碰撞阶段新生的新元古代地壳物质熔融的产物。青玉中的锆石可分为两类,其中主要锆石群——I类锆石呈补丁状环带、面状环带或无环带,且具有与黑云二长花岗岩中的岩浆锆石明显不同的稀土元素及Hf同位素特征,显示典型的热液锆石特点,其U-Pb年龄416.4±1.5 Ma代表了青玉的形成时间;II类锆石(416 Ma、471 Ma、818 Ma)呈韵律振荡环带,为热液流体从围岩中捕获的继承锆石。小灶火地区成岩-成矿作用的同时性(~416 Ma)表明岩浆岩侵入是软玉矿床形成的岩浆岩条件,软玉成矿作用方式为热液交代和充填作用。值得注意的是,用热液锆石的Hf同位素来示踪软玉成矿流体性质时应十分谨慎,因为成矿热液中的Hf元素在同时结晶的两种不同矿物(热液锆石和透闪石)间发生了重新分配。     

新疆西天山呼斯特杂岩体岩石学、锆石U-Pb年龄及Hf同位素特征

呼斯特岩体是新疆西天山博罗科努岛弧带上的一个与矽卡岩成矿有关的复式杂岩体,由二长花岗岩、花岗闪长岩、正长花岗岩、花岗细晶岩、闪长玢岩、辉长岩和中基性包体等组成。本文对该岩体不同岩相岩石开展了岩石学、锆石LAICP-MS U-Pb同位素定年和Hf同位素研究,探讨岩石成因及构造意义。锆石U-Pb定年结果表明,正长花岗岩、闪长玢岩、花岗闪长岩和二长花岗岩加权平均年龄分别为380.2±4.6Ma、372.8±5.9Ma、367.7±4.5Ma和366.2±4.5Ma,岩体侵位时代为晚泥盆世,在大约15Myr期间,至少发生了3~4次岩浆侵入。在地球化学组成上,除辉长岩外,岩体为准铝质-弱过铝质、高钾钙碱性-低钾(拉斑)系列的I型花岗岩,轻重稀土分馏明显,具Eu负异常;富集Th、U,亏损Ba、P和高场强元素(如Nb、Ta、Zr、Ti),为晚古生代北天山洋向南俯冲于伊犁地块背景下岩浆活动的产物。二长花岗岩锆石Hf同位素组成较为均一,εHf(t)值为1.3~3.0,二阶段Hf模式年龄为1171~1280Ma,远大于成岩年龄,说明原始岩浆从地幔分异后经历了较长时间的地壳滞留。研究认为,高钾中酸性岩(花岗岩、闪长玢岩和中基性包体)由元古代新生基性下地壳部分熔融而成,伴有受俯冲沉积物熔体交代的幔源岩浆混合。低钾花岗闪长岩高Sr、低Y和Yb,属O型埃达克岩,与同源的辉长岩一起由俯冲的大洋板片部分熔融形成,源岩为低钾的拉斑玄武岩。     

西昆仑西北缘大洋斜长花岗岩带的岩石地球化学特征、成因及其构造环境

大洋斜长花岗岩一般作为蛇绿岩的组成部分,发育规模往往较小,目前世界上不与蛇绿岩共生或有成因关系的斜长花岗岩实例较少,关于不发育蛇绿岩的大规模大洋斜长花岗岩的报道更是少见。本文通过岩石学、岩石地球化学、锆石UPb定年和Hf同位素研究,论证西昆仑造山带西北缘发育着大规模由英云闪长岩、石英闪长岩和奥长花岗岩组成的大洋斜长花岗岩带。以该斜长花岗带中奥依塔克岩体和萨罗依岩体为研究对象,测得其锆石LA-ICP-MS U-Pb年龄分别为322.8±2.2Ma、319.0±1.7Ma,锆石均具较高的正εHf(t)值(11.06~16.93),模式年龄为320~540Ma(平均值为396.1Ma),大于其形成年龄。岩石具低的Al2O3、高Ca O和Mg O含量,强烈的富钠贫钾,稀土元素总量较低,LREE稍亏损或平坦型配分型式,通过与世界典型大洋斜长花岗岩的对比,该斜长花岗岩带属于典型大洋斜长花岗岩,但相对具负Eu异常,富集K、Rb,亏损Nb、Ta元素。对该大规模斜长花岗岩的成因研究进行了探索,认为该斜长花岗岩带不是传统的玄武质岩浆结晶分异成因,而是在低压(0.1GPa)低温(737~781℃)条件下镁铁质洋壳发生部分熔融的产物,残留相为斜长石+角闪石±斜方辉石±钛铁矿(无石榴石)。结合区域资料,西昆仑西北缘斜长花岗岩带是在晚石炭世弧后盆地的伸展裂解环境下以乌鲁阿特组(玄武岩夹沉积岩)为代表的早石炭世新生镁铁质洋壳部分熔融所形成的产物。     

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.     

Définition d'une limite multicritère ; stratigraphie du passage Campanien–Maastrichtien du site géologique de Tercis (Landes,SW France)Definition of a multi-criteria boundary; stratigraphy of the Campanian–Maastrichtian interval of the geological site at Tercis (Landes,SW France)

Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.     

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).     

NONMETALS DEPOSITS

正20141520 Bo Ying(Key Laboratory of Metallogeny and Mineral Assessment,MLR,Beijing 100037,China);Liu Chenglin Saline Spring Hydrochemical Characteristics and Indicators for Potassium Exploration in Southwestern and Northern Tarim Basin,Xinjiang(Acta Geoscientica Sinica,ISSN1006-3021,CN11-3474/P,34(5),2013,p.594-602,5 illus.,3 tables,28 refs.)     

MATHEMATICAL GEOLOGY

正20141243Chen Ge(Hangzhou Research Institute of Petroleum Geology,PetroChina,Hangzhou 310023,China);Si Chunsong Study on Sedimentary Numerical Simulation Method of Fan Delta Sand Body(Journal of Geology,     

PROSPECTING EXPLORATION

正20142599Chen Sanming(Guangxi Key Laboratory of Concealed Deposits Exploration,Guilin University of Technology,Guilin541004,China);He Yuzhou Block Model and Reserves Estimation of Panzhihua Iron Deposit Based on 3D Geological Modeling(Journal of Guilin University of Technology,ISSN1674-9057,CN45-1375/N,33(4),2013,p.610-615,9illus.,1table,15refs.)     

STRUCTURAL GEOLOGY

正20140594 Bai Daoyuan(Hunan Institute of Geology Survey,Changsha 410016,China);Zhong Xiang Faults in the Jingzhou Basin and Their Tectonic Settings(Geotectonica et Metallogenia,ISSN1001-1552,CN44-1595/P,37(2),2013,p.173-183,6illus.,59refs.)Key words:basin evolution,tectonic setting,South China In the Upper Paleozoic and Jurassic se-     

STRUCTURAL GEOLOGY

正20141912Cao Hui(State Key Laboratory for Continental Tectonics and Dynamics,Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China)Gravitational Collapse and Folding during Orogenesis:A Comparative Study of FIA Trends and Fold Axial Plane Traces(Geology in China,ISSN1000-3657,CN11-1167/P,40(6),2013,p.1818-1828,9illus.,35refs.,with