Abstract:

The Hongshuiquan Formation, widely exposed in the northern Da Hinggan area, consists mainly of greywacke, sand-slate, carbonate rocks and tuffs, in which brachiopods, corals and bryozoans flourished in Early Carboniferous. LA-ICP-MS zircon U-Pb dating of the sandstones from the Hongshuiquan Formation in Ergun and Zhalantun area is carried out in order to discuss the Early Carboniferous basin type. Results show that 87 zircon concordant ages give four age groups: 353-379 Ma with peak age at 366 Ma, 428-473 Ma with peak age at 441 Ma and 464 Ma, 487-521 Ma with peak age at 502 Ma and 1 790-1 943 Ma with peak age at 1 848 Ma. In this frame, the peak ages of 366 Ma, 441 Ma, 464 Ma and 502 Ma are consistent with the magmatic events in Ergun and Xing’an blocks, and the peak age of 1 848 Ma is widely existed in the two blocks, suggesting that sediments of the Hongshuiquan Formation mainly derive from Ergun-Xing’an blocks. The youngest peak age of 366 Ma indicates that the sediments come partly from the Late Devonian volcanic arc. The sandstones from the Hongshuiquan Formation have bidirectional sources (continent and volcanic arc). Combined with regional sediments in Early Carboniferous, we believe that the Hongshuiquan Formation is a suite of sedimentary sequence formed in a backarc basin setting.

Key words: Hongshuiquan Group, detrital zircon, U-Pb geochronology, northern Da Hinggan area, geology dating