甘肃北山晚古生代花岗岩体内基性岩墙群弧形展布的成因及其构造意义

在甘肃北山一个东西向展布、椭圆状的晚古生代花岗岩体内主要发育着3期岩墙群,其中中期基性岩墙群最密集,呈现出弧形展布的特征,在该侵入体北部呈北北东向趋势,向南逐渐偏转为北北西向。关于中期岩墙群弧形展布的原因有两种可能的解释,即：纵弯褶皱和应力场扰动。野外观察不支持第一种解释,因为在岩墙或围岩内都没有观察到与褶皱有关的变形构造。本文利用Poly3D软件模拟了近东西向隐伏断层活动对上覆应力场的扰动。计算结果表明,当北北西-南南东向的区域性拉张叠加上沿着隐伏断层发生不协调的右行走滑时,水平大主压应力迹线在隐伏断层上方出现类似的弧形展布。这意味着稍早的花岗岩侵入体冷凝冷却并没有完全焊接地壳内一些大尺度断层,地壳断块的相对独立活动可以造成沿着这些断层发生与区域变形场不协调的右行走向滑动,进而形成岩墙群弧形展布所需要的地应力场。     

大巴山弧形构造带中段渔渡地区侏罗纪叠加变形研究

大巴山构造带是秦岭造山带南部发育的一个以逆冲推覆构造为特征的构造带。通过在大巴山弧形构造带中段渔渡地区进行的详细构造解析发现,大巴山构造带在侏罗纪以来经历了至少两期变形叠加,变形地层三叠系嘉陵江组—侏罗系沙溪庙组。早期变形以与滑脱构造相关的轴向北西—北北西向箱状或隔挡状褶皱为主,并在深部发育顺层滑脱构造,变形时代为晚侏罗世到早白垩世。晚期变形与北侧逆冲相关,导致右行走滑变形,主要形成右行走滑断层和北西—北北西向紧闭褶皱,变形时代比第一期稍晚,为晚侏罗世之后到早白垩世。两期变形形成的褶皱延伸方向一致,与区域构造线的方向协调,而且在远离北侧镇巴断裂的地区变形强度有减弱的趋势,两期变形叠加形成共轴或斜交叠加构造。研究表明,变形与大巴山冲断—推覆构造带向南逆冲有关。     

鄂西弧形构造变形特征及成因机制

对川东-湘鄂西断褶带内鄂西地区的弧形构造,从构造剖面特征、叠加褶皱样式和断裂性质入手进行几何学和运动学分析。结果发现鄂西弧形构造具有多期变形特征:早期普遍为北东东向的直线型褶皱,随着弧形带扩展,在东、西两翼分别发育右行和左行的逆冲-走滑断裂,同时分别形成北北东向和北西西向的弧形褶皱。晚期弧形带中部发育北北东向构造并叠加改造了早期北东东和北西西向褶皱,同时在黄陵背斜以西还发育交切早期构造的北北西向仙女山右行走滑断裂。根据弧形带扩展的几何学-运动学分类原则,并结合前人的古地磁研究结果,推测鄂西弧形构造应属于构造弯曲形成的弯曲弧。区域滑脱层和黄陵隆起阻挡可能是控制弧形样式的主要原因。区域滑脱层控制了拆离滑脱褶皱的构造样式; 黄陵基底隆起的阻挡作用使弧形带东翼进一步弯曲变形,并导致了构造应力场方向发生改变,造成了晚期北北东向与早期北东东向构造的叠加。由此恢复的鄂西弧形构造变形过程对于揭示川东-湘鄂西断褶带构造演化具有重要的指示意义。     

香港中生代火山作用的构造背景和构造控制

香港中侏罗－早白垩酸性火山岩和花岗岩类侵入体,是展布于中国东南部的ＮＥ向燕山构造浆带的一部分,香港火山碎屑沉积充填线状排列的喇叭形火山口和椭圆形破火山口,岩浆是通过裂隙充填到复杂的断裂和剪切带中,形成岩墙杂岩体和花岗岩类侵入体,岩墙显示了破火山口的边界,火山口,破火山口,岩墙和侵入体的空间分布和几何形态,受到４期火山活动和侵入活动期间的构造所控制,ＥＷ向和ＮＥＥ向的拉伸和转换拉张作用主导,随时间的     

塔里木盆地西南缘构造样式及其主导因素

塔里木盆地西南缘是西昆仑山前北北西—近东西向的构造变形带.具有南北3带、东西3段、上下3层的展布特点.各带、段和层以基底卷入的冲断构造和盖层滑脱的断层相关褶皱为主,包括:破冲褶皱、断层扩展褶皱、断层滑脱褶皱和断层弯曲褶皱等.通过识别地震剖面上不整合面和同构造沉积现象,认为构造变形时间在上新世—第四纪;第一排背斜带形成于...     

东帕米尔变质核杂岩构造的厘定

卡拉库鲁木变质核杂岩是慕土塔格岩体的南缘部分，由长城系片麻岩以及燕山期花岗岩组成，其中长城系片麻岩为一套低角闪岩相的变质侵入岩，主要岩性为（石榴石）黑云二长片麻岩、（石榴石）黑云斜长片麻岩；根据变形程度，将其划分为内带、中带及外带，其中在内带见有燕山期花岗岩。剥离断层沿变质核杂岩边缘呈向南凸出的弧形展布。剥离断层上盘滑脱体由长城系赛图拉岩群高绿片岩－低角闪岩相的变质岩系构成。变质核杂岩构造的形成时代为早－中侏罗世。     

滇西腾冲—梁河地区花岗岩的年代学、地球化学及其构造意义

滇西腾冲-梁河地区位于喜马拉雅东构造结的东侧,区域内广泛分布的中、新生代花岗岩（简称腾梁花岗岩）由古永岩群、宾榔江岩群的若干个花岗岩体组成,以岩基、岩株、岩墙状态产出。花岗岩呈现带状沿着一系列北北东向弧形断裂平行分布,展示明显的同构造剪切被动侵位和岩墙扩展侵位特征。岩浆锆石SHRIMP U-Pb定年结果显示,东侧的古永岩群花岗岩结晶年龄为白垩世晚期（76~68Ma）;而西侧的槟榔江岩群花岗岩结晶年龄为稍晚的始新世（53Ma）。腾梁花岗岩主要为中、粗粒黑云母二长花岗岩、黑云母条纹长石花岗岩、伟晶花岗岩,缺少典型的富铝矿物。地球化学特征表明腾梁花岗岩是起源于中下地壳的过铝-强过铝高钾钙碱性花岗岩,源岩是富含泥质的硬砂岩,并具有岛弧-后碰撞花岗岩特征。由于喜马拉雅新特提斯封闭及印度陆块与亚洲陆块的陆陆碰撞发生于65Ma, 进一步推测腾梁花岗岩是新特提斯封闭到陆陆碰撞造成陆壳增厚所引起的中下地壳部分熔融的产物。腾梁花岗岩是冈底斯的东延部分,但在形成机制上,与冈底斯花岗岩具有明显的差别。     

关于彭山高挥发份花岗岩底辟穹窿构造及其控矿作用

江西省德安县彭山锡矿田,是一个典型的高挥发份花岗岩底辟穹窿构造。穹窿面积约180km~2,构成穹窿的地层为晚元古代震旦纪及早古生代地层。穹窿核部有一中生代高挥发份花岗岩隐伏岩体,围岩中有大量极其发育的圆弧形层间重力滑动断层及滑裂岩带,并伴有大量以隐伏花岗岩体为中心的放射状裂隙及断层。些种隐伏的高挥发份花岗岩侵入体,具有强大的底辟上升刺穿能力,并伴有极其丰富的气液成矿热流体,有关的内生热液矿床,严格受层间重力滑动断层及滑裂岩带控制。     

河北东北部兴隆煤田区逆冲构造的特征及其区域构造意义

兴隆煤田及邻区的逆冲构造系基底卷入变形的厚皮逆冲构造,并具有典型的断坪-断坡式几何学结构.断层上盘逆冲方向指向NNW,沿着主干逆冲断层发生的倾向位移量约为13.1 km,逆冲断层及相关褶皱变形所造成的局部表层地壳缩短率约32.3%.对兴隆逆冲构造的几何学结构、运动学性质及其地层效应的分析表明,在申家胡同到黄土梁近东西向一线以南的区域,寻找到因逆冲断层作用导致的隐伏煤田的可能性是极小的.主干逆冲断层上、下盘地层大面积陡立乃至倒转的特征,更容易用断展褶皱,尤其是三角形剪切断展褶皱模型做出合理解释.该逆冲构造主要逆冲断层的上、下盘盖层岩系不整合于基底结晶变质岩系之上,地层序列发育完整而且可以一一对应,不存在沿着相对软弱层发育的大规模逆冲断层之断坪,因此,将该逆冲构造作为区域上承德逆冲构造的根带是不合适的.     

上扬子北部褶皱带的构造应力场演化规律

在对大量逆冲与平移断层运动学详细分析与观测的基础上,本文利用实测断层擦痕矢量数据组进行了区域应力场反演,根据对断层叠加关系的分析及叠加褶皱的验证,划分出上扬子北部经历过3期挤压构造应力场演化,从早到晚分别为:第1期北西—南东向挤压应力场,第2期近东西向挤压应力场和第3期北东—南西向挤压应力场。结合相关的地质现象,认为在这3期挤压应力场作用下分别形成了晚侏罗世末—早白垩世初的湘鄂西隔槽式褶皱带、早白垩世末—晚白垩世初的川东隔档式褶皱带和南大巴山弧形褶皱带。由此表明,上扬子北部褶皱带的形成顺序为湘鄂西隔槽式褶皱带→川东隔档式褶皱带→南大巴山弧形褶皱带。     

Late Paleoproterozoic basic dikes in the Ulkan-Uchur district, eastern Aldan-Stanovoi Shield: Structural position, composition, and paleogeodynamic setting

Late Paleoproterozoic dikes of the Maimakan Complex were studied in the Ulkan-Uchur district at the eastern margin of the Aldan-Stanovoi Shield. The dikes are parallel or arranged en echelon in the Uchur-Uyan, South Uchur, and Ukikan fields of dike swarms. The spatial distribution of the dike swarms pertaining to the Maimakan Complex in the Ulkan Trough and its framework shows that the area of their intersection is located in the center of the Ulkan granitoid batholith. The basic dikes, which are distinguished by elevated contents of alkali metals, Fe, Ti, and P in combination with a low Mg content, are defined as moderately alkaline rocks transitional from tholeiitic to alkaline series similar in composition to within-plate basalts and E-MORB. The REE pattern is comparable to that of tholeiitic and subalkaline series in extensional settings. Along with the geological data, this indicates that the complex was formed under conditions of intracontinental extension. As follows from geological relationships, the age of dikes is estimated as 1670–1715 Ma.     

Neotectonics of the Eastern Margin of the Tibetan Plateau: New Geological Evidence for the Change from Early Pleistocene Transpression to Late Pleistocene-Holocene Strike-slip Faulting

We present in this paper some new evidence for the change during the Quaternary in kinematics of faults cutting the eastern margin of the Tibetan Plateau. It shows that significant shortening deformation occurred during the Early Pleistocene, evidenced by eastward thrusting of Mesozoic carbonates on the Pliocene lacustrine deposits along the Minjiang upstream fault zone and by development of the transpressional ridges of basement rocks along the Anninghe river valley. The Middle Pleistocene seems to be a relaxant stage with local development of the intra-mountain basins particularly prominent along the Minjiang Upstream and along the southern segment of the Anninghe River Valley. This relaxation may have been duo to a local collapse of the thickened crust attained during the late Neogene to early Pleistocene across this marginal zone. Fault kinematics has been changed since the late Pleistocene, and was predominated by reverse sinistral strike-slip along the Minshan Uplift, reverse dextral strike-slip on the Longmenshan fault zone and pure sinistral strike-slip on the Anninghe fault. This change in fault kinematics during the Quaternary allows a better understanding of the mechanism by which the marginal ranges of the plateau has been built through episodic activities.     

Deformed dike swarms as an implication of transpression deformation in Western Arabian shield,Wadi Fatima,Saudi Arabia

Utilization of satellite images and field observations of dike swarms in pre-Fatima basement show that these dikes are older than the overlaying Fatima Formation. Dikes digitization and orientation analysis on satellite images show that the prevailing trend of the dikes is ENE-WSW. The granitic rocks of pre-Fatima basement and its hosted dikes expose evidences of completely a different deformation regime from the overlaying Fatima Formation. These evidences include shearing, dextral shear indicators, isoclinal folds, deflection and rotation of crystals, mineral elongation, and mylonitic and gneissose textures. Strain analysis results of using Fry method on quartz and feldspar grains support the presence of deformation in these ENE-WSW dikes. These results gave a strain ratio of 2.1:1.3:1, which suggest an amount of 40% stretching in the ENE-WSW direction parallel to the dike walls, and an amount of 30% shortening in the NNW-SSE direction. Mesoscopic and microscopic scale structures confirm the existence of dextral ductile-brittle shearing followed the emplacement of the dikes and before the pure shear deformation that caused the thrusting and folding of Fatima Formation. This ductile-brittle deformation is correlated with the dextral transpression that formed the Fatima Shear Zone (FSZ).     

Spatiotemporal relationships of dike magmatism in the Kola region, the Fennoscandian Shield

A brief geological and petrographic characterization of the Early Precambrian dike complexes of the Kola region is given along with data on new estimates of dike age and analysis of their distribution over the entire Fennoscandian Shield. The emplacement of dikes in the Archean core of the shield continued after consolidation of the sialic crust 2.74?C1.76 Ga ago. After the Svecofennian Orogeny, dikes continued to form in the west in the area of newly formed crust, while the amagmatic period began in the Archean domain. The intense formation of dikes in the Svecofennian domain lasted approximately for 1 Ga (1.8?C0.84 Ga). The younger igneous rocks in the crustal domains of different age are less abundant and localized at their margins. A similar distribution of dikes is characteristic of other shields in different continents. This implies that the formation of the sialic crust in the shields is not completed by its consolidation and formation of the craton. For 1 Ga after completion of this process, the crust is underplated by mantle-derived magmas. This process is reflected at the Earth??s surface in the development of mantle-derived mafic and anorogenic granitoid magmatism. The process of crust formation is ended as the subcratonic lithosphere cools and the amagmatic period of the craton history is started. Beginning from this moment, the manifestations of cratonic magmatism were related either to the superposed tectonomagmatic reactivation of the cold craton under the effect of crust formation in the adjacent mobile belts or to the ascent of mantle plumes.     

Fault tectonics of the Baja California Peninsula and the opening of the Sea of Cortez,Mexico

A detailed field analysis of Neogene and Quaternary faults in Baja California has enabled us to reconstruct the stress pattern and the tectonic evolution of the central and southern parts of the peninsula. The deformation, which is related to the opening of the gulf, affects the whole peninsula, but decreases from east to west. Most observed faults, normal and/or dextral, strike NNW-SSE to WNW-ESE; their mechanisms include both strike-slip and dip-slip, as well as intermediate motions. Compressional events have occurred since Late Neogene times, but were probably of minor quantitative importance because reverse faults are rare and small.The principal fault pattern includes dextral NNW-SSE Riedel shears and N-S tension faults induced by dextral strike-slip along two main NW-SE fault zones bordering the peninsula: the Gulf of California to the east, which is the most important, and the Tosco-Abreojos fault to the west. The resulting pattern of deformation shows that the eastern part has been a complex transform-extensional zone since Late Miocene-Early Pliocene times.     

Successive Extensional Tectonic Regimes during the Mesozoic as Evidenced by Neptunian Dikes in the Pontide Magmatic Arc,Northeast Turkey

The eastern Pontide magmatic arc extends ～600 km in an E-W direction along the Black Sea coast and was disrupted by a series of fault systems trending NE-SW, NW-SE, E-W, and N-S. These fault systems are responsible for the formation of diachronous extensional basins, rift or pull-apart, in the northern, southern, and axial zones of the eastern Pontides during the Mesozoic. Successive extensional or transtensional tectonic regimes caused the abortive Liassic rift basins and the Albian and Campanian pull-apart basins with deep-spreading troughs in the southern and axial zones. Liassic, Albian, and Campanian neptunian dikes, which indicate extensional tectonic regimes, crop out within the Paleozoic granites near Kale, Gumushane, and the Malm–Lower Cretaceous platform carbonates in Amasya and Gumushane. These neptunian dikes correspond to extensional cracks that are filled and overlain by the fossiliferous red pelagic limestones. Multidirectional Liassic neptunian dikes are consistent with the general trend of the paleofaults (NE-SW, NW-SE, and E-W), and active dextral North Anatolian fault (NAF) and sinistral Northeast Anatolian fault (NEAF) systems. The Albian neptunian dikes in Amasya formed in the synthetic oblique left-lateral normal faults of the main fault zone that runs parallel to the active North Anatolian fault zone (NAFZ).

Kinematic interpretation of the Liassic and Albian neptunian dikes suggests N-S extensional stress or northward movement of the Pontides along the conjugate fracture zones parallel to the NAFZ and NEAFZ. This northward movement of the Pontides in Liassic and Albian times requires left-lateral and right-lateral slips along the conjugate NAFZ and Northeast Anatolian fault zones (NEAFZ), respectively, in contrast to the recent active tectonics that have been accommodated by N-S compressional stress. On the other hand, mutual relationships between the neptunian dikes and the associated main fault zone of Campanian age extending in an E-W direction in the Kale area, Gumushane suggest the existence of a main left-lateral transtensional wrench zone. This system might be accommodated by the counterclockwise convergence of the Turkish plate with the Afro-Arabian plate relative to the Eurasian plate, and the southward oblique subduction of Paleotethys beneath the eastern Pontide magmatic arc during the Mesozoic.     

Andesite–Basaltic Dike Magmatism in the Paleoproterozoic Rift System of the Kola Craton,Baltic Shield

New structural and petrogeochemical data are obtained on poorly known dikes composed of quartz dolerites of andesite–basaltic composition and located at the northwestern termination of the Murmansk block (Kola Craton). These data allowed us to compare the studied dikes with more well-known units from the dike swarm in the area of the settlement of Liinakhamari and the volcanics of the Pechenga structure, and to discuss their joint geodynamic position. Dolerite dikes are 2.3 Ga in age and intrude granites and plagiogranites of 2.4 and 2.8 Ga in age, respectively. The specificity of the composition of the rocks of andesite–basaltic composition from the dike series, as well as that of the volcanics from the first (Akhmalakhti) formation of the Pechenga structure, is determined by their structural position in the marginal part of the “fading” Sumian plume and in the zone of dynamic influence of regional strike–slip fault zones.     

论河北省兴隆一带东西向走滑断裂系统

河北省兴隆县一带地处燕山造山带的中段，是中生代构造变形的典型地区。该区广泛发育了东西向和北东向联合构造，东西向主走滑断裂呈右行右阶式（Ｐ断裂），北东向次级构造由北盘的雁列式褶皱、分枝断裂及南盘次级断裂等组成。燕山台褶带变形是由尚义─平泉断裂和密云─洪山口断裂在侏罗纪时发生右行走滑形成的，其间的剪切变形带，总体特征类似于一个大型Ｓ─Ｃ构造或平面对冲构造。区内古基底断裂不仅控制中晚元古代的沉积地层和岩浆活动，而且对中生代的构造变形方式也产生重要作用。主走滑断裂与古基底断裂的复活有直接的关系     

Cenozoic tectonic evolution of the central Wassuk Range,western Nevada,USA

The central Wassuk Range is ideally located to investigate the interplay of Basin and Range extension and Walker Lane dextral deformation along the western Nevada margin of the Basin and Range province. To elucidate the Cenozoic evolution of the range, the author conducted geologic mapping, structural data collection and analysis, geochemical analysis of igneous lithologies, and geochronology. This research delineates a three-stage deformational history for the range. A pulse of ENE–WSW-directed extension at high strain rates (～8.7 mm/yr) was initiated immediately after the eruption of ～15 Ma andesite flows; strain was accommodated by high-angle, closely spaced (1–2 km), east-dipping normal faults which rotated and remained active to low angles as extension continued. A post-12 Ma period of extension at low strain rates produced a second generation of normal faults and two prominent dextral strike–slip faults which strike NW, subparallel to the dextral faults of the Walker Lane at this latitude. A new pulse of ongoing extension began at ～4 Ma and has been accomodated primarily by the east-dipping range-bounding normal fault system. The increase in the rate of fault displacement has resulted in impressive topographic relief on the east flank of the range, and kinematic indicators support a shift in extension direction from ENE–WSW during the highest rates of Miocene extension to WNW–ESE today. The total extension accommodated across the central Wassuk Range since the middle Miocene is >200%, with only a brief period of dextral fault activity during the late Miocene. Data presented here suggest a local geologic evolution intimately connected to regional tectonics, from intra-arc extension in the middle Miocene, to late Miocene dextral deformation associated with the northward growth of the San Andreas Fault, to a Pliocene pulse of extension and magmatism likely influenced by both the northward passage of the Mendocino triple junction and possible delamination of the southern Sierra Nevada crustal root.