Geological characteristics and structure evolution of Rongxuka magmatic-dome in Songpan-Ganzi orogenic zone

Rongxuka magma diapir dome is located in the northeastern part of Yajiang domes in Songpan-Ganzi orogenic zone, it has undergone multi-stage tectonic evolution, and the interior structure is extremely complex. In order to clarify the evolution relationships between magma and dome in Rongxuka area, the authors studied the geological characteristics and structure evolution of the dome on the basis of field geological survey and indoor comprehensive research. The rootless or ptygmatic folds in the center of the dome were well developed, as well as ‘S-type’, ‘Z-type’ folds and ‘A-type’ recumbent folds. Superposed folds were developed in the periphery of the dome structure, which reflected that the orogenic zone was subjected to SN and EW biaxial compression in the early stage. Rongxuka dome has mainly underwent SN and EW biaxial compression in Indo-Chinese epoch or late Triassic. The time limited for the magma intruding upward to form the dome was (214.4±1.2) Ma. After the dome was formed, it went through the stages of extrusion nappe and stress relaxation. Owing to the rapid tectonic uplift of the southeastern margin of Tibetan Plateau during the early Miocene(17~10 Ma), the NW-SE sinistral strike slip faults of Xianshuihe were formed, which contributed to a series of NNW ductile and brittle fractured shear zones in Rongxuka area.