Physical simulation for faults originated from magmatism: Insight into the faults developed in Nanpu Sag

In order to study the structural patterns formed by magmatism, four sets of physical simulation experiments were conducted using quartz sand, balloons, and silicone layers. The simulation results show that the development of structural deformation induced by magma emplacement proceeds through four main stages, progressively characterized by surface uplift, reverse ring-fault, normal radial fault, and normal ring fault. The section view of the simulation results is characterized by the dome controlled by inward-dipping reverse faults and concentric normal faults developing at the crest. It is confirmed by stress analysis that the compressional stress difference of distribution along the arc top surface of the magma chamber is responsible for the coexistence of normal faults and reverse faults. The experimental results for the caldera collapse simulation show that the main factors controlling the formation of outward-dipping reverse faults are differential uplift and space allocation. The experimental results of the superposition between extension and magma emplacement show that the faults forming in the late stage will change both the dipping and dip angles of those faults developing in the early stage. The four magmatic fault interpretation models established based on the experiment results can be used to explain the mechanism of the different fault patterns developed on the No. 1 tectonic belt of the Nanpu Sag in the Bohai Bay Basin, providing a theoretical basis and research examples for faults that originate from magmatism.