THE PROVENANCE RECORD OF DETRITAL WHITE MICA AND ZIRCON GRAINS FROM THE SONGPAN–GANZI COMPLEX (CHINA)

This study investigates the provenance record of detrital white mica and zircon grains from the Middle to Late Triassic Songpan–Ganzi Complex, using single grain laser fusion 40Ar/39Ar dating and microprobe analysis of the Si-in-white mica content, and zircon U-Pb dating. The combination of these two mineral phases not only allows discriminating between crustal blocks as potential source areas but also between the surrounding orogenic belts. The Northern Songpan–Ganzi Complex was a separate deposystem supplied with detritus from the north located North China block, the East Kunlun magmatic/volcanic arc, and the Qinling orogen. The Southern Songpan–Ganzi Complex was supplied from the northeast and east located Qinling and Hongan throughout the Ladinian and Carnian. The Late Carnian sample indicates an eastward extension of the drainage area into the Dabie Shan, suggesting an increased exhumation of the Triassic orogenic belt. Norian samples from the Southern Songpan–Ganzi Complex indicate a strong fed from the exhuming Qinling–Hongan–Dabie Shan and the South China block, signifying long channels of drainage along the northern and western margin of the South China block. The triple junction configuration (Kunlun-Qinling-Dabie suture zones and western South China block margin) probably plays a significant role for the sedimentation in the southeastern part of the Southern Songpan–Ganzi Complex. An additional supply from the east located Emeishan magmatic province is speculated based on the very rare white mica content of these samples and the west directed paleocurrent orientations. The white mica ages of the Rhetian sample from the northwestern margin of the Sichuan Basin shows the best consistency with the mica ages known from the Qinling–Hongan–Dabie orogen, indicating a clear fed from the exhuming orogenic belt. However, similar to other samples of this study, the Si-content in white micas give no evidence that the Triassic HP-UHP rocks of the Hongan–Dabie Shan were already exhumed to the surface in the Late Triassic.