华北太行晚中生代煌斑岩地球化学特征及成因探讨

华北克拉通太行山地区煌斑岩脉广泛发育。这些煌斑岩高度富集大离子亲石元素(如Rb、Sr、Ba和K)和轻稀土元素，具有高度分异的REE模式，在化学成分和Nd—Sr同位素组成上亦显示出规律性的变化。其特征表明：太行山地区的晚中生代煌斑岩来源于同一个岩浆源区，而且煌斑岩浆在上升过程中曾经遭受过下地壳的混染。此外，最原始的煌斑岩样品具有低SiO2、高MgO以及高度富集同位素[εNd(120Ma)＝-8．3，Ist＝0．7052]的特征，表明形成煌斑岩的母岩浆来自富集地幔，是富集地幔部分熔融的产物；富集地幔可能是下部软流圈释放的富挥发分、低密度的熔体与上部的岩石圈发生了交代反应而形成的。     

桂北罗城垒洞煌斑岩形成过程:地球化学、年代学和Sr-Nd-Pb同位素约束

对桂北罗城垒洞煌斑岩进行了锆石LA-ICP-MS U-Pb定年,获得的岩浆侵位年龄为约100Ma。其高钾(K2O/Na2O=15.7~24.0),富碱[w(K2O+Na2O)=6.18%~8.25%],富集大离子亲石元素和轻稀土元素,亏损高场强元素、Sr及重稀土元素,高(87Sr/86Sr)i(0.718 832~0.719 730),低εNd(t)(-9.15~-8.97),富集放射性Pb的特征,显示源区可能为早期俯冲交代作用形成的EMⅡ型富集地幔,该富集地幔形成于新元古代扬子和华夏地块的俯冲作用。煌斑岩岩浆的形成与华南陆块在白垩纪(100Ma)伸展拉张的背景下软流圈上涌促使这些富集地幔部分熔融有关。区域上NNE向的深大断裂为岩浆侵位提供了良好的通道。     

湖南锡矿山锑矿矿区煌斑岩的地球化学特征

对湖南锡矿山矿区煌斑岩脉进行了系统的元素和同位素地球化学研究，来探讨煌斑岩的成因。本区煌斑岩形成时代大约为120Ma，早于锑成矿时间，并与锑成矿有密切相关。其微量元素MORB蛛网图，以富集高场强元素，Nb-Ta亏损和Ti不亏损，Th强富集和Ce弱富集为特征，具有岛弧型玄武岩微量元素分配模式，构造环境可能为大陆内部破坏板块边缘。稀土元素具有总量高，无明显的负铕异常，配分模式呈轻稀土富集的右倾型特征。同位素以高^87Sr/^86Sr、低^143Nd/^144Nd为特征。结合元素地球化学、同位素特征和地质发展史分析，煌斑岩可能为富含REE和高场强元素的俯冲带流体交代过的富集地幔部分熔融所产生的岩浆，在上升过程中同化和混合很少量的矿区隐伏花岗岩浆和灰岩的产物。     

煌斑岩的分类、特征及成因

作为最早被识别出的碱性岩石之一,煌斑岩因富含金和金刚石等矿产资源以及对理解深部地球动力学过程的重要作用而受到广泛重视,但是目前对于煌斑岩的成因还存在不同的认识。本文基于近年来对煌斑岩的研究成果,对它们的分类、特征以及岩石成因进行综述。根据国际地科联(IUGS)的分类标准,煌斑岩可以分为超镁铁质煌斑岩、钙碱性煌斑岩和碱性煌斑岩。研究发现,超镁铁质煌斑岩往往是伸展环境下岩浆作用的产物,与金伯利岩和碳酸岩有密切的成因关系;钙碱性煌斑岩通常发育在汇聚或被动大陆边缘环境,其岩石成因可能有多种机制(如基性岩浆的分异、岩浆混合以及交代富集地幔的部分熔融);碱性煌斑岩出露在离散型大陆边缘和板内构造环境,通常和碱性玄武质岩浆作用密切相关。不管岩石的形成环境和过程如何,超镁铁质煌斑岩、钙碱性煌斑岩和碱性煌斑岩被普遍认为是来自于经历了交代富集作用的地幔源区。最后,文章指出了煌斑岩研究过程中存在的一些科学问题,如富集的地幔源区存在的矿物相(金云母和角闪石)对产生钠质还是钾质岩浆的影响,控制岩浆在结晶过程中影响含水矿物斑晶形成的因素以及部分煌斑岩中碳酸岩球粒和钠长石的形成原因等。     

云南大坪金矿区煌斑岩的地球化学特征及成因探讨

大坪金矿区闪长岩体中发育多条煌斑岩脉,并且多伴随石英脉出现。在岩石化学组成上,SiO2含量为44.86%~54.10%、K2O/Na2O在0.56~2.09之间,属钾玄质系列;岩石富集大离子亲石元素(Sr、U、Rb和Ba)和轻稀土元素(LREE)、相对亏损高场强元素(Ta、Nb和Ti),且Ta、Nb和Ti具"TNT"负异常;δEu值为0.72~1.36,负Eu异常不明显;87Sr/86Sr值范围为0.706 6~0.707 4,均值0.707 1,高于原始地幔现代值0.704 5;143Nd/144Nd值范围为0.512 4~0.512 5,均值0.512 4,低于原始地幔现代值0.512 638;εNd值范围为-2.5~-4.2,均值-3.98。Nb/Ta比值为48.96~82.58(平均62.99),远高于原始地幔值的17.5±2.0;Zr/Hf比值为20.45~47.53(平均39.57),略高于原始地幔值的36.27±2.0;Nb/Ta和Zr/Hf都远大于陆壳值11和33。表明煌斑岩源区可能来自早期俯冲洋壳或造山带根部拆沉组分脱水形成富集流体在地幔源区发生交代作用形成的富集地幔,岩浆在上升侵位过程中受到地壳物质的混染较弱,形成于碰撞后的板内构造环境。     

湘东北中生代基性岩脉微量元素地球化学特征及岩石成因

湘东北中生代基性岩脉可以分为煌斑岩和辉绿岩两类，前者形成于136.61Ma，后者形成于86.18Ma,与华南中生代主要拉张时期相对应。岩石富集LREE，Eu负异常不明显，其形成主要受地幔部分熔融作用制约。早期煌斑岩类微量元素和Sr、Nd同位素总体上具有富集地幔（EMⅡ型）洋岛玄武岩（OIB）特征，富集Nd、P、Cs，而K、Rb、Sr、U、Th等富集程度不明显，Ta、Nb略有富集，具有软流圈地幔上涌地幔热柱玄武岩岩浆源区性质，表现出软流圈地幔上涌部分熔融的成岩特点。晚期辉绿岩类表现出Ta、Nb、Ti亏损，但LILE并不富集，反映地壳混染程度的增强，具有大陆拉张带（裂谷初期）形成的玄武岩岩浆源区性质，为岩石圈地幔部分熔融形成。二者具有不同的岩浆源区性质，从早期到晚期岩浆源区向上迁移并致使部分陆 物质混入，反映由热点式拉张到岩石圈伸展－减薄的作用过程。     

湖南锡矿山超大型锑矿床煌斑岩脉地质地球化学特征

湖南锡矿山超大型锑矿床是世界上已知最大的锑矿床,本文对该矿床矿区内唯一的岩浆活动显示——煌斑岩脉进行了较系统研究,研究表明该岩脉为幔源成因,结晶分异程度较低,其微量元素、稀土元素特征均表明锑矿床所在壳体的上地幔部分曾发生过广泛地幔交代作用,存在锑元素的富集。     

云南白马寨镍矿区煌斑岩地球化学Ⅰ.主要元素和微量元素

云南白马寨镍矿区煌斑岩呈岩墙和岩脉穿切矿区各时代地层、基性-超基性岩和矿体，为成矿期后产物；采自矿区不同中段和不同产状的煌斑岩具有相似矿物组合，岩石类型均为云煌岩；岩石化学特征表明岩石均为钾质-富钾质钙碱性煌斑岩；微量元素配分模式为相似的“骆峰型”，与MORB相比，富集LILE和HPSE；REE配分模式为相似的LREE富集型；主要元素和微量元素与镁指数(M值)之间存在一定的相关关系；在La—La／Sm图中样品既有水平分布趋势、也有倾斜分布趋势。总体上，该区煌斑岩为相同岩浆源区的产物，源区地幔部分熔融程度和岩浆结晶分异作用对岩石主要元素和微量元素地球化学性质均有一定的影响。比较老王寨金矿区煌斑岩形成地质背景、岩石类型、主要元素和微量元素地球化学特征，认为两地区煌斑岩地幔源区具有相同或相似、的性质。     

云南白马寨镍矿区煌斑岩^40Ar-^39Ar定年和地球化学特征

云南白马寨镍矿区煌斑岩全部为云煌岩.两个样品的40Ar/39Ar定年结果分别为32.46±0.62Ma和32.01±0.60Ma,表明矿区煌斑岩为哀牢山断裂带新生代早期高钾岩浆活动的产物.在化学组成上,矿区煌斑岩具有高M值[100×Mg/(Mg+Fe2+)](67.42～86.35)、高ALK(K2O+Na2O为7.01%～9.81%)、富钾(K2O/Na2O为1.66～2.64)、富大离子亲石元素(如Sr、Rb、Ba等)和LREE、明显的Ta、Nb、Ti负异常的特征.Sr-Nd同位素具有高(87Sr/86Sr)0比值(0.70625～0.70912)和低εNd(-5.22～-3.68)的特征,位于EM1和EM2地幔端元之间,有更靠近EM2的趋势.元素和同位素地球化学特征表明矿区煌斑岩的源区为交代富集地幔,进一步判别表明源岩处于尖晶石相方辉橄榄岩和石榴石相二辉橄榄岩的混合线上,以尖晶石相方辉橄榄岩为主.源区交代富集的矿物既有金云母,也有角闪石.岩浆演化过程中经历了橄榄石+斜长石±磷灰石±铁钛氧化物的结晶分异.岩浆形成于大陆弧的构造背景,俯冲的陆壳和古特提斯洋壳对富集的源区均有贡献.白马寨镍矿区煌斑岩和哀牢山断裂带新生代早期其它高钾岩浆岩具有相近的年代、一致的地球化学特征,表明它们具有相似的源区,受控于相同的构造背景.     

个旧老厂钾质煌斑岩矿物学特征及其锆石U-Pb和黑云母~(40)Ar-~(39)Ar年龄

个旧老厂锡铜多金属矿区出露多条钾质煌斑岩脉,是个旧白垩纪岩浆活动的重要组成部分。本文利用电子探针对煌斑岩进行矿物学特征分析,利用锆石TIMS U-Pb和黑云母~(40)Ar-~(39)Ar进行了煌斑岩年代学研究。煌斑岩辉石斑晶和微晶化学成分近一致,均属普通辉石;黑云母斑晶属壳源铁质-镁质黑云母,而黑云母微晶属壳幔混源型镁质黑云母;中长石斑晶偏基性(An25~40),透长石微晶偏酸性(An1~6)。煌斑岩2颗锆石TIMS U-Pb年龄(87.1±1.3)Ma为捕获的围岩(老卡花岗岩体)锆石的年龄。煌斑岩脉的6个黑云母~(40)Ar-~(39)Ar同位素坪年龄集中在75~70 Ma间(平均72.9 Ma),代表煌斑岩侵位时代,稍晚于个旧中酸性岩浆活动的时代(85~78 Ma)。个旧老厂钾质煌斑岩脉代表壳-幔的相互作用,岩浆起源于古特提斯洋壳板块俯冲的残留板片对地幔楔的交代富集作用而形成的地幔源区。煌斑岩浆侵位的构造背景为俯冲-碰撞后的板内拉伸环境。     

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