共查询到20条相似文献，搜索用时 31 毫秒
1.
Palaeozoic late collisional strike-slip deformations in Tianshan and Altay, Eastern Xinjiang, NW China 总被引：12，自引：0，他引：12
ABSTRACT In Central Asia, thrusts and shear zones resulting from Palaeozoic accretional events were reworked by E–W-trending ductile strike-slip faults during late Palaeozoic–early Mesozoic time. In the Tianshan range, microstructures and quartz C-axis fabrics show a main dextral shearing associated with sinistral localized shear zones. The relationship between these conjugate structures indicates a NNW–SSE-trending bulk shortening. In the Chinese Altay mountains, the existence of δ-type microstructures in an important sinistral mylonitic zone infers high rates of deformation. This shear zone is bordered by a late dextral ductile fault synchronous with a granite emplacement. Field evidence and datings from the literature provide chronological constraints. In the late Carboniferous, the sinistral mylonitic deformation took place in the Erqishi–Irtysh shear zone in the northeastern part of Xinjiang and in Kazakhstan. During the Early Permian, a regional dextral event occurred in the Tianshan range and under the whole of northern Xinjiang. 相似文献
2.
3.
Michel Faure 《Journal of Structural Geology》1985,7(2):175-186
Two Jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the Mesozoic chain of SW Japan. The first phase was synmetamorphic, and took place under HP/LT conditions. Microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from W to E, parallel to the stretching and mineral lineation. At the regional scale the first phase corresponded to the obduction of the Greenschist nappes upon the Kurosegawa continent. During the second phase the Greenschist nappes were sliced, leading to an apparent reverse metamorphic zoning. The first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear. 相似文献
4.
Fluid controlled eclogitization of granulites in deep crustal shear zones,Bergen arcs,Western Norway 总被引：1，自引：0，他引：1
Bjørn Jamtveit Kurt Bucher-Nurminen Håkon Austrheim 《Contributions to Mineralogy and Petrology》1990,104(2):184-193
During the Caledonian orogeny large parts of the western margin of the Baltic shield were disrupted, sliced and stacked. Caledonian deformation resulted in a massif thickening of the continental crust. Mafic granulites and granulite facies meta-anorthosites build up a large portion of the Bergen Arcs terrane in southwestern Norway. The rocks represent typical Precambrian continental lower crust. These rocks experienced extensive eclogitization in response to stacking and crustal thickening during the Caledonian orogenic cycle. Eclogite formation resulted from shear deformation and associated infiltration of H2O-rich fluids (X
H2O0.75). During an early stage, eclogite facies mineralogy formed in extension fractures (veins). The veins are probably related to hydraulic fracture systems which transported the inferred fluid phase. During the main stage, eclogitization occurred along shear zones ranging from centimeters to tens of meters in thickness. Eclogite forming reactions are shown to consume H2O, alkalies and to release SiO2. Much of the SiO2 released by the eclogitization process can be found in late quartz vein systems. The eclogitization took place at a temperature of about 700°C and a pressure between 18 and 21 kbar. Fluid infiltration was supported by a decrease in rock volume during reaction (V
solids<0). The negative volume change of reaction occurs despite that the process of eclogitization involves hydration reactions. The formation of eclogite from granulite produces approximately 15 KJ heat per 100 cm3 original granulite. Numerical modeling of the regional temperature effects associated with partial hydration of the lower crust suggests that these processes may not cause large perturbations on the geotherm. Both, transport of heat and matter by advection of the fluid phase is negligible on a regional scale. 相似文献
5.
6.
Kinematic models of various types of transpression have been used to explain fabric features and strain in many natural deformation studies. Here, a mathematical model that encompasses all monoclinic and triclinic transpressional deformations including triclinic deformation with inclined simple shear (ϕ) and/or inclined extrusion orientations (υ) can be tested using a step-by-step approach with available field evidence. Two cases are presented. The first case from the Wabigoon–Quetico boundary in the Archean Superior Province utilizes both fabric orientation and quantified strain data. The best fit of the field evidence to the model indicates that deformation likely took place along subvertical shear zones via transpression with subhorizontal simple shear (ϕ = 0–20°) and variable inclined extrusion direction (extrusion can be either east or west and υ typically indicates extrusion orientations between 0 and 50° from vertical). The second case of the South Iberian shear zone has fabric orientation data, but no quantifiable strain possibilities. The best fit of the field evidence to the model indicates that deformation likely took place along a moderately inclined shear zone via transpression with subhorizontal simple shear (ϕ = 0–20°) and variable inclined extrusion direction (υ values between 0° and 80° from the true dip of the shear zone). Using this protocol in other examples of natural deformation will allow further constraints to be applied to kinematic models. 相似文献
7.
8.
Summary Rock mechanical tests and subsequent investigations in scanning electron microscopy (SEM) have been carried out on samples
retrieved from the Late Cretaceous Springar Fm offshore Mid-Norway. Mineralogical and petrophysical analyses pertinent to
this study have been conducted according to standard methods. The Springar Fm has a clay content of 45–50%, with smectite
rich mixed-layer illite/smectite as the dominating clay mineral. Consolidated undrained (CU) triaxial tests show a geomechanically
brittle behaviour at all test conditions. The brittle behaviour is mainly due to diagenetic siderite cement. During the rock
mechanical consolidation phases only minor reductions in the pore volumes took place. During the induced shear deformation
local orientation of small mica grains parallel to the direction of shear occurred in the vicinity of the failure zone. The
small fabric changes observed in the SEM are in agreement with the low deformations seen from the CU triaxial test data of
the Springar Fm. 相似文献
9.
内蒙古固阳地区太古宙乌拉山群构造变形分析 总被引：1，自引：0，他引：1
乌拉山群的变质－变形问题一直有不同的认识＾「１～３」。该文以固阳地区３幅１∶５万区调资料为基础,结合９０年代以来周边地区１∶５万区调成果,提出晚太古宙乌拉山群经历了两期主要的构造变形。第一期为伸展体制下近水平分层剪切形成的固态流变褶皱和高温顺层韧性剪切带,属高角闪岩相－麻粒岩相,变形时间为太古代末;第二期构造变形为地壳抬升之后的剂压体制下,中、浅层次的紧闭同斜相似褶皱－－主期褶皱和低温韧性剪切带, 相似文献
10.
Magdalena Scheck Ulf Bayer Volker Otto Juliette Lamarche Dirk Banka Tim Pharaoh 《Tectonophysics》2002,360(1-4):281-299
The Elbe Fault System (EFS) is a WNW-striking zone extending from the southeastern North Sea to southwestern Poland along the present southern margin of the North German Basin and the northern margin of the Sudetes Mountains. Although details are still under debate, geological and geophysical data reveal that upper crustal deformation along the Elbe Fault System has taken place repeatedly since Late Carboniferous times with changing kinematic activity in response to variation in the stress regime. In Late Carboniferous to early Permian times, the Elbe Fault System was part of a post-Variscan wrench fault system and acted as the southern boundary fault during the formation of the Permian Basins along the Trans-European Suture Zone (sensu [Geol. Mag. 134 (5) (1997) 585]). The Teisseyre–Tornquist Zone (TTZ) most probably provided the northern counterpart in a pull-apart scenario at that time. Further strain localisation took place during late Mesozoic transtension, when local shear within the Elbe Fault System caused subsidence and basin formation along and parallel to the fault system. The most intense deformation took place along the system during late Cretaceous–early Cenozoic time, when the Elbe Fault System responded to regional compression with up to 4 km of uplift and formation of internal flexural highs. Compressional deformation continued during early Cenozoic time and actually may be ongoing. The upper crust of the Elbe Fault System, which itself reacted in a more or less ductile fashion, is underlain by a lower crust characterised by low P-wave velocities, low densities and a weak rheology. Structural, seismic and gravimetric data as well as rheology models support the assumption that a weak, stress-sensitive zone in the lower crust is the reason for the high mobility of the area and repeated strain localisation along the Elbe Fault System. 相似文献
11.
自中三叠世扬子与华北板块发生碰撞—深俯冲作用以来,大别造山带南界上的襄樊—广济断裂带主要经历过两次变形事件: 1)早期变形事件发生在中三叠世末—晚三叠世初的造山带折返阶段,表现为造山带南边界上的韧性剪切带。这期北西—南东走向的剪切带向南西陡倾,发育北西—南东向的矿物拉伸线理,主要为右行走滑的运动性质,属于造山带斜向折返的侧边界走滑剪切带。造山带折返过程中将前陆褶断带北缘原先东西向褶皱改造为北西—南东走向。2)晚期变形事件发生在晚侏罗世,表现为脆性逆冲断层,使得前陆褶断带向北东逆冲在造山带南缘之上,同时在前陆上形成了一系列的逆冲断层。该断裂带的晚期逆冲活动与郯庐断裂带左行平移同时发生,代表了滨太平洋构造活动的开始。 相似文献
12.
ABSTRACT In the Hlinsko region (Variscan Bohemian Massif, Czech Republic) a major extensional shear zone separates low-grade metasedimentary series (Hlinsko schists) and high-grade rocks of the Moldanubian terrane (Svratka Crystalline Unit). During late-Variscan extension, a tonalite intruded syntectonically into the normal ductile shear zone, and caused contact metamorphism of the overlying schists. Concurrent syntectonic sedimentation of a flysch series took place at the top of the hangingwall schists. In order to decipher the detailed petrological evolution of the Hlinsko unit situated in the hangingwall of this tectonic contact, a phase diagram approach and petrogenetic grids, calculated with the thermocalc computer program, were used. The crystallization/deformation relationships and the paragenetic analysis of the Hlinsko schists define a P–T path with an initial minor increase in pressure followed by cooling. Calculated pseudosections constrain this anticlockwise P-T evolution to the upper part of the andalusite field between 0.36 and 0.40 GPa for temperatures ranging from 570 to 530°C. A low aH2O is required to explain the presence of andalusite-biotite-bearing assemblages, and could be related to the presence of abundant graphite. In contrast, the footwall rocks of the Svratka Crystalline Unit record decompression from around 0.8 GPa at a relatively constant temperature, followed by cooling. Thus, the footwall and the hangingwall units display opposite, but convergent P–T histories. Decompression in the footwall rocks is related to a rapid exhumation. We propose that the inverse, anticlockwise P–T path recorded in the hangingwall pelites is related to the rapid, extension-controlled sedimentation of the overlying flysch series. 相似文献
13.
Pedro Oyhantçabal Siegfried Siegesmund Klaus Wemmer Paul Layer 《International Journal of Earth Sciences》2010,99(6):1227-1246
The Sierra Ballena Shear Zone (SBSZ) is part of a high-strain transcurrent system that divides the Neoproterozoic Dom Feliciano
Belt of South America into two different domains. The basement on both sides of the SBSZ shows a deformation stage preceding
that of the transcurrent deformation recognized as a high temperature mylonitic foliation associated with migmatization. Grain
boundary migration and fluid-assisted grain boundary diffusion enhanced by partial melting were the main deformation mechanisms
associated with this foliation. Age estimate of this episode is >658 Ma. The second stage corresponds to the start of transpressional
deformation and the nucleation and development of the SBSZ. During this stage, pure shear dominates the deformation, and is
characterized by the development of conjugate dextral and sinistral shear zones and the emplacement of syntectonic granites.
This event dates to 658–600 Ma based on the age of these intrusions. The third stage was a second transpressional event at
about 586 to <560 Ma that was associated with the emplacement of porphyry dikes and granites that show evidence of flattening.
Deformation in the SBSZ took place, during the late stages, under regional low-grade conditions, as indicated by the metamorphic
paragenesis in the supracrustals of the country rocks. Granitic mylonites show plastic deformation of quartz and brittle behavior
of feldspar. A transition from magmatic to solid-state microstructures is also frequently observed in syntectonic granites.
Mylonitic porphyries and quartz mylonites resulted from the deformation of alkaline porphyries and quartz veins emplaced in
the shear zone. Quartz veins reflect the release of silica associated with the breakdown of feldspar to white mica during
the evolution of the granitic mylonites to phyllonites, which resulted in shear zone weakening. Quartz microstructures characteristic
of the transition between regime 2 and regime 3, grain boundary migration and incipient recrystallization in feldspar indicate
deformation under lower amphibolite to upper greenschist conditions (550–400°C). On the other hand, the mylonitic porphyries
display evidence of feldspar recrystallization suggesting magmatic or high-T solid-state deformation during cooling of the
dikes. 相似文献
14.
通过沂沭断裂带内晚元古代至古生代益层变形的详细研究，发现这套盖层遭受了明显的顺层左旋走滑剪切变形。这期盖层变形是与沂沭断裂带基底中北北东走向左行韧性剪切带同期形成的。它们是郯庐断裂带中生代大规模左行平移运动在不同层次上所造成的不同产物。这套益层的变形及其特征证明了郯庐断裂带大平移发生在中生代。 相似文献
15.
龙泉关韧性剪切带同变形花岗岩的构造特征及其独居石定年 总被引：7，自引：0，他引：7
龙泉关韧性剪切带强变形部位发育一系列平行剪切带走向展布的花岗岩脉体，构造变形特征表明它们可能是同变形花岗岩，是剪切作用下围岩部分熔融的产物。通过独居石电子探针定年，测得龙泉关韧性剪切带的年龄分别为：主变形幕发生于1877～1846Ma，第2个变形幕发生于1812-1782Ma，晚期1725Ma左右又经历了流体活动。龙泉关韧性剪切带的发生、发展与华北克拉通中部带古元古代晚期的变质事件同期，是东、西陆块碰撞的一个主要剪切带。 相似文献
16.
Melt infiltration into quartzite took place due to generation and migration of partial melts within the high‐grade metamorphic rocks of the Big Cottonwood (BC) formation in the Little Cottonwood contact aureole (UT, USA). Melt was produced by muscovite and biotite dehydration melting reactions in the BC formation, which contains pelite and quartzite interlayered on a centimetre to decimetre scale. In the migmatite zone, melt extraction from the pelites resulted in restitic schollen surrounded by K‐feldspar‐enriched quartzite. Melt accumulation occurred in extensional or transpressional domains such as boudin necks, veins and ductile shear zones, during intrusion‐related deformation in the contact aureole. The transition between the quartzofeldspathic segregations and quartzite shows a gradual change in texture. Here, thin K‐feldspar rims surround single, round quartz grains. The textures are interpreted as melt infiltration texture. Pervasive melt infiltration into the quartzite induced widening of the quartz–quartz grain boundaries, and led to progressive isolation of quartz grains. First as clusters of grains, and with increasing infiltration as single quartz grains in the K‐feldspar‐rich matrix of the melt segregation. A 3D–μCT reconstruction showed that melt formed an interconnected network in the quartzites. Despite abundant macroscopic evidence for deformation in the migmatite zone, individual quartz grains found in quartzofeldspathic segregations have a rounded crystal shape and lack quartz crystallographic orientation, as documented with electron backscatter diffraction (EBSD). Water‐rich melts, similar to pegmatitic melts documented in this field study, were able to infiltrate the quartz network and disaggregate grain coherency of the quartzites. The proposed mechanism can serve as a model to explain abundant xenocrysts found in magmatic systems. 相似文献
17.
Flat prismatic soil samples were subjected to creep and recovery experiments in newly developed shear cells. The deformation took place below failure in simple shear, that is, in plane strain. The pore-water pressure in the sample was measured at the same time. 相似文献
18.
新疆准噶尔北缘玉勒肯哈腊苏铜(钼)矿区韧性剪切变形时代——来自白云母和黑云母Ar-Ar年龄的约束 总被引：6，自引：0，他引：6
玉勒肯哈腊苏斑岩铜(钼)矿主要赋存于闪长玢岩中,少量在北塔山组火山岩及似斑状石英二长岩中。矿化呈细脉状、细脉-浸染状和浸染状。成矿过程经历了斑岩期、剪切变形期和表生期。矿区发育韧性剪切变形带,中泥盆统北塔山组、下石炭统姜巴斯套组、岩体及矿体均发生了剪切变形作用。沿剪切面发育黑云母和白云母新生矿物。白云母的坪年龄和等时线年龄分别为283.8±1.5Ma和285.4±3.1Ma,黑云母的坪年龄和等时线年龄分别为277.0±2.0Ma和277.0±4.0Ma,在误差范围内基本一致,限定矿区韧性剪切变形时间在早二叠世(284～277Ma),与区域额尔齐斯-玛因鄂博断裂活动时间一致。主要成矿作用形成于斑岩期,成矿时代为中泥盆世(374Ma),早二叠世的韧性剪切变形作用只对铜(钼)矿化进行改造。 相似文献
19.
丹东韧性剪切带的实例表明:韧性剪切带的持续变形包含了共轴与非共轴两种应变线路或状态,由于分布的不均匀性,导致变形分域现象,形成平面的变形岩石分区。持续变形过程中,又存在应变线路的转换和叠加。微构造是确定变形体制的主要依据。野外观测与应变分析证实,变形分域存在于不同尺度,在总体剪切(非共轴)变形条件下,初始糜棱岩往往表现以共轴变形占优势,而糜棱岩和超糜棱岩则以非共轴变形为主。持续变形导致从共轴向非共轴转变,最后形成后者的主体地位。 相似文献
20.
《Journal of Structural Geology》1988,10(7):735-743
The eastern Western Gneiss Region of central Norway is part of the deepest exposed Norwegian Caledonides, where basement gneisses and an overlying thrust-nappe sequence have been folded into large fold-nappes. Structural analysis of a fold-nappe within the central part of the district (the Grøvudal area) suggests that it has a strongly sheath-like form, and that other fold-nappes of the Western Gneiss Region may also have sheath-like forms. The structural history within the Grøvudal area is dominated by intense east-directed subhorizontal shear in an overthrust sense, followed by asymmetric refolding with an easterly vergence. A computer-generated kinematic model was developed to test whether the regional interference patterns could be explained by sheath-fold development during this type of deformation. The computer model shows that the major regional interference patterns could have been formed by such a kinematic history, but does not rule out other possibile histories. The proposed kinematic history is, however, compatible with the regional tectonic history of the main Caledonian nappe pile, suggesting that the complex nappe interference patterns typical of the region were formed in a kinematically simple, but intense, ductile deformation associated with Caledonian continental imbrication. 相似文献