| 哀牢山韧性平移剪切带的特征 |
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| 引用本文：崔军文.1989.哀牢山韧性平移剪切带的特征[J].地球学报,11(1):21-35. |
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| 中文摘要:标志冈瓦纳古陆向华夏古陆俯冲的云南中西部哀牢山古俯冲带,在始新世—渐新世、中新世—上新世时转化为右旋韧性平移剪切带。计算的剪切带的最大应变值(γ)为12.6,角应变(φ)为85.5°,获得的塑性应变的应力场有两期:第一期,主压应力(σ_1)方位为3°/49°,应力张量为-1.575;第二期,主任应力(σ_1)方位为252°/1°,应力张量为-0.876,流动应力值最高达389MPa。 |
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| CHARACTERISTICS OF THE AILAOSHAN DUCTILE STRIKE-SLIP SHEAR BELT |
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| Abstract:The Ailaoshan fault, regarded as an important boundary of tectonic units in western Yunnan (separating Cathaysia in the east from Gondwana in the west), is a large lithospheric fault developing progressively on the Precambrian oceanic crust. It exhibited strong subduction in the early stage of development before the Middle Jurassic to Early Cretaceous and gradually became ductile strike-slip shearing in nature from the end of Late Gre-taceou to Eocene and was basically a ductile strike-slip shear belt in the late stage fome the terminal Oligocene to Pliocene.The deformation structures in the Ailaoshan ductile strike-slip shear belt mainly include flow (and also fracture) cleavages, lineations and micro-folds.A series of microstructural evolution may be observed perpendicular to the direction of the shear belt which consists from northeast to southwest zones of dominant gneissic structure (granular mosaic texture), augen-like to flaser or phacoidal structures (porphro-clastic and other cataclastic textures) , schistose-folded structure (schistose to phyllonitic textures) and slaty -phyllitic structure (fine granoblastic to lepidoblastic textures). Of these, the zone of schistose-folded structure is the centre of the shear belt which exhibits the strongest plastic strain.The deformation structures and fabric evolution have shown that this belt is a dextral one. The main criteria for determining the shear direction are S-C fabric, folded (wavy)foliation, pressure shadow, rotationaJ porphyro-clasts and oblique extinction zones of crystals as well as echelon shear fractures.Theγ-X and ψ-X curves of the belt assume an irregular sine shape of which the highest peak value appears at the centre of the belt, with the shear strain γ=12.6 and the angle strain ψ = 85.5°, and the next highest peak appears near the Red River fault, with γ = 8 and ψ = 82.9°. The flow stress value and strain value obtained by calculation of dynamic recrystallized grains show the same regularity of changes, which are the greatest in the centre of the belt, being up to 389 MPa. Another high value appears near the Red River fault, being 224.5MPa. The shear belt has a cumulative displacement of about 53km.The calcite fabric shows that the Ailaoshan ductile shear belt underwent two stages of dextral strike-slip shearing.In the first stage, the principal compressive stress (σ1) was 3°/49° and the stress tensor -1.575, and in the second stage, 252°/1° and -0.876. It is estimated by referance to the regional geological information that the dextral shear stress originated from the lateral dextral shearing resulting from northward subduction of the Indian plate.In addition, the microstructures and stress field show that in the process of formation and evolution of the Ailaoshan shear belt there possibly existed a stage of sinistral strike-slip shearing, which was earlier than the dextral one.The study of the Ailaoshan ductile strike-slip shear belt also indicates that in the process of formation and evolution the Red River fault experen-ced dextral strike-slip shearing. |
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