The subduction of the Paleo-Pacific Plate to the Jiamusi Block: Evidence from the Early Mesozoic sedimentary rocks of the eastern Jiamusi Block

摘要

In order to provide references of the subduction process of the Paleo-Pacific Plate beneath the Jiamusi Block, this paper studied the clastic rocks of the Nanshuangyashan Formation using modal analysis of sandstones, mudstone elements geochemistry, and detrital zircon U-Pb dating. These results suggest the maximum depositional age of the Nanshuangyashan Formation was between the Norian and Rhaetian (206.8 +/- 4.6 Ma, mean standard weighted deviation (MSWD) = 0.17). Whole-rock geochemistry of mudstone indicates that source rocks of the Nanshuangyashan Formation were primarily felsic igneous rocks and quartzose sedimentary rocks, which were mainly derived from the stable continental block and a magmatic arc. Detrital zircon analysis showed the Nanshuangyashan Formation samples recorded four main age groups: 229-204 Ma, 284-254 Ma, 524-489 Ma and 930-885 Ma, and the provenances were attributed to the Jiamusi Block and a Late Triassic magmatic arc near the study area. Furthermore, the eastern Jiamusi Block was a backarc basin, affected by the subduction of the Paleo-Pacific Plate in the Late Triassic, but the magmatic arc related to the subduction near the study area finally died out due to tectonic changes and stratigraphic erosion.