碧口地块东南缘韧性剪切带构造特征浅析

碧口地块东南缘发育多条倾向不同、呈NEE走向逆冲平行展布的韧性剪切带,地质信息丰富,对碧口地块构造特征解析意义重大.为探讨地块东南缘韧性剪切带的地质构造特征,对剪切带中发育的糜棱岩化绿泥石英片岩、糜棱岩进行了野外观测、显微组构和石英c轴组构分析,估算了剪切带变形温度、差应力、应变速率及运动学涡度.结果显示,韧性剪切带变...     

舒兰韧性剪切带应变分析及石英动态重结晶颗粒分形特征与流变参数估算

舒兰北东向韧性剪切带位于佳木斯-伊通断裂带(佳-伊断裂带)中南段, 剪切带内糜棱岩具有明显左行走滑特征, 片麻理产状近NNE向.糜棱岩中长石有限应变Flinn图解判别岩石类型为L-S型构造岩, 属拉长型应变.石英C轴EBSD组构分析表明, 石英组构以中低温菱面为主, 滑移系为{0001} < 110>.剪切带内糜棱岩的剪应变为0.44, 不同方法计算所得运动学涡度值均大于0.95, 指示剪切变形以简单剪切为主.综合矿物变形温度计、石英C轴EBSD组构、石英的粒度-频数图及Kruhl温度计综合估计该韧性剪切带变形机制以位错蠕变机制为主, 变质相为低绿片岩相, 发生韧性变形和糜棱岩化温度范围在400~500 ℃之间.糜棱岩内石英动态重结晶新晶粒边界普遍具有锯齿状或港湾状结构, 利用分形方法对其重结晶新晶边界研究表明, 这些晶粒边界具有自相似性, 表现出分形特征, 分形维数值为1.195~1.220.根据石英重结晶粒径估算差应力值为24.35~27.59 MPa, 代表了舒兰韧性剪切带糜棱岩化作用过程的差异应力下限.使用不同实验方法估算、比较和分析了该剪切带古应变速率, 认为该速率应为10-12.00~10-13.18 s-1, 与区域性应变速率10-13.00~10-15.00 s-1对比, 说明舒兰韧性剪切带的应变速率与世界上大多数韧性剪切带中的糜棱岩应变速率一致, 是缓慢变形的结果, 其形成可能与早白垩世伊泽纳崎板块向欧亚大陆俯冲发生转向有关.      

辽西兴城—台里韧性剪切带北段变形特征

辽西兴城—台里地区发育系列花岗质岩石,强烈构造变形特征均显示其具有韧性剪切带的特点。对剪切带北段进行详细宏微观构造解析,结合岩石变形强度差异性分析、有限应变测量、石英C轴EBSD测试以及古差异应力值估算等研究,结果表明剪切带内花岗质片麻岩和眼球状花岗质片麻岩具有NEE向左行剪切变形特征,变形岩石为S-L构造岩,应变类型属于平面应变,古差异应力值介于30~40 MPa之间。长石-石英矿物温度计以及石英C轴EBSD组构指示剪切带以中低温变形为主,温度在400℃~500℃,属绿片岩相变质,具中-低温韧性剪切带特征。韧性剪切带内普遍存在变形分解现象,弱变形带内岩石残斑含量较高,眼球状构造和S-C组构较为发育;强变形带岩石残斑含量较低,剪切面理较为发育,糜棱面理发育较弱或者不发育。     

江南造山带东段璜茅-五城-屯溪韧性剪切带塑性变形及流变学研究

江南造山带东段皖赣相邻区璜茅-五城-屯溪韧性剪切带野外现象、室内显微构造特征表明其经历了较为强烈的韧性剪切变形。岩石经历了NNE向右行剪切改造,变质变形程度为初糜棱岩-糜棱岩阶段,少量达超糜棱岩阶段。结合石英普遍发育边界迁移重结晶、长石多以塑性拉长和少量膨凸重结晶的变形行为特征、石英C轴组构显示出中-高温柱面和菱面滑移为主、重结晶石英颗粒大小-频数及分形维数(1.1646～1.2007),Kruhl温度计测算,揭示了璜茅-五城-屯溪韧性剪切带以中高温位错蠕变变形为主,变形和糜棱岩化环境在450～600℃的中深地壳范围,相当于中高绿片岩相-低角闪岩相。同时,岩石变形的古差异应力为20.76～30.04 MPa,估算所得应变速率主要介于10~(-14)～10~(-11) s~(-1),指示了中高温、低应变速率的韧性变形条件。已有的变形年龄显示,该韧性剪切带为加里东构造事件产物,主要的动力来源与江山-绍兴断裂带发育的陆内俯冲作用主应力在远离造山带的转变相关。     

俯冲隧道中含水矿物的变形及其构造意义

研究表明,俯冲隧道中发生显著脱水作用形成富水流体,并交代地幔楔物质形成富含水矿物(蛇纹石、绿泥石、角闪石等)的橄榄岩。这些含水矿物的变形特征对了解俯冲带的动力学过程具有重要意义。我们研究了来自意大利Monviso地区俯冲带折返所形成的变质混杂蛇绿岩套内部出露的绿泥片岩、透闪石绿泥岩、蛇纹片岩以及绿泥蛇纹岩的变形特征。研究结果表明,地幔楔的流体交代所形成的含水矿物一方面降低了橄榄岩的密度,另一方面绿泥石、叶蛇纹石以及透闪石均发生了强变形并形成强变形组构。绿泥石的组构特征表现为(001)面近平行页理面,[100]轴在平行线理方向形成强极密或在页理面内形成大圆环。叶蛇纹石发育[010]轴平行线理和(001)面平行面理的强组构。角闪石发育[001]轴平行线理和(100)面平行面理的中等强度组构。这些富含水矿物的岩石,沿平行页理面的纵波速度大于垂直页理面的速度,且剪切快波的极化面近平行于页理面。绿泥片岩的最大的剪切波各向异性为33.4%,大于叶蛇纹石片岩的最大剪切波各向异性(17.8%)。研究认为:俯冲隧道中的流体交代形成低密度的含水矿物为俯冲隧道中地幔物质的上升提供了浮力;低流变强度(由强变形组构指示)含水矿物的为地幔物质的折返提供了主要的润滑和上升通道;3)叶蛇纹石和绿泥石变形可以合理解释大角度低温俯冲带(60o~90o)的平行海沟的剪切快波,而低角度(30o~60o)高温俯冲带平行海沟的剪切快波可能主要与角闪石变形相关。     

秦岭商丹糜棱岩带石英组构特征变化及成因分析

商丹糜棱岩带岩湾、沙沟和商南等3个区段石英C-轴组构和显微构造特征表明,该带自西向东石英C-轴组构形式由单一环带型转为Y-轴方向的点极密型,然后变为Ⅰ型交叉环带型,构造变形环境从低绿片岩相过渡到中-高绿片岩相,然后变为高绿片岩相-低角闪岩相。构造变形环境差异是造成石英组构形式变化的主要因素。随着温压条件的升高,石英滑移系从以底面〈a〉滑移系和柱面〈a〉滑移系的共同作用为主转向以单一柱面〈a〉滑移系为主,进而底面〈a〉滑移系和柱面〈a〉滑移系又重新变得活跃,且菱面滑移系的作用也变得十分重要。     

皖南天井山地区大型韧性剪切带特征及EBSD石英组构分析

证明璜茅-五城-屯溪韧性剪切带的存在能证实前人的推断和认识,为区域构造研究特别是皖浙赣断裂的研究提供研究资料,也能为区域内金矿找矿提供新的找矿方向。针对皖南天井山地区璜茅-五城-屯溪韧性剪切带进行的剖面地质研究,结果显示,璜茅-五城-屯溪韧性剪切带为大型韧性剪切带,在研究区内总体呈喇叭状展布,宽约2km~5km,向NE发散,向SW收敛。并在元古代中形成了大型的A型褶皱。宏观上强弱分带明显,以元古代地层和晋宁期岩体的接触带为最强应变带,发育超糜棱岩,应变强度向两侧逐渐减弱,在弱应变带发育糜棱岩化千枚岩和初糜岩。微观上,韧性变形显微构造发育较好,以发育旋转碎斑、压力影和石英的膨突动态重结晶为主,其韧性变形机制为中低温条件下的位错滑移、碎裂流动以及扩散物质迁移。EBSD对韧性剪切带的石英组构分析显示,石英以菱面{10-11}a和底面{0001}a滑移为主,变形温度为中低温(400℃~550℃)及低温(400℃)。宏微观运动学特征和石英组构特征显示韧性剪切带至少经历了两次活动。塑性变形机制和EBSD石英组构显示韧性剪切带变质相为低绿片岩相-高绿片岩相,局部可达低-中角闪岩相。     

西秦岭天水地区新阳—元龙韧性剪切带构造变形特征及其地质意义

西秦岭北缘新阳—元龙韧性剪切带作为西秦岭造山带与北祁连造山带之间的区域韧性构造边界,带内构造样式复杂多样,多期构造叠加,不同部位韧性变形强度不同,兼具左行、右行剪切特征,但以右行为主,宏观构造显示由NNE向SSW斜向逆冲特征,且多被后期构造改造。EBSD组构分析结果显示,石英C轴优选方位指示非共轴变形,显示明显的中温柱面a-中低温菱面-低温底面组构的右行剪切及不太明显的低温底面组构(偶见中低温组构)左行剪切特征;方解石C轴组构显示e1双晶滑移与r1平移滑动,兼具左行、右行剪切特征。组构特征反映该剪切带可能经历了中温—中低温—低温、以右行韧性走滑为主并曾出现过左行逆冲的复杂变形过程,综合分析推断该韧性剪切带经历了低绿片岩相—高绿片岩相—低角闪岩相韧性变形环境。区域对比分析认为,新阳—元龙韧性剪切带响应古生代构造演化的构造变形记录主要为2期:一是志留纪天水—武山洋闭合导致大规模NNE-SSW向的陆-弧或陆-陆碰撞逆冲造成的左行逆冲剪切变形;二是晚泥盆世—早石炭世秦祁结合部位强烈的大规模右行走滑拼贴运动形成的右行剪切变形和反"S"构造样式。     

华北克拉通基底花岗质片麻岩变形和流变学研究——以辽西寺儿堡地区为例

辽西寺儿堡镇新太古代花岗质片麻岩内发育的宏观、微观构造变形特征表明该地区曾遭受了强烈的韧性变形改造。花岗质岩石变形程度在初糜棱岩–糜棱岩之间,岩石经历了SWW向左行剪切作用改造。岩石中石英有限应变测量判别结果表明,构造岩类型为L-S型,为平面应变。岩石的剪应变平均值为1.43,运动学涡度值为0.788~0.829,指示岩石形成于以简单剪切为主的一般剪切变形中。此外,石英颗粒以亚颗粒旋转重结晶和颗粒边界迁移重结晶作用为主,长石颗粒塑性拉长,部分发生膨凸式重结晶作用;石英组构特征(EBSD)揭示石英以中–高温柱面滑移为主;石英颗粒边界具有明显的分形特征,分形维数值为1.151~1.201,指示了中高温变形条件。综合石英、长石的变形行为、石英组构特征以及分形法Kruhl温度计的判别结果,推断辽西寺儿堡镇新太古代花岗质片麻岩经历过480~600℃的中高温变形,其同构造变质相为高绿片岩相-低角闪岩相。花岗质岩石的古差异应力为10.62~12.21 MPa,估算的应变速率为10~(–11.67)~10~(–13.34) s~(–1),即缓慢的变形,可能记录早期中高温、低应变速率的韧性变形过程,反映华北克拉通基底中下部地壳变形特征。     

长春东南劝农山地区早二叠世范家屯组岩石变形组构及流变学特征

劝农山地区位于长春市东南部,处于佳-伊断裂和西拉木伦河缝合带交汇处.详细野外调查发现,该区曾遭受强烈韧性剪切变形,剪切带内岩石普遍糜棱岩化,主要由下二叠统范家屯组（P₁f）钙质糜棱岩与侵入其中的燕山期花岗质糜棱岩组成,变形程度处于初糜棱岩至糜棱岩之间,多具有糜棱结构.岩石应变类型主要为压扁型应变,偏一般压缩,为L=S型构造岩,指示其形成于挤压型剪切带的构造环境.多种宏微观韧性剪切变形标志,指示明显的左行剪切运动.电子探针方解石-白云石地质温度计、方解石和石英EBSD组构特征、方解石e双晶形态以及石英长石变形行为等均显示岩石具有低温塑性流变特点,变形环境不超过绿片岩相.剪切带内应变速率偏高,应变集中带应变速率最大,在10-6.95~10-8.89之间,远离强变形带应变速率在10-9.25~10-12.17之间,糜棱岩化作用过程中差异应力下限应大致为51.27~65.46 MPa,代表剪切带糜棱岩化作用为低温中等强度应变,在稍快的应变速率条件下形成.压溶扩散和双晶滑移为劝农山韧性剪切带变形初期的主要变形机制,随着递进变形,逐渐以双晶滑移和晶内滑移为主,递进变形晚期,局部强变形域内发生了粒间滑移.劝农山韧性剪切带形成与早白垩世中晚期伊泽纳崎板块NNW向高斜度斜向俯冲于欧亚大陆之下有关,是佳-伊断裂带左旋走滑事件的局部表现.      

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