| Strain and shear types of the Louzidian ductile shear zone in southern Chifeng, Inner Mongolia, China |
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| 作者姓名： | WANG XinShe ZHENG YaDong & WANG Tao Institute of Geology Chinese Academy of Geological Sciences Beijing China The Laboratory of Orogenic Belts and Crustal Evolution Peking University Beijing China |
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| 作者单位： | WANG XinShe1，ZHENG YaDong2 & WANG Tao1 1 Institute of Geology，Chinese Academy of Geological Sciences，Beijing 100037，China; 2 The Laboratory of Orogenic Belts and Crustal Evolution，Peking University，Beijing 100871，China |
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| 基金项目： | 国家自然科学基金;高等学校博士学科点专项科研项目 |
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| 摘 要： | The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-medium- angles. This ductile shear zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone, a brittle fault and a gouge zone. All these zones share similar planar attitudes, but contain different linear attitudes and kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These meas- urements yield Fulin indexes of 1.25―3.30, Lode's parameters of -0.535―-0.112 and strain parameters of 0.41―0.75 for the protomylonite, respectively. These data are plotted within the apparent constric- tional field in Fulin and Hossack diagrams. In contrast, for the mylonite, corresponding parameters are 0.99―1.43, -0.176―-0.004 and 0.63―0.82, respectively, and located in the apparent constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67―0.95, suggesting that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so the lineation in the ductile shear zone could not deflect 90° in the progressively deformation.
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| 收稿时间： | 28 February 2006 |
| 修稿时间： | 30 May 2006 |
Strain and shear types of the Louzidian ductile shear zone in southern Chifeng,Inner Mongolia,China |
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| WANG XinShe,ZHENG YaDong & WANG Tao Institute of Geology,Chinese Academy of Geological Sciences,Beijing ,China, The Laboratory of Orogenic Belts and Crustal Evolution,Peking University,Beijing ,China.Strain and shear types of the Louzidian ductile shear zone in southern Chifeng, Inner Mongolia, China[J].Science in China(Earth Sciences),2007,50(4):487-495. |
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| Authors: | Wang XinShe Zheng YaDong Wang Tao |
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| Institution: | 1. Institute of Geology,Chinese Academy of Geological Sciences,Beijing 100037,China
2. The Laboratory of Orogenic Belts and Crustal Evolution,Peking University,Beijing 100871,China |
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| Abstract: | The Louzidian ductile shear zone at the south of Chifeng strikes NE-SW and dips SE at low-medium-angles. This ductile shear
zone is mainly composed of granitic mylonite, which grades structurally upward into a chloritized zone, a microbreccia zone,
a brittle fault and a gouge zone. All these zones share similar planar attitudes, but contain different linear attitudes and
kinematic indicators. Finite strain measurements were performed on feldspar porphyroclasts using the Fry method. These measurements
yield Fulin indexes of 1.25–3.30, Lode’s parameters of −0.535–−0.112 and strain parameters of 0.41–0.75 for the protomylonite,
respectively. These data are plotted within the apparent constrictional field in Fulin and Hossack diagrams. In contrast,
for the mylonite, corresponding parameters are 0.99–1.43, −0.176–−0.004 and 0.63–0.82, respectively, and located in the apparent
constrictional field close to the plane strain. The mean kinematic vorticity numbers of the protomylonite and mylonite by
using three methods of polar Mohr circle, porphyroclast hyperbolic and oblique foliation, are in the range of 0.67–0.95, suggesting
that the ductile shearing is accommodated by general shearing that is dominated by simple shear. Combination of the finite
strain and kinematic vorticity indicates that shear type was lengthening shear and resulted in L-tectonite at the initial
stage of deformation and the shear type gradually changed into lengthening-thinning shear and produced L-S-tectonite with
the uplifting of the shear zone and accumulating of strain. These kinds of shear types only produce a/ab strain facies, so
the lineation in the ductile shear zone could not deflect 90° in the progressively deformation.
Supported by the National Natural Science Foundation of China (Grant Nos. 40102017, 40572123 and the 40472101) and Doctoral
Programme of Higher Education (Grant No. 2000000128) |
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| Keywords: | ductile shear zone strain path kinematic vorticity shear type Chifeng |
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