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1.
郯庐断裂带肥东段出露的桃源韧性剪切带内发育有长英质超糜棱岩、长英质伟晶岩脉体等。这两种构造岩与剪切带呈现不同的穿切关系, 分别代表着剪切活动不同时期的产物, 它们可以为郯庐断裂带的剪切年限提供重要的年代学制约。本次研究从长英质超糜棱岩的U-Pb锆石测年得出了133.3±4.1 Ma的变质锆石年龄。结合笔者先前得出的伟晶岩脉129±3.3 Ma年龄判断, 郯庐断裂带在133 Ma左右有一次剪切活动, 该次剪切活动在129 Ma左右仍有着较弱的持续, 指示肥东地区在137~126 Ma的时间段内, 有一次挤压活动叠加。此外, 长英质超糜棱岩样品中捕获的1.9 Ga和2.4 Ga的锆石, 很可能来自华南板块基底。 相似文献
2.
The Klondike Schist that forms the basement rocks for the famous Klondike placer goldfield was emplaced as km-scale thrust
slices in Early Jurassic time, along with some thin (10 to 30 m-scale) slices of greenstone and ultramafic rocks. Permian
metamorphic fabrics in the schists were deformed during thrust emplacement by structures formed as the rocks passed through
the brittle–ductile transition. Early-formed thrust-related structures were almost-pervasive recumbent folds that affected
both the schist and greenstone/ultramafic slices and imposed a spaced cleavage with minor recrystallisation of micas. These
structures gave way to shallow-dipping phacoidal cleavage near (within <100 m of) thrust structures. Thrust-related structures
have been overprinted locally by well-defined steeply dipping reverse fault-fold zones, and associated upright folding on
regional (km) to mesoscopic (m) scales. The fold-fault zones occur as two orthogonal sets of structures oriented NW to N and
NE to E. Some of these steeply dipping fault zones have been reactivated by Late Cretaceous normal faulting. Orogenic (mesothermal)
gold-bearing veins were emplaced in local sites of extension during or after formation of the compressional fault-fold zones
and before normal fault reactivation. Over 400 veins (m to cm-scale) observed in this study imply a general NW strike for
mineralised structures (W to N), but with a broad scatter of orientations. Vein emplacement was controlled principally by
fold axial surfaces of kink folds of the fault-fold generation. However, some other local extension sites have opened along
preexisting structures to host veins locally, including metamorphic foliation and spaced cleavage planes. In addition, irregular
extensional fractures with no obvious structural control host some veins. The Klondike mineralised veins formed as swarms
with broad regional structural control, but represent relatively diffuse mineralised zones, with numerous scattered small
veins, compared to most orogenic vein systems. These diffuse vein swarms appear to be sufficient sources for the rich and
geographically localised placer gold deposits that formed in overlying gravels during erosion of the Klondike Schist basement. 相似文献
3.
Incipient metamorphism and deformation in the Variscides of SW Dyfed, Wales: first steps towards isotopic equilibrium 总被引：3，自引：0，他引：3
D. J. SLATER B. W. D. YARDLEY B. SPIRO R. J. KNIPE 《Journal of Metamorphic Geology》1994,12(3):237-248
Incipient metamorphism accompanying thrusting, folding and cleavage development has been investigated in a varied sequence of Palaeozoic sediments near the Variscan front in SW Dyfed, Wales. The aim was to evaluate a critical stage in the progression from heterogeneous sediment, whose detrital phases are neither in equilibrium with one another, nor with pore fluids, through indurated sedimentary rock to metamorphic rock comprising newly formed crystals that equilibrated with one another as they grew. Quartz veins are widely developed in the area, especially in the more psammitic lithologies, while finer grained rocks became cleaved during tectonic deformation. Mineralogical constraints and fluid inclusion measurements suggest maximum temperatures around 200-310d? C (slightly higher in the Marloes-Musselwick Thrust Sheet than in other parts of the structural succession) at depths of the order of 6-13 km. Quartz veins yield distinctly heavier oxygen isotopic compositions than detrital quartz grains in the adjacent wall rocks, although care must be taken in interpreting the data because slivers of detrital grains may become incorporated into veins, while matrix detrital grains may incorporate veinlets or rims of newly formed quartz. It is concluded that vein quartz grew in isotopic equilibrium with a fluid phase whose isotopic composition was primarily controlled by exchange with phyllosilicates, not detrital quartz grains. Vein and matrix quartzes from the Marloes-Musselwick Thrust Sheet are distinctly lighter (δ18Oveins=+14 to +18% and δ18Omatrix=+11 to +14%) than those from other thrust sheets (δ18O =+17 to +20% and +14 to +17%, respectively). We conclude that vein quartz and phyllosilicate grains in cleavage domains probably attained equilibrium with a locally buffered pore fluid at the peak of metamorphism, but many relict grains of different chemical and isotopic composition remained elsewhere in the rock. Local fluid migration along veins and through cleavage lamellae facilitated the attainment of equilibrium, but there is little evidence for large-scale infiltration of externally derived fluids. With further metamorphism the quartz in these rocks would attain an isotopic composition intermediate between that of the heavy vein material and light detritus which coexist here. 相似文献
4.
内蒙古西部狼山温更逆冲断层发育在温更侏罗纪沉积盆地西北边界, 是一条规模较大的逆冲断裂构造带。断层倾向北西, 上盘由太古宙-元古宙变质地层和古生代深成侵入体构成, 下盘为侏罗纪沉积, 由北西向南东方向逆冲。断层切割改造了早-中侏罗世沉积地层, 被早白垩世沉积地层覆盖, 表明了逆冲断层形成在下中侏罗统沉积之后白垩系固阳组沉积之前。断层带同构造石英脉中流体包裹体的分析结果表明, 断层形成于5.5～6 km浅部地壳构造层之上, 温度为195℃～210℃, 围压为50 ～60 MPa, 断层带的宏观和显微构造显示断层以脆性变形机制为主。 相似文献
5.
The 3D architecture of fold-thrust belts commonly involves thin-skinned and thick-skinned deformation. Both thick- and thin-skinned deformation styles have been suggested to occur in the Marañón Fold-Thrust Belt (MFTB) in Peru, but the relative timing and strain partitioning associated with them are not well understood. We demonstrate that inherited basement structures along the Peruvian convergent margin reactivated during the evolution of the MFTB. We present results from field mapping, interpretation of remote sensing imagery, and cross section construction and restoration. The results show that the Chonta Fault, a median pre-folding basin normal fault, was inverted and acted as a mechanical buttress during initial east-vergent contraction of the fold-thrust belt. This fault separates the belt into two domains of distinctly different structural styles. During the Eocene, units to the west of the Chonta Fault deformed by folding, using the fault as a buttress, and subsequently propagated eastward by thin-skinned thrusting. This was followed in the Miocene by west-vergent, basement-involved deformation, which overprinted the earlier east-vergent, thin-skinned structures. The proposed tectonic model of the MFTB highlights the role of basement-fault reactivation during orogenesis and the involvement of deep structures in partitioning deformation styles. 相似文献
6.
“承德逆掩片”之商榷——来自燕山地区中元古代长城系的沉积地质证据 总被引：9，自引：1，他引：8
外来岩片不但在构造变形上应具有显著的特征标志,而且在其卷入的各类地质体中也应该表现出与原地系统之间具有明显的差异.近年来,承德地区两条断裂之间所夹地质体,被部分学者认为是晚侏罗世时期从该地区南部向北推覆而来的"逆掩片",水平位移量超过40km.本文对比研究了"逆掩片"内部和"根带区"中元古代长城系原始沉积特征和相带展布以及其他证据,发现承德地区长城系各相带原始展布和格局与周边同期沉积并无显著差别,这表明晚侏罗世期间发生自南向北大规模水平位移(＞40km)的可能性很小,研究结果不支持"外来岩片"的认识. 相似文献
7.
8.
New structural and stratigraphic data for a selected area of the Ligurian Alps are combined in order to assess and discuss the role played by extensional structures in the southernmost segment of the Western Alps during thrusting. Restored cross-sections and field data suggest that the structural style in the external sector of the chain may depend upon the presence of pre-orogenic normal faults ascribed to three extensional events linked to different geodynamic contexts: (i) Permian post-Variscan plate reorganisation, (ii) Mesozoic rifting–drifting phases leading to the opening of the Alpine Tethys, and (iii) Eocenic development of the European foreland basins. During positive inversion in Eocene times, a thin-skinned thrust system developed in this area, followed by a thick-skinned phase. In both situations the inherited extensional structures played fundamental roles: during the thin-skinned phase they conditioned the thrusting sequence, also producing large-scale buckle folds and partial reactivations; during the thick-skinned phase the strain was compartmentalized and partitioned by pre-existing faults.The kinematic model of the external sectors of the Ligurian chain also allows the re-assessment of the Alpine evolution of the front-foreland transition, including: (i) indirect confirmation that in the Eocene the Ligurian Briançonnais and Dauphinois domains were not separated by the Valais-Pyrenean oceanic basin; (ii) that the thin-skinned phase progressively changed into thick-skinned; (iii) the assertion that there were no significant deformations from the Oligocene to the present-day, and the Corsica–Sardinia block rotation only produced a change in orientation of previously formed structures and normal fault system development. 相似文献
9.
The origin of an apparently syndeformational chemical remanent magnetization (CRM) and geochemical alteration in a fault zone in the Bristol Channel Basin, southwest England, was investigated. Deformation in the fault zone occurs in Jurassic aged, organic-rich limestones and consists of numerous normal and oblique-slip faults and associated folds. Migration of basinal, radiogenic fluids is indicated by elevated 87Sr/86Sr values for calcite veins that occur throughout the fault zone. Some of the calcite veins contain hydrocarbons sourced from deeper strata. Elevated 87Sr/86Sr values in the host Jurassic limestones indicate that they were also extensively altered by radiogenic fluids that migrated through microfractures in addition to major fault and fracture planes. Folded and tilted host limestones contain a pervasive secondary CRM residing in magnetite that was acquired during deformation in the Tertiary. The association between this pervasive CRM and the pervasive geochemical alteration is consistent with a genetic connection between the orogenic fluids and the CRM although the timing of CRM acquisition (Tertiary) is not consistent with structural interpretations for the timing of most veining. An alternative remagnetization mechanism which is not triggered by externally derived fluids, such as diagenesis of hydrocarbons, might account for the CRM. Hydrocarbon-bearing veins also contain a CRM that resides in magnetite, although the time for remanence acquisition is not well constrained by field tests. © 1998 John Wiley & Sons, Ltd. 相似文献
10.
On the basis of detailed geological mapping in the Talea Ori of Crete, metamorphic rocks previously interpreted as basement to the Plattenkalk Series are re-interpreted as down-faulted parts of the overlying Phyllite-Quartzite Series nappe. A supposed unconformity separating these two units is shown to be a high-angle fault. The Phyllite-Quartzite Series and overlying nappes were affected by two major deformational phases, whereas the Plattenkalk Series has a simpler structural history and was folded and imbricated by southwards-directed overthrusting which emplaced the Phyllite-Quartzite Series nappe and other overlying nappes in the Oligocene. We reject previous models of a huge inversion of the Plattenkalk Series and we also consider that considerable local inversion by tight to isoclinal folding and thrusting means that the stratigraphic thickness is much less than previously appreciated. The differences between the structural and sedimentological histories of the Plattenkalk Series and the overlying nappes implies that they were separated by a major crustal discontinuity, such as a transform or transcurrent fault, before the Oligocene overthrusting. 相似文献
11.
柯坪塔格推覆构造几何学、运动学及其构造演化 总被引：29，自引：1，他引：29
大量野外构造地质调查和深部构造解释表明柯坪塔格推覆构造由多组倒转复式背斜、复式箱状背斜构成的推覆体及其前缘逆冲断裂组成 ,由寒武系—第四系组成的推覆体由北向南逆—斜冲 ,平面上构成向南凸出的弧形推覆构造 ;普昌断裂由各不相连的逆冲斜冲断裂段组成 ,而不是完整的一条走滑断层 ,各推覆体前缘逆冲断裂与各推覆体的普昌断裂段共同构成统一的前缘逆冲斜冲逆冲断裂和推覆构造系统 ;普昌断裂段以西的推覆体具有向东抬升、向西倾覆的鼻状构造特征 ,普昌断裂段以东的推覆体具有向西抬升、向东倾覆的鼻状构造特征 ,普昌基底隆起带是巴楚隆起隐伏在柯坪塔格推覆构造之下的部分。各推覆体前缘断裂在深部均归并于统一的寒武系底部的滑脱面 ,其南浅北深 ,东浅西深 (普昌隆起带以西 )或西浅东深 (普昌隆起带以东 ) (6 10km ) ,埋深较大区发育多组滑脱面。柯坪塔格推覆构造的形成时期为晚第四纪 ,为现今活动的推覆构造系统。文中认为各推覆体向南西的倾覆端基底滑脱面和中新生界内部的滑脱面没有贯通 ,是未来 6级以上地震的发震构造部位。 相似文献
12.
Niels Jöns Wolfgang Bach Timothy Schroeder 《Contributions to Mineralogy and Petrology》2009,157(5):625-639
We examined small-scale shear zones in drillcore samples of abyssal peridotites from the Mid-Atlantic Ridge. These shear zones
are associated with veins consisting of chlorite + actinolite/tremolite assemblages, with accessory phases zircon and apatite,
and they are interpreted as altered plagiogranite melt impregnations, which originate from hydrous partial melting of gabbroic
intrusion in an oceanic detachment fault. Ti-in-zircon thermometry yields temperatures around 820°C for the crystallization
of the evolved melt. Reaction path modeling indicates that the alteration assemblage includes serpentine of the adjacent altered
peridotites. Based on the model results, we propose that formation of chlorite occurred at higher temperatures than serpentinization,
thus leading to strain localization around former plagiogranites during alteration. The detachment fault represents a major
pathway for fluids through the oceanic crust, as evidenced by extremely low δ18O of altered plagiogranite veins (+3.0–4.2‰) and adjacent serpentinites (+ 2.6–3.7‰). The uniform oxygen isotope data indicate
that fluid flow in the detachment fault system affected veins and adjacent host serpentinites likewise.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
Early Cretaceous exhumation of the Qiangtang Terrane during collision with the Lhasa Terrane,Central Tibet 总被引：1，自引：0，他引：1 
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下载免费PDF全文 The timing of the closure of the Bangong Ocean between the Lhasa and South Qiangtang Terranes in central Tibet and the resulting crustal thickening are still under debate. We integrate published apatite fission track and (U–Th)/He thermochronometer data with new zircon (U–Th)/He ages from eight samples and with structural profiles to document that the South Qiangtang Terrane experienced slow exhumation between 200 and 150 Ma, associated with the opening of the Bangong Ocean. Accelerated exhumation (around 0.2–0.3 mm/a) of the South Qiangtang Terrane was initiated at around 150 Ma. This exhumation event is interpreted to reflect collision between the Lhasa and South Qiangtang Terranes after closure of the Bangong Ocean, associated with crustal thickening via thick‐skinned folding and thrusting within the South Qiangtang Terrane. The amalgamation of the Lhasa and South Qiangtang Terranes recorded here may represent the first stage of crustal thickening in the central Tibetan Plateau. 相似文献
14.
The structure and occurrence of deformation within the hanging wall of the Nobeoka Thrust in Kyushu, Japan, was investigated to understand the dynamic aspects of splay faulting in relation to seismic events. From field observations, hanging wall is suggested to have undergone four phases of deformation. The first phase involved horizontal shortening, as documented by folding and thrusting, followed by a phase of vertical loading shown by the development of horizontal slaty cleavages, pressure solution, and cleavage-parallel mineral vein precipitation. A third phase involved shearing, and deformation along cleavage restricted to near the Nobeoka Thrust, while the fourth phase produced widespread, brittle fracturing associated with the development of pseudotachylyte-bearing faults and tension crack filling veins high angle to cleavage. These four phases can be explained as follows.During the inter-seismic period, an extensionally stable taper was maintained in the inner wedge of the accretionary prism by dominant vertical loading (σ1), in combination with a lesser amount of horizontal compression (σ2) related to the locking of the mega-thrust. Elastic strain energy in the hanging wall of the inner wedge was co-seismically released by slip on the mega-thrust and horizontal shortening in the outer wedge associated with dynamic ductile weakening of the fault plane. This sudden release of elastic strain caused brittle fracturing with σ1 at a high angle to the shear surface of the Nobeoka Thrust, most of the displacement resulting from deformation of the footwall. 相似文献
15.
The Río Guanajibo serpentinite body (RGSB) near Mayagüez, Puerto Rico, is part of an ophiolite mélange thrust in an oceanic convergent zone. The aim of this study was to characterize the extent and chronology of serpentinization within this peridotite mass. Mineralogy, microstructures, and veining episodes within the RGSB were characterized using optical microscopy, x-ray diffraction (XRD), scanning electron microscopy (SEM), and structural analyses. This study identified, for the first time, all three serpentine polymorphs (i.e., antigorite, chrysotile, lizardite) in serpentinite samples collected from Puerto Rico. Lizardite, the initial serpentine mineral formed from widespread hydration of olivine, was found throughout serpentinite samples. Chrysotile was the most abundant polymorph observed in sheared serpentinite samples, consistent with conditions favoring low fluid to rock ratios, supersaturation and abundant porosity. Antigorite was observed as a replacement texture in serpentinites that were not exposed to greenschist facies metamorphic conditions, and were frequently found in veins with a shear component. The results indicate that metamorphic conditions do not exclusively dictate polymorph formation.The mineralogy and textures observed within the different vein generations reflect the formation conditions, and deformational mechanisms, that occurred during the serpentinization process; six veining episodes (V1 – V6) were identified and grouped into four stages of serpentinization. Stage one (V1 and V2 type veins) represents the earliest stages of serpentinization and was characterized by microscopic fracture networks that formed as a result of cracking during the initial hydration of olivine under low water/rock ratios. During stage two (V3 and V4 type veins), fibrous crack - seal veins formed to accommodate continued volume expansion, via incremental fracture openings, caused by continued hydration of olivine. The ascension of serpentinite into the upper lithosphere was inferred to occur during Stage three; V5 type veins are associated with this stage. Textures and vein morphologies, representing supersaturated conditions and a decrease in temperature, were observed. Stage 4 (V6 type veins) was characterized by shear deformation features, which formed as a result of thrusting associated with the emplacement of the RGSB or Late Eocene transpression and fault reactivation along the Caribbean plate boundary. 相似文献
16.
东准噶尔蒙西斑岩铜钼矿床脉体特征及其形成机制 总被引：5，自引：1，他引：4
蒙西斑岩铜钼矿床位于东准噶尔伊吾县琼河坝花岗岩北侧,以发育细脉、网脉状矿化为特征。脉体类型多样,包括石英脉、石英硫化物脉和硫化物脉等。根据脉体力学成因机制,其又可划分为水压破裂充填脉和构造破裂充填脉。构造破裂充填脉体按破裂形成的位错特征有正断与逆断两种。地表石英脉产状陡立,明显受断裂控制。脉体体积分数统计结果显示流体富集区呈向北缓倾的带状分布于深100～400m范围内,并与矿化富集带有较好的对应关系。脉体富集带内,脉体以共轭形式存在,一组为倾角较小的逆断破裂充填脉,另一组为倾角较大的正断破裂充填脉,他们可能为缓倾逆冲剪切带的次级破裂与充填脉,即富矿带内脉体是沿矿区低角度逆冲断裂次级破裂面充填的。矿区地表及深部(400m以下)脉体以陡立为主,矿化较弱。矿区流体的运移具先沿水压直立破裂往上运移,进入剪切带后沿剪切带次级破裂侧向和向上运移,并在剪切带中富集成矿。低温矿物组合脉体穿切高温矿物组合脉体的特征说明脉体形成过程矿区处于隆升构造环境,这对斑岩铜矿成矿有利。 相似文献
17.
伏牛山构造带由多条近平行的断裂带和夹持其间的变形岩片组成,洛南-栾川断裂带和瓦穴子-乔端断裂带为其中的两条主要断裂带。这两条断裂带虽遭受多期强烈构造活动的影响,但主造山期的构造特征至今仍然保存完好,并以中深层次的韧性剪切变形为主,形成了典型的糜棱岩和同构造期石英脉。本文从宏观、微观、超微观变形特征及年龄等方面对这些变质流体脉进行了研究,以探讨与其形成密切相关的构造活动特征、年代及其在秦岭造山带和华北板块南缘强变形带中的作用。石英脉中石英颗粒动态重结晶特征总体显示远离剪切带只有少量的膨凸式,靠近断裂带为亚颗粒式,形成核-幔结构,位错特征显示远离剪切带位错密度较小,靠近断裂带较大,位错形态显示瓦乔断裂带以挤压为主,洛南-栾川断裂带以剪切为主。两条断裂带石英脉的变形特征说明它们的糜棱岩化过程均为塑性变形中的晶质塑性变形,形成过程均为挤压在先,剪切在后。所测糜棱岩中石英脉的ESR年龄分别为372.9±30.0 Ma、275.0±20.0 Ma和218.0±20.0 Ma,真实地记录了晚加里东至中-晚海西期北秦岭的构造活动及所受影响。其中372.9±30.0 Ma是宽坪岩块向华北板块下的斜向俯冲汇聚和走滑的年代, 275.0±20.0 Ma是瓦乔断裂带的形成年龄。218.0±20.0 Ma的年龄则反映了华南、华北两大板块印支晚期全面闭合作用在秦岭造山带内部的影响。从以上3个年龄可以看出:北秦岭各构造带自北向南演化,时代上自北向南变新。 相似文献
18.
A horizontal cleavage and associated lineation are developed in a low-pressure igneous-related metamorphic terrain in southestern Sinai. The cleavage is axial planar to recumbent folds, which are never large, and varies from a smooth slaty cleavage to a discrete crenulation cleavage. Structural evidence on the macro, meso and microscales suggests that cleavage and lineation were formed during irrotational extension and not by simple shear. Estimates of strain using the March method indicate 50–70% vertical shortening. This structural evidence when combined with metamorphic and age data strongly suggests that the cleavage was formed by the forceful emplacement of a pluton at depth. 相似文献
19.
The emplacement of calcite-filled veins perpendicular to the Dead Sea Fault Zone in northern Israel reflects strain partitioning during transpression. We present structural, geochemical, and U–Th geochronological data that constrain the mechanism, conditions and timing of vein formation. Vein walls are strongly brecciated and commonly cemented with coarsely crystalline calcite, whereas calcite-filled veins are composed of wall-parallel bands of calcite crystals. Elongated blocky and fibrous calcite crystals grew perpendicular to the vein walls and are characterised by a truncate sealing-hiatus morphology, indicating episodes of partial or complete sealing of the fractures during calcite precipitation. Stable isotope and rare-earth element and yttrium (REY) analyses indicate that calcite-filled veins precipitated by karst processes, involving meteoric water and limited fluid-rock interactions. U–Th dating results show a prolonged history of vein growth. While some veins initiated prior to 500 ka, the majority of the veins were active between 358 and 17 ka. Age constraints on vein activity correspond to an ∼E–W regional shortening phase in this sector of the Dead Sea Fault Zone, associated with an increased component of convergence during the late-Pleistocene. 相似文献
20.
渤海湾盆地是在中生代华北克拉通破坏基础上,经由新生代深埋形成的叠合盆地,遭受了多期不同性质构造叠加改造。渤海海域油气资源的勘探逐步走向深层,深部潜山油气藏成为重要的勘探目标。本文以石臼坨东428潜山构造(以下简称428构造)为例,探索渤海湾盆地潜山的形成和构造演化。基于前人对渤海湾盆地内构造和储层特征的研究成果,通过对地震剖面的精确解析,结合相干切片和其他地质资料,系统研究428构造各个阶段的变形特征,特别是对428构造的断裂特征进行了平面和剖面上的解析与断裂组合分析。结果发现:428构造东、西侧现今差异主要是由一条斜跨该构造的NEE向断裂导致的,对比邻区野外应变测量分析,识别出五期构造应力场,分别对应于印支期、燕山期和喜山期的各阶段应力场变化,并结合428构造及其周缘残留地层等方面的证据,进而认为428构造经历了中生代印支期-燕山早期逆冲、燕山中-晚期伸展、燕山末期挤压及新生代右行右阶的走滑-拉分构造叠加的多期复合构造模式。 相似文献