Timing Determination of Phase B of the Yanshanian Movement in the Eastern North China Craton: Evidence from Dating of a Ductile Shear Zone in Sihetang, Northeastern Beijing
详细信息
- 责任者：Chen Yin (Hefei University of Technology ; Hefei 230009 ; China) ; Zhu Guang
- 刊名：Acta Geologica Sinica
- 出版年：2013
- 卷期：87(3)
- 关键词：剪切带 ; shear zones ; 燕山运动 ; Yanshan Movement ; 北京 ; Beijing
- 页码：p.295-310
- 图表：illus., 5 tables, 65 refs.
- 分类号：0300
- issnNo：ISSN0001-5717
- isbnNo：CN11-1951/P
摘要
The Yanshanian orogenic belt is an important Mesozoic tectonic feature in north of the North China Craton (NCC). It was named after its position by Wong (1927, 1929, Bulletin of Geological Society of China). The "Yanshanian orogeny" is believed to consists of two phases (A and B), represented by two regional angular unconformities, but their timing has not been defined. Both phases are characterized by crustal shortening. Phase A is marked by the unconformity beneath the andesite volcanic rocks of the Tiaojishan Formation and Phase B by the unconformity beneath volcanic rocks of the Zhangjiakou Formation. The famous Sihetang ductile shear zone developed within the Yunmeng area in the central segment of the Yanshan tectonic belt, and was the product of Phase B of Yanshanian Movement. The Sihetang shear zone is located in the north margin of the Early Cretaceous Yunmengshan pluton, with hanging wall thrusting to near SSW. Adjacent metamorphic basement, Meso-and-Neoproterozoic cover layers, and Late Jurassic to Early Cretaceous plutons were involved in the ductile shear zone deformation. Many syntectonic dykes present in the Shihetang shear zone were found to emplace in three stages, which correspond to three different stages of the shear belt (early, middle and late) based on their geometries within the shear zone. This study collected the zircons from dykes of each stage for dating. LA-ICP-MS zircon U-Pb ages for the three stages are 143.0±2.1 Ma, 140.8±1.4 Ma, and 137.5±2.4 Ma respectively, consistent with dyke emplacement order constrained from structural analysis. This also suggests that 143~138 Ma should be the time period for the B phases of the Sihetang ductile shear zone deformation. This result couples with that of the zircon of volcanic rocks sampled from neighboring strata around the shear zone.