Mesozoic tectonic evolution of eastern China: Insights from the Changshan Islands, NE China

Abstract

The Changshan islands are scattered among the Yellow Sea east of the Liaodong Peninsula, west of North Korea and north of the Sulu Orogenic Belt. They consist of three lithotectonic units: i) Archean gneiss, ii) Paleoproterozoic marble and micaschists, and iii) Neoproterozoic weakly metamorphic sedimentary rocks. Three stages of deformation (D1-D3) documented in this study indicate that Changshan islands are a key region to decipher the Mesozoic tectonic evolution of eastern China. The earliest deformation D1 corresponds to a ductile deformation with NE-SW trending mineral and stretching lineations and top-to-the-NE sense of shear. The deformation D2, observed in the micaschists and sedimentary rocks, is characterized by the SW-verging folds with NE-dipping axial planar cleavage S2 and SW-directed thrusting. D2 could be considered as the back-folding and back-thrusting of the D1. D3 is expressed by the NE-SW trending low-angle brittle and ductile detachment faults representing a NW-SE extensional event.To the east of Guanglu and Guapi islands, two samples from a granite pluton that only record D3 fabrics yield SIMS zircon ages of 165.4 ± 1.6 Ma and 164.7 ± 1.5 Ma, which indicate that D1 and D2 occurred earlier than 165 Ma, while D3 is younger than this age. Similar geometric and kinematic features with those of the South Liaodong Peninsula suggest that D1 and D2 occurred in the Middle-Late Triassic as the structural response of overriding plate to the continental subduction of the South China Block (SCB) beneath the North China Craton (NCC), while the D3 occurred in the Early Cretaceous during the development of the Liaonan Metamorphic Core Complex (MCC). The ductile shear zone and brittle normal faults of the Changshan islands represent the early extensional structures of the Liaonan MCC. They may develop further southeastward and controlled the early development of the North Yellow Sea Basin.