Structure of metamorphic strata of the khondalite series in the Daqingshan-Wulashan area, central Inner Mongolia, China, and their geodynamic implications

Study of the high-grade metamorphic complex in the Daqingshan-Wulashan area,Inner Mongolia,indicates that the khondalite series in the area has undergone subhorizontal bedding-parallel decollement deformation and then modification by the dome-fold structure and nearly E-W-trending steeply dipping foliation belts.The former resulted in "omission of strata and hiatal contact of originally separated layers,which in space is indicated by the structure of metamorphic strata formed in the early stage by stacking of subhorizontal podiform bodies with nearly E-W-trending long axes.The stacking of the nearly E-W-trending steeply dipping foliation belts in the late stage caused the metamorphic strata to occur as irregular bands,patches or lenses and various metamorphic units and series to occur in a jigsaw-like form and interlock each other.It is concluded that the khondalite series underwent at least two orogenic cycles.The subhorizontal bedding-parallel decollement deformation structure and its corresponding structure of metamorphic strata are the product of the late stage of the first orogenic cycle,while the nearly E-W-trending steeply dipping foliation belts and their corresponding structure of metamorphic strata are attributed to the second orogenic cycle.