Protolith ages and deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone

• Published in: Science China. Earth sciences 2014-11, Vol.57 (11), p.2740-2757
• Main Authors: Zhao, Tian, Zhu, Guang, Lin, ShaoZe, Yan, LeJia, Jiang, QinQin
• Format: Article
• Language: English
• Subjects: Earth and Environmental Science; Earth Sciences; Fault lines; LA-ICP-MS; Metamorphic rocks; Research Paper; Rock deformation; 原岩; 变形机制; 变质岩; 大别山造山带; 年龄; 郯庐断裂带; 隆起
• ISSN: 1674-7313; 1869-1897
• DOI: 10.1007/s11430-014-4959-4

Protolith ages and Indosinian deformation mechanism of metamorphic rocks in the Zhangbaling uplift segment of the Tan-Lu Fault Zone are important, unsolved problems. Our LA-ICP-MS zircon dating work indicates that protolith ages of the greenschist-facies Zhangbaling Group are 754-753 Ma, and those of the amphibolite-facies Feidong Complex are 800-745 Ma. These rocks belong to the earliest cover of the Yangtze Plate. Their ages and metamorphic features suggest that the rocks did not come from the Dabie Orogen. The Indosinian structures in the Zhangbaling Group and lower Sinian strata formed in a flat- lying ductile detachment zone with a shear sense of top-to-the-SSW whereas those in the underlying Feidong Complex are characterized by ENE-WSW inclined folds developed under a ductile regime. It is suggested therefore that the sinistral Tan-Lu Fault Zone of the Indosinian period is buried under the Hefei Basin west of the Zhangbaling uplift segment and the uplift seg- ment is a displaced block neighboring the fault zone. Detachment deformation between the upper rigid and lower ductile crust during displacement of the Zhangbaling uplift segment resulted in the formation of the flat-lying ductile detachment zone and its underlying drag fold zone of a ductile regime. The protolith ages and deformation mechanism in the Zhangbaling uplift segment further prove sinistral origination of the Tan-Lu Fault Zone during the continent-continent collision of the North Chi- na and Yangtze plates and support the indentation model for the two-plate collision that considers the Tan-Lu Fault Zone as an oblique convergence boundary.