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1.
This work deals with the preliminary relationship between strain path and strain partitioning pattern in a sinistral transpressional zone,Lancangjiang shear zone,located to the southeast of Tibet.Various ductile rocks provide an opportunity to investigate quantitative finite strain(Rs),kinematic vorticity values(Wm),and proportions of simple and pure shear components.The mean kinematic vorticity values(Wm) were evaluated based on three methods,such as Rs-θ,prophyroclast hyperbolic distribution method(PHD),a... 相似文献
2.
在沂沭断裂带中段的泰山群结晶基底中,存在着一系列北东、北北东走向的左行韧性剪切带。对其中发育糜棱岩的韧性剪切带的结构构造、应变测量、变形岩石的显微构造、显微组构以及长石粒度和含量的变化规律进行了观测分析。讨论了韧性剪切带的变形条件和机制。及其递进发展的趋势。指出基底韧性剪切带是沂沭断裂带元古宙时期断裂活动时在地壳较深层次上形成的构造表象。在此基础上,讨论了地壳不同层次上的断裂变形及断裂岩石的综合分类问题 相似文献
3.
The structural characteristics,age of origin,and tectonic attribute of the Erguna Fault,NE China 总被引：1，自引：0，他引：1
The Erguna Fault runs along the east bank of the Erguna River in NE China and is a large-scale ductile shear zone comprising granitic mylonites. This paper reports on the geometry, kinematic indicators, and 40Ar/39 Ar biotite ages of the granitic mylonites, to constrain the structural characteristics, forming age, and tectonic attribute of the Erguna ductile shear zone. The zone strikes NE and records a top-to-the-NW sense of shear. A mylonitic foliation and stretching lineation are well developed in the mylonites, which are classified as S-L tectonites. Logarithmic flinn parameters(1.18–2.35) indicate elongate strain which approximates to plane strain. Kinematic vorticity numbers are 0.42–0.92 and 0.48–0.94, based on the polar Mohr diagram and the oblique foliation in quartz ribbons, respectively, suggesting that the ductile shear zone formed under general shear, or a combination of simple and pure shear. According to finite strain and kinematic vorticity analyses, the Erguna Fault is a lengthening-thinning ductile shear zone that formed by extension. The deformation behavior of minerals in the mylonites indicates that the fault was the site of three stages of deformation: an initial stage of middle- to deep-level, high-temperature shear, a post-stress recovery phase of high-temperature static recrystallization, and a final phase of low-temperature uplift and cooling. The 40Ar/39 Ar plateau ages of biotite from the granitic mylonites are 106.16 ± 0.79 and 111.55 ± 0.67 Ma, which constrain the timing of low-temperature uplift and cooling but are younger than the ages of metamorphic core complexes(MCCs) in the Transbaikalia-northeast Mongolia region. Using measured geological sections, microtectonics, estimates of finite strain and kinematic vorticity, and regional correlations and geochronology, we conclude that the Erguna Fault is an Early Cretaceous, NNE-trending, large-scale, sub-horizontal, and extensional ductile shear zone. It shares a similar tectonic background with the MCCs, volcanic fault basins, and large and super-large volcanic-hydrothermal deposits in Transbaikalia-northeast Mongolia and the western Great Khingan Mountains, all of which are the result of overthickened crust that gravitationally collapsed and extended in the Early Cretaceous after plate collision along the present-day Sino-Russia-Mongolia border tract. 相似文献
4.
ＣｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｆａｕｌｔｒｏｃｋｓａｎｄｐａｌｅｏｅａｒｔｈｑｕａｋｅｓｏｕｒｃｅａｌｏｎｇｔｈｅＫｏｋｔｏｋａｙＥｒｔａｉｆａｕｌｔｚｏｎｅ，Ｘｉｎｊｉａｎｇ，ＣｈｉｎａＬＡＮＢＩＮＳＨＩ１）（史兰斌）ＣＨＵＡＮＹＯＮ... 相似文献
5.
Kinematics and dynamics of the Mesozoic orogeny and late-orogenic extensional collapse in the Sino-Mongolian border areas 总被引：7，自引：1，他引：7
ZHENG Yadong & WANG Tao . Key Laboratory of Orogenic Belts Crustal Evolution 《中国科学D辑(英文版)》2005,48(7)
Extensional tectonic models with the major features of metamorphic core complexes were established in the Cordilleran region of western North America dur- ing the late 1970s to early 1980s of last century[1—4].Since there were previous thrust events, some re- searchers attributed the extension to crust-thickening of Mesozoic orogen[5—8], i.e. the crust thickening dur- ing orogeny led to the fact that the materials at depthswere heated and partially melted, and the heated and low-density mat… 相似文献
6.
The ancient flow regime in natural shear zones is often considered to have followed a deformation path comparable to that in theoretical shear zones, i.e. progressive simple shear between rigid wall rocks with a persistent flow plane orientation parallel to the edges of the zone. This is often based on the presence of monoclinic fabric elements in the zones which indicate a dominantly non-coaxial flow regime, though not necessarily persistent simple shear. The deformation fabric of a shear zone from the Pyrenees illustrates that, even at a kinematic vorticity number ofW′ = 1 (simple shear) along the entire deformation path, obliqueness of the flow planes with the edges of the zone is possible for some time if incremental stretching axes were rotating with respect to zone edges. This implies that ductile deformation must have taken place in the wall rock of the zone. Such a flow regime may be difficult to recognize with the fabric criteria used at present but leads to an unusual kinematic significance of the shear zone involved; in extreme cases the zone may have acted as a passive marker in a ductilely deforming medium. It also means that not onlyW′ must be known to reconstruct the ancient flow regime in natural shear zones, but at least also the time dependence of the orientation of the incremental stretching axes. 相似文献
7.
Guido Ventura 《Bulletin of Volcanology》1998,59(6):394-403
A basaltic andesite lava flow from Porri Volcano (Salina, Southern Tyrrhenian Sea) is composed of two different magmas. Magma
A (51 vol.% of crystals) has a dacitic glass composition, and magma B (18 vol.% of crystals), a basaltic glass composition.
Magma B is hosted in A and consists of sub-spherical enclaves and boudin-like, banding and rolling structures (RS). Four types
of RS have been recognized: σ–type;δ–type; complex σ-δ–types and transitional structures between sub-spherical enclaves and rolling structures. An analysis of the RS has been performed
in order to reconstruct the flow kinematics and the mechanism of flow emplacement. Rolling structures have been selected in
three sites located at different distances from the vent. In all sites most RS show the same sense of shear. Kinematic analysis
of RS allows the degree of flow non-coaxiality to be determined. The non-coaxiality is expressed by the kinematic vorticity
number Wk, a measure of the ratio Sr between pure shear strain rate and simple shear strain rate. The values of Wk calculated from the measured shapes of microscopic RS increase with increasing distance from the vent, from approximately
0.5 to 0.9. Results of the structural analysis reveal that the RS formed during the early–intermediate stage of flow emplacement.
They represent originally sub-spherical enclaves deformed at low shear strain. At higher strain, RS deformed to give boudin-like
and stretched banding structures. Results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous
non-ideal shear flows in which the degree of non-coaxiality increases with the distance from the vent. In the vent area, deformation
is intermediate between simple shear and pure shear. Farther from the vent, deformation approaches ideal simple shear. Lateral
extension processes occur only in the near-vent zone, where they develop in response to the lateral push of magma extruded
from the vent. Lateral shortening processes develop in the distal zone and record the gravity-driven movement of the lava.
The lava flow advanced by two main mechanisms, lateral translation and rolling motion. Lateral translation equals rolling
near the vent, while rolling motion prevailed in the distal zones.
Received: 6 November 1997 / Accepted: 29 November 1997 相似文献
8.
New40Ar/39Ar plateau ages from rocks of Changle-Nanao ductile shear zone are 107.9 Ma(Mus), 108.2 Ma(Bi), 107.1 Ma(Bi), 109.2 Ma(Hb)
and 117.9 Ma(Bi) respectively, which are concordant with their isochron ages and record the formation age of the ductile shear
zone. The similarity and apparent overlap of the cooling ages with respective closure temperatures of 5 minerals document
initial rapid uplift during 107–118 Ma following the collision between the Min-Tai microcontinent and the Min-Zhe Mesozoic
volcanic arc. The40Ar/39 Ar plateau ages, K-Ar date of K-feldspar and other geochronologic information suggest that the exhumation rate of the ductile
shear zone is about 0.18–1.12 mm/a in the range of 107–70 Ma, which is mainly influenced by tectonic extension. 相似文献
9.
The main problem,in determining the shear displacement of a general shear zone with volume change using the available formula,is that it is hard to know the initial angle between the planes (or lines) in the plane of shear.A planar deformation analysis of this kind of ductile shear zone is carried out with the polar Mohr diagram.If the volume change is induced by homogeneous contraction in the Z direction of the shear zone,there are sufficient conditions for constructing a polar Mohr diagram regardless of sequence of the simple shear and volume change.Therefore,the angle between a line and the shear direction before and after the deformation can be measured.Making use of these lines the shear strain and the volume change can be calculated and the shear displacement can be determined. 相似文献
10.
11.
Polar Mohr diagram method and its application in calculating the shear displacements of general shear zones with volume loss 总被引：2，自引：0，他引：2
The main problem, in determining the shear displacement of a general shear zone with volume change using the available formula,
is that it is hard to know the initial angle between the planes (or lines) in the plane of shear. A planar deformation analysis
of this kind of ductile shear zone is carried out with the polar Mohr diagram. If the volume change is induced by homogeneous
contraction in the Z direction of the shear zone, there are sufficient conditions for constructing a polar Mohr diagram regardless
of sequence of the simple shear and volume change. Therefore, the angle between a line and the shear direction before and
after the deformation can be measured. Making use of these lines the shear strain and the volume change can be calculated
and the shear displacement can be determined. 相似文献
12.
Jafar Hadizadeh 《Pure and Applied Geophysics》1994,143(1-3):255-280
The mineralogical and elemental variations across the main shear zone of the Saltville thrust at Sharp Gap in Knoxville, Tennessee, U.S.A., were studied in a suite of deformed and undefromed carbonate rock samples using X-ray diffraction and electron microprobe methods. An examination of the samples for deformation effects at mesoscopic scale and under the optical microscope reveals familiar cataclastic deformation features including foliated cataclasites and microbreccias occurring in a well-defined, 1–2 m wide zone of intense deformation, plus evidence of hydrofracturing and extensive syndeformational pressure solution. There exists a clear correlation between the observed cataclastic deformation and mineral and elemental distribution which we interpret to result from a deformation-induced dolomite to calcite transformation in the shear zone. The transformation has resulted in removal of Mg from the shear zone, selective deposition of calcite as an intergranular cement in cataclasite/microbreccia units and a relative increase in the concentration of detrital quartz and feldspars.The compositional difference between the shear zone and wall rocks is explained in connection with cataclastic deformation features in terms of a model in which a dual pressure-solution/cataclastic flow mechanism leads to a gradual cementation-hardening of segments of the shear zone. Instabilities could occur via permeability reduction and increased pore pressure within these segments. Hydrofracturing of the hardened segments along with high strain rate reordering of the shear zone materials reset the ruptured zone back to the dual deformation mechanism regime. As a long-term effect, the compositional transformation of the shear zone is expected to prolong periods of creep and cause smaller coseismic stress drops since under the imposed conditions calcite is more ductile and soluble than dolomite. 相似文献
13.
NI JinLong LIU JunLai TANG XiaoLing ZHAO ChunQiang & ZENG QingDong 《中国科学:地球科学(英文版)》2014,57(4):600-613
The combination of field surveys with analysis of microstructure of tectonite and Electron Backscatter Diffraction (EBSD) on quartz fabric indicated that three periods of ductile shear events developed in the Paishanlou gold deposits and the E-W and NE-striking ductile shear zones were formed during each event. The E-W-striking ductile shear zone, accompanied by compressional and dextral shear slip, was shear-cut by the NE-striking shear zones, accompanied by compressional-sinistral shear slip and sinistral-normal shear slip, successively. An E-W-striking ductile shear zone developed at a deeper tectonic level and at middle- to high-temperatures, accompanied by abundant microstructures, including microlayering between a polycrystal quartz belt and mica, and quartz deformation was depended on cylinder (10-10) 〈a〉 or 〈c〉 glide. The development of an E-W-striking shear zone can be seen as a tectonic pattern in the region of the Paishanlou gold deposits of the collision between the Mongolian tectonic belt and the North Archean Craton from Suolun to the Linxi suture zone during the Indosinian. The NE-striking ductile shear zone developed approximately 160 Ma during the early Yianshanian at middle to shallow tectonic levels and at middle- to low-temperatures, accompanied by typical microstructures, including polycrystal quartz aggregation and quartz subgrain rotation recrystallization, etc., and quartz deformation was depended on prismatic (1011) 〈a〉 glide. The last ductile shear event around the NE-striking shear zone developed at low temperatures and shallow tectonic levels, yielding to a pre-existing NE-striking shear zone, accompanied by abundant microstructures, including low-temperature quartz grain boundary migration and bulging recrystallization. The last ductile shear movement may be related to lithosphere thinning and the destruction of the North China Craton from approximately 130-120 Ma, and this shear event resulted directly in the mineralization in the Paishanlou region. 相似文献
14.
The Pengguan tectonic dome of Longmen Mountains, Sichuan Province: Mesozoic denudation of a Neoproterozoic magmatic arc-basin system 总被引：3，自引：0，他引：3
DanPing Yan MeiFu Zhou GuoQing Wei JianFeng Gao ShaoFeng Liu Ping Xu XiaoYing Shi 《中国科学D辑(英文版)》2008,51(11):1545-1559
Neoproterozoic igneous and metamorphic complexes occur as tectonic domes in the Longmen Mountains of the western margin of the Yangtze Block, and are important in reconstructing the Rodinian supercontinent and constraining the timing and mechanism of tectonic denudational processes. The Pengguan dome consists of granitic intrusions and metamorphic rocks of the Huangshuihe Group and is tectonically overlain by ductilly deformed Sinian to Paleozoic strata. The plutonic intrusions consist of granites with abundant amphibolite enclaves. New LA-ICP-MS zircon U-Pb dating yielded an emplacement age of 809±3 Ma and a protolith age of 844±6 Ma for the granite. The granitic rocks have geochemical signatures typical of A-type granites, indicating their formation under an extensional environment, by melting of newly formed tonalite-trondhjemite-granodiorite (TTG) rocks. A detachment fault, characterized by variable ductile shear deformation of S-C fabric and ESE-ward kinematics, separates the Pengguan dome from the Sinian-Paleozoic cover. 40Ar/39Ar dating of muscovite from the mylonite in the detachment fault of the dome demonstrates that ductile deformation occurred at ~160 Ma. This study indicates the existence of a Neoproterozoic magmatic arc-basin system, which was denudated by a Jurassic middle crustal ductile channel flow along the Longmenshan thrust belt. 相似文献
15.
Geometry,kinematics and evolution of the Tongbai orogenic belt 总被引：2，自引：0，他引：2
1 Introduction spectively[2,3]. Several tectonic units such as the Bei- The Qinling-Dabie orogenic belt has attracted huaiyang, north Dabie, south Dabie and Susong belts worldwide attention by its very complex and abundant have been recognized in eastern Dabie[4]. Nine tec- geological characters, and has been a “hot point” of tonic units have been recognized in western Dabie and international geological research[1]. A vast amount of a more detailed division has been suggested especially … 相似文献
16.
Water contents and deformation mechanism in ductile shear zone of middle crust along the Red River fault in southwestern China 总被引：1，自引：0，他引：1
Using Fourier transform infrared spectroscopy (FTIR), we measured water contents of quartz and feldspar for four thin sections of felsic mylonite and two thin sections of banded granitic gneiss col- lected from a ductile shear zone of middle crust along the Red Rivers-Ailaoshan active fault. The ab- sorbance spectra and peak position suggest that water in quartz and feldspar of granitic gneiss and felsic mylonite occurs mainly as hydroxyl in crystal defect, but also contains inclusion water and grain boundary water. The water contents of minerals were calculated based on the absorbance spectra. Water content of feldspar in granitic gneiss is 0.05 wt%-0.15 wt%, and that of quartz 0.03 wt%-0.09 wt%. Water content of feldspar ribbon and quartz ribbon in felsic mylonite is 0.095 wt%-0.32 wt%, and those of fine-grained feldspar and quartz are 0.004 wt%-0.052 wt%. These data show that the water content of weakly deformed feldspar and quartz ribbons is much higher than that of strongly deformed fine-grained feldspar and quartz. This suggests that strong shear deformation leads to breakage of the structures of constitutional water, inclusion and grain boundary water in feldspar and quartz, and most of water in minerals of mylonite is released to the upper layer in the crust. 相似文献
17.
广宁深层次推覆构造前缘陡倾带变形构造研究 总被引：6，自引：0，他引：6
河台含金韧性剪切带是广宁深层次推覆构造前缘的一个陡倾带，它又是继推覆剪切之后再行右旋走滑剪切的复合带。首先解析了河台带中推覆与走滑两期构造变形的存在，并研究了带中的变形特征和运动规律及估算了几个主要糜棱岩带的水平走滑距离。通过显微镜和透射电镜，还研究了糜棱岩的显微、超显微构造，估算了变形的差异应力和应变速率 相似文献
18.
Abstract Meso- and microscale structural analyses were carried out in the Hatagawa shear zone, north-eastern Japan. The shear zone is a sinistral strike–slip ductile shear zone, and has a 1-km wide north-south trending region where quartz mean grain size of approximately 35 μm does not vary significantly. Two types of quartz microstructures, A and B, occur in the western and eastern part of the shear zone, respectively. The lattice preferred orientation (LPO) patterns are characterized by a type I crossed girdle in the samples with the quartz microstructure A, and a Y maximum in the samples with the quartz microstructure B. The microstructures under optical and transmission electron microscopes indicates that the quartz recrystallization occurred predominantly by progressive subgrain rotation in microstructure A, and by both progressive subgrain rotation and grain boundary migration in microstructure B. This suggests different deformation conditions in the western and eastern parts of the shear zone. Quartz LPO patterns, presence of myrmekite, feldspar compositions, and dislocation density also suggest difference in the deformation conditions. The syn-deformation temperature in the western part of the shear zone was lower than that of the eastern part of the shear zone. The stress in the western part of the shear zone was higher than that of the eastern part of the shear zone. The difference in the deformation conditions would affect not only the quartz microstructure, but also the quartz LPO patterns and the presence of myrmekite around K-feldspar porphyroclasts. 相似文献
19.
The massive unit of a lava flow from Porri volcano (Salina, Aeolian Islands) displays many unusual structures related to
the physical interaction between two different magmas. The magma A represents approximately 80% of the exposed lava surface;
it has a crystal content of 51 vol.% and a dacitic glass composition (SiO2=63–64 wt.%). The magma B has a basaltic-andesite glass composition (SiO2=54–55 wt.%) and a crystal content of approximately 18 vol.%. It occurs as pillow-like enclaves, banding, boudin-like and
rolling structures which are hosted in magma A. Structural analysis suggests that banding and boudin-like structures are the
result of the deformation of enclaves at different shear strain. The linear correlation between strain and stratigraphic height
of the measured elements indicates a single mode of deformation. We deduce that the component B deformed according to a simple
shear model. Glass analyses of the A–B boundary indicate that A and B liquids mix together at high shear strain, whereas only
mingling occurs at low shear strain. This suggests that the amount of deformation (i.e. forced convection) plays an important
role in the formation of hybrid magmas. High shear strain may induce stretching, shearing and rolling of fluids which promote
both forced convection and dynamical diffusion processes. These processes allow mixing of magmas with large differences in
their physical properties.
Received: 15 July 1995 / Accepted: 30 May 1996 相似文献
20.
Early Cretaceous sinistral shearing and associated folding in the South Kitakami Belt, northeast Japan 总被引：1，自引：0，他引：1
Migiwa Sasaki† 《Island Arc》2003,12(2):92-109
Abstract Early Cretaceous structural development of the southern part of the South Kitakami Belt, northeast Japan, is discussed through precise structural mapping and the measurement of semiquantitative strain. The mapping and measurement revealed that wide north- to northeast-trending sinistral shear zones occupied by the 'slate' with higher strain than the surrounding rocks run from the axial part to the western limb of major synclines, with the wavelength of 5–10 km. The major synclines with a U-shaped rock distribution opening to the south are interpreted to be drag folds along the sinistral shear zones. These structures were modified by a second stage of Early Cretaceous sinistral shearing characterized by localized high-temperature mylonite zones along the rim of some of the 120 Ma granitoids that cut the major folds and baked the 'slate' in the older shear zones mentioned above. The rocks of the South Kitakami Belt, which had undergone two stages of shearing, were rapidly exhumed before the deposition of the Late Aptian–Albian Miyako Group. Finally, a restoration model is presented of the Early Cretaceous sinistral displacement and deformation in the study area. 相似文献