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位于福建省东南沿海地区的长乐—诏安构造带(以下简称长—诏带),是一条自中生代形成以来经历过多期次强烈活动的深大断裂构造带,亦是一条强震活动带。由于本断裂带地处我国东部活动大陆地壳的边缘地带,同时又紧邻西太平洋巨型岛弧—海沟系中的台湾岛弧——现代构造运动最强烈的构造带,因而使长—诏带的地壳结构、岩浆活动、岩石—构造变动及其演化、地震地质等均有许多独特之处。本文仅就其新构造活动特征的成因机制作一初步分析与探讨。 相似文献
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在印度洋板块与欧亚板块的碰撞-挤压作用下,不仅形成了喜马拉雅弧形山造山带,而且导致其东部弧顶—东构造结似一尖楔沿NNE方向插入青藏高原的东北缘.造成了巴颜喀拉块体和龙门山断裂系深、浅部构造强烈活动和变形,并导致高原腹地壳、幔物质以大型走滑断裂为通道边界向E-ES方向运移.2008年5月12日汶川—映秀MS8.0地震就发生在这相对活动的巴颜喀拉块体与相对稳定的四川盆地之间的龙门山断裂系辖区内.基于该区深部壳、幔结构和主震（MS8.0）与7万多次余震震中位置与震源深度的展布研究表明,汶川—映秀MS8.0地震的发震断裂不是震中在地表投影位置附近,而是龙门山断裂系3条以不同角度西倾、且向下在15±5 km深处汇聚的断裂带CF.该发震断裂带不是一条简单的线性断裂带,而是一半径为5 km左右的柱状震源体,沿NE向展布.在青藏高原东北缘深部物质向东与向东南运动过程中地壳各层整体逐渐抬升,且在龙门山断裂系地带为减薄的转折部位,而地壳低速层却在这里尖灭.在两陆-陆板块碰撞力系作用下,壳、幔介质以上地壳底部低速层（深20±5 km）为上滑移面,并与上地壳解耦,而在深处则以岩石圈底部漂曳的软流层顶部（深100±10 km）为下滑移,故下地壳和上地幔盖层物质才能同步运动.它们在四川盆地高速“刚性”壳、幔物质阻隔下,龙门山断裂系的3条向下汇聚的断裂带与下地壳和上地幔盖层物质同步沿龙门山断裂系的断层面向上逆冲,当向上与向下同步运动的固态壳、幔介质二者在15±5 km深处强烈碰撞时激发了这次MS8.0地震和一系列强余震的发生和发展.基于上述可见,对强烈地震孕育,发生和发展的深部介质与构造环境,深部物质与能量的交换、运移和深层动力过程的研究乃核心所在. 相似文献
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2015年4月25日发生在尼泊尔博克拉MS8.1大地震的深层动力过程与“地中海-喜马拉雅-南亚地震带”的中段喜马拉雅地震活动带密切相关.这次大地震是该地震强烈活动带上长期以来深部物质与能量强烈交换、运动，并导致构造活动和应力积累的产物.综合分析与研究提出：（1）博克拉MS8.1大地震的孕育、发生和发展具有长期活动和近年来相邻地带地震活动频繁的背景；这一地带自1505年-2015年，即500多年来相继发生多次MS≥8.0的大地震.（2）这一地带具有特异的地球物理边界场响应和深层动力过程，显示深部物质的重新分异、调整与能量交换.（3）大地震发生与周边地带应力场分布特异，壳、幔结构与介质属性变异及破裂响应与断层面解的属性相关.（4）喜马拉雅地带的三条北倾断裂带以不同角度向深部延伸、震源位置及浅表层的变形特征尚应深化理解.（5）MS8.1大地震的发生对相邻地带的波场影响强烈，故应强化高精度地球物理场的观测和探测，以“捕捉”未来可能大地震的孕育与发生. 相似文献
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本文对近年来在攀枝花-西昌（攀西）构造带所做的重力、地磁、航磁、古地磁、遥感、天然地震、大地电磁测深、地热和爆炸地震探测资料,进行了综合分析和研究,得出了该构造带的深部结构和地球物理场的特征。基于此,提出了攀西吉裂谷存在的地球物理标志,论述了该裂谷带与现代强烈活动的裂谷带和已消亡的古裂谷的差异与其“活化”的证据。本文最后提出,这是一个被动“活化”的古裂谷的论点。 相似文献
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利用最新的重磁数据对冲绳海槽南部的基底构造进行了推断解释，研究表明，在冲绳海槽南部，莫霍面构造为一南北两端高，中间低的鞍状构造，地壳厚度在15.5~21 km之间变化.基底深度一般在4~6 km之间变化，表现为南段深度大，北段深度小，在北西向断裂系的作用下，基底局部构造大都成北西向展布，说明冲绳海槽早期的北东向带状构造受到了后期的北西向构造活动的强烈改造作用.在冲绳海槽南部发育有两条沿北北东向展布的火成岩带，一条分布在冲绳海槽扩张轴以东及琉球岛弧西侧下坡；另一条分布在冲绳海槽与琉球岛弧隆褶带的结合部位，火成岩主要是由北东向构造活动产生的，而与北西向断裂关系不密切. 相似文献
7.
东昆仑活动断裂带及其强震活动 总被引：17，自引：0，他引：17
本文在简述东昆仑活动断裂带的构造背景与演化历史的基础上，重点叙述了该活动断裂带的展布，几何结构，第四纪运动和强震活动等特征，指出，这是一条具有长期演化历史，深部构造背景和第四纪乃至全新强烈活动的断裂带。因而在我国大地构造演化，尤其在青藏高原隆起形成，占有重要地位，同时，它还是我国西部地区一条主要的强震活动构造带，根据现代强震活动记录和在全带新发现的多期全新世古地震及其地表破裂带，分析了大震在断裂带 相似文献
8.
青藏高原东缘龙门山构造带是研究青藏高原地壳物质向东侧向挤出的焦点地区.为探索龙门山构造带活动构造特征及其与发震构造的关系，本文通过布置垂直龙门山构造带南段芦山地震震源区的大地电磁测深剖面，运用多种数据处理手段，得到研究区可靠的电性结构，并通过与已有龙门山中段和北段剖面进行对比分析.研究表明：（1）青藏高原东缘岩石圈存在明显的低阻异常带--松潘岩石圈低阻带，该低阻异常带沿龙日坝断裂-岷山断裂-龙门山后山断裂分布，形成松潘-甘孜地块向扬子地块俯冲的深部动力学模式，通过统计研究区的历史强震，发现震源主要沿低阻异常带东侧分布，同时，低阻异常带也是低速度、低密度异常带，松潘岩石圈低阻带可能是扬子地块的西缘边界；（2）青藏高原物质东移过程中，受到克拉通型四川盆地的强烈阻挡，龙门山构造带表层岩块和物质发生仰冲推覆，表现为逆冲推覆特征的薄皮构造，中下地壳和上地幔顶部物质向龙门山构造带岩石圈深部俯冲，印支运动晚期，扬子古板块持续向华北板块俯冲，在上述构造运动作用下，呈现出刚性的上扬子地块西缘高阻楔形体向西插入柔性青藏块体的楔状构造；（3）根据电性结构推断，芦山地震受到深部上里隐伏壳幔韧性剪切带向上扩展的影响，构成芦山地震的深部主要动力来源；汶川地震的发生，在龙门山南段形成应力加载区，是触发或加快芦山地震孕育发生的另一个动力来源. 相似文献
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克拉通化与华北陆块的形成 总被引：16，自引：0，他引：16
翟明国 《中国科学:地球科学》2011,(8):1037-1046
克拉通化是稳定的大陆形成的重要事件,在地球演化历史上未见重复.华北克拉通的形成经历了两期克拉通化事件,为理解早期陆壳的形成与演化提供了难得的实例.第一期克拉通化发生在新太古代末期,很可能是在2.53~2.60Ga的微陆块拼合之后很短的时间内,以陆壳岩石和初生地壳岩石（基性岩浆岩）的部分熔融形成广泛分布的花岗质岩石的侵入、岩墙群和裂谷型火山-沉积盖层为标志.古元古代华北克拉通出现了裂谷-俯冲-增生-碰撞的陆内造山事件,以三条古元古代的活动带为代表.第二期克拉通化即克拉通再造发生在古元古代末的陆内造山之后约1.95~1.82Ga期间,出现麻粒岩相-高级角闪岩相的克拉通基底岩石的整体抬升,伴随壳熔花岗岩形成和强烈的混合岩化,而后有镁铁质岩墙群侵入、裂陷槽和裂谷形成,以及奥长环斑花岗岩-斜长岩-碱性花岗岩-碱性火山岩的非造山岩浆活动（在18~16.5亿年）.中元古代后华北进入地台演化阶段. 相似文献
11.
Structural features of the typical continental paleorift in Panxi area are revealed by seismic tomography. (1) In the profile along the minor axis of Panxi paleorift, we found alternating high and low-velocity strips existing at different depths in the crust, presenting itself as a “sandwich” structure. The existence of these high and low-velocity anomaly strips is related to the basal lithology in the rift area. (2) An addition layer with velocity values of 7.1-7.5 km/s and 7.8 km/s exists from the base of lower crust to uppermost mantle and its thickness is about 20 km. Some study results indicate that the addition layer results from the invasion of mantle material. (3) A lens-shaped high-velocity body surrounded by relatively low-velocity material is observed at depths of 110-160 km between Huaping and Huidong in the axis of the paleorift. This is the first time to discover it in the upper mantle of the paleorift. Based on the results of geology, petrology and geochemistry, we infer that the formation of the addition layer and the lens-shaped high-velocity body in the upper mantle are related to the deep geodynamic process of generation, development and termination of the rift. On the one hand, the upwelling of asthenosphere mantle caused partial melting, and then the basaltic magma from the partial melted material further resulted in underplating and formed the crustal addition layer. On the other hand, the high-density content of mineral facies was increased in the residual melted mass of intensely depleted upper mantle, formed by basalt withdrawing. The solid-melt medium in the depleted upper mantle was mainly an accumulation of garnet and peridotite because the heating effect of lithosphere was relatively weakened in the later riftogenesis, so that a lens-shaped high-density and high-velocity zone was produced in the upper mantle. The results indicate that the energy and material exchange between asthenosphere and lithosphere and remarkable underplating would have an important effect on the material state and propagation of seismic wave in the lower crust, crust-mantle interface, asthenosphere and lithosphere. This process possibly is an important mechanism on the growth of continental crust and the evolution of deep mantle. 相似文献
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Structural features of the typical continental paleorift in Panxiarea are revealed by seismic tomography. (1) In the profile along the minor axis of Panxi paleorift, we found alternating high and low-velocity strips existing at different depths in the crust, presenting itself as a "sandwich" structure. The existence of these high and low-velocity anomaly strips is related to the basal lithology in the rift area. (2) An addition layer with velocity values of 7.1-7.5 km/s and 7.8 km/s exists from the base of lower crust to uppermost mantle and its thickness is about 20 km. Some study results indicate that the addition layer results from the invasion of mantle material. (3) A lens-shaped high-velocity body surrounded by relatively low-velocity material is observed at depths of 110-160 km between Huaping and Huidong in the axis of the paleorift. This is the first time to discover it in the upper mantle of the paleorift. Based on the results of geology, petrology and geochemistry, we infer that the formation of the addition layer and the lens-shaped high-velocity body in the upper mantle are related to the deep geodynamic process of generation, development and termination of the rift. On the one hand, the upwelling of asthenosphere mantle caused partial melting, and then the basaltic magma from the partial melted material further resulted in underplating and formed the crustal addition layer. On the other hand, the high-density content of mineral facies was increased in the residual melted mass of intensely depleted upper mantle, formed by basalt withdrawing. The solid-melt medium in the depleted upper mantle was mainly an accumulation of garnet and peridotite because the heating effect of lithosphere was relatively weakened in the later riftogenesis, so that a lens-shaped high-density and high-velocity zone was produced in the upper mantle. The results indicate that the energy and material exchange between asthenosphere and lithosphere and remarkable underplating would have an important effect on the material state and propagation of seismic wave in the lower crust, crust-mantle interface, asthenosphere and lithosphere. This process possibly is an important mechanism on the growth of continental crust and the evolution of deep mantle. 相似文献
14.
A numerical model describing the thermomechanical state of the “cold” upper mantle near a mid-oceanic ridge (MOR) spreading at a moderate rate is constructed in the approximation of the boundary layer theory. The condition of rift valley formation leads to a constraint on the temperature and shows what temperature distribution corresponds to the “cold” upper mantle. Taking into account the dependence of mantle rheology on the pressure, temperature, and viscous stresses, the model distributions of the pressure and normal viscous stresses at the base of the lithosphere result in a bend of the heterogeneous lithosphere near the MOR, producing a seafloor topography typical of a rift valley with a depth of a few hundred meters and a spreading rate of ～2.5 cm/yr, characteristic of the Atlantic Ocean. The model width of the rift valley (～10–15 km) agrees with observations fairly well. The model is consistent with the typical heat-flow values observed in the spreading zone. 相似文献
15.
P. Brotzu M. T. Ganzerli-Valentini L. Morbidelli E. M. Piccirillo R. Stella G. Traversa 《Journal of Volcanology and Geothermal Research》1981,10(4):365-382
The different basalt types related to rift structure development have been investigated, starting from the pre-rift stage in the northern Ethiopian rift and its eastern escarpment and plateau.The basic volcanic rocks are represented mainly by transitional basalts, both in the pre-rift (plateau) and rift (escarpment and rift floor) stages. A striking feature is that although the plateau basalts show clear tholeiitic affinity and the rift basalts reveal a somewhat pronounced “alkaline” character, the REE and LILE element abundances, however, progressively decrease from the “tholeiitic” basalts of the plateau to the “alkaline” basalts of the rift.All data support the view that such contrasting features may be attributed to a continuous depletion of hygromagmatophile (REE, LILE) elements in the mantle source material, related to the large volumes of magmas produced in the early phase of rift structure development. The transition from “tholeiitic” (plateau) to “alkaline” (rift) transitional basalts is related to decreasing intensity of extensional movements. 相似文献
16.
对横穿辽河裂谷的闾阳－海城－东沟剖面的深部地震探测、重力测量、大地电磁测深、大地热流测量资料做了进一步分析,发现辽河裂谷地带壳幔间具有多个薄层过渡的特征,与东西两侧的辽东台隆和燕山台褶带明显不同。壳幔过渡带的薄层结构、速度结构、温度结构以及壳内低速层和软流圈顶面构造特点表明辽河裂谷的构造演化过程自西向东侧向迁移,当前上地幔物质运动的前锋不在裂谷之下,而是向东移至金州地震带附近的析木一带,深部物质运动是辽河裂谷形成及其活动性侧向迁移的主要动力学因素 相似文献
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青藏高原内部除大规模的东西向走滑断裂以外,另一个显著的地质特征就是在藏南及高原腹地广泛发育东西向的伸展构造,形成走向近南北的断裂构造,如亚东一谷露裂谷带及双湖断裂.伸展构造已经成为青藏高原地质研究的一个焦点问题.在羌塘地块89°E附近存在明显的低重力、负磁、深度达300 km的低速异常及连通壳幔的高导异常,且地表伴生大规模的新生代火山岩,这些特殊的地质及地球物理场特征的发生位置与地表双湖断裂的位置基本对应.本文通过卫星重力数据的多尺度小波分析结果发现,双湖断裂之下,存在一明显由上地壳一直向下延伸至地幔深部的低重力异常,说明双湖断裂向下延伸深度大,且上下连通性好.结合已有的地质和地球物理资料,认为由于双湖断裂的存在,使得深部幔源岩浆沿断裂构造薄弱带上涌,从而导致羌塘地块之下壳幔温度的升高及大规模部分熔融的发生. 相似文献
18.
A dynamic mechanism that accounts for the sinking of a lithospheric plate near an accretion zone in the vicinity of a passive rift is revealed. It is shown that the influence of the underlying “cold” mantle can be described in terms of a concentrated vertical force applied to the rift axis. At a moderate spreading rate, the value of this force is an order of magnitude smaller than the characteristic values of forces acting in the plate tectonics. The average viscosity coefficient of the cold upper mantle is estimated at ～1021 P. The concentrated force at the rift axis produces a characteristic topography of the rift valley type of mid-ocean ridges. 相似文献
19.
Volker Haak 《Surveys in Geophysics》1980,4(1-2):57-69
Laboratory data of the electrical conductivity of rocks and minerals pertinent to the deeper crust and upper mantle and summarized. They are discussed in the context of a theory to calculate effective conductivities of materials in the state of partial melt. Most published data have been obtained by too rapid measurements, i.e. without reaching an equilibrium state of the sample. Conductivity measurements on a material similar to the composition of pyrolite are not het known, their importance is outlined. A global conductivity distribution obtained by electromagnetic induction studies is represented by a few results covering oceanic and continental areas. Till today it seems to be a doubtful venture to deduce the temperature of the upper mantle or even the existence of a partial molten asthenosphere from a global conductivity distribution. On a more local scale the correlation of electrical conductivity with temperature and state of the material seems to be more realistic. This is tentatively shown by two petrological models of the Afar depression in Ethiopia and of the midoceanic rift. 相似文献
20.
Thomas K. Nielsen Hans Christian Larsen John R. Hopper 《Earth and Planetary Science Letters》2002,200(3-4):271-286
We present new and reprocessed seismic reflection data from the area where the southeast and southwest Greenland margins intersected to form a triple junction south of Greenland in the early Tertiary. During breakup at 56 Ma, thick igneous crust was accreted along the entire 1300-km-long southeast Greenland margin from the Greenland Iceland Ridge to, and possibly 100 km beyond, the triple junction into the Labrador Sea. However, highly extended and thin crust 250 km to the west of the triple junction suggests that magmatically starved crustal formation occurred on the southwest Greenland margin at the same time. Thus, a transition from a volcanic to a non-volcanic margin over only 100–200 km is observed. Magmatism related to the impact of the Iceland plume below the North Atlantic around 61 Ma is known from central-west and southeast Greenland. The new seismic data also suggest the presence of a small volcanic plateau of similar age close to the triple junction. The extent of initial plume-related volcanism inferred from these observations is explained by a model of lateral flow of plume material that is guided by relief at the base of the lithosphere. Plume mantle is channelled to great distances provided that significant melting does not take place. Melting causes cooling and dehydration of the plume mantle. The associated viscosity increase acts against lateral flow and restricts plume material to its point of entry into an actively spreading rift. We further suggest that thick Archaean lithosphere blocked direct flow of plume material into the magma-starved southwest Greenland margin while the plume was free to flow into the central west and east Greenland margins. The model is consistent with a plume layer that is only moderately hotter, 100–200°C, than ambient mantle temperature, and has a thickness comparable to lithospheric thickness variations, 50–100 km. Lithospheric architecture, the timing of continental rifting and viscosity changes due to melting of the plume material are therefore critical parameters for understanding the distribution of magmatism. 相似文献