华北克拉通中元古代基性岩墙群形成机制及构造应力场

本文通过研究华北克拉通中部中元古代基性岩墙群的单体形态和分布规律,分析岩墙群形成的力学机制,认为这些基性岩墙群主要是基性岩浆侵位于先存的张性或张剪性破裂中而成。晋北地区和五台－太行山地区的岩墙群主要为张剪性的,吕梁山地区和中条山地区的主要为张性。根据岩墙群的分布规律、侵位方向和力学机制及其与燕辽－中条拗拉槽系之间的关系,认为华北克拉通中部中元古代的区域构造应力场是张性和张剪性构造环境,其主压应力来     

Dike swarms and related igneous complexes in the Urals

The dike swarms of the entire Urals are classified for the first time; the related igneous complexes associated with them in space and time are named. The following types and chronological levels of the Uralian dikes are distinguished (proper names are given after type localities). The epicontinental type comprises the Middle Riphean Mashak, Late Riphean Arsha-Serebryanka, Late Cambrian-Early Ordovician Kidryasovo-Lemva, Ordovician-Silurian Ushat, Devoninan Inzer-Timaiz (the most extended of all), Early Carboniferous Magnitogorsk-Mugodzhary, and Triassic Borisovo dike swarms. Many of them are probably related to plume events. The existence of the Early Riphean dike complex remains unclear. Oceanic (spreading or suprasubduction) dike-in-dike type: Ordovician Man’ya oceanic type, Devonian Aktogai backarc and Khabarny suprasubduction types. The igneous complexes associated with dike swarms are rather diverse. In addition to rhyolite dikes, in many cases determining the contrasting character of magmatism, large comagmatic gabbro and gabbro-granite intrusions are noted, as well as minor intrusions of subalkali granitoids, syenites, and, apparently, carbonatites and kimberlites. Flood basalt fields are noted at the periphery of the Urals, implying the occurrence of a feeding dike swarm beneath them.     

Identification of Five Stages of Dike Swarms in the Shanxi-Hebei-Inner Mongolia Border Area and Its Tectonic Implications

Dike swarms are generally ascribed to intrusion of mantle-source magma result from extension. Basic dike swarms around the Shanxi-Hebei-Inner Mogolia borders in the northern peripheral area of the North China Craton can be divided into five age groups according to isotopic dating: 1800-1700 Ma, 800-700 Ma, 230 Ma, 140-120 Ma, and 50-40 Ma. Geological, petrological and isotope geochemical features of the five groups is investigated in order to explore the variation of the mantle material composition in the concerned area with time. And the various extensional activities reflected by the five groups of dike swarms are compared with some important tectonic events within the North China Craton as well as around the world during the same period.     

北大巴基性岩墙群地球化学特征、LA-ICP-MS锆石U-Pb定年及其大地构造意义

北大巴地区广泛分布了呈北西-南东向产出的基性岩墙群,主要侵位于下古生界。对该套岩系的地球化学分析表明,w（K2O＋Na2O）、w（TiO2）高,总稀土元素质量分数高并呈轻稀土元素富集型,大离子亲石元素明显富集,Ta、Nb的质量分数远高于洋中脊玄武岩,具大陆裂谷玄武岩的地球化学特征。采用LA-ICP-MS法对北大巴基性岩墙中的岩浆锆石进行了U—Pb同位素定年,获得岩体结晶年龄为（431．0＋3．2）Ma。地球化学及年代学数据表明,北大巴基性岩墙群具有大陆裂谷玄武岩的地球化学特征,表明北大巴早古生代伸展构造受到扬子板块北缘的幔源裂谷作用制约。在裂谷演化过程中,上地幔物质上涌造成岩石圈板块拉伸减薄,使北大巴地区中上地壳发生强烈构造伸展并形成大面积呈线状分布的基性岩墙群,并且该处（431．0±3．2）Ma的年龄值代表了在早志留世北大巴裂谷盆地的伸展裂陷幅度达到最大。     

青海西金乌兰湖地区移山湖晚泥盆世辉绿岩墙群——西金乌兰洋初始裂解的重要证据

在青海西金乌兰湖地区移山湖和倒流沟一带发现的辉绿岩墙,侵入于泥盆系拉竹龙组变质石英砂岩、长石石英砂岩和元古宇宁多群灰白色白云母石英片岩、黑云母石英片岩中,岩石类型为辉绿岩、辉长辉绿岩,结合同位素测年及古生物证据分析其地质时代为晚泥盆世,可能与古特提斯北部河卡山东段克觉杂尔根基性岩墙群一样,反映了可可西里地区壳幔演变过程,是古陆块裂解、西金乌兰洋初始形成的证据。     

Mineralogy, geochemistry, and origin of felsic dike swarms in Aqaba complex (Wadi Al-Yutum), South Jordan

The present work deals with the geologic setting and mineralogical and geochemical study of Late Precambrian magmatic rocks especially the felsic dike swarms of northeast Aqaba complex in South Jordan. The northeast Aqaba complex represents one of the most significant regions in the South Jordan basement. The basement rocks in the studied region are composed of schists, gneisses, migmatites, met gabbros, diorite, and granite. It is invaded by post-orogenic dike swarms. The post-orogenic dike swarms have been recognized as felsic dikes of dacite, rhyodacite, and rhyolite composition. They are composed of plagioclase, K-feldspar, quartz, biotite, and hornblenble with a porphyritic texture. Chemically, they are enriched in compatible elements especially in the large ion lithophile elements such as K, Rb, and Ba. The values of A/NK are more than A/CNK, indicating that dacitic dike swarms have metaluminous nature. Meanwhile, the values of A/NK are less than A/CNK in rhyodacitic and rhyolitic dike swarms of prealuminous nature. This felsic dike can be related to an intercontinental setting that was accompanied by a chemical evolution of the extensional movements and is formed by partial melting of crustal rocks, which are already known from other areas in the northeast portion of the Arabian-Nubian Shield.     

新疆哈密南部北山地区基性岩墙群的地质特征及形成构造环境

新疆北山地区广泛发育一系列相互平行的基性岩(墙)脉群,总体呈北北西—北北东向展布,与区域构造线(北东东向)大角度相交,岩石类型主要为辉绿岩、辉绿玢岩,岩石地球化学特征与库鲁克塔格地区的基性岩墙群相似。基性岩(墙)脉群的形成与北山地区二叠纪裂谷作用有关,可能是地幔柱上涌、“三连点式”破裂之后,在废弃的石炭纪裂谷或裂谷陆缘上侵位的产物。     

LA-ICP-MS U-Pb Zircon Geochronology of Basic Dikes within Maxianshan Rock Group in the Central Qilian Orogenic Belt and Its Tectonic Implications

A large number of basic dikes, which indicate an important tectonic-magmatic event in the eastern part of the Central Qilian (祁连) orogenic belt, were found from Maxianshan (马衔山) rock group, Yongjing (永靖) county, Gansu (甘肃) Province, China. According to the research on the char- acteristics of geology and petrology, the basic dike swarms, widely intruded in Maxianshan rock group, are divided into two phases by the authors. U-Pb isotope of zircons from the basic dikes above two phases is separately determined by LA-ICP-MS in the Key Laboratory of Continental Dynamics of Northwest University, China and the causes of formation of the zircons are studied using CL images. The formation age of the earlier phase of metagabbro dikes is (441.1±1.4) Ma (corresponding to the early stage of Early Silurian), and the age of the main metamorphic period is (414.3±1.2) Ma (corre- sponding to the early stage of Early Devonian). The formation age of the later phase of diabase dike swarms is (434±1.0) Ma (corresponding to the late stage of Early Silurian). The cap- tured-zircons from diabase dike swarms saved some information of material interfusion by Maxianshan rock group(207Pb/206Pb apparent ages are (2 325±3)–(2 573 ±6) Ma), and some zircons from diabase dike swarms also saved impacted information by tec- tonic thermal event during the late period of Caledonian movement (206Pb/238U apparent ages are (400±2)–(429±2) Ma). By combining the results of the related studies, the basic dikeswithin Maxianshan rock group were considered to be formed in the transfer period, from subductional orogeny towards collisional orogeny, which represents geological records of NW-SE extension during regional NE-SW towards intense compression in the Central Qilian block.     

造山后脉岩组合与内生成矿作用

造山带大规模花岗质岩浆活动之后往往有一期区域性脉岩产出,被称为岩基后岩墙群。这类脉岩具有近同时形成、宽成分谱系和小体积的特点。根据太行山、燕山、东昆仑山、天山等造山带的观察,这类脉岩可以划分成煌斑岩质、玄武质、闪长质(安山质)、花岗闪长质(英安质)和花岗质(流纹质)等5组。前人大多偏重于研究其中基性部分,因而常常将其与大陆裂解相关基性岩墙群混为一谈。岩石地球化学分析表明,虽然同组脉岩不同样品之间可能存在演化关系,不同脉岩组之间很难相互演化。结合近年来有关岩浆过程速率的研究成果,推测这些脉岩是原生或近原生岩浆固结的产物。这意味着区域地温曲线在不同深度同时穿过所有相应原岩的固相线。基于岩浆起源热体制和区域岩石圈岩石学结构分析,笔者曾经指出,这样的岩浆产生条件要求造山带岩石圈拆沉作用。因此,这类岩墙群的形成是区域构造应力场由挤压向伸展转换阶段的产物,可以用来标定造山过程的结束,因而称其为造山后脉岩组合。进一步对比分析表明,这类脉岩组合分布非常普遍,是地球上业已发现的三类区域性岩墙群之一。尽管如此,基于热传递速率的分析,造山后脉岩组合的形成还应当伴随大规模流体活动。由于深部流体中成矿元素的浓度强烈依赖于压力,新的岩石成因模型意味着造山后脉岩组合与成矿作用相伴生。野外检验表明,可以基于露头观察识别成矿流体的通道和成矿元素大规模堆积的场所。因此,造山后脉岩组合不仅可以用来标定区域造山过程结束的时间,也是区域找矿预测的有效标志。     

日喀则蛇绿岩研究中的几个问题

日喀则蛇绿岩是中国最著名的蛇绿岩,但是,许多问题存在争论,许多现象没有搞清楚。文中讨论了日喀则蛇绿岩中一些重要的现象以及对目前发现的许多矛盾如何考虑的问题。例如,(1)日喀则蛇绿岩中是否存在席状岩墙群?是否存在席状岩床群?本文认为,席状岩墙群应当是存在的,因为有不对称冷凝边出现。而席状岩床群可能是有问题的,岩床作为侵入体可以出现在许多地方,但是,蛇绿岩中不可能出现席状岩床群,尤其还把它作为蛇绿岩岩石组合的一个单元。笔者认为,所谓的席状岩床群可能是席状岩流群,它不是一个独立的单元,是玄武岩单元下部的成员。(2)日喀则蛇绿岩是否统统是蛇绿岩是一个需要考虑的问题,雅鲁藏布江东西两段出现的岩石组合及其产出背景与日喀则地区的蛇绿岩明显不同,其中有些可能未必是蛇绿岩。(3)自1972年彭罗斯会议以来,蛇绿岩研究发展到现在,可能已经进入了一个关键时期。文中回顾了蛇绿岩的定义及其构造意义,指出1972年彭罗斯会议关于蛇绿岩的定义仍然是适用的。蛇绿岩可以概括为洋壳+地幔,这个洋壳来自板块扩张脊,是年轻的;这个地幔是大洋岩石圈地幔,也可能保留有古老岩石圈地幔的印记。蛇绿岩产于板块扩张脊,这是蛇绿岩构造含义的唯一解,蛇绿岩不存在多解性。(4)日喀则蛇绿岩的许多基本观点主要是法国学者提出来的,如关于岩床群的见解,慢速扩张的见解等。但是,上述见解是否都是对的是需要思考的。日喀则蛇绿岩具有得天独厚的条件,我们应当很好利用这个条件,努力把我们的研究做好,为全球蛇绿岩研究贡献我们的一份力量。     

中祁连马衔山岩群内基性岩墙群锆石LA-ICP-MS U-Pb年代学及其构造意义

马衔山岩群变质基底岩系中发现大量基性岩墙, 作为中祁连造山带东部一次重要的构造-岩浆事件的标志.根据地质-岩石学特征, 将马衔山岩群中的基性岩墙分为两期.利用LA-ICP-MS(激光剥蚀等离子体质谱)方法, 分别对两期基性岩墙进行单颗粒锆石微区U-Pb同位素测定, 并应用CL图像对所测锆石进行了成因研究.获得早期变辉长岩墙的侵入年龄为(441.1± 1.4)Ma(早志留世早期), 主变质期年龄为(414.3± 1.2)Ma(早泥盆世早期); 晚期辉绿(玢)岩墙群的侵入年龄为(434± 1.0)Ma(早志留世晚期), 并保留有曾遭受马衔山岩群混染的信息(捕获锆石的207Pb/206Pb表面年龄为(2 325± 3)Ma~(2 573± 6)Ma), 以及遭受了加里东晚期构造-热事件的改造的信息(206Pb/238U表面年龄为(400± 2)Ma~ (429± 2)Ma).结合相关研究成果, 认为马衔山岩群中的两期基性岩墙群形成于祁连地区由俯冲造山向碰撞造山的转换时期, 代表了中祁连地块在区域上遭受北东-南西向强烈挤压的过程中派生北西-南东向扩张作用的地质纪录.      

Assessment of Discharge through a Dike Breach and Simulation of Flood Wave Propagation

This paper presents a simple and fast method to calculate flow through a dike breach. The approach was based on two-dimensional numerical simulations of idealized dike breakages at straight river-sections. As a result, computation of discharge through a breach can be achieved by use of the new developed formula (denoted as dike break formula). Furthermore, a methodology that combines one-dimensional hydrodynamic modelling, the dike break formula and a simple GIS-based method to estimate inundation areas is described. This fast and easy-to-handle tool can be utilized for near real-time forecasting or evacuation decisions. Detailed predictions were made for a number of flood and dike break scenarios at the River Rhine to prove the accuracy of the new method compared with two-dimensional numerical models.     

Dealing with Uncertainty in Flood Risk Assessment of Dike Rings in the Netherlands

Current flood protection policies in the Netherlands are based on design water levels. This concept does not allow for a proper evaluation of costs and benefits of flood protection. Hence, research is being carried out on the introduction of a flood risk approach, which looks into both the probability of flooding and the consequences of flooding. This research is being carried out within the framework of a major project called the Floris project (FLOod RISk in the Netherlands). To assess the probability of flooding the Floris project distinguishes different failure modes for dikes and structures within the dike ring. Based on a probabilistic analysis of both loads and resistance the probability of failure is determined for each failure mode. Subsequently the probabilities of failure for different failure modes and dike sections are integrated into an estimate of the probability of flooding of the dike ring as a whole. In addition the Floris project looks into the different consequences of flooding, specifically the economic damages and the number of casualties to be expected in case of flooding of a particular dike ring. The paper describes the approach in the Floris project to assess the flood risk of dike rings in the Netherlands. One of the characteristics of the Floris project is the explicit attention to different types of uncertainties in assessing the probability of flooding. The paper discusses the different starting-points adopted and presents an outline on how the Floris project will deal with uncertainties in the analysis of weak spots in a dike ring as well as in the cost benefit analysis of flood alleviation measures.     

The genetic relationship between mafic dike swarms and plutonic reservoirs in the mesozoic of central chile (30°–33°45′S): insights from AMS and geochemistry

Five mafic dike swarms between 30° and 33°45′S were studied for their geochemical signature and kinematics of magma flow directions by means of AMS data. In the Coastal Range of central Chile (33°−33°45′S), Middle Jurassic dike swarms (Concón and Cartagena dike swarms, CMDS and CrMDS, respectively) and an Early Cretaceous dike swarm (El Tabo Dike Swarm, ETDS) display the presence of dikes of geochemically enriched (high-Ti) and depleted (low-Ti) basaltic composition. These dikes show geochemical patterns that are different from the composition of mafic enclaves of the Middle Jurassic Papudo-Quintero Complex, and this suggests that the dikes were injected from reservoirs not related to the plutonic complex. The mantle source appears to be a depleted mantle for Jurassic dikes and a heterogeneous-enriched lithospheric mantle for Cretaceous dikes. In the ETDS, vertical and gently plunging magma flow vectors were estimated for enriched and depleted dikes, respectively, which suggest, together with variations in dike thickness, that reservoirs were located at different depths for each dike family. In the Elqui Dike Swarm (EDS) and Limarí Mafic Dike Swarm (LMDS), geochemical patterns are similar to those of the mafic enclaves of the Middle Jurassic plutons. In the LMDS, east to west magma flow vectors are coherent with injection from neighbouring pluton located to the east. In the EDS, some dikes show geochemical and magma flow patterns supporting the same hypothesis. Accordingly, dikes do not necessarily come from deep reservoir; they may propagate in the upper crust from coeval shallow pluton chamber. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

北京南口中生代双峰式岩墙群的组成及其特征

在北京南口地区发现了一套NNW走向、颇具规模的、由基性钾玄岩和酸性花岗质岩石组成的双峰式岩墙群，其K－Ar同位素年龄为119-114Ma。本文重点讨论了岩墙群的野外地质特征及其岩石学特征。研究表明酸性岩墙和基性岩墙的稀土配分模式非常接近，并且无明显的铕异常，推测它们的岩浆来自两个有成因联系的岩浆源，而且两套岩浆之间不存在的结晶分异作用的关系，我们称之为双峰式岩墙群。研究还表明，两种岩浆最初占位时共呈液相，彼此接触部位成分发生一定程度的混染作用，但总体是互相独立的，岩墙产状和地球化学特征反映岩墙群是在伸展构造背景下侵位的,具有深源浅侵位的特征，反映了晚中生代研究区存在的伸展构造这对于全面认识华北“燕山运动”是有价值的。     

The nature of the heat source of mafic magmatism during the formation of the Vilyui rift based on the ages of dike swarms and results of numerical modeling

Possible mechanisms of rifting and the thermal regime of the lithosphere beneath the rift zone of the Vilyui sedimentary basin are considered based on the available isotopic ages of dike swarms, rates of sedimentation, and results of numerical modeling. Temporal correlations between the intrusion of mafic magma and a sharp increase in the rate of subsidence and sedimentation in the rift basin prove the contribution of both plate-tectonic and magmatic factors to the formation of the Vilyui rift. The results show a relationship between the rapid extension of the lithosphere and the formation of mafic dike swarms in the Yakutsk-Vilyui Large Igneous Province of the Siberian Platform at the Frasnian-Famennian boundary, with a peak at ~ 374.1 Ma, and at the end of the Late Devonian, with a peak at ~ 363.4 Ma. There were two pulses of dike formation during rapid subsidence of the basin basement in the period 380-360 Ma, with a sedimentation rate of 100-130 m/Myr, at a background rate of 10-20 m/Myr. Analysis of numerical thermomechanical models revealed that the best-fit model is that combining the mechanisms of intraplate extension (passive rifting) and the ascent of a mantle magmatic diapir (active rifting). A conclusion about the nature of the heat source of trap magmatism has been drawn: The plume-driven regime of the lithosphere can better explain the dynamics of extension during rifting than the decompression melting mechanism.     

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.     

Wallrock Melting and Reaction Effects along the Higganum Diabase Dike in Connecticut: Contamination of a Continental Flood Basalt Feeder

The question of whether continental flood basalts are contaminatedwith crustal material during ascent through the lithosphereis addressed through a study of the feeder dike to the firstof the Mesozoic flood basalts in the Hartford basin of Connecticut.Faulting associated with basin formation exposed the dike, notonly where it connects with the flood basalt, but also at levelsthat may have been as deep as 10 km at the time of crystallization.Wallrocks at all levels of exposure and along the entire 250-kmlength of this 50–60 m wide dike show evidence of partialmelting and contamination of the diabase magma. Melting of the wallrocks took place on grain boundaries betweenquartz and feldspar, especially where these boundaries werefluxed with water released from the breakdown of biotite. Themelts were simple mixtures of quartz and the particular feldsparinvolved rather than equilibrium minimum compositions, probablybecause heating rates were faster than melting rates. The meltscrystallized to form granophyre. Feldspars in direct contactwith the diabase partly melted, with plagioclase developingthe fingerprint texture and orthoclase being converted to anexceptionally fine-grained mixture of plagioclase and quartz. Melts generated in the wallrocks were forced into the marginsof the dike by the volume expansion caused by melting. The earliestmelts to enter the dike are preserved as felsic wisps in thechilled margins, but at distances of more than a few centimetersfrom the edge of the dike they appear to have been assimilatedby the diabase magma. Melts that entered the dike after themargins had solidified were intruded as crosscutting granophyreveins. Chemical profiles across the dike reveal that the contaminantswere not restricted to narrow marginal zones but entered themain body of the dike. Thus, by the time this magma had risento the surface and erupted as the Talcott basalt it had assimilateda significant amount of crustal material, which accounts forthe change from olivine normative compositions in the deepestlevel exposures of the dike to quartz normative ones in thebasalt. Mass balance calculations indicate that the Talcottbasalt may have had {small tilde}6% granophyre added to it duringthe magma's ascent through the last 10 km of the crust. Theamount assimilated in traversing the entire continental crustwould therefore be greater than this.     

Field characteristics of laterally emplaced dikes: Anatomy of an exhumed Miocene dike swarm in Reydarfjördur, eastern Iceland

Many dikes of the Tertiary Breiddalur dike swarm in Reydarfjördur have a great lateral extent but are vertically (upward and/or downward) discontinuous. Field relationships indicate that they are not the feeders of the lava pile they intrude. Their characteristics can be best interpreted as them constituting the fossil expression of lateral magma emplacement analogous to that occurring in the actively spreading Krafla volcanic center of the neovolcanic zone. Average dike thickness increases clearly with depth and the thickness versus depth relationship is different from that described for other Tertiary dike swarms in eastern Iceland. It is suggested that dikes represent the extent of finite spreading which at higher levels in the crust is expressed by fissures and other extensional structures.     

泰山地区古元古代末期基性岩墙形成时代厘定——斜锆石U-Pb精确定年

华北克拉通经过吕梁运动在～1.85Ga完成克拉通化,之后从1.80Ga至1.32Ga发育大量标志哥伦比亚超级大陆裂解的地质记录。本文利用高精度热电离质谱法(ID-TIMS)和离子探针质谱法(SIMS),对发育于泰山红门景区的辉长辉绿岩墙进行了斜锆石U-Pb同位素年龄测定,获得了在误差范围内一致的辉长辉绿岩侵位年龄1621.1±8.8Ma(ID-TIMS)和1632.4±4.2Ma(SIMS)。该研究成果修正了前人对泰山红门景区辉长辉绿岩侵位年龄的模糊认识,证明了红门景区辉长辉绿岩是与华北克拉通南缘龙王碱性花岗岩、华北克拉通北缘大红峪期碱性火山岩和岩床同期的岩浆事件的产物,是哥伦比亚超级大陆初始裂解作用在华北克拉通的岩浆作用响应。