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In order to determine the tectonic regime change of the early Mesozoic in the South China Block, this study analyzed sedimentary rocks in the Middle Jurassic of southwestern Fujian by modal analysis of sandstones, elemental geochemical analysis of mudstones, and detrital zircons U–Pb dating. The results show that the detrital zircons in Southwestern Fujian mainly consist of Paleoproterozoic to early Mesozoic zircons in the Middle Jurassic. Within the Dongkeng profile of the Zhangping Formation, DK5 sample (lower part) showed a major age peak at ca. 1,848 Ma and two secondary age peaks at ca. 235 and 180 Ma, while DK15 sample (middle part) showed a major age peak at ca. 1,876 Ma and two secondary age peaks at ca. 233 and 190 Ma; the age compositions of these two samples’ were similar. Modal analysis of sandstones indicated that sediments of Zhangping Formation might source from arc orogen and recycled orogen, and element geochemical analysis showed that source rocks of Zhangping Formation might be sedimentary rocks and granites. The Indosinian zircons were mainly derived from the Wuyi region, and the Yanshanian zircons were mainly derived from the Nanling region. The major age group changes from ca. 230 to 220 Ma of the Late Triassic – Early Jurassic to ca. 190 to 180 Ma of the Middle Jurassic in Southwestern Fujian, and main sources changed from Indosinian magmatic rocks in the Late Triassic – Early Jurassic to early Yanshanian magmatic rocks in the Middle Jurassic.

The Jiamusi Block is a crucial geological unit joining multiple tectonic regimes, including the Late Palaeozoic Palaeo‐Asian Ocean and the superposition of the Early Mesozoic Palaeo‐Pacific tectonic domain. However, the duration of the Palaeo‐Pacific Plate subduction beneath the Jiamusi Block has long been controversial. In this paper, we focus on clastic rocks from the Nanshuangyashan and Yunshan formations on the east margin of the Jiamusi Block and use the modal analysis of sandstones and detrital zircon U–Pb dating to trace the subduction history of the Palaeo‐Pacific Plate. Our analysis results suggest that the two groups of samples are characterized by a high content of monocrystalline quartz and a low content of lithic and feldspar, indicating that the sedimentary provenances were stable continental blocks and magmatic arcs. The detrital zircon ages of the Nanshuangyashan Formation have a major peak at ca. 245 Ma and two secondary peaks at ca. 470 and 228 Ma, respectively. The Yunshan Formation has a major peak at ca. 494 Ma and a secondary peak at ca. 265 Ma. The provenances of the Nanshuangyashan Formation were attributed to the Jiamusi Block, Khanka Block, and a Late Triassic magmatic arc. Similarly, the provenances of the Yunshan Formation were attributed to the Jiamusi and Khanka blocks. Detrital zircon analysis results show that the eastern margin of the Jiamusi Block was in the same back‐arc basin settings in the Late Triassic and the Late Jurassic. Thus, we propose that the eastern margin of the Jiamusi Block had been affected by the Palaeo‐Pacific Plate subduction in the Late Triassic and had continued to the Late Jurassic.