The Ordovician Arc–Basin System in the Northern Great Xing'an Range (Northeast China): Constraints from Provenance Analysis of the Luohe Formation.

The Northeast China Block is a major component of the Central Asian Orogenic Belt, and its tectonic evolution has attracted much research attention. Ordovician strata are important in reconstructing the tectonic evolution of the Northeast China Block. This paper presents the results of sedimentological, zircon U–Pb, and geochemical analyses of sandstones of the Luohe Formation in the Wunuer area, Northern Great Xing'an Range, Northeast China. Lithological data, sedimentary structures, and grain-size analysis indicate that the Luohe Formation was deposited in a shallow marine environment. Detrital zircon U–Pb dating yields age peaks of 463, 504, 783, 826, 973, and 1882 Ma for sandstones from the Luohe Formation. The youngest zircon grain age of 451 ± 6 Ma represents the maximum depositional age of the Luohe Formation. The peak age at 463 Ma is consistent with the timing of post-collisional magmatism and the formation of the Duobaoshan island arc, while the peak at 504 Ma is consistent with the timing of magmatic activity related to the collision between the Erguna and Xing'an blocks. The peaks at 788, 826, 973, and 1882 Ma correspond to magmatism in the Erguna block, these ages indicate that the sandstones of the Luohe Formation were derived mainly from the Erguna block. Sandstone modal compositional analysis indicates that the provenance of the Luohe Formation was mainly a magmatic arc. The geochemical compositions of the sandstones suggest that the source rocks have continental island arc signatures. Based on the depositional age, sedimentary environment, provenance, and regional geology, it is concluded that the Luohe Formation was deposited in a back-arc basin setting during the formation of the Duobaoshan island arc–basin system in response to subduction of the Paleo-Asian oceanic plate. [ABSTRACT FROM AUTHOR]