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1.
医巫闾山地区早白垩世同伸展花岗岩就位机制 总被引：2，自引：2，他引：0
石山岩体形成的时间约为124Ma,是医巫闾山地区早白垩世NWW向伸展变形的同构造花岗岩体。花岗岩的主量、微量元素含量表现出埃达克质岩浆的特点,SiO 2、Al2O3及碱性组分含量较高,而Fe2OT3和MgO含量较低,岩浆锆石εHf(t)值=-26.7~-20.3、tDM2=2.0~2.3Ga,表明岩浆来源于华北陆块加厚下地壳的部分熔融。通过对围岩变形组构与岩体中岩浆组构的分析,可将石山岩体的就位过程划分为三个阶段。在岩浆底劈、膨胀作用和围岩伸展滑移的共同影响下,石山岩体最终形成了主体呈近圆形、西部发育两个岩墙的形态。岩浆就位过程与围岩变形组构的相互关系,表明中、浅部地壳的伸展变形可以控制岩浆的就位过程和最终形态,但与下地壳部分熔融的关系不大,岩石圈减薄及区域伸展应力场是下地壳发生部分熔融的诱因。 相似文献
2.
晚中生代期间医巫闾山地区经历了早期的高温韧性变形和晚期的低温脆韧性变形,并最终形成了变质核杂岩。该变质核杂岩中发育多个中-晚侏罗世花岗岩体,通过分析花岗岩体的岩浆组构及围岩中变形组构的特点,确定该期次的岩浆活动与高温韧性变形同时发生,且这些岩体就位于中部地壳的高温韧性剪切带内。岩浆就位的过程包括三个阶段：部分熔融与垂向运移阶段(D1)、水平运移阶段(D2)和固态变形阶段(D3)。尖砬子岩体的主量、微量元素分析结果显示岩浆为埃达克质岩浆,并具有过铝质和由钙碱性向高钾钙碱性过渡的特点。岩石的Th/U比值和碱性组分含量较高,Mg、Cr、Fe2OT3含量较低,岩浆锆石εHf(t)值=-29.5～-23.3、TDM2=2.51～2.18 Ga。这些特点指示岩浆来源于古老的华北陆块下地壳的部分熔融,表明岩浆具有从地壳深部向地壳浅部运移的过程。中-晚侏罗世岩体的产出形态、岩浆组构及磁组构的优选方位,表明岩浆在就位于中部地壳的过程中受到围岩剪切作用的控制,发生强定向的水平流动,形成了NE-SW向延伸最长、垂向最短的扁纺锤状岩浆房。对比中-晚侏罗世和早白垩世两期同构造岩浆就位机制,发现岩浆就位机制与围岩构造环境关系密切。同为下地壳部分熔融并向浅部运移的两期岩浆活动,岩浆就位机制差异很大：中-晚侏罗世岩浆就位于中部地壳的强剪切部位,就位过程中岩浆以侧向流动为主、气球膨胀作用为辅;早白垩世岩浆就位于浅部地壳的弱剪切部位,岩浆以气球膨胀作用和底辟作用为主。岩浆就位过程中不但受到围岩剪切作用的控制,岩浆房的扩张也会挤压围岩,使围岩叶理的产状发生变化,进而影响对构造性质的判断。 相似文献
3.
位于燕山构造带东端的医巫闾山变质核杂岩经历了两次地壳伸展活动,早期在NNE-SSW拉伸背景下形成了现今围
绕医巫闾山岩体周缘分布的拆离韧性剪切带与相应的变质核杂岩,晚期隆升过程中由于拉伸方向转变又叠加发育了瓦子峪
伸展韧性剪切带。早期伸展变形中,围绕在拆离韧性剪切带及变形下盘中侵入了大量不同变形样式的同构造花岗岩脉。通
过对不同阶段侵入的岩脉进行LA-ICP-MS 锆石U-Pb 定年,显示该核杂岩的活动时间为157~149 Ma。医巫闾山地区晚侏罗
世伸展活动的确定,暗示华北克拉通北部可能从晚侏罗世已经开始发生破坏,到早白垩世达峰期并遍及整个华北克拉通东部。 相似文献
4.
内蒙古苏尼特左旗早白垩世宝德尔花岗岩伸展穹隆的确定及其地质意义 总被引：3，自引：1，他引：2
内蒙古宝德尔穹隆是发育在苏尼特左旗中蒙边境地区的不对称同构造伸展穹隆。该穹隆由内向外由核部早白垩世花岗岩、边缘韧性剪切带和脆性拆离断层组成,上盘为未变形的早二叠世花岗闪长岩、泥盆系片岩和早白垩世盆地,韧性剪切带和拆离断层仅发育在穹隆西南部。区域构造解析和显微构造分析表明,岩体侵位和韧性剪切带形成于同一构造应力场,指示上盘统一向NW方向剪切,变形程度由未变形的岩体核部向外侧逐渐增强,面理的形成与岩体的侵位和隆升过程密切相关。因此,该穹隆和东北亚其他岩浆穹隆相似,是不对称的花岗岩穹隆,反映了区域伸展拆离环境下侵位的同构造花岗岩穹隆的特点。 相似文献
5.
医巫闾山岩体同伸展侵位的证据及其地质意义 总被引：2，自引：0，他引：2
医巫闾山岩体是医巫闾变质核杂岩的重要组成部分。根据医巫闾山地区花岗岩变形特征及与周围构造带的相互关系,确定医巫闾山岩体为同伸展侵位的岩体,且以岩床的形式顺层侵入在医巫闾山伸展型韧性剪切带之中,修正了前人挤压环境下岩浆侵位的观点。医巫闾山岩体及尖砬子山岩体的侵位时间在160 Ma左右,表明医巫闾山地区及燕山地区中侏罗世晚期发生过强烈的地壳伸展运动,华北北部的构造体制在中侏罗世已经改变。区内中生代存在2期伸展作用：早期伸展作用发生在中侏罗世晚期,与医巫闾山岩体的侵位同期;晚期伸展作用发生在早白垩世,形成了瓦子峪拆离断层。 相似文献
6.
辽南变质核杂岩饮马湾山和赵房岩体锆石SHRIMP U-Pb年龄及其地质意义 总被引：4，自引：2，他引：2
辽南变质核杂岩形成于晚中生代华北岩石圈伸展和减薄背景下,其演化过程分为三个阶段：第一阶段（约130Ma）,在伸展作用下辽南地区发育拆离断层及其下伏韧性剪切带;第二阶段（130~120Ma）,同构造花岗质岩体的主动侵位影响了拆离断层的演化;同时在124Ma变质核杂岩的构造-岩浆活动达到峰值;第三阶段（113Ma之后）花岗质岩体在较浅层次侵位于停止活动的拆离断层带。辽南变质核杂岩发育与演化过程在年代学意义上揭示了华北板块晚中生代时期的区域性岩石圈伸展与减薄过程。本文认为由伸展后期侵位的赵房岩体所记录的拆离断层停止的时限（113Ma）可以作为华北岩石圈强烈构造岩浆活动的转捩点,113Ma之前华北板块广泛发育变质核杂岩、拉分盆地等一系列伸展构造,之后则以平稳的隆升和冷却过程为主。 相似文献
7.
华北克拉通及邻区晚中生代伸展构造及其动力学背景的讨论 总被引：13，自引：8，他引：5
欧亚大陆东部晚中生代伸展构造十分显著,表现为大量发育的变质核杂岩、同构造岩浆岩、韧性拆离断层带等伸展成因的穹隆和地堑-半地堑盆地.通过对这些伸展构造进行系统分析、归纳和总结,将欧亚大陆东部晚中生代伸展构造发育区划分为:泛贝加尔-鄂霍次克带、华北西部带、华北东部带、华北南缘及秦岭-大别带和华南内陆带.这些伸展构造记录了大区域上的NW-SE方向伸展,构成了全球最大的陆壳伸展地区.这些伸展构造使地壳深部的岩石沿拆离断层折返至地表,从而使中下地壳结构发生了强烈的改造.除华北东部带给出了一个较为宽泛的伸展时段外,各个研究区所涉及的伸展穹隆及其相关的拆离断层所表现的伸展峰期时间均十分相近:位于130 ～ 126Ma之间.岩石圈根部的拆沉可能是这个巨型伸展构造带形成的动力学机制.这个模型为探讨华北克拉通破坏和减薄的时限、机制、模式及深部动力学背景提供直接的构造证据. 相似文献
8.
穿地壳岩浆系统模型是近年新提出的一个全新的岩浆系统概念.聚焦山东东部早白垩世青山期穿地壳岩浆系统,在野外地质踏勘的基础上,结合火成岩年代学、断裂体系分布、大地构造学与地球化学的相关研究成果,系统探讨了不同性质火山岩浆的时空演化与分布特征.首先,在时间序列上,早白垩世青山期穿地壳岩浆系统,表现为酸性岩浆侵位-基性岩浆侵入-中性岩浆喷发的特征;其次,在不同的地壳深度,穿地壳岩浆系统有不同的表现,由深到浅,呈现岩基/岩株-岩脉岩墙-火山机构的变化;空间分布上,酸性岩体多位于古隆起区,火山机构沿深大断裂呈现串珠状分布.穿地壳岩浆系统的发育特征指示了青山期岩石圈的构造特征:岩体自身近E-W向展布,说明岩体侵入时的中上地壳的断裂体系主要为近E-W向,而岩体整体上沿着NE-SW向分布,说明了更深部断裂体系主要为NE-SW向,控制了整个区域构造的发育.早白垩世早期（莱阳期）区域发育的浅层构造断裂系统为早白垩世晚期（青山期）的穿地壳岩浆系统的发育提供了通道.早白垩世青山期穿地壳岩浆系统的发育伴随着区域热隆-伸展-滑脱作用,在此过程中山东东部青山期盆地格局形成.花岗岩抬升速率初步计算的结果表明山东东部地区早白垩世青山期的热隆速率略快于2.7~4.1 mm/a,强烈的"热隆-伸展-滑脱"作用是同期沉积盆地形成的主要动力学机制. 相似文献
9.
华北克拉通岩石圈减薄和破坏机理长期以来存在争议,基于岩石学、岩石地球的化学分析研究突出强调深部过程的重要性。前人提出了两种重要模式:包括以拆沉作用为代表的top-down tectonics模型和以热-机械侵蚀与化学侵蚀,或地幔置换、交代作用的bottom-up tectonics模型。然而,对于这两种模式而言尚存在许多无法合理解释的问题,比如在此深部过程中,区域性岩石圈伸展有多大的贡献?地壳伸展构造是作为深部过程的响应,还是同为岩石圈伸展的产物?本文基于早白垩世东亚地区(尤其是华北克拉通东部地区)伸展构造与岩浆活动的综合分析,揭示出华北克拉通东部不同地区伸展构造变形与岩浆活动之间的时、空和成因关系有一定的差异。但整体上看,岩石圈伸展起着主导作用,控制着岩浆上侵和就位,在拆离断层下盘侵入形成各种规模的花岗质为主的侵入体,或于上盘喷发形成火山-沉积岩盆地。在伸展构造发育的不同阶段,可以有伸展早期、伸展期及伸展期后的岩浆活动。岩浆活动的强度及岩浆源区特点有显著的时空变化。一方面,在同一地区不同演化阶段其源区有很大的差异。表现为主体上是早期以古老下地壳源为主,随着壳/幔伸展作用演化,逐渐向混合源或独立幔源的演化。同时,不同地区岩浆源区的变化规律也显著不同。以胶辽地区为例,胶东整体上是壳幔混合源区对于岩浆演化有重要贡献;而辽东地区具有显著的源区演化特点:从剪切早期古老下地壳源区为主,并伴有幔源物质加入,剪切期古老下地壳为主,到剪切晚期和剪切期后以新生下地壳为主。本文认为岩石圈伸展的壳/幔拆离模型(Parallel Extension Tectonics),可以合理地解释华北克拉通及邻区早白垩世构造-岩浆活动性。在该模型中,遭受伸展的华北克拉通岩石圈发生壳-幔拆离作用。在岩石圈伸展作用期间,地壳层次的拆离作用与岩石圈地幔层次上的拆离作用可以是耦合的或者是解耦的,从而导致华北克拉通岩石圈减薄过程中在地壳尺度上的拆离作用与变质核杂岩的剥露有三种不同的类型:同岩浆活动型伸展(C型:Co-magmatism mode extension)、无岩浆活动型伸展(A型:Amagmatism mode extension)和多阶段混合型(M型:Multi-mode extension)。 相似文献
10.
张八岭隆起广泛分布的平缓韧性剪切带与郯庐断裂带平移作用形成的陡立韧性剪切带明显不同。通过对平缓韧性剪切带的几何学、运动学分析,结合早白垩世盆地特征、中国东部变质核杂岩伸展拆离断层和同构造岩浆岩同位素定年结果,厘定出张八岭隆起早白垩世变质核杂岩。该变质核杂岩上盘由南华纪-奥陶纪沉积地层和早白垩世盆地组成,下盘为新元古代浅变质碎屑沉积岩、变海相火山岩（基底）以及早白垩世侵入岩,上下盘之间被一条主伸展拆离断层所分隔。变质核杂岩长轴为NE-SW向,指示构造反映上盘向SE剪切滑动,与中国东部变质核杂岩的伸展方向完全一致。通过本次变质核杂岩的厘定,结合野外地质事实,笔者认为管店-马厂断裂是郯庐断裂带的次级断裂,是对郯庐断裂带早白垩世末第三次左行平移的响应。在综合研究的基础上,建立了区域构造-岩浆-成矿关系模型,揭示了张八岭隆起早白垩世经历了早期伸展（变质核杂岩阶段）-挤压走滑（管店-马厂断裂形成阶段）-晚期伸展（闪长质脉岩侵位阶段）3个构造阶段,多期构造、岩浆的叠加作用下,形成了本区的金多金属矿产。 相似文献
11.
小秦岭文峪和娘娘山花岗岩体锆石SHRIMP U-Pb年龄及其意义 总被引：13，自引：0，他引：13
对小秦岭文峪和娘娘山花岗岩体进行的锆石SHRIMP U-Pb定年和岩石地球化学分析结果表明,文峪和娘娘山黑云母二长花岗岩体属于Ⅰ型花岗岩,是太古宙太华群高级变质岩系经部分熔融的产物。它们的成岩年龄分别为138.4±2.5 Ma和141.7±2.5 Ma,略早于本区拆离伸展活动的时限,暗示了中下地壳部分熔融形成的岩浆热穹窿和花岗质岩浆在上地壳的大面积侵位导致了小秦岭变质核杂岩的发育。花岗岩体的成岩年龄都早于本区金矿床的主期成矿时代,从时间上表明了花岗质岩浆活动与金矿成矿作用无直接关系。 相似文献
12.
The role of regional extension on the rise and emplacement of granites in the crust is still debated. Pluton ascent and emplacement widely occurred in Tuscany (Italy) since late Miocene during the post-orogenic collapse of the inner Apennines, and are presently occurring in the geothermal areas of Amiata and Larderello. Tuscany offers a preferred test site to study the role of regional extension on pluton ascent and emplacement at different crustal levels. Ductile extension enhanced the segregation and ascent of granitic melts in the lower crust, controlling pluton emplacement in correspondence with the brittle–ductile transition. In the brittle crust, magma ascent occurred through subvertical faults and fractures compatible with the regional extension direction; pluton emplacement mainly occurred by means of roof lifting. The case of Tuscany suggests that the extensional structures enhance melt segregation and ascent in the ductile crust, but are not efficient alone to provide a pathway for the ascent of granitic magmas in the brittle-extending crust. The estimated magmatic strain rates due to pluton emplacement in the geothermal areas are much larger than the regional tectonic strain rates. This suggests that regional tectonics did not control magma emplacement in the brittle crust and explains why nontectonic processes (roof lifting) accommodated the space required for pluton emplacement. 相似文献
13.
辽南金州拆离断层带中花岗质岩石的变形:显微构造、组构与年代学分析 总被引：1，自引：0，他引：1
花岗岩(脉)在中下地壳韧性剪切带中普遍发育,如何正确鉴别剪切带中剪切前、剪切期及剪切后花岗岩(脉)以及正确理解剪切过程中构造变形与岩浆作用之间的关系一直是一个重要课题。本文以辽南金州拆离断层带为研究对象,选取中部地壳伸展作用过程中具有不同变形表现的花岗岩(脉)开展宏观-微观构造观察、石英EBSD组构分析及锆石LA-ICP-MS年代学测试等工作,从而进一步丰富构造-岩浆关系判别准则。剪切前花岗岩(脉)多变形强烈且具有后期固态变形叠加在早期高温岩浆组构之上的特点,而剪切期的花岗岩由于侵位的时间不同,岩石的变形程度也会不同。剪切晚期侵入的岩脉遭受了较弱的晶内塑性变形,而剪切早期的岩脉可以显示岩浆流动或结晶后高温至中温固态变形。从组构特点上看,剪切前和剪切期花岗质岩石石英c轴组构大多表现为中高温组构叠加有低温组构的特点。剪切后的花岗质岩石仅发生微弱的晶内变形或未变形而显示低温或无规律的组构特征。对五个典型的样品进行年代学测试,其结果符合相应的期次划分类型。应用宏观构造、显微构造与组构分析,结合年代学测试综合分析,对于辽南变质核杂岩构造-岩浆活动性进行了精细划分,包括134~130Ma初始伸展阶段,130~115Ma峰期伸展与强烈岩浆活动阶段,以及115Ma前后伸展作用结束。 相似文献
14.
Hot collisional orogens are characterized by abundant syn-kinematic granitic magmatism that profoundly affects their tectono-thermal evolutions. Voluminous granitic magmas, emplaced between 360 and 270 Ma, played a visibly important role in the evolution of the Variscan Orogen. In the Limousin region (western Massif Central, France), syntectonic granite plutons are spatially associated with major strike–slip shear zones that merge to the northwest with the South Armorican Shear Zone. This region allowed us to assess the role of magmatism in a hot transpressional orogen. Microstructural data and U/Pb zircon and monazite ages from a mylonitic leucogranite indicate synkinematic emplacement in a dextral transpressional shear zone at 313 ± 4 Ma. Leucogranites are coeval with cordierite-bearing migmatitic gneisses and vertical lenses of leucosome in strike–slip shear zones. We interpret U/Pb monazite ages of 315 ± 4 Ma for the gneisses and 316 ± 2 Ma for the leucosomes as the minimum age of high-grade metamorphism and migmatization respectively. These data suggest a spatial and temporal relationship between transpression, crustal melting, rapid exhumation and magma ascent, and cooling of high-grade metamorphic rocks.Some granites emplaced in the strike–slip shear zone are bounded at their roof by low dip normal faults that strike N–S, perpendicular to the E–W trend of the belt. The abundant crustal magmatism provided a low-viscosity zone that enhanced Variscan orogenic collapse during continued transpression, inducing the development of normal faults in the transpression zone and thrust faults at the front of the collapsed orogen. 相似文献
15.
基于对辽南变质核杂岩主拆离断层及下伏韧性剪切带的几何学分析以及拆离断层带构造岩的显微构造研究,结合变质核杂岩构造—岩浆活动及其形成过程和力学机制,重点讨论了主拆离断层的波瓦状构造的特点及其形成条件。结果表明:波瓦状构造的发育与下盘晚期阶段花岗质岩体的侵位具有同时性。伸展构造发育初期就位的深成岩体加热和软化了上部地壳,此时岩石力学属性控制的钝角锯齿状断裂构成了波瓦状构造的雏形,晚期阶段花岗质深成侵入岩的不均匀侵位制约了波瓦状构造的发育。 相似文献
16.
《Journal of Structural Geology》1999,21(8-9):1125-1130
Integrated studies that correlate gravity data with magmatic structures or geochemical analysis reveal that the organization of granitic plutons (shape and feeder) varies according to the tectonic regime (brittle or ductile) and type (extension, strike-slip or compression) under which magma was generated. Deformation clearly controls granite emplacement. It also has influence during the ascent, segregation of melt and indirectly during the phase of initial melting. Because of the contrast of viscosity between melt and its plastic matrix, strain partitioning develops during magma ascent that facilitates melt flow, which bears consequences for the chemical evolution of the magma. Fast rate of melt extraction out of the source may lead to chemical disequilibrium. At a larger scale, petrochemical zoning of plutons is described as a dynamic process that results from the competition between the rate of magma emplacement (the rate of the room provided by deformation) and the rate of magma delivery. 相似文献
17.
花岗岩可以视为一种很好的构造标志体,犹如褶皱、断裂一样。从花岗岩浆的形成、融体分离、岩浆上升到岩体定位以及变形改造的全过程都蕴含着丰富的构造动力学信息。研究花岗岩浆上升、迁移和定位可以探讨构造块体抬升及区域构造动力学。岩体生长方式与构造块体的运动学、动力学有密切的关系,极性生长揭示了上、下构造块体或岩石圈之间的相对的近水平方向剪切运移。变形花岗岩体是一种区域尺度的应变标志体,可以进行岩石有限应变测量和流变学参数估算,为分析区域构造变形特征提供应变参数。以对不同期次、不同变形程度花岗岩体为间接标志体,通过锆石定年可以限定变形的时间,特别是有可能确定早期变形的时间。岩体定位深度的系统研究有利于了解构造块体的抬升和深部构造作用。花岗岩构造与花岗岩成因类型特别是其演变研究的结合是判别构造块体动力学背景以及其转换的有效途径。通过这几方面的系统研究和有机结合,可以提供丰富的构造动力学信息,是否可能发展成较系统的花岗岩构造动力学值得探讨。 相似文献
18.
The Swakop River exposes a unique structural section into the root of the Pan-African Damara orogenic belt (DOB) in Namibia formed as a result of collision between the Congo and the Kalahari cratons from ca. 550 to 500 Ma. The Central Zone of the Damara orogenic belt is characterized by amphibolite to granulite facies metamorphism accompanied by intense partial melting. Three tectonic units are defined in the Central Zone based on the proportion and distribution of the granitic fraction, namely (1) a lower unit dominated by diatexites and comprising plutons of homogeneous granites, (2) a middle unit composed by metatexites with mainly a metasedimentary protolith, and (3) an upper unit corresponding to metamorphic rocks with intrusive leucogranitic sills and laccoliths. The increase in the granitic fraction with structural depth is suggesting an increase in the degree of partial melting and implies a relative inefficiency of magma mobility from the source to higher structural levels. The transition from metatexites of the middle unit to diatexites and granites of the lower unit is interpreted as reflecting the former transition from partially molten rocks to a crustal-scale magmatic layer. Mushroom-shaped granitic plutons in the lower unit are consistent with their emplacement as diapirs and the development of gravitational instabilities within the magmatic layer. In the middle unit, granitic veins concordant and discordant to the synmigmatitic foliation localized in structurally-controlled sites (foliation, boudin’s necks, shear zones, fold hinges) indicate that, within the partially molten zone, deformation plays the dominant role in melt segregation and migration at the outcrop scale. Melt migration from the partially molten zone to the intrusive zone is related to the build-up of an interconnected network of dikes and sills with diffuse contacts with the migmatitic hosts in the middle unit. In contrast, the upper unit is characterized by homogeneous leucogranitic plutons in sharp intrusive contact with genetically unrelated host rocks suggest that part of the melt fraction has migrated upward from its source to an intrusive zone. 相似文献
19.
The northern Menderes metamorphic core complex has complex exhumation history and is one of the key localities to investigate the spatial and temporal relationships of extensional and compressional structures. Detachment faults and syn-extensional plutons are linked to a series of antiforms and synforms and the denudation of the northern Menderes Massif occurred in three stages. The first stage is related to the development of detachment faults under the consistent NE–SW-directed extension. The second stage is represented by a series of elongated magmatic domes that were oriented parallel, oblique and perpendicular to the regional extension direction. Emplacement of these asymmetrical magmatic domes appears to have been controlled by heterogeneous extension and post-dates the extensional Simav detachment fault. On the third stage, progressive heterogeneous extension that led to updoming of plutons has been finally accommodated by a localised and short-lived transfer zone, which was described as the Gerni shear zone for the first time in this study. The transfer zone is formed by a NE-striking, dextral ductile/brittle shear zone that accommodated the propagation of folds, conjugated strike-slip faults and normal- and oblique-slip faults. Mylonites associated with the transfer zone are related to the localisation of strain along the thermally weakened strike-slip fault systems by short-lived intrusions rather than to the development of regional-scale detachment faults. These structures are consistent with a transtensional simple shear model, which properly explains the evolution of extensional and compressional structures exposed in the northern Menderes core complex. Structural setting of the E?rigöz region is somewhat similar to that of the NE-trending gneiss domes in the northern Menderes Massif and updoming of magma during late stages of detachment faulting appears to have played an important role in the exhumation of lower and upper plate rocks. 相似文献