Abstract
The Trans-North China Orogen (TNCO) is a tectonic zone that records significant magmatic, metamorphic, and tectonic events during the Paleoproterozoic. The central part of the TNCO comprises several Precambrian blocks (the Hengshan Block, the Wutai Block, the Fuping Block, and the Fanshi Block) that are separated by three Paleoproterozoic ductile shear zones as tectonic boundaries. The Hengshan Block and the Fuping Block are represented by a group of large-scale gneissic domes, whereas the Wutai Block characterized by the ENE–WSW-trending synclinorium, and the framework of the Fanshi Block is dominated by strike-slip ductile shear zones superimposed on tight folds. We present detailed structural analysis of the Zhujiafang ductile shear zone in the central Hengshan, the Wangjiahui ductile shear zone at the northern margin of the Wutaishan, and the metamorphic complex between these two shear zones. The macro- and microstructures indicate that the ductile shear zones show different kinematics. The Zhujiafang ductile shear zone is E–W-trending and record sinistral strike-slip shearing, and the Wangjiahui ductile shear zone is WSW–ENE-trending and record dextral strike-slip shearing. Both of shear zones have similar deformation ages according to the 40Ar/39Ar dating results, and they cut through all the gneissosity and the fold developed in these metamorphic rocks. The kinematic difference between the Zhujiafang and the Wangjiahui ductile shear zones clearly define the Fanshi Block sandwiched between them, which is characterized by movement from west to east. The Fanshi block differs from the Hengshan Block and the Wutai Block in terms of deformation history, metamorphism, and magmatism. In addition, a series of NE-trending ductile–brittle thrust nappes inside the Wutai Block under the influence of the indention of the Fanshi Block inside. Therefore, we propose that the Fanshi Block was indented to the TNCO from west to east, accompanied by strong strike-slip ductile shearing and thrusting during the late Paleoproterozoic.
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