Kinematics and geochronology of the ductile shear zones in the western Shandong granite-greenstone belt: Implications for the Neoarchean plate tectonics of the North China Craton

Abstract

The granite-greenstone belt is the main component of Archean crust, and is critical for resolving the disputes on the tectonic evolution and dominant regime of the early Earth. The North China Craton (NCC) is one of the oldest cratons in the world, and is composed of several continental micro-blocks. The greenstone belts, welding the micro-blocks, were generally considered to be continental or arc-continental collision belts during the amalgamation of the micro-blocks in the late Neoarchean. Thus, the structural pattern of these greenstone belts can provide essential clues for the crustal deformation style during early Precambrian orogeny. The western Shandong granite-greenstone belt (WSGB) located in the eastern NCC was considered as the collision belt of the Jiaoliao and Qianhuai Blocks. There exists a series of ductile shear zones with strike-slip kinematics, including Qixingtai, Nanliu, Yanlingguan, Xintai, Dongling–Huacun, Mengshan, Fengyang–Liangqiu, Qingyi and Baiyan. This paper conducts detailed geometric, kinematic and deformation geochronology studies, and reveal that the mylonitic foliation of the ductile shear zones in the WSGB strikes NW280–350° with angles of 60–80°. The mineral stretching lineation gently plunges to NE or SW at 2–25°. Kinematic indicators show sinistral strike-slip shearing sense. The deformation temperature can be divided into two ranges: 550–600 ℃ and 400–500 ℃, implying that the ductile shear zones in the WSGB was ought to experience early-stage high-temperature and late-stage low-temperature deformation. The deformation age is ∼ 2.58–2.47 Ga constrained by zircon LA-ICP-MS U–Pb and ⁴⁰Ar–³⁹Ar dating, and this age range includes early-stage high-temperature deformation. Structural restoration through balanced profiles and stereographic projection shows that the initial orientation of NW–NWW-trending ductile shear zones was dipping to the SW, and still were featured by strike-slip kinematics. Syn-kinematic arc-affinity magmatism and sedimentation demonstrate that the NW–NWW-trending ductile shear zones in the WSGB were caused by SE-ward plate convergence, which also led to the NW–SE-trending movement of different blocks along the strike of ductile shear zones. The WSGB represents an active continental margin in the southwestern Jiaoliao Block with intense arc-affinity magmatism and back-arc sedimentation, post-collision crustal-derived granites, traspressive shearing deformation, also indicating that the NCC was dominated by modern-style plate tectonism in the late Neoarchean.