Deformation style in the damage zone of the Mondy fault: GPR evidence (Tunka basin,southern East Siberia)

The Mondy strike-slip fault connects the W-E Tunka and N-S Hovsgol basins on the southern flank of the Baikal rift system. Ground penetrating radar (GPR) surveys in its damage zone provide constraints on thicknesses, dips, and plunges of fault planes, as well as on the amount and sense of vertical slip. Strike-slip faulting in the southern segment of the Mondy fault within the territory of Russia bears a normal slip component of motion along the W-E and NW planes. These motions have produced negative flower structures in shallow crust appearing as grabens upon Pleistocene fluvioglacial terraces. The amount of normal slip estimated from the displacement of reflection events varies over the area and reaches its maximum of 3.4 m near Mondy Village. In the Kharadaban basin link, left-lateral strike slip displaces valleys of ephemeral streams to 22 m, while normal slip detected by GPR reaches 2.2 m; this normal-to-strike slip ratio corresponds to a direction of ~ 6° to the horizon. The angles of dips of faults are in the range 75°-79°; the thicknesses of fault planes marked by low- or high-frequency anomalies in GPR records vary from 2.5 to 17.0 m along strike and decrease with depth within a few meters below the surface, which is common to near-surface coseismic motions. Many ruptures fail to reach the surface but appear rather as sinkholes localized mainly in fault hanging walls. The deformation style in the damage zone of the Mondy fault bears impact of the NW Yaminshin fault lying between its two segments. According to photoelasticity, the stress field changes locally at the intersection of the two faults, under NE compression at 38°, till the inverse orientations of principal compression and extension stresses. This stress pattern leads to a combination of normal and left-lateral strike slip components.     

Mapping crustal structure beneath southern Tibet: Seismic evidence for continental crustal underthrusting

Receiver function imaging along a temporary seismic array (ANTILOPE-2) reveals detailed information of the underthrusting of the Indian crust in southern Tibet. The Moho dips northward from ~ 50 km to 80 km beneath the Himalaya terrane, and locally reaches ~ 85 km beneath the Indus–Yalung suture. It remains at ~ 80 km depth across the Lhasa terrane, and shallows to ~ 70 km depth under the Qiangtang terrane. An intra-crustal interface at ~ 60 km beneath the Lhasa terrane can be clearly followed southward through the Main Himalaya Thrust and connects the Main Boundary Thrust at the surface, which represents the border of the Indian crust that is underthrusting until south of the Bangong–Nujiang Suture. A mid-crustal low velocity zone is observed at depths of 14–30 km beneath the Lhasa and Himalaya terranes probably formed by partial melt and/or aqueous fluids.     

辽南庄河地区夹河山韧性剪切带构造特征及其大陆动力学背景

辽南庄河地区的夹河山韧性剪切带发育于晚三叠世—早侏罗世花岗岩岩体中,通过对其几何学、运动学、动力学及质量平衡分析等方面的研究后认为,该剪切带为自NWW向SEE运动的近水平伸展型正剪切带,形成于早燕山期,与Izanagi板块向中国东部挤压过程中因应力松弛导致的后造山伸展作用有关。     

Evolution of the Murphy synclinorium,southern Appalachian Blue Ridge,USA

The western Blue Ridge allochthon of the southern Appalachians is dominated by the >180 km-long Murphy synclinorium, paired with anticlinoria to the northwest. These are first generation, northwest overturned, doubly plunging, large amplitude and wavelength (>10 km) isoclinal folds contemporaneous with peak Neo-Acadian orogeny (Visian, ∼335–345 Ma) regional metamorphism. The synclinorium folds a regional unconformity separating Neoproterozoic rift and lower Paleozoic drift sequences from a younger successor-basin sequence. Strain analysis of metaconglomerates from lithologic groups above and below the unconformity indicates coaxial, low to moderate, oblate to nearly plane strain in both groups. The synclinorium evolved via NNW-SSE-crustal shortening (∼32%), combined with orthogonal NNE-SSW-sub-horizontal flow (stretching) (∼35–45%) sub-parallel to the developing fold axes. Differences in metamorphic grade and paleodepth (∼10–17 km) of the exposed synclinorium had essentially no effect on strain magnitudes. Retrodeformation of the embedded regional unconformity reveals a very broad synclinal warping of the rift and drift-facies units predating superposition of the Murphy synclinorium, suggesting tectonic inheritance in the latter structure's origin. The earlier mild deformation is post-Early Cambrian and may represent the only vestige of the dynamic effects of the Middle Ordovician Taconic orogeny to be found in this region.     

西秦岭北缘早古生代天水—武山构造带及其构造演化

西秦岭北缘早古生代天水-武山构造带位于甘肃省东部天水地区,主要由寒武纪关子镇-武山蛇绿岩带、晚寒武世-早奥陶世李子园群浅变质活动陆缘沉积-火山岩系、奥陶纪草滩沟群岛弧型火山-沉积岩系以及加里东期岛弧型深成侵入岩体、俯冲-碰撞型花岗岩体等组成.关子镇蛇绿岩中变质基性火山岩属于N-MORB型玄武岩,武山蛇绿岩中变质基性火山岩属于E-MORB型玄武岩,是洋脊型蛇绿岩的重要组成部分,形成时代大致在534～489Ma之间的寒武纪.李子园群火山岩主要形成于岛弧或与岛弧相关的弧前盆地构造环境,草滩沟群火山岩形成于与俯冲作用相关的岛弧环境.关子镇流水沟和百花中基性岩浆杂岩总体形成于中晚奥陶世(471～440Ma)古岛弧构造环境,同时发育加里东期俯冲型(450～456Ma)花岗岩类和碰撞型(438～400Ma)花岗岩类岩浆活动.西秦岭北缘早古生代古洋陆构造格局经历了从洋盆形成-洋壳俯冲消减直至陆-陆碰撞造山的板块构造演化过程.总体构造演化可划分为四个阶段:①晚寒武世古洋盆初始形成阶段;②早奥陶世洋盆初始俯冲阶段;③中晚奥陶世洋壳大规模俯冲与古岛弧发育阶段;④志留纪陆-陆或陆-弧碰撞造山阶段.     

青藏高原康西瓦—狮泉河地区1:100万区域重力调查成果与进展

提供岩石磁性参数统计表、各地层岩石密度统计表和布格重力异常图,并做初步分析。     

Seismic velocities from the Yaquina forearc basin off Peru: evidence for free gas within the gas hydrate stability zone

Multichannel seismic (MCS) data from the Yaquina forearc basin off Peru reveal a complex distribution of gas and gas hydrate related reflections. Lateral variations of the reflection pattern at the assumed base of the gas hydrate stability zone in terms of continuity, amplitude, and signal attenuation underneath are observed, as well as the possible occurrence of paleo-bottom simulating reflectors (BSRs). Phase reversed reflections above the bottom simulating reflector point to free gas within the gas hydrate stability zone (GHSZ). To constrain the interpretation of the observed reflection pattern we calculated the velocity distribution along the MCS line from high-resolution ocean bottom hydrophone recordings with two independent methods. Heat flux values estimated on the basis of the velocity-depth functions increase with decreasing amplitude of the BSR and peak near chemoherms. These results suggest a model of the Yaquina Basin where free gas is trapped under parts of the BSR, and within the GHSZ, particularly under the seafloor and under an erosional unconformity. The hypothesis of a paleo-BSR that reflects the uplift of the base of the hydrate stability zone caused by the deposition of a particular sediment sequence is supported by the estimated heat flux values.     

Tectonic history of the ophiolitic rocks of the highland border fracture zone, Scotland: Stable isotope evidence from rock-fluid interactions during obduction

The mafic and ultramafic rocks of the Highland Border Fracture Zone are ophiolitic remnants of a pre-Grampian marginal basin that opened either within, or to the north of, the Dalradian sedimentary pile. Closure of the basin was achieved through a combination of northerly-directed subduction, and obduction of ophiolitic thrust-slices onto the basin's southern margin. During the early stages of obduction, young hot peridotite slabs were thrust over the cold upper surfaces of lower thrust sheets, producing a dynamothermal metamorphic sole. Serpentinisation of these peridotites, whilst they were still cooling, occurred in a near-surface position through the interaction of meteoric waters. Subsequently, the ophiolitic thrust-sheets, which comprise lizardite serpentinites, spilitic pillow lavas, and aureole rocks, were thrust over the uppermost Dalradian nappes which were themselves being expelled southwards, thereby accommodating basement shortening. Grampian regional metamorphism of the nappe pile and overlying Highland Border Suite ophiolitic thrust sheets, produced greenschist metaspilites from the spilitic pillow lavas, induced minor retrogression in the aureole rocks, and caused the lizardite in the serpentinites to be recrystallised and replaced by antigorite. The Highland Border Suite greenschist facies metamorphic fluids were D-enriched compared with low-grade Dalradian metamorphic waters, and may have been mixtures of the latter and D-rich dehydration fluids released from the mafic rocks during dynamothermal metamorphism. Brittle fracturing and shearing in the serpentinites were responses to late deformation at different crustal levels during the final stages of emplacement, which involved gravity-sliding as well as downbending of the Dalradian nappes and ophiolitic thrust-sheets against the elevated Midland Valley block.     

Late Mesozoic crustal extension along the southern Eurasian margin: evidence from volcanic rocks of the Bangong-Nujiang Suture zone, Tibet

The Mesozoic was a period of marginal basin formations, closures and reactivations along segments of the southern Eurasian margin. Remnants of some of these events are now preserved as exposures of Juras-sic-Cretaceous ophiolites and ophiolitic mélanges, thick sequences of Jurassic flysch deposits and Middle Cretaceous sedimentary and volcanic formations along the Bangong-Nujiang Suture Zone (BNS).     

吐哈盆地南缘构造演化及其对层间氧化带砂岩型铀矿成矿作用的控制

吐哈盆地南绕构造演化划分为4个阶段：(1)新疆古陆台发展阶段(An∈)，(2)准吐陆块南绕被动大陆边缘沉积阶段(∈～C1)；(3)岛弧前线增生推覆体及类前陆盆地发育阶段(C2～T)；(4)次造山区——斜坡带发育阶段(J～Q)。第三阶段为本区中新生代沉积及层间氧化带砂岩型铀矿成矿奠定了良好的物质来源和长期稳定的斜坡带构造基础，第四阶段的山间盆地发育期控制了本区层间氧化带的发育及砂岩型铀矿的形成。“中新生代次造山区背景上的稳定斜坡带—河流相富还原剂可渗透平缓单斜层—局部背斜、鼻隆及断层复活”的构造叠加组合为本区层间氧化带砂岩型铀矿的构造定位标志。     

Emplacement of the Monteregian Hills of Quebec; Geophysical evidence

Constraints are placed on the shape of intrusions of the Monteregian Hills and a model of their emplacement is proposed. Integrated geophysical data (magnetic, gravimetric and seismic reflection) and drainage pattern information indicate that the Monteregian Hills are shallow intrusives having the form of saucers nourished by thin planar feeders. These feeders are apparently tectonically controlled by steeply dipping normal faults in the crystalline basement and intermediate to low-angle thrust faults in the overlying Lower Paleozoic sequence. Field geological evidence, geochemical and geophysical data indicate a slow ascending motion of the cooling magma and a sub-vertical rather than sub-horizontal injection mode. In view of the relatively cold state of the intruded magma and paleomagnetic data, partial and progressive melting of an olivine basalt magma is a more acceptable origin for the Monteregian Hills than a continental hot spot theory.     

皖南地区加里东运动构造特征

前人认为皖南地区加里东运动仅表现为抬升造陆运动。文中从构造运动不整合接触关系证据、盖层构造、劈理及变形变质程度,以及古构造应力场特征等方面开展研究。于皖南地区多处发现了上泥盆统与下伏志留系呈角度不整合接触,表明了区内发育加里东褶皱。通过区域地质调查和构造解剖,揭示了区内复式褶皱为加里东和印支两期褶皱叠加的产物。其中,加里东期构造样式主要为区域性开阔褶皱,规模巨大,其轴迹呈北东东向或近东西向延伸,然而,印支期构造样式为线性中常褶皱,规模较小,其轴迹主要呈北东向展布。应用赤平极射投影法对研究区内的褶皱轴面产状、劈理产状要素进行统计分析,结果显示发育加里东期、印支期等多期变形构造;并利用该法求得褶皱两翼优势产状,应用数学计算法计算出区内3期构造应力场特征值,显示华南地块自南而北向扬子地块俯冲挤压的陆内造山动力学过程。早古生代盖层造山属性为陆内造山。区内加里东期褶皱构造属性的厘定和深入研究,对区域构造格架的建立具有重要意义。     

Duplex style and triangle zone formation: insights from physical modeling

Duplexes are a common feature in thrust belts at many scales. Their geometries vary significantly from antiformal stacks with significant forethrusting in the cover (e.g. southern Pyrennes, Spain) to triangle zones (e.g. foreland Canadian Rockies) to low-displacement individually spaced ramp-anticlines (e.g. Sub-Andean thrust belt, Bolivia). We present a series of physical experiments demonstrating that the strength of the décollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style. The models comprise brittle layers made of dry quartz sand and décollements made of two types of viscous silicone polymers. The strength of the décollements in the models is a function of the shortening rate applied to the model. The relative strength of the décollements and surrounding rocks affects the development of active- or passive-roof duplexes (triangle zones). It also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps, which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp-anticlines. Model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions. The presence of relatively strong décollements promotes local underthrusting of the cover, individual ramp-anticlines, internal deformation of thrust sheets, low early layer-parallel shortening, and sequential towards-the-foreland propagation of structures. Weak décollements promote forethrusting of the cover, antiformal stacks, coeval growth of structures, and low internal strain, with the exception of significant early layer-parallel shortening. No underthrusting at a regional scale occurred in any model.     

开合构造环境下花岗岩体的构造样式与变形差异

传统研究认为,大量花岗岩体的侵入发生于区域性伸展环境,是碰撞造山后应力松弛阶段侵位的,称之为造山后或非造山侵入体。近年来,对造山带和古岩浆弧的深入研究发现,花岗岩不但可以侵位于伸展构造环境,也可侵位于挤压构造环境(同构造侵入体),两者在三维空间形态、宏观尺度、露头尺度、显微尺度上的构造样式与变形往往是不同的。区分2类不同构造样式的岩体,对于分析区域构造和造山带演化有着重要的意义。     

东至断裂带构造变形特征及其构造演化

东至断裂带是皖西南一条重要的北北东向断裂带。详细的构造解析表明,该断裂带主要经过3期构造变形,分别是发生在晚侏罗世末—早白垩世初的左行平移断层、早白垩世期间的伸展构造和晚白垩世—新生代的右行平移断层。通过断层擦痕矢量反演和断层叠加改造关系分析,认为东至断裂带及其两侧多期构造变形对应的区域应力场分别为近南北向挤压、北北西—南南东向挤压、北西—南东向伸展和近东西向挤压应力场。东至断裂带的形成和演化与郯庐断裂带相似,主要与华南与华北板块俯冲碰撞、伊泽奈崎板块和古太平洋板块向欧亚板块俯冲碰撞与弧后扩张、及印度板块向北碰撞后产生向东的构造挤出等多构造体制共同作用有关。     

Seismic history and consistent seismicity: Evidence from southern Italy

In this paper a method is proposed to evaluate the seismicity level of an area in a given historical period, based on records of seismic events, source characteristics and intensity attenuation with distance. Also considered is the seismic activity recorded in southern Italy during the 10th and 11th centuries, seismic records being obtained from all available sources. To determine the level of seismicity, a key role is played by source characteristics, i.e. recording modalities and activity periods of recording centers. In addition, models of intensity attenuation with distance allow the assessment of the size of the area under investigation. This paper identifies the areas, in the 10th and 11th centuries, where major earthquakes (M 6.5) did not occur during periods of silence of sources, as well as those where such events cannot be excluded. For each area, different levels of probability were determined by applying the Cox linear logistic model to historical seismic data. The completeness analysis, in terms of area and time-span coverage, is a valuable tool to assess seismicity in seismogenetic areas. The reproducibility of the model for lower magnitude earthquakes (M < 6.5) is reliable.     

中国阿尔泰南缘构造变形层次与变形序列

中国阿尔泰造山带发育了一套被认为是早古生代的变质岩系,保留了原始成分层理S₀。岩石在下-中地壳层次经历了塑性变形及最深达到角闪岩相变质作用的改造。通过对岩石构造层次及变形序列分析,在造山带南缘识别出由深至浅、由早到晚发育的4个构造层次的变形样式,分别为流变构造、韧性剪切构造、褶皱劈理构造和断裂节理构造。流变构造以轴面NW走向、枢纽近直立的流动褶曲和NW走向近直立片麻岩面理为特征,局部发育长英质和镁铁质矿物分异条带,相当于下构造层次变形（约15～18 km）。韧性剪切构造以NW-NNW向和NNE-NEE向近直立的糜棱岩面理和片理面为特征,相当于下-中构造层次变形（约8～12 km）。褶皱劈理构造对应轴向NW、枢纽近水平的等厚褶皱、NWW和NNW向近直立劈理的产出,为中-上构造层次变形（约5～8 km）。上构造层次的断裂、节理构造在造山带南缘广泛发育,变形深度约浅于3～ 4 km。根据变形几何学、运动学关系及变形次序,确认它们是3期构造应力场作用的结果。在二叠—三叠纪,阿尔泰经历NE向（47°～55°）挤压应力场,在下-中构造层次发育317°～325°走向的流动褶皱、片麻理构造S_1-1,306°～308°走向左行和328°～332°走向右行近直立韧性剪切面理S_1-2,290°～295°走向左行和350°～355°走向右行、近直立片理面S_1-3。在古近纪NW向挤压应力场下,中-上构造层次发育20°～22°走向左行和78°走向右行片理面S_2-1,10°～20°和70°～78°近直立脆—韧性剪切面S_2-2和5°～8°压扭性断裂构造S_2-3。新近纪近N-S向应力场下,在浅地壳层次产出320°～325°和340°～345°走向右行走滑断裂,NWW向破劈理和NE向节理构造S₃。下构造层次变形被中-上构造层次变形叠加改造,体现变形深度层次与变形序列的一致性,反映了同构造挤压期的地壳抬升现象。     

藏南古堆地区的新生代构造样式

藏南古堆地区具南北分带特征。北部地区靠达拉岩体,受也拉香波穹窿影响,断层以倾向南的正断层为主,地层呈多期次挤压褶皱形态,且出现呈楔形构造夹片出露的红柱石板岩、石榴石片岩等变质核杂岩地层;中部地区断层、褶皱较发育,褶皱呈紧闭的层间同斜褶皱,断层以倾向北的叠瓦状脆-韧性逆冲断层为主;南部地区为相对稳定区,该区地层相对较完整,褶皱以宽缓向斜形式出现,且越往南越宽缓。这一构造样式是印度板块与欧亚板块碰撞之后,在喜马拉雅造山运动影响及后期伸展作用的背景之下,由北向南的挤压推覆的结果,总体上它是一套挤压褶皱～推覆逆冲断层的组合,呈叠瓦状展布的隆子断裂是主推覆断层。     

勉略构造带构造变形过程及其地质意义

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