The 1.90–1.88 Ga magmatism in the southernmost Guyana Shield, Amazonas, Brazil: Geology, geochemistry, zircon geochronology, and tectonic implications     

Cristvo da Silva Valrio  Valmir da Silva Souza  Moacir Jos Buenano Macambira 《Journal of South American Earth Sciences》2009,28(3):304-320

The southernmost Guyana Shield-Uatumã subdomain, northeastern Amazonas State, Brazil is dominantly formed by granitoid and volcanic rocks from the Água Branca Suite (ABS), undivided Granite Stocks (GS) and São Gabriel volcano–plutonic system (SGS). The ABS is characterized by a granite series that exhibits comparatively low Fe/(Fe + Mg) ratio, low (Nb/Zr)_N, high Sr values and high Rb/Zr ratio. Its rocks display metaluminous to weakly peraluminous (A/CNK 0.94–1.06), high-K calc-alkaline, I normal-type character and have moderately to strongly fractionated rare earth elements (REE) pattern. The SG granites and SGS effusive–ignimbrite–granite association is metaluminous to weakly peraluminous (A/CNK 0.84–1.18), high-K calc-alkaline, has moderately to weakly fractionated REE trend, higher Fe/(Fe + Mg) ratio, lower Sr content and lower Rb/Zr ratio. The ABS geochemical signature is consistent with formation from volcanic arc rocks and small participation of collisional setting rocks, whereas the SG and SGS have post-collisional tectonic rocks-related geochemical signature. This model is in harmony with a post-collisional extensional regime, started with the 1.90–1.89 Ga Água Branca magmatism, and culminated with the 1.89–1.88 Ga São Gabriel system at an early stage of intracratonic reactivation, which included intrusion of mafic dikes. The Uatumã subdomain was related to mantle underplating with continental uplift and its origin involved contributions of 2.3–2.44 Ga Archean-contaminated Trans-Amazonian, 2.13–2.21 Ga Trans-Amazonian, 1.93–1.94/2.0 Ga Tapajós-Parima. Foliation styles point out that part of the Água Branca granitoids recorded later deformational effects, likely related to the Rio Negro Province formation.  相似文献   

招平断裂带北段北延构造及找矿方向浅析          下载免费PDF全文

钮涛  康恺  张志远 《山东国土资源》2022,38(3):19-26

招远-平度断裂带是胶西北地区三大控矿断裂之一,其北部延伸趋向于破头青断裂带.本文分别从招平断裂带北部的2条主要控矿断裂带向深部延伸的规模,蚀变破碎程度、矿化显示、所控制的矿体数量、主矿体规模、所探获资源量、典型矿床特征等方面进行对比,分析确定九曲蒋家断裂带为招平断裂带北延的主要控矿断裂,预测其深部具有较大的找矿潜力.  相似文献   

裂陷盆地断层的形成和演化——目标砂箱模拟实验与认识   总被引：4，自引：0，他引：4  

童亨茂  孟令箭  蔡东升  吴永平  李绪深  刘明全 《地质学报》2009,83(6):759-774

摘要 断层的分布、活动和演化是裂陷盆地构造研究的核心,也是其油气勘探的关键。大量高精度的三维地震资料表明裂陷盆地内断层分布组合十分复杂,无法用经典构造地质学理论——Anderson模式作出合理的解释, 现有的模式（叠加模式和斜向伸展模式等）也还没有很好地揭示裂陷盆地断层复杂性的实质和断层形成和演化的内在规律。本文以渤海湾盆地张巨河构造带和北部湾盆地涠西南凹陷两个有高精度三维地震资料覆盖、断层分布与组合十分复杂并富含油气的典型裂陷盆地区为原形,进行了目标砂箱模拟实验,再现了目标区构造的基本特征。砂箱实验所揭示裂陷盆地断裂系统的基本特征是：1）基底先存构造（主要所控制的断层构成了盆地断裂系统的基本格架;2）断层的形成与演化决定于基底先存断裂的取向、区域伸展方向及伸展量。首先形成的是有刚性边界基底先存断裂控制的断层。其次,形成的是薄弱带基底先存断裂控制的断层。继而,形成的是小型基底先存断裂控制的断层。最后,在远离基底先存构造的区域,形成与伸展方向垂直的新生断层。3）伸展作用早期,断层的方位主要决定于基底先存断裂的方位。随着伸展量的增大,受伸展方向的影响越来越大,晚期形成的断层常反映区域伸展作用方向。4）不协调递进伸展变形过程是导致裂陷盆地复杂断层体系的根本原因。上述砂箱模拟实验揭示的裂陷盆地在不协调性伸展作用下断层的形成与演化规律可以利用“不协调性准则”从理论上给予解释,表明在裂陷盆地中具有普遍意义。  相似文献   

新疆东部哈尔里克山闪长岩锆石SHRIMP U-Pb定年及其地质意义   总被引：49，自引：0，他引：49  

孙桂华  李锦轶  高立明  杨天南 《地质论评》2005,51(4):463-469

新疆东部哈尔里克山出露大量闪长岩和花岗岩岩体。一般认为,该区晚古生代岩浆活动中,闪长岩形成比较早,花岗岩形成比较晚。对其中一个闪长岩中的锆石进行SHRIMP U-Pb定年,获得了316±3 Ma的206Pb/238U表面年龄。结合岩体及锆石的矿物学特征,该年龄被解释为代表了哈尔里克山晚古生代岩浆初始侵入活动的时间。通过与前人从博格达山和哈尔里克山获得的岩浆活动年代学资料的比较研究,得出的结论是博格达山与哈尔里克山晚古生代岩浆初始侵入活动的时间大体相同,都发生在该区地壳形成演化的后碰撞阶段;由此进一步推论哈尔里克山晚石炭世期间的构造背景与博格达山基本相同,为与康古尔塔格一带洋岩石圈板块向北俯冲有关的板缘伸展环境下的滞后弧后盆地或者是后碰撞伸展环境下的火山沉积盆地。  相似文献   

Evolution, Migration, Controlling Factors and Forming Setting of Mesozoic Basins in Western Shandong     

ZHANG Zhongyi  WU Ganguo  Guo Jinghui  ZHANG Da Key Laboratory of Lithospheric Tectonics  Lithoprobing Technology  Ministry of Education  University of Geosciences  Beijing  E-mail: zy_zhang@sina.com Institute of Geology  Geophysics  Chinese Academy of Sciences  Beijing 《《地质学报》英文版》2005,79(4):519-532

The distinctive topography in western Shandong province consists of several NW-WNW-trending mountain ranges and intervening basins. Basins, in which late-stage sediments to the south have progressively overlapped the earlier sediments and ＂basement＂ rocks of the hanging-wall block, are bounded by S-SW-dipping normal faults to the north. Basin analysis reveals the Jurassic-Cretaceous sedimentary rocks accumulated both within the area of crustal extension and during extensional deformation; they contain a record of a sequence of tectonic events during stretching and can be divided into four tectonic-sequence episodes. These basins were initially developed as early as ca. 200 Ma in the northern part of the study area, extending dominantly N-S from the Early Jurassic until the Late Cretaceous. Although with a brief hiatus due to changes in stress field, to keep uniform N-S extensional polarity in such a long time as 130 Ma requires a relatively stable tectonic controlling factor responsible for the NW- and E-W-extensional basins. The formation of the extensional basins is partly concurrent with regional magmatism, but preceded magmatism by 40 Ma. This precludes a genetic link between local magmatism and extension during the Mesozoic. Based on integrated studies of basins and deformation, we consider that the gravitational collapse of the early overthickened continental crust may be the main tectonic driver for the Mesozoic extensional basins. From the Early Jurassic, dramatic reduction in north-south horizontal compressive stress made the western Shandong deformation belt switch from a state of failure under shortening to one dominated by extension and the belt gravitationally collapsed and horizontally spread to the south until equilibrium was established; synchronously, the normal faults and basins were developed based on the model of simple-shear extensional deformation. This may be relative to the gravitational collapse of the Mesozoic plateau in eastern China.  相似文献   

郯庐断裂带北延及中新生代构造体制转换问题的探讨   总被引：23，自引：0，他引：23  

张庆龙  王良书  解国爱  杜菊民  徐士银  胡旭芝 《高校地质学报》2005,11(4):577-584

郯庐断裂带北段在进入东北地区后主要分为走向北东—北北东的三支断裂,由西向东依次为沈阳—长春—哈尔滨断裂、依兰—伊通断裂和敦化—密山断裂。由于不同时期的大地构造背景和地球动力学的不同,它们在中、新生代的构造体制转换主要表现有如下5个阶段:(1)早、中侏罗世直到早白垩世时以拉张为主,形成一系列断陷盆地或坳陷盆地,并伴有中-酸性岩浆侵入和喷发,形成了独特的火山-湖相沉积盆地;(2)早白垩世末,为北西—南东向的压缩构造应力场,使盆地内的中、上侏罗统地层发生走向近北东的逆冲推覆构造;(3)晚白垩世,为北东向左行剪切构造应力场,区内侏罗系和早白垩世早期的沉积物发生褶皱,与上覆地层呈明显的不整合;(4)古近纪时为北西—南东向拉张构造应力场,日本海从古近纪开始逐渐拉开,直到新近纪完成现在的格局;(5)新近纪时又转换为挤压构造应力场,以北西—南东向挤压为主,使古近系沉积物发生轻微的褶皱。  相似文献   

赣中地区早中生代OIB碱性玄武岩的厘定及构造意义   总被引：50，自引：3，他引：47  

王岳军  廖超林  范蔚茗  彭头平 《地球化学》2004,33(2):109-117

通过40Ar/39Ar年代学、元素、同位素地球化学研究,在赣中地区安塘组上部厘定了早中生代OIB型碱性岩浆作用.研究表明,位于赣中安塘组上部的玄武岩为碱性橄榄玄武岩,形成于168Ma,具有狭窄的元素、同位素变化范围,地壳混染作用不明显,经历了橄榄石和单斜辉石的结晶分异.其LILE和HFSE富集,Nb/La=1.4～1.5,Ce/Pb=21～25,Nb/U=42～45,εNd(t)= 5.22～ 6.58,(87Sr/86Sr)I=0.703 13～0.70336,具有Hawaii-OIB型元素、同位素地球化学特征,是含石榴子石橄榄岩低度部分熔融的产物,其起源与软流圈地幔上涌和岩石圈伸展减薄有关.这为华夏陆块早中生代岩石圈伸展减薄提供了更为直接的证据.  相似文献   

基于PFC2D数值模拟的交替压裂中应力阴影效应研究     

夏磊  曾亚武 《岩土力学》2018,39(11):4269-4277

为了探究应力阴影效应对交替压裂中压裂间距选取的影响,基于优化后的颗粒流离散元流固耦合计算模型,模拟并分析了双初始水力裂缝下因应力阴影效应产生的诱导应力的分布情况,并与理论解析解进行对比,证明了该数值方法的合理性。在此基础上,分析了应力阴影效应在不同各向异性地应力场及初始压裂间距条件下对新水力裂缝的起裂压力及扩展形态的影响,研究结果表明：初始各向异性应力场不改变裂缝周边的应力场,不影响新水力裂缝的起裂压力;随着初始压裂间距的减小,应力阴影效应增强,新水力裂缝的起裂压力逐渐增加。初始水力裂缝间距与初始各向异性应力场共同影响新水力裂缝的扩展形态,随着初始水力裂缝间距或初始水平地应力场差异系数的增大,应力阴影对新水力裂缝的扩展方向的影响逐步减弱;初始水力裂缝对新水力裂缝的扩展有一定的限制作用,在一定程度上不利于形成复杂的裂缝网络。根据以上分析结果,对交替压裂中压裂间距的优化进行了定性的探讨。  相似文献   

西藏南部冈底斯大陆弧早白垩纪弧前伸展作用   总被引：9，自引：8，他引：1  

曾令森  高利娥  郭春丽  侯可军  王倩 《岩石学报》2017,33(8):2377-2394

在现今活动的俯冲带系统中,俯冲板片的后撤或回卷都可能导致弧前伸展作用,但弧前伸展作用是否局限于浅部构造层次,还是涉及整个岩石圈,是理解岛弧构造演化和地球化学效应的重要课题。在西藏冈底斯岩基南缘,保留着世界上典型的弧前盆地——日喀则弧前盆地。在该盆地的北缘,除了发育中新世闪长玢岩脉外,还发育一系列近东西向展布的辉绿岩脉,形成时代为106.6±0.8Ma(锆石U-Pb年龄)。基性岩脉在岩石学、矿物学和地球化学特征上较均一,具体表现为:(1)富集LREE,亏损HREE,但HREE平直;(2)强烈亏损Rb、Ba、Nb和Ta,微弱亏损Ti,但Zr和Hf不具亏损现象;(3)锆石Hf同位素组成(εHf(t)=+11.7~+15.4)较高;和(4)包含捕获的早侏罗世岩浆锆石。上述数据表明:在日喀则弧前盆地形成过程中,伴随着强烈的早白垩纪弧前伸展作用,诱发较亏损地幔发生部分熔融,形成不同于典型岛弧岩浆岩的基性岩,可能是在新特提斯洋北向俯冲过程中,海沟后撤,在弧前形成强烈的地幔角流的结果。同时,日喀则弧前盆地可能构建于早侏罗纪结晶岩系之上。  相似文献   

Discontinuous deformation analysis of super section tunnel surrounding rock stability based on joint distribution simulation     

《Computers and Geotechnics》2017

Based on binocular stereo photography measurement technology, the actual distribution information of joints and fractures in the tunnel face were obtained via image processing and feature extraction, and the preliminary evaluation of surrounding rock stability of Laohushan tunnel was conducted according to surrounding rock classification method. Since all available surrounding rock classification approaches didn’t consider the influences of the size effect of tunnel excavation span and unfavorable geologic bodies such as weak-fracture zones, an improved discontinuous deformation analysis (DDARF) method was adopted to conduct a numerical simulation of the deformation and fracture processes of the surrounding rock. Using the traveling wave method, triangle DDA blocks were automatically generated in the calculation zone, and the block boundaries were divided into real joints and virtual joints. Based on the real joint information obtained via aforementioned photographic measurement, the real joints in the tunnel face were dynamically modified, in order to achieve the simulation of joint distribution. The results revealed that the fracture evolution regularity, deformation failure mechanism, and block dropping phenomenon that the DDARF joint simulation model calculated are in good agreement with actual conditions, while those obtained based on conventional models present differences from field situation. Additionally, focusing on the localised rockfall phenomenon of Laohushan tunnel, the crack extension rate was introduced to conduct a quantitative comparison of the rock crack evolution process with or without anchor supporting. The research results offer practical guidance for field construction and anchorage support scheme optimization.  相似文献