Strain, Kinematic Vorticity and Ductile Thinning along the Detachment Zone of the Yunmeng Shan Metamorphic Core Complex, Beijing, China  

作　　者：LI Jianbo WANG Tao GUO Lei TONG Ying OUYANG Zhixia ZENG Tao 

机构地区：[1]Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, East China Institute of Technology [2]East China Institute of Technology [3]Institute of Geology, Chinese Academy of Geological Sciences [4]Geological Survey Institute Guangdong Nonferrousmetals Geological Survey Bureau

出　　处：《Acta Geologica Sinica(English Edition)》2013年第4期989-1004,共16页地质学报（英文版）

基　　金：supported by National Natural Science Foundation of China(Grant No.41102129,90714006 and 41002073);the foundation of Fundamental Science on Radioactive Geology and Exploration Technology Laboratory,East China Institute of Technology(Grant No.REGT1207);the Deep Exploration Technology and Experimentation Program of China(Grant No.SinoProbe-08-01-03);projects of China Geological Survey(1212011120135,1212010611803,1212011085474,1212011085473)

摘　　要：The Yunmeng Shan metamorphic core complex （MCC） is composed of the lower plate, the upper plate and the detachment zone. The detachment zone consists of ductile shear zone （mylonite zone）, chloritized microbreccias zone and the brittle fault plane. The ductile shear zone contains mylonitic rocks, protomylonites, and mylonites. Finite strain measurements of feldspar porphyroclasts from those rocks using the Rf/φ method show that the strain intensities increase from mylonitic rocks （Es=0.66-0.72） to protomylonites （Es=0.66-0.83）, and to mylonites （Es=0.71-1.2）. The strain type is close to flatten strain. Kinematic vorticity estimated by Polar Mohr diagrams suggest that foliations and lineation of mylonite （0.47〈Wk〈0.85） record a bulk simple-dominated general shearing at the initial evolution stage of the Yunmeng Shan MCC＇s detachment zone; and the extensional crenulation cleavage（ecc） （0.34〈Wk〈0.77） recorded a bulk pure-dominated general shearing at the later stage of the evolution. Kinematic vorticity measurements also show that the Yunmeng Shan MCC detachment zone is a result of a combination of simple-dominated general shearing caused by crustal extension at the early stage and pure-dominated general shearing caused by MCC uplifting at the late stage. The ductile thinning estimated by finite strain measurements and estimation of Kinematic vorticity ranges from 52% to 82%, which is the minimum thining estimation. Our studies provide new evidence for mechanisms of the Yunmeng Shan MCC detachement zone.The Yunmeng Shan metamorphic core complex （MCC） is composed of the lower plate, the upper plate and the detachment zone. The detachment zone consists of ductile shear zone （mylonite zone）, chloritized microbreccias zone and the brittle fault plane. The ductile shear zone contains mylonitic rocks, protomylonites, and mylonites. Finite strain measurements of feldspar porphyroclasts from those rocks using the Rf/φ method show that the strain intensities increase from mylonitic rocks （Es=0.66-0.72） to protomylonites （Es=0.66-0.83）, and to mylonites （Es=0.71-1.2）. The strain type is close to flatten strain. Kinematic vorticity estimated by Polar Mohr diagrams suggest that foliations and lineation of mylonite （0.47〈Wk〈0.85） record a bulk simple-dominated general shearing at the initial evolution stage of the Yunmeng Shan MCC＇s detachment zone; and the extensional crenulation cleavage（ecc） （0.34〈Wk〈0.77） recorded a bulk pure-dominated general shearing at the later stage of the evolution. Kinematic vorticity measurements also show that the Yunmeng Shan MCC detachment zone is a result of a combination of simple-dominated general shearing caused by crustal extension at the early stage and pure-dominated general shearing caused by MCC uplifting at the late stage. The ductile thinning estimated by finite strain measurements and estimation of Kinematic vorticity ranges from 52% to 82%, which is the minimum thining estimation. Our studies provide new evidence for mechanisms of the Yunmeng Shan MCC detachement zone.

关 键 词：Yunmeng Shan MCC detachment zone MYLONITE STRAIN Kinematic vorticity the ductilethinning 

分 类 号：P588.3[天文地球—岩石学]