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胶-辽-吉古元古代造山/活动带巨量变沉积岩系的研究进展 总被引：37，自引：32，他引：5
华北克拉通发育三条古元古代构造带,包括:东部陆块内部的胶-辽-吉带(Jiao-Liao-Ji belt)、西部陆块内部的孔兹岩带(Khondalite belt)以及两个陆块之间的中部造山带(Trans-North China Orogen)。通过二十多年的深入研究,在区域构造、变质地质、岩浆作用、地球化学、同位素年代学以及地球物理等方面积累了大量资料,并取得了一系列重要的科学进展。其中,胶-辽-吉带是华北克拉通最具代表性的一条古元古代造山/活动带,它不仅接受了古元古代巨量的陆壳物质沉积,而且经历了十分复杂的构造演化过程,并经受了多期岩浆-变质事件的改造。胶-辽-吉造山/活动带的物质组成最为丰富,以大面积分布的巨量(火山)沉积岩系为特征,在中国境内包括吉南地区的集安群和老岭群、辽东南地区的南辽河和北辽河群、胶北地区的荆山群和粉子山群,向南西则有可能穿越郯庐断裂延伸至徐州-蚌埠一带的五河群,总体呈NE向展布,延伸规模长约1000km。从巨量沉积岩系的岩石组合和空间分布特征来看,荆山群与南辽河群、集安群可以对比,而粉子山群则与北辽河群、老岭群相当。然而,由于多期/多阶段强烈构造变形作用的影响,原来各群、组中地层的上下层位及接触关系已完全破坏,目前均已呈规模不一的构造岩片形式叠置在一起,彼此之间呈断层或韧性剪切带接触。巨量变沉积岩系的源区物质主要来源于造山/活动带内古元古代花岗质岩石和两侧古老陆块的变质基底,原岩形成时代为1.95~2.15Ga左右。以往研究表明,胶-辽-吉造山/活动带变质作用的强度十分不均匀,(中-高压)麻粒岩相变质只局限于胶北的荆山群及相关岩石,而粉子山群以及辽东南的南、北辽河群和吉南的集安群、老岭群只经历了角闪岩相变质,局部甚至只达到绿片岩相变质。粉子山群、北辽河群和老岭群变质演化P-T-t轨迹具有顺时针型式,而荆山群、南辽河群和集安群的P-T-t轨迹则具有逆时针型式。本文最新研究发现,古元古代麻粒岩相变质作用并非只局限于胶北地区的荆山群及其邻区,而是贯穿于整个辽东南地区的南辽河群和吉南地区的集安群,其变质演化P-T-t轨迹与胶北地区荆山群泥质麻粒岩以及基性麻粒岩一样,均具有典型近等温减压(ITD)顺时针型式,整个胶-辽-吉造山/活动带的麻粒岩相峰期变质时代为1.9~1.95Ga左右。野外观察和室内岩相学研究表明,在麻粒岩相变质作用过程中,胶北的荆山群及相关岩石、辽东南的南辽河群以及吉南的集安群中的泥质麻粒岩均广泛发生了深熔作用,长英质脉体呈不规则细脉状、网脉状和透镜状分布于寄主岩石中,且与寄主岩石之间呈渐变过渡关系。深熔锆石U-Pb定年结果显示,区域性的深熔作用(或部分熔融)时代为1.84~1.86Ga之间,表明这期广泛的深熔事件应发生于胶-辽-吉造山/活动带整体构造折返的中-低压麻粒岩相退变质阶段。有关胶-辽-吉古元古代造山/活动带的空间展布、南北边界、延伸规律及其形成的大地构造背景一直存在着分歧和争议,最新研究表明,蚌埠-霍邱一带地表露头及其以西第四系覆盖区之下的花岗质岩石、基性麻粒岩和富Al片麻岩岩心,均记录了1.85~1.95Ga的麻粒岩相变质事件,暗示着胶-辽-吉造山/活动带更有可能穿越郯庐断裂,向鲁西南延伸至蚌埠-霍邱一带及其以西的第四系覆盖区之下的变质基底。而辽南地块和狼林地块大量1.85~1.95Ga变质热事件和1.8~1.9Ga、~2.1Ga两期岩浆事件的记录,则表明辽南地块和狼林地块(至少是一部分变质基底)曾卷入到胶-辽-吉古元古代构造演化事件之中。有关胶-辽-吉古元古代造山/活动带构造演化过程及其形成的大地构造背景,目前有三种构造模式,包括:裂谷开启-闭合模式、弧(陆)-陆碰撞模式和先裂谷-后碰撞造山演化模式,然而,带内异常复杂的巨量火山-沉积岩系的物质组成、多期/多阶段的岩浆作用事件、多种变质作用类型和十分复杂的变质演化P-T-t轨迹样式、多期/多阶段复杂的构造变形特征,难以采用上述任何一种构造演化模式来加以合理解释。由此可见,有关胶-辽-吉古元古代构造/活动带南侧边界需要进一步准确厘定,有关狼林地块和辽南地块的构造归属,特别是胶-辽-吉造山/活动带在古元古代构造演化的动力学过程及其形成的大地构造背景还有待进一步深入探讨。 相似文献
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前寒武纪盆地演化及造山作用一直是造山带研究中的热点和难点，通过对华北克拉通东部陆块胶-辽-吉构造带中辽东半岛河栏镇火山-沉积岩进行深入的野外及室内研究，反演该地区古元古代大地构造演化过程.通过对辽河群里尔峪组火山岩、高家峪组钙质泥岩以及大石桥组碳酸盐岩野外的详细构造解析，识别出各类岩石单元中发育同沉积伸展构造（D1-0），包括同沉积不对称褶皱、层间平卧褶皱和滑脱面理及线理，指示辽吉弧后盆地早期伸展张裂过程.通过对河栏镇蒲石河地区基性侵入岩及喷出枕状熔岩进行详细的野外构造填图及解析，提出伴随基性枕状熔岩的喷发，辽吉弧后盆地张裂到最大程度.此外，在各组相关岩石中观察到大量逆冲推覆构造及不对称断展褶皱，构造归为D1-1或者D1-2，指示辽吉弧后盆地受挤压应力影响发生收缩.锆石年代学研究指示高家峪组沉积物物源主要来自于~2.5 Ga基底，少量来自古元古代（2 172 Ma）火山弧.综合区域内已有岩石地球化学及年代学资料，研究表明辽吉弧后盆地的拉张及闭合过程伴随着古元古代增生造山作用，并暗示板块构造在古元古代已经开启. 相似文献
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胶-辽-吉造山带北辽河变基性岩的成因、地球化学属性及其构造意义 总被引：4，自引：4，他引：0
大规模出露于胶-辽-吉造山带的北辽河变基性岩(NLHmetabasicrocks)是恢复造山带构造演化的关键之一,然而,研究者们对这些变基性岩的成因和构造环境有很大争议,制约了对胶-辽-吉造山带早期构造演化的深入研究。基于详细的野外地质调查,本文对北辽河变基性岩进行了系统的岩石学研究并提供了新的全岩地球化学数据,结合前人的测试结果,我们对这些变基性岩的成因和构造环境进行了相关探讨。变基性岩侵入于北辽河群的大理岩和碎屑岩中,经历了一定程度的蚀变以及绿片岩相-角闪岩相变质。岩石类型包括变质辉长岩、变质辉绿岩、斜长角闪岩以及石榴斜长角闪岩;前两者具有明显的变余辉长或者辉绿结构,可见自形斜长石,少见原生矿物单斜辉石的残留;后两者主要由斜长石和角闪石组成,部分含有石榴子石变斑晶;此外,岩石中出现大量Fe-Ti氧化物(磁铁矿和钛铁矿)。地球化学研究表明,北辽河变基性岩均属于拉斑玄武岩系列(SiO_2=44.55%~54.11%,Nb/Y=0.16~0.31),以低TiO_2(0.69%~1.99%)和低MgO(多数5.47%~7.97%)为特征,轻稀土轻微富集((La/Sm)_N=1.22~2.66;(La/Yb)_N=1.66~4.56),并具有明显的Nb、Ta、P以及轻微的Zr、Ti亏损,岩石经历了橄榄石、单斜辉石和斜长石等矿物的三相结晶分异以及Fe-Ti氧化物(磁铁矿和钛铁矿)的堆晶;它们的微量元素配分型式类似于E-MORB和地壳岩石,并且地球化学组成与MORB相近,而不同于弧玄武岩和板内玄武岩;这些变基性岩的Ce/Pb(3.07~26.58)、(Ta/La)PM(0.47~1.45)以及(Hf/Sm)PM(0.91~1.15)显示出有限的俯冲相关流体的交代作用;此外,大多数不相容元素比值(例如Th/Nb、La/Nb及Th/La等)的变化趋势则表明北辽河变基性岩的岩浆源区不可能是大陆岩石圈地幔,并且在形成过程中经历了明显的地壳物质混染。基于这些野外地质调查和地球化学研究,我们认为北辽河变基性岩应形成于相对成熟的弧后盆地,这样一个形成环境也表明胶-辽-吉造山带在早期存在~2.1Ga的洋壳俯冲过程,该构造带应该是~1.9Ga岛弧与大陆碰撞形成的一条古元古代造山带。 相似文献
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古元古代是华北克拉通形成过程中重要的造山构造演化阶段，该阶段形成的基性岩墙群，为深入理解裂解-俯冲-碰撞-抬升的造山构造-岩浆过程提供了重要信息.本文报道了天镇-怀安地区广泛分布于新太古代-古元古代变质基底中的变质基性岩墙（二辉麻粒岩），野外产状与区域主期构造面理协调一致，主要由单斜辉石、斜方辉石、斜长石和少量角闪石组成.LA-MC-ICPMS锆石U-Pb同位素定年获得变质基性岩墙的变质年龄为1 820~1 834 Ma，与区内麻粒岩相变质事件一致，结合区域基性岩墙年龄记录，推测其原岩形成年龄为1.95~1.91 Ga.根据岩石地球化学特征可将变质基性岩墙划分为高Mg低Ti型和低Mg高Ti型两类，两者经历了不同程度的橄榄石、单斜辉石和斜长石的分离结晶.两类基性岩墙均亏损高场强元素（如Nb、Ta、Ti、Zr和Hf），结合锆石Hf同位素分析，研究表明基性岩墙来源于俯冲流体交代的岩石圈地幔或者受到过地壳物质的混染.华北克拉通古元古代存在2.16~2.04 Ga和1.97~1.83 Ga两期基性岩墙侵位事件:早期代表在初始克拉通基础上发生的板内裂解过程，晚期记录了由俯冲碰撞到伸展的转换过程，即碰撞造山构造体制由水平挤压转变为垂向抬升，构造转换时限大致介于1.95~1.91 Ga. 相似文献
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钴矿是重要的战略性金属矿产资源之一,对其成矿作用(如构造与成矿的关系)进行深入的研究能为前期指导找矿提供理论依据。本文对中国东部吉林白山市三道沟镇三岔河村大横路Cu-Co矿开展了相关工作,包括野外构造解析、钻孔-岩芯资料分析、钻孔薄片综合矿物分析系统(TIMA)实验和区域相关岩石年代学等。构造解析显示大横路Cu-Co矿围岩变形包括层片交切、S1面理和褶劈理等构造要素。钻孔-岩芯资料分析矿区发育大量F2紧闭褶皱、逆冲断层及断层相关褶皱、倒转褶皱F2等。钻孔、探槽薄片样品TIMA实验显示含Co流体大量富集于低角度逆冲断裂、倒转褶皱韧性剪切域和断层相关褶皱转折端处。这些工作显示走向为NE的低角度逆冲断裂及断层相关褶皱对大横路Cu-Co矿的富集起到关键的控制作用。相关年代学工作,结合前人研究及大量区域地质资料表明:(1)矿区内逆冲断层及褶皱等控矿构造要素为古元古代构造事件的产物;(2)中生代构造事件对成矿作用的制约(Cu-Co矿的再富集)可能来自于白垩纪大规模的伸展作用。 相似文献
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胶北地体多期变质事件的P-T-t轨迹及其对胶-辽-吉带形成与演化的制约 总被引：2，自引：2，他引：0
胶北地体位于华北克拉通东部陆块胶-辽-吉带南端,主要由闪长质-TTG-花岗质片麻岩、变质表壳岩系和变质镁铁-超镁铁质岩所组成。本文通过对胶北早前寒武纪变质岩系的岩石学、矿物化学、变质反应结构和序列、变质温度和压力估算与同位素年代学资料的综合研究和总结,得出以下重要结论:(1)与华北克拉通东部陆块其它地区太古宙变质基底类似,本区也存在~2500Ma区域性新太古代变质事件,且与本区2550~2500Ma岩浆作用在时间上非常接近,其变质作用发生的时间比岩浆作用要晚10~50Myr,指示本区~2500Ma区域性变质事件可能与大规模的幔源岩浆底侵作用存在密切的成因关系。(2)胶北还存在1950~1850Ma区域性古元古代变质事件,并导致了大量高压基性和泥质麻粒岩的形成,高压基性麻粒岩主要以不规则透镜体、变形岩墙群或岩脉群的形式赋存于闪长质-TTG-花岗质片麻岩之中,并集中分布在安丘-平度-莱西-莱阳-栖霞一带,大致沿北东-南西向断续带状分布,构成了一条长约300km的古元古代高压麻粒岩相变质带。(3)本区古元古代高压麻粒岩以记录近等温减压(ITD)及随后近等压降温(IBC)的顺时针P-T-t轨迹为特征,指示本区变质杂岩在古元古代晚期曾强烈地卷入了与俯冲-拼贴-碰撞造山有关的构造过程,并可能经历了如下复杂的构造演化:(I)在古元古代晚期2000~1950Ma,随着有限大洋地壳的持续俯冲作用,本区各类变质岩的原岩开始经历一次构造增厚事件,并导致了它们的原岩经历了早期绿片岩相-角闪岩相进变质作用;(II)1950~1870Ma,大洋地壳俯冲作用结束,本区开始发生弧-陆拼贴和陆-陆碰撞作用,大陆地壳持续缩短和加厚,在加厚下地壳或岛弧根部带约50km的深度,发生了区域性高压麻粒岩相变质作用,并导致了本区变基性岩和变泥质岩分别形成了石榴石+单斜辉石+斜长石±角闪石±石英±铁-钛氧化物和石榴石+蓝晶石+钾长石+斜长石+黑云母+石英+铁-钛氧化物+熔体的高压麻粒岩相矿物组合。(III)1870~1800Ma,在同碰撞峰期变质结束之后,本区造山作用进入了后碰撞构造折返-伸展演化阶段,先后经历了早期快速构造折返和晚期缓慢冷却降温两个构造热演化阶段。其中,在早期快速构造折返阶段,高压麻粒岩经历了峰后近等温或略微增温减压退变质作用的叠加,高压基性麻粒岩表现为沿石榴石边部形成了含斜方辉石的后成合晶。与此同时,早期快速构造折返阶段还伴随着热松弛和伸展作用,出现一系列的幔源基性岩浆活动,不仅导致了本区大量未经历高压麻粒岩相变质的变基性岩群的形成,同时也诱发了区内大规模的地壳深熔作用的发生。自温度高峰期之后,本区地壳岩石还经历了一个近等压冷却降温过程,并发生了区域性角闪岩相退变质作用,高压基性麻粒岩表现为石榴石和斜方辉石边部常出现含角闪石的退变边或后成合晶。最终,在1800Ma左右,本区含电气石花岗伟晶质岩脉的大量出现,则标志着胶北地体古元古代晚期(2000~1800Ma)俯冲-拼贴-碰撞造山作用的最终结束。 相似文献
8.
大别-苏鲁超高压和高压变质带构造演化 总被引：12，自引：0，他引：12
大别—苏鲁是世界上超高压 (UHP) ( >2 .7GPa)和高压 (HP)变质岩石出露最为广泛的地区。通过区域研究 ,尤其是在选择的 30多个关键位置上不同尺度构造记录的深入观察 ,结合已有的可利用的变质、热事件及同位素年代学资料分析 ,揭示出它们曾遭受过一个复杂的从深俯冲到折返构造演化历程 ,识别出 5个主要的构造变质事件 :( 1)由块状榴辉岩中发育的微弱面理和线理所代表的第 1期变形变质事件 (D1) ;( 2 )面状榴辉岩中发育的含拉伸线理的透入性主面理、中小型鞘状褶皱及网络状韧性剪切带 ,代表第 2期构造变质事件 (D2 ) ;( 3)第 3期变形事件主体发生于麻粒岩 /角闪岩相后成合晶形成之后 ,主要构造记录是区域性陡倾斜面理及不均一置换的成分层、榴辉岩透镜体及布丁群、面理内褶皱、网状韧性剪切带系统以及减压部分熔融作用形成的混合岩和含榴花岗质岩石组构 ;( 4)区域性的碰撞期后地壳韧性薄化及剪张作用 (D4)形成缓倾斜角闪岩相主面理及线理、穹状及弧形构造和多层韧性拆离带 ,它们主导了现今观察到的大别—苏鲁超高压和高压变质带的区域构造几何图像 ;( 5 )第 5期构造热事件 (D5)表现为不均一断块抬升、红色沉积盆地发育及大规模的岩体和岩脉就位 ,代表造山晚期的构造揭顶及坍陷作用 ,该期构造控制着造山带 相似文献
9.
大别-苏鲁区超高压变质岩的多期构造变质演化 总被引：3，自引：0，他引：3
对大别-苏鲁地区超高压(UHP)变质岩的详细构造和岩石学研究揭示了其复杂的构造变质演化历史。除前超高压事件外,至少可识别出5个相继发育的构造变质事件或阶段(D_1-D_5)。D_1和 D_2同超高压事件与三叠纪(250～230Ma)中朝克拉通和扬子克拉通间的大陆深俯冲及碰撞有关,而超高压后的 D_3和 D_4韧性变形及其伴生的减压部分熔融作用和退变质作用事件,则是超高压岩石向中上地壳折返过程中(230～140Ma)发生的。碰撞后形成的 D_4构造,主导了大别-苏鲁超高压和高压变质带区域尺度的构造格架。第5阶段的构造以摩擦或摩擦-粘性过渡性变形机制为主,并伴随有大规模的未变形的花岗质岩体就位,该期构造热事控制了现今大别-苏鲁地区的地貌学特征。新的构造和岩石学资料并结合可利用的地质年代学和地球化学等资料,提出一个涉及中朝与扬子克拉通间三叠纪大陆深俯冲、碰撞及相继超高压变质岩石向地表的多期折返构造变质演化模式。 相似文献
10.
辽吉古元古代造山带的地层单元划分与构造属性 总被引：14，自引：0，他引：14
辽吉古元古代造山带位于华北克拉通东部,造山带的沉积构造背景和地层格架长期存在争议。最近的研究表明,辽吉古元古代造山带的沉积环境为一活动大陆边缘弧后盆地,经历了早期弧后盆地扩张和晚期盆地收缩-俯冲-造山的演化过程。北辽河群的浪子山组—里尔峪组(含老岭群达台山组)与南辽河群的里尔峪组和老岭群的蚂蚁河组应是同时异相的产物,前者沉积在弧后盆地大陆边缘一侧,以陆缘碎屑沉积为主夹少量酸性火山岩;后者发育在弧后盆地岩浆弧一侧,火山作用强烈。集安群(荒岔沟组和大东岔组)和南辽河群的中上部(南高家峪组—大石桥组)所构成的孔兹岩系为弧后盆地收缩-俯冲阶段的沉积建造(相当于弧前构造背景),遭受了~1.9 Ga的变质作用,并被~1.9 Ga的石榴石花岗岩侵入。河栏—草河口地区的"大石桥组一段"为一套大理岩夹变质基性火山岩的沉积建造,变质基性火山岩和变质基性岩脉均具有岛弧拉斑玄武岩特征,形成于弧后盆地的构造背景。依据其中基性火山岩~1.87 Ga的SHRIMP锆石U-Pb年龄,推测其为弧后盆地俯冲收缩阶段的产物。狭义的盖县组及其相当地层的碎屑锆石反映出大量古元古代的年龄信息,太古宙年龄信息相对较少,故推测物源区主要来自南侧的岩浆弧,所谓的"狼林地块"不是一个太古宙陆块,而主要表现为一条古元古代岩浆弧。 相似文献
11.
辽东半岛辽河群变泥质岩变质变形研究:对古元古代造山作用及折返过程的启示 总被引：1，自引：0，他引：1
前寒武纪造山带解析是地球科学研究的重点。胶-辽-吉造山带作为华北克拉通最具代表性的造山带之一,是研究前寒武纪造山过程和物质折返的理想场所。本文以辽东半岛辽河群为研究对象,以变质变形为研究手段,系统解析胶-辽-吉造山带的造山及折返过程。含夕线石榴黑云片麻岩(样品18TZH49)位于造山带核心部分,其岩相学观察和相平衡模拟表明,其峰期和峰后变质阶段矿物组合分别为Sil+Grt+Pl+Bi+Qz+Ilm+Melt和St+Grt+Pl+Bi+Chl+Qz+Ilm,变质温压条件为720~780℃/5.9~6.9kbar和540~565℃/3~4.1kbar,从峰期到峰后记录了一个降温降压的顺时针P-T演化轨迹。锆石UPb年代学研究表明其退变质年龄为1851Ma。结合南、北辽河群其他变泥质岩研究工作,提出造山带北部北辽河群泥质岩经历低角闪岩相变质作用,以典型的巴罗式变质带为特征;造山带南部南辽河群经历角闪岩相至麻粒岩相变质作用,退变质特征明显。从构造角度来说,北辽河群受向北逆冲推覆构造影响,显示向龙岗基底的运动学特征;造山带核心部位的南、北辽河群直立褶皱发育,指示地壳强烈收缩过程;南辽河群受向南逆冲推覆构造影响,显示向南侧狼林陆块的运动学特征。变质变形及年代学共同指示,辽河群经历1.95~1.90Ga造山作用,构造增厚作用使不同类型岩石相互叠置并发生不同程度变质作用。随后,~1.85Ga发生造山后伸展作用,不同变质等级岩片剥露于地表。 相似文献
12.
This paper examines the metamorphic evolution of three juxtaposed units of the Maures massif (France) with respect to the tectonic processes related to the Variscan orogeny. All sampled rocks are metabasalts or metagabbros metamorphosed during Palaeozoic tectonic events. The inferred metamorphic evolution takes into account the relative chronology of mineral parageneses with respect to microstructures, the mineral chemistry of zoned amphiboles, and calculated P–T–t–d paths derived from each unit. Three successive and contrasting tectono-metamorphic events are clearly identified. The D1 event is associated with coarse-grained amphiboles of an early S1–L1 fabric that recorded prograde/retrograde anticlockwise paths at high-grade amphibolite facies conditions (7–8 kbar/700–750 °C). The D2 event is related to fine-grained amphiboles of the main S2 foliation that recorded prograde/retrograde clockwise paths at MP–MT conditions (4–6 kbar/550–650 °C). The D3 event corresponds to late post-S2 amphiboles crosscutting the main foliation and recording retrograde clockwise paths at lower grade conditions (4–2 kbar/500–350 °C). The D1 event results from Silurian–Devonian continental subduction and subsequent thrust tectonics during an early stage of the Variscan evolution, before the Carboniferous. The D2 event is connected to the Visean continental collision, marked by nappe stacking (burial) then crustal folding and sinistral strike-slip shearing (exhumation). The D3 event is an effect of the Namurian late-orogenic extension (late exhumation) that mostly affected the previously thickened whole central block. This paper demonstrates that the whole metamorphic history of the Maures massif consists of two successive stages of burial/exhumation at different metamorphic conditions during the Variscan mountain building. Similar stages of subduction-uplift then collision-uplift processes have also been recognised in others parts of the Variscan belt and in the Alpine orogen. 相似文献
13.
《Journal of Asian Earth Sciences》2005,24(5):659-674
The Paleoproterozoic Liaohe assemblage and associated Liaoji granitoids represent the youngest basement in the Eastern Block of the North China Craton. Various structural elements and metamorphic reaction relations indicate that the Liaohe assemblage has experienced three distinct deformational events (D1 to D3) and four episodes of metamorphism (M1 to M4). The earliest greenschist facies event (M1) is recognized in undeformed or weakly deformed domains wrapped by the S1 schistosity, suggesting that M1 occurred before D1. The D1 deformation produced small, mostly meter-scale, isoclinal and recumbent folds (F1), an associated penetrative axial planar schistosity (S1), a mineral stretching lineation (L1) and regional-scale ductile shear zones. Concurrent with D1 was M2 metamorphism, which occurred before D2 and produced low- to medium-pressure amphibolite facies assemblages. Regionally divergent motion senses reflected by the asymmetric F1 folds and other sense-of-shear indicators, together with the radial distribution of the L1 lineation surrounding the Liaoji granitoids, imply that D1 represents an extensional event. The D2 deformation produced open to tight F2 folds of varying scales, S2 axial crenulation cleavages and ENE-NE-striking thrust faults, involving broadly NW–SE compression. Following D2 was M3 metamorphism that led to the formation of sillimanite and cordierite in low-pressure type rocks and kyanite in medium-pressure rocks. The last deformational event (D3) formed NW-WNW-trending folds (F3), axial planar kink bands, spaced cleavages (S3), and strike–slip and thrust faults, which deflect the earlier D1 and D2 structures. D3 occurred at a shallow crustal level and was associated with, or followed by, a greenschist facies retrograde metamorphic event (M4).The Liaohe assemblage and associated Liaoji granitoids are considered to have formed in a Paleoproterozoic rift, the late spreading of which led to the occurrence of the early extensional deformation (D1) and the M1 and M2 metamorphism, and the final closing of which was associated with the D2 and D3 phases of deformation and M3 and M4 metamorphism. 相似文献
14.
Structural overprinting relationships indicate that two discrete terranes, Mt. Stafford and Weldon, occur in the Anmatjira Range, northern Arunta Inlier, central Australia. In the Mt. Stafford terrane, early recumbent structures associated with D1a,1b deformation are restricted to areas of granulite facies metamorphism and are overprinted by upright, km-scale folds F1c), which extend into areas of lower metamorphic grade. Structural relationships are simple in the low—grade rocks, but complex and variable in higher grade equivalents. The three deformation events in the Mt. Stafford terrane constitute the first tectonic cycle (D1-D2) deformation in the Weldon terrane comprises the second tectonic cycle. The earliest foliation (S2a) was largely obliterated by the dominant reclined to recumbent mylonitic foliation (S2b), produced during progressive non-coaxial deformation, with local sheath folds and W- to SW-directed thrusts. Locally, (D2d) tectonites have been rotated by N—S-trending, upright (F2c) folds, but the regional upright fold event (F2d), also evident in the adjacent Reynolds Range, rotated earlier surfaces into shallow-plunging, NW—SE-trending folds that dominate the regional outcrop pattern.The terranes can be separated on structural, metamorphic and isotopic criteria. A high-strain D2 mylonite zone, produced during W- to SW-directed thrusting, separates the Weldon and Mt. Stafford terranes. 1820 Ma megacrystic granites in the Mt. Stafford terrane intruded high-grade metamorphic rocks that had undergone D1a and D1b deformation, but in turn were deformed by S1c, which provides a minimum age limit for the first structural—metamorphic event. 1760 Ma charnockites in the Weldon terrane were emplaced post-D2a, and metamorphosed under granulite facies conditions during D2b, constraining the second tectonic cycle to this period.Each terrane is associated with low-P, high-T metamorphism, characterized by anticlockwise P—T—t paths, with the thermal peaks occurring before or very early in the tectonic cycle. These relations are not compatible with continental-style collision, nor with extensional tectonics as the deformation was compressional. The preferred model involves thickening of previously thinned lithosphere, at a stage significantly after (>50 Ma) the early extensional event. Compression was driven by external forces such as plate convergence, but deformation was largely confined to and around composite granitoid sheets in the mid-crust. The sheets comprise up to 80% of the terranes and induced low-P, high-T metamorphism, including migmatization, thereby markedly reducing the yield strength and accelerating deformation of the country rocks. Mid-crustal ductile shearing and reclined to recumbent folding resulted, followed by upright folding that extended beyond the thermal anomaly. Thus, thermal softening induced by heat-focusing is capable of generating discrete structural terranes characterized by subhorizontal ductile shear in the mid-crust, localized around large granitoid intrusions. 相似文献
15.
Ivano Gasco Marco Gattiglio Alessandro Borghi 《International Journal of Earth Sciences》2011,100(5):1065-1085
A new structural and petrological study, associated with a detailed geological mapping, allowed to better understand the tectonic
relationships between the Dora Maira Massif and the Piedmont Zone in the middle Susa Valley. In the study area, a thick sequence
of calcschists, previously attributed to the stratigraphic cover of the Dora Maira, is interpreted as belonging to the Piedmont
Zone. Four deformation phases were identified: D1 represents the eclogite facies stage, D2 developed under greenschist facies conditions, transposed the early foliation and was responsible for the development of
the regional schistosity S2. D3 is characterized by close to open folds with N dipping axial surfaces and finally, D4 developed macro-scale folds with E-dipping axial planes. Structural analyses allow to infer a relative timing for the tectonic
contact between the two nappes which were coupled after the eclogite facies metamorphism but before the development of the
S2 foliation under greenschist facies conditions. Petrographic investigation into metapelite samples permitted to identify two
main metamorphic assemblages within the Dora Maira polymetamorphic basement: M1 (Phe + Pg + Cld + Grt + ChlI + Qtz + Rt) assemblage defines the S1 relict foliation, while M2 (Ms + Pg + Ab + ChlII + Qtz + Ilm ± Bt) assemblage is related to the regional foliation S2. PERPLE_X pseudosection modelling allowed to reconstruct a P-T path for a garnet–chloritoid-bearing micaschist from the northern
part of the Dora Maira Massif, which reached eclogite facies conditions at 18–20 kbar and 515–525°C (M1/S1 event) and then was exhumed during increasing T (10–11 kbar and 555–565°C). The M2 assemblage defining the S2 regional foliation developed at P < 7 kbar and T < 575°C. According to the structural evolution, the tectonic coupling between Dora Maira and Piedmont Zone took place during
exhumation along the subduction channel. 相似文献
16.
KAUSHIK DAS SANKAR BOSE SUBRATA KARMAKAR SUPRIYA CHAKRABORTY 《Journal of Earth System Science》2012,121(1):1-17
Granulite-facies rocks occurring north-east of the Chilka Lake anothosite (Balugan Massif) show a complex metamorphic and
deformation history. The M1–D1 stage is identified only through microscopic study by the presence of S1 internal foliation shown by the M1 assemblage sillimanite–quartz–plagioclase–biotite within garnet porphyroblasts of the aluminous granulites and this fabric
is obliterated in outcrop to map-scale by subsequent deformations. S2 fabric was developed at peak metamorphic condition (M2–D2) and is shown by gneissic banding present in all lithological units. S3 fabric was developed due to D3 deformation and it is tectonically transposed parallel to S2 regionally except at the hinge zone of the F3 folds. The transposed S2/S3 fabric is the regional characteristic structure of the area. The D4 event produced open upright F4 folds, but was weak enough to develop any penetrative foliation in the rocks except few spaced cleavages that developed in
the quartzite/garnet–sillimanite gneiss. Petrological data suggest that the M4–D4 stage actually witnessed reactivation of the lower crust by late distinct tectonothermal event. Presence of transposed S2/S3 fabric within the anorthosite arguably suggests that the pluton was emplaced before or during the M3–D3 event. Field-based large-scale structural analyses and microfabric analyses of the granulites reveal that this terrain has
been evolved through superposed folding events with two broadly perpendicular compression directions without any conclusive
evidence for transpressional tectonics as argued by earlier workers. Tectonothermal history of these granulites spanning in
Neoproterozoic time period is dominated by compressional tectonics with associated metamorphism at deep crust. 相似文献
17.
Three sheet‐like bodies of felsic gneiss containing abundant K‐feldspar megacrysts (megacrystic felsic gneiss, augen gneiss or granite gneiss) surrounding the Broken Hill Line of Lode in western New South Wales, Australia, are inferred to be pre‐ to syn‐D1 granitoids. We interpret the Feral gneiss to be a pre‐ to early syn‐D1 intrusion, as it contains S1 as its earliest foliation. However, it has no magmatic flow foliation. The Alma Gneiss, and the megacrystic portions of the Rasp Ridge Gneiss, northwest of the Line of Lode, both contain S1 parallel to a magmatic flow foliation, and are interpreted as having been magmatic during D1. Therefore, the Alma and Rasp Ridge Gneisses may have been intruded during D1, probably just after the Feral gneiss, as the Alma Gneiss intrudes the Feral gneiss. S1 in the augen gneisses and the wall rocks is defined by biotite, sillimanite, garnet and ribbon quartz, and indicates that high‐grade metamorphic conditions accompanied D1. Evidence suggesting that these rocks were originally granitoids includes: (i) the Alma Gneiss transecting and intricately intruding the Feral gneiss, the contacts being transected by S1; (ii) euhedral to subhedral K‐feldspar porphyroclasts (former phenocrysts), especially those with concentrically arranged inclusions; (iii) microgranitoid enclaves, particularly where megacrystic and relatively large; (iv) aplite dykes (most common in plutonic rocks and therefore reliable indicators); (v) metasedimentary xenoliths; (vi) magmatic flow foliations overprinted by parallel tectonic foliations; and (vii) chemical affinities with undoubted Australian Proterozoic granitoids. Therefore, felsic gneisses at Broken Hill should not be used for stratigraphic correlation, unless they can be definitely determined to be of volcanic flow or tuffaceous origin. The inferred intrusion of granitoids early in the tectonic history of the Broken Hill Block suggests that they may have contributed to the metamorphic and/or hydrothermal heat, and may have helped concentrate metals to form orebodies. 相似文献
18.
辽河群区域变质特征及其大陆动力学意义 总被引：23，自引：0，他引：23
辽河群是胶辽吉古元古代造山带的主要组成部分。近年来对其区域变质作用的PTt轨迹研究发现：同一造山带内PTt轨迹具有多样性。进一步研究认为,这一碰撞造山带南、北空间上PTt轨迹的逆向性起因于造山带南、北部的结构构造、变形过程和同变形变质花岗岩空间分布上的差异。就南辽河群和盖县岩组而言,早期、中期变质阶段,因中深部地壳大面积“辽吉花岗岩”的底垫式侵位及其诱发的沉积盖层顺层滑脱减薄作用,变质作用表现为近等压和小幅度增压而温度快速上升的过程;峰期变质阶段,又因收缩挤压增厚,表现为等温升压过程（盖县岩组）或升温升压过程（南辽河群）;最后晚期变质阶段,差异剥蚀引起降温降压（盖县岩组）或近等压降温过程（南辽河群）。对北辽群而言,早期、中期变质阶段,因盖层南辽河群及盖县岩组的大规模向北滑覆增厚作用而及花岗岩浆不发育,仅有正常传导热及放射热,因而△P＞△T;峰期变质阶段温、压同时达峰值,之后等温快速降压过程,与构造剥蚀有关;至晚期变质阶段,同盖县岩组一样,经历降温降压过程。通过对比上述北、南辽河群及盖县岩组的大陆动力学过程,表明早期大陆动力学过程正好是一个互为消长的过程,从而也决定了它们的PTt轨迹的逆反性。最后,本文提出了辽河群变质的底侵＋拆沉模型。 相似文献
19.
Structural and geochronological constraints on the tectonic evolution of the Dulong-Song Chay tectonic dome in Yunnan province, SW China 总被引：14，自引：1，他引：14
Dan-Ping Yan Mei-Fu Zhou Christina Yan Wang Bin Xia 《Journal of Asian Earth Sciences》2006,28(4-6):332-353
The Dulong-Song Chay tectonic dome lies on the border of China (SE Yunnan Province) and northern Vietnam, and consists of two tectonic and lithologic units: a core complex and a cover sequence, separated by an extensional detachment fault. These two units are overlain unconformably by Late Triassic strata. The core complex is composed of gneiss, schist and amphibolite. SHRIMP zircon U–Pb dating results for the orthogneiss yield an age of 799±10 Ma, which is considered to be the crystallization age of its igneous protolith formed in an arc-related environment. A granitic intrusion within the core complex occurred with an age of 436–402 Ma, which probably formed during partial closure of Paleotethys. Within the core complex, metamorphic grades change sharply from upper greenschist-low amphibolite facies in the core to low greenschist facies in the cover sequence. There are two arrays of foliation within the core complex, detachment fault and the cover sequence: S1 and S2. The pervasive S1 is the axial plane of intrafolial S0 folds. D1 deformation related to this foliation is characterized by extensional structures. The strata were structurally thinned or selectively removed along the detachment faults, indicating exhumation of the Dulong-Song Chay tectonic dome. The major extension occurred at 237 Ma, determined by SHRIMP zircon U–Pb and 39Ar/40Ar isotopic dating techniques. Regionally, simultaneous tectonic extension was associated with pre-Indosinian collision between the South China and Indochina Blocks. The S2 foliation appears as the axial plane of NW-striking S1 buckling folds formed during a compressional regime of D2. D2 is associated with collision between the South China and Indochina Blocks along the Jinshajiang-Ailao Shan suture zone, and represents the Indosinian deformation. The Dulong granites intruded the Dulong-Song Chay dome at 144±2, 140±2 and 116±10 Ma based on 39Ar/40Ar measurement on muscovite and biotite. The dome was later overprinted by a conjugate strike-slip fault and related thrust fault, which formed a vortex structure, contemporaneously with late Cenozoic sinistral movement on the Ailao Shan-Red River fault. 相似文献