Late Mesozoic–Cenozoic décollement structure and its deep geological background in western Shandong, China

Data from seismic reflection profiles, drilling, stratigraphy, structural deformation studies and physical rock properties reveal the existence of décol1ement structures in both shallow and deep levels in western Shandong, China. The most outstanding shallow décol1ement structures occur along the regional unconformity surface between the Cambrian and Archean, and the disconformity surface between the Carboniferous and Ordovician. The décol1ement structure surface manifests as a fault zone with cataclastic rocks and asymmetrical folds. Some of the cataclastic rocks underwent dynamic metamorphism and hydrothermal alteration, including silicification, marbleization and specularite mineralization. Above the décol1ement structure, the bottom of the Cambrian might be missing or overprinted because of décollement. The striations, asymmetrical folds and boudinage structures indicate the direction of the main décollement to the NNW and NNE. A deep level décollement structure occurs at a depth of 12–22 km and up to 30 km distance to the south. The early Cretaceous and Eocene are two main periods of activity, with the Cretaceous décollement probably initiated by mantle upwelling derived from subduction and collision of the Yangtze Plate with the North China Plate along the Tancheng-Lujiang Fault in the late Triassic–early Jurassic. This circumstance implies a multidirection of subduction and collision of these two plates in the early late Mesozoic.