LAUSR

The southwest margin of the Yangtze Block underwent multiple tectonic events including the collision between the Yangtze and the South China Plate, Caledonian folding and uplift of South China, subduction of the western Pacific Plate, and Cenozoic continental escape during the Indo–Asia collision. The structural framework and tectonic evolution of the area are currently unclear. Through field petrologic and structural studies, microstructures within the deformed units, and estimates of the temperature of deformation, we constrain the conditions of deformation and further classify at least four-stage deformation. The first stage involved northeastward thrusting that produced folds, mylonites, and dynamically recrystallized quartz and calcite. Electron backscatter diffraction data indicate that deformation during this event occurred at < 400 °C, corresponding to a depth of ~ 10 km. The second stage of deformation involved uplift, extension, and the generation of a domal structure. During the third event, high-angle normal faults formed within the cover sequence that surrounds the dome. The fourth stage of deformation occurred in the Cenozoic and involved motion along sinistral and dextral strike–slip faults, which cut structures that formed during the previous stages of deformation. The first deformation event was related to Triassic N–S collision with the Indochina block; the second and third stages resulted from far-field compression related to westward subduction of the paleo-Pacific plate; and the fourth event was related to displacement along the Ailaoshan Red-River strike–slip fault. The dome in the study area represents a transitional structure between a metamorphic core complex and a gneissic dome, which we refer to as structural doming.