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1.
张臣  侯贵廷 《地质论评》1994,40(3):245-251
华北克拉通区内的吕梁-晋北地区广泛发育晚前寒武纪镁铁质岩墙群。该地区近EW向和NW-NNW向岩墙的磁组构测量结果表明,岩墙群磁各向异性与岩墙侵位的关系密切,磁化率的长轴能指示其岩浆侵位的流向。该区的岩墙群的岩浆源位于东侧的燕辽拗拉槽处,岩浆沿岩墙走向以一定仰角由ESE(或E)朝NW-NNW(或W)向流动,具板内裂谷模式。  相似文献   

2.
张臣  侯贵廷 《地质论评》1994,40(3):245-251
华北克拉通区内的吕梁-晋北地区广泛发育晚前寒武纪镁铁质岩墙群,该地区近EW向和NW-NNW向岩墙的磁组构测量结果表明,岩墙群磁各向异性与岩墙侵位的关系密切,磁化率的长轴能指示其岩浆侵位的流向,该区的岩墙群的岩浆源位于东侧的燕辽拗拉槽处,岩浆沿岩墙走向以一定爷角由ESE朝NW-NNW向流动,具板内裂谷模式。  相似文献   

3.
华北克拉通晚前寒武纪镁铁质岩墙群K-Ar年龄及地质意义   总被引:3,自引:0,他引:3  
华北克拉通腹地山西地块内广泛发育大规模的晚前寒武纪镁铁质岩墙群。通过对晋北地区新平堡镁铁质岩墙群9个样品的K-Ar年龄等时线分析,这些岩墙可能形成于1430Ma.从山西各地所采集的64个镁铁质岩墙群样品的K-Ar表观年龄统计分析可见,华北克拉通腹地内广泛发育的镁铁质岩墙群主要形成于中元古代1000~1800Ma间,活动高峰期在1200~1600Ma。  相似文献   

4.
华北克拉通晚前寒武纪镁铁质岩墙群K—Ar年龄及地质意义   总被引:13,自引:0,他引:13  
华北克拉通腹地山西地块内广泛发育大规模的晚前寒武纪镁铁质岩墙群。通过对晋北地区新平堡镁铁质岩墙群9个样品的K-Ar年龄等时线分析,这些岩墙可能形成于1430Ma。从山西各地所采集的64个镁铁质岩墙群样品的K-Ar表现年龄统计分析可见,华北克拉通腹地内广泛发育的镁铁质岩墙群主要形成于中元古代1000~1800Ma间,活动高峰期在1200~1600Ma。  相似文献   

5.
晋北地区中元古代岩墙群的地球化学特征和大地构造背景   总被引:18,自引:7,他引:18  
晋北地区发育大规模的中元古代北北西向岩墙群,未变形和未变质,是华北克拉通前寒武纪构造演化研究的最显著标志,根据本区岩墙群的岩石学和地球化学研究,这些岩墙群的岩石属于板内大陆裂谷玄武岩系列,形成于大陆裂谷拉张的构造环境,与东侧的燕辽-中条拗拉槽内的火山岩岩石化学对比分析,本区岩墙群的基性岩浆可能来自拗拉槽深部,这些基性岩浆从拗拉槽的深部向北西方向侵位于晋北地区先存的构造裂隙中形成了基性岩墙群。  相似文献   

6.
华北南缘古元古代末岩墙群侵位的磁组构证据   总被引:7,自引:3,他引:4  
侯贵廷  王传成  李乐 《岩石学报》2010,26(1):318-324
华北克拉通南缘的中条山及邻区广泛发育元古宙放射状基性岩墙群,与五台山-恒山和大同地区的北北西向基性岩墙群以及熊耳中条拗拉谷的火山岩在时空分布和地球化学方面均具有密切的相关性。中条山及邻区放射状基性岩墙群的宏观和微观流动构造(包括捕虏体、冲痕构造、矿物线理和定向斑晶)指示岩墙群以一定的仰角向北西侵位。通过该区岩墙群磁化率各向异性(AMS)测量得到磁组构的最大磁化率长轴优势方位分布图和磁组构各向异性特征分析进一步指示华北南缘古元古代末岩墙群从熊耳中条拗拉谷的底部向北西侵位。岩墙群的流动构造和磁组构的统计成果夯实了华北克拉通古元古代末基性岩墙群与熊耳中条拗拉谷的成生联系。  相似文献   

7.
大陆克拉通广泛发育元古代镁铁质岩墙群,其形成时限短,侵位机制复杂,可以侵位于不同的地壳层次,岩墙群的岩浆可能有多种来源,但主要来自陆下软流圈或地幔岩石圈,很少经历结晶分异与地壳混染,岩墙群的总体化学成分量富集型的,从古元古代到新元古代,其碱性组分逐渐增多,反映地幔演化特征,板块构造理论可应用于晚太古代-古元古代的构造研究,元古代以超级大陆的聚合及裂解为特征,岩墙群的形成普遍与伸展体制相联系,是超级大陆开始裂解或地幔柱活动的重要标志。华北克拉通区广泛发育中元古代镁铁质岩墙群,对其进行多学科的研究,将为确定华北克拉通在中元古代超级大陆中的构造位置及其古板块再造提供重要依据。  相似文献   

8.
东昆仑造山带中灶火地区镁铁质岩墙群以闪长玢岩为主,含少量闪斜煌斑岩、辉绿玢岩及辉绿岩,LA-ICPMS锆石U-Pb年代学指示该套岩墙群结晶侵位年龄为(249±1)Ma。稀土元素含量整体较高,富集轻稀土元素(∑REE=99.9×10-6~173.9×10-6,(La/Yb)N=3.5~9.3);微量元素表现出富集大离子亲石元素(LILE),亏损高场强元素(HFSE)的特征;源区分析表明,镁铁质岩浆为俯冲洋壳析出的流体交代富集地幔的结果,且在岩石成因中部分熔融起到主导作用,地壳混染和分离结晶作用对岩浆成分分异起到的作用有限。构造环境分析表明,岩石的形成与俯冲作用有关,结合区域构造演化认为镁铁质岩墙群的成因为:早三叠世,在古特提斯洋向北俯冲的环境下,俯冲板片释放的流体交代富集地幔,诱发地幔部分熔融形成镁铁质岩浆,受弧后伸展的动力学背景影响,岩浆最终上升侵位形成镁铁质岩墙群。  相似文献   

9.
福建湄洲岛的镁铁质岩墙群侵入于花岗岩中。镁铁质岩墙主要由斜长石(An=45~55,中-拉长石)、普通角闪石及少量辉石和石英等组成,锆石SHRIMP U-Pb年龄为(95±2)Ma。寄主花岗岩主要由石英、钾长石、斜长石(An=22~25,更长石)及少量的黑云母组成,锆石SHRIMP U-Pb年龄为(105±3)Ma。它们的形成时差约10 Ma。在岩石地球化学上,镁铁质岩墙群具有低CaO、MgO、TiO2而高Al2O3、轻稀土元素和大离子亲石元素富集、高场强元素亏损等特点,(87Sr/86Sr)i=0.705 2~0.705 4,εNd(t)=-0.03~1.57,与福建沿海同时代镁铁质岩墙群相似。寄主花岗岩与沿海高钾钙碱性花岗岩基本相同,都具有高硅、富碱的特点,它们的w(SiO2)>75%,A/CNK=1.05~1.12,w(K2O+Na2O)=7.68%~8.12%,w(K2O)>w(Na2O),(87Sr/86Sr)i=0.705 5,εNd(t)=-3.92。综合研究表明:湄洲岛寄主花岗岩是由受消减作用影响的岩石圈地幔部分熔融而产生的玄武岩浆底侵,并熔融中下地壳所产生的花岗岩浆形成;而镁铁质岩墙是底侵、滞留并经过结晶分异的玄武质岩浆,因地壳再次伸展,而沿花岗岩体中节理侵入形成。湄洲岛花岗岩与镁铁质岩墙群形成于伸展构造环境,对应福建沿海2次地壳伸展事件。湄洲岛花岗岩和镁铁质岩墙群的研究为沿海晚中生代构造-岩浆活动提供了一个新例证,同时为福建沿海晚中生代岩石圈伸展时限提供了制约。  相似文献   

10.
华北克拉通中北部变质基底发育大规模的前寒武纪基性岩墙群,由于基性岩墙同位素定年技术存在问题,因此一直未获得岩墙群的确切年龄数据。本文利用单颗粒锆石U-Pb化学法,首次获得恒山地区北西向基性岩墙群的U-Pb年龄为1769.1±2.5Ma,并证明它代表基性岩墙群的侵位年龄,这一年龄数据也是华北克拉通大规模分布的未变质基性岩墙群已知的最古老年龄。综合分析同期岩浆活动的同位素年龄记录,本文提出中元古代早期华北的岩浆侵位发生于伸展构造背景下。  相似文献   

11.
The Bastar craton has experienced many episodes of mafic magmatism during the Precambrian. This is evidenced from a variety of Precambrian mafic rocks exposed in all parts of the Bastar craton in the form of volcanics and dykes. They include (i) three distinct mafic dyke swarms and a variety of mafic volcanic rocks of Precambrian age in the southern Bastar region; two sets of mafic dyke swarms are sub-alkaline tholeiitic in nature, whereas the third dyke swarm is high-Si, low-Ti and high-Mg in nature and documented as boninite-norite mafic rocks, (ii) mafic dykes of varying composition exposed in Bhanupratappur-Keskal area having dominantly high-Mg and high-Fe quartz tholeiitic compositions and rarely olivine and nepheline normative nature, (iii) four suites of Paleoproterozoic mafic dykes are recognized in and around the Chattisgarh basin comprising metadolerite, metagabbro, and metapyroxenite, Neoarchaean amphibolite dykes, Neoproterozoic younger fine-grained dolerite dykes, and Early Precambrian boninite dykes, and (iv) Dongargarh mafic volcanics, which are classified into three groups, viz. early Pitepani mafic volcanic rocks, later Sitagota and Mangikhuta mafic volcanics, and Pitepani siliceous high-magnesium basalts (SHMB). Available petrological and geochemical data on these distinct mafic rocks of the Bastar craton are summarized in this paper. Recently high precision U-Pb dates of 1891.1±0.9 Ma and 1883.0±1.4 Ma for two SE-trending mafic dykes from the BD2 (subalkaline) dyke swarm, from the southern Bastar craton have been reported. But more precise radiometric age determinations for a number of litho-units are required to establish discrete mafic magmatic episodes experienced by the craton. It is also important to note that very close geochemical similarity exist between boninite-norite suite exposed in the Bastar craton and many parts of the world. Spatial and temporal correlation suggests that such magmatism occurred globally during the Neoarchaean-Paleoproterozoic boundary. Many Archaean terrains were united as a supercontinent as Expanded Ur and Arctica at that time, and its rifting gave rise to numerous mafic dyke swarms, including boninitenorite, world-wide.  相似文献   

12.
Mafic dyke swarms and aulacogens are major anorogenic extensional events in the Late Paleoproterozoic North China Craton (NCC). The N–NNW mafic dyke swarms are widespread in the NCC, whose ages span between 1.83 and 1.77 Ga. The similar ages and orientations of  1.8 Ga dyke swarms in the NCC demonstrate that the amalgamated NCC experienced widespread extension at this time.Based on the width statistics of dyke swarms on ten survey lines, an average crustal extension ratio of 0.35% was found for the NCC. The small magnitude of overall extension suggests that the mafic dyke swarms were emplaced into the elastic fractures, and indicates that the NCC had become a brittle plate prior to the emplacement of the mafic dyke swarms.Precisely dated mafic dyke swarms, when used as paleostress indicators, can be employed in the paleostress field reconstruction of Precambrian cratons. Two dimensional finite element modeling (2-D FEM) of the NCC, in which the various blocks were assigned densities and elastic constants, shows that north–south compression favors dyke intrusion along generally N–NW lines, and that deviations in dyke trends can be explained by the effects of boundary constraints and the physical properties of the crust. The best fitting model can be considered a plausible representation of the tectonic force acting on the NCC that produces the intraplate stress field that is most consistent with the observed orientation of dyke swarms. The results of modeling of the Late Paleoproterozoic stress field suggest a common tectonic setting for the emplacement of mafic dyke swarms in the Central Orogenic Zone, Western and East Blocks of the NCC. The results also show that the north–south tectonic forces play an important role in determining the paleostress field in the NCC. The widespread extension of the NCC resulted from the north–south tectonic forces which may be related to the break-up of the Late Paleoproterozoic supercontinent. The paleostress field modeling provides a possible approach to consider the supercontinent paleostress reconstruction and to reveal the mechanisms of the supercontinent break-up.  相似文献   

13.
Paleoproterozoic mafic igneous rocks (2450–1970 Ma) are exposed in the form of layered intrusions, dykes, and volcanic rocks in the Karelian, Kola and Murmansk provinces and in the form of dykes and small intrusions in the Belomorian Province, Eastern Fennoscandian Shield. The age and sequence of mafic dyke emplacement during the Paleoproterozoic are very similar in these regions. Further comparisons of geochemical characteristics of mafic dyke swarms in the Belomorian Province and neighboring cratons show considerable similarities.  相似文献   

14.
The Mersin ophiolite, which is a relic of the late Cretaceous Neotethyan ocean domain in the eastern Mediterranean, is situated on the southern flank of the central Tauride belt. The ophiolite body is cross-cut at all structural levels by numerous mafic dyke intrusions. The dykes do not intrude the underlying melange of platform carbonates. Therefore, dyke emplacement post-dates the formation of the opholite and metamorphic sole but pre-dates the final obduction onto the Tauride platform. The post-metamorphic dyke swarms suggest the geochemical characteristics of Island Arc Tholeiites (IAT). 40Ar/39Ar geochronology of the post-metamorphic microgabbroic-diabasic dykes cutting both mantle tectonites and metamorphic sole revealed ages ranging from 89.6 ± 0.7–63.8 ± 0.9 Myr old, respectively, indicating widespread magmatic activity during the Late Cretaceous-early Palaeocene in the Neotethyan ocean. These data suggest that island arc development in the Neotethyan ocean in southern Turkey was as early as Late Cretaceous.  相似文献   

15.
华北克拉通1.75Ga基性岩墙群特征及其研究进展   总被引:2,自引:1,他引:2  
基性岩墙群是地壳伸展背景下,来自地幔的基性岩浆侵入体。华北克拉通同世界上其它克拉通一样,广泛发育前寒武纪基性岩墙群。它们在不同时代均有产生,其中1.75Ga前后的规模最大,分布范围最广,几乎遍布整个克拉通,对其进行深入研究,可以揭示华北克拉通该期构造演化过程。华北克拉通1.75Ga前后的岩墙几何形态多变,直立或近直立,走向主要为NNW向和近EW向。岩石以拉斑玄武质岩类占绝对优势(>80%),主要造岩矿物为单斜辉石和斜长石。根据岩墙走向、岩浆分异程度和岩石地球化学特征可将其分五组:低分异LT组、低分异HT组、高分异NW组、高分异EW组,以及具明显差异的高铁系列。同位素和微量元素研究显示,岩浆源区主要与富集Ⅰ型地幔(EMⅠ)、弱亏损的常规地幔(DM-PREMA)以及陆下岩石圈地幔有关。目前对华北克拉通1.75Ga基性岩墙群产出的构造环境在认识上有分歧,其中地幔柱观点和碰撞后伸展观点最为人们所关注。  相似文献   

16.
陈宁华  董津津  厉子龙  倪妮娜 《岩石学报》2013,29(10):3540-3546
新疆北山地区广泛发育晚古生代侵入岩和基性岩墙群。本文利用多源高分辨率卫星遥感影像(ETM+, SPOT,CORONA KH4B, Geoeye1,Quickbird2)在该区约26880km2范围定量提取基性岩墙1375条。基性岩墙侵入石炭、二叠系火山岩、侵入岩、沉积岩和前寒武纪变质岩。岩墙单体长250m至34km,平均长度5km,厚度从1m至31m,平均厚度7.9m,岩墙长度和厚度均呈负指数分布。约70%的岩墙呈NNW-NNE方向展布。受NEE向走滑断层影响,在断裂带附近岩墙发生强烈扭曲。从北到南垂直岩墙的主要走向,取3条剖面,分段统计岩墙的厚度并计算伸展量。结果表明:该区二叠纪地壳伸展量为0.59%~2.01%,自南向北伸展率逐渐减小,在侵入岩体伸展量高达8.32%,沉积岩/变质岩区的伸展量为0.05%~0.3%。该区二叠纪基性岩墙发育与侵入岩体有密切的时空关系并受断裂控制和改造。  相似文献   

17.
The Moyar Shear Zone(MSZ) of the South Indian granulite terrain hosts a prominent syenite pluton (~560 Ma) and associated NW-SE to NE-SW trending mafic dyke swarm(~65 Ma and 95 Ma). Preliminary magnetic fabric studies in the mafic dykes,using Anisotropy of Magnetic Susceptibly(AMS) studies at low-field,indicate successive emplacement and variable magma flow direction.Magnetic lineation and foliation in these dykes are identical to the mesoscopic fabrics in MSZ mylonites,indicating shear zone guided emplacement.Spatial distribution of magnetic lineation in the dykes suggests a common conduit from which the source magma has been migrated.The magnetic foliation trajectories have a sigmoidal shape to the north of the pluton and curve into the MSZ suggesting dextral sense of shear.Identical fabric conditions for magnetic fabrics in the syenite pluton and measured field fabrics in mylonite indicate syntectonic emplacement along the Proterozoic crustal scale dextral shear zone with repeated reactivation history.  相似文献   

18.
吉南地区太古宙基底中发育大量早前寒武纪基性岩墙群,是陆壳伸展的直接证据。对白山市东部天桥太古宙基底出露区内基性岩墙及其围岩进行了锆石U-Pb定年和地球化学分析,以确定该期伸展事件的形成机制及地质意义。天桥地区基性岩墙岩性为斜长角闪岩,侵位于TTG片麻岩中。英云闪长质片麻岩(TN1)中锆石具核-边结构,岩浆核的LA-ICP-MS测年结果为2500±6Ma,指示其形成于新太古代末期。天桥岩墙(TN3)中的锆石内部结构与TN1相同,酸性岩浆核的SHRIMP测年结果为2490±17Ma,与TN1在误差范围内一致,表明这些锆石不是基性岩墙原生锆石,而是岩墙侵位过程中在围岩中捕获的锆石,但根据岩墙仅侵位在太古宙基底中且变质程度高于周围古元古界老岭群,将其侵位年龄大致限制在新太古代末期-古元古代早期。地球化学特征显示,基性岩墙具有低SiO_2、Na_2O、K_2O含量,高CaO、MgO含量,A/CNK=0.56~0.59,属于准铝质的拉斑玄武岩系列岩石,∑REE低、配分曲线平坦,富集LILE(Rb、Ba和K),亏损HFSE(Th、U、Nb和Ta),具有与原始地幔相同的Nb/Ta、Zr/Hf比值及接近地壳的Nb/U、Ta/U比值,指示其岩浆可能来源于地幔且在上升过程中受到地壳混染,形成于板内伸展环境。TTG片麻岩具有中等的SiO_2和MgO含量,高Al_2O_3和Na_2O含量以及低CaO含量,A/CNK=1.00~1.14,属弱过铝质的钙碱性系列岩石,∑REE低、具有右倾的REE配分曲线,轻稀土富集、重稀土亏损,富集LILE(Rb、Ba、K和Sr),强烈亏损HFSE(U、Nb、Ta、Sm和Ti),其岩浆可能来源于变质玄武质岩石和极少量沉积岩的部分熔融,结合邻区TTG的研究成果,认为其形成于与俯冲相关的活动大陆边缘环境。前人研究表明,新太古代晚期板块构造体制可能已经启动,结合我们以往研究,认为新太古代晚期华北克拉通东北部可能发生了弧陆碰撞造山运动,天桥岩墙的侵位标志着新太古代末期至古元古代早期之间华北克拉通东北部进入造山后伸展环境,可能是对新太古代造山运动结束的响应。  相似文献   

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