The Jurassic major tectonic events of the Yanshanian intraplate deformation belt

Abstract

Through a review and summing-up of the progress in the study of the Mesozoic intraplate deformation in the Yanshan area, it has been determined that phases A and B and the intermediate phase of the Yanshan movement recognized and proposed by W.H. Wong 75 years ago all took place in the Jurassic. The Jurassic tectonic deformation finally formed the framework of the E-W-trending Yanshanian fold-thrust belt. Based upon an analysis and study of regional typical basins, it is found out that phase A of the Yanshanian movement- marked by angular unconformity below andesites of the Tiaojishan Formation- is prior to 160±5 Ma, the geological phase is during the Middle Jurassic Longmenian-Jiulongshanian, and its inferred age is 175-160 Ma. Phase A was the most important tectonic event in the Yanshan intraplate deformation belt and is the indication of the transformation of the Eastern Asian tectonic regime. The intermediate phase is represented by volcanic rocks of the Tiaojishan and Lanqi formations, ranging in age from 165 to 156 Ma. Intense thrusting in phase B gave rise to coarse clastic deposits of the Tuchengzi and Houcheng formations. Its date is prior to 135±1 Ma and its isotopic ages ranging from 156 to 139Ma. From the Early Cretaceous on, regional deformation was gradually dominated by extensions then the tectonic environment changed significantly, volcanic eruptions took place repeatedly and strongly and tectonic deformation was relatively weak. It is evident that the tectonic development that began in the Early Cretaceous does not belong to the Yanshan movement.