Structure in western Shandong and its genetic mechanism

Abstract: The structural characteristics of the western Shandong mantle branch and its genetic mechanism are discussed according to the outward-younging ring distribution of the strata, ring faults and radial faults, gently dipping detachments and mantle-derived magmatism, as well as regional petrology, petrochemistry and isotope geology. These studies suggest that the NW-trending, steeply dipping ductile shear belt cuts deep-seated pyrolite of the mantle sub-plume beneath North China, resulting in depressurizing and load-releasing to form anatectic magma. The magmatic evolutionary series shows a general trend of evolution from high to low basicity of magma, from great to shallow depths of magmatic intrusion and from strong to weak wall-rock alteration. Strong magmatic intrusion resulted in the uplift of the metamorphic basement and detachment of the cover, thus forming the typical western Shandong mantle branch structure. A number of obviously detached, tilted fault blocks are developed on top of this mantle branch.