Evolution of Sedimentation and Tectonics of the Youjiang Composite Basin, South China

Abstract

Abstract Located at the southern margin of the South China plate, the Youjiang basin is a closely related to the NW ‐ and NE ‐ trending syndepositional faults in respect to the configuration and structure of the basin. The evolution of the Youjiang basin progressed through two stages. In the Hercynian period, the opening of the Ailaoshan‐Honghe ocean basin gave rise to a number of NW ‐ trending rift belts in the Youjiang area. During this period, deep ‐ water sediments were dominant and the basin was possesed of the characteristics of the rift system of passive continental margins. In the early Indosinian after the Dongwu movement, the circum ‐ Pacific tectonism led to a major change in the configuration and structure of the basin. In the meantime, the Ailaoshan ocean basin began to be subducted towards the northeast, thus causing the basin to be split and expand again, and then the basin developed into the stage of the back ‐ arc basin. At the end of the Indosinian period, the basin gradually closed from east to west, thus ending up the history of development of the Youjiang basin. In the various developmental stages, sediments in the basin, also limited by the Dongwu movement, were formed by superposition of sedimentation systems with different features, and a typical two‐layered structure, which consisted of starved and compensated sediments, also occurred in the early stage. Likewise, volcanic activity in the basin involved two stages. Basin volcanic rocks of alkali and alkali ‐ calcic series, which were controlled by NW ‐ trending faults, occurred in the early stage, and basic and intermediate ‐ acid volcanic rocks of calc‐alkali and calcic series, which were controlled by NW ‐ and NE ‐ trending faults. From the above it follows that the Youjiang basin was formed by the combined action of the Palaeotethys and circum ‐ Pacific tectonism.