Prolonged evolution of syn-collisional progressive deformation of the Trans-North China Orogen: Structural and geochronological evidence from the Xiaoqinling region, central China

Abstract

Significant understanding of the Trans-North China Orogen (TNCO) has been achieved through previous studies. However, the lack of structural analyses, especially for its southern part, has restricted our understanding of the structural evolution of the TNCO. In this contribution, we present new structural and geochronological data from the Taihua Complex of the Xiaoqinling region to reconstruct the collision-induced deformation history and provide constraints on the structural evolution of the TNCO. Paleoproterozoic collision-induced structures in the Xiaoqinling region are characterized by the development of penetrative, ductile deformation fabrics, localized ductile shear zones, and syn-shearing folds, notably sheath folds. The evolution of the folds and syn-tectonic migmatites records the occurrence of non-coaxial progressive shear deformation within ductile shear zones. Vorticity analysis confirms simple-shear-dominated general-shear deformation within the shear zones, with an increase in a pure shear component during the later stages. The integrated results, encompassing the geometry, kinematics, finite strain, and geochronology of these shear zones and folds, reveal the presence of the regional-scale, collision-induced sheath folds that were associated with low-angle thrust shear zones with WNW-directed kinematics. Deformation temperatures of 500–650 °C indicate that the ductile shear zones and simultaneous sheath folds formed during the exhumation process of the TNCO. New zircon U–Pb ages constrain the timing of the metamorphism and ductile deformation to between 1951 and 1840 Ma. Integration of this and previous dating results reveals a history of prolonged collision for the TNCO, lasting from as early as ∼ 1.97 Ga and continuing until as late as ∼ 1.84 Ga, with the earlier period of 1.97–1.88 Ga representing the continental subduction stage and the later period of 1.88–1.84 Ga corresponding to the subsequent exhumation stage. The protracted orogenic evolution for the TNCO supports the notion that large-scale collisional orogenesis can occur over such long durations (over 100 Mya). These structural and geochronological data support the orogenic model of SE-directed subduction polarity.