Geochemistry of Mesozoic siliceous rocks in the Tongjiang accretionary complex of Northeast China: Implications for the evolution of the Paleo-Pacific subduction zone

The subduction of the Paleo-Pacific Plate was an important tectonic feature of northeastern Eurasia in Mesozoic times. Owing to the great thickness of sedimentary cover, the nature of the tectonic units along the eastern edge of Eurasia remain uncertain. In this paper, we describe Mesozoic siliceous rocks from the Heitongdi 1(HTD-1) borehole in the Sanjiang Basin of northeast China to improve knowledge of the paleogeography and paleoenvironment of this region. Our study focuses on the genesis, sedimentary environment, and significance of these Mesozoic siliceous rocks, to provide insights into the subduction of the Paleo-Pacific Plate and the palaeoenvironment of northeastern Eurasia at this time. Geochemical indicators from the siliceous rock cores suggest a biogenic origin and formation in a continental margin arc environment. Our study provides evidence for the initiation of subduction of the Paleo-Pacific Plate beneath the Eurasian plate during the Early Jurassic, which led to the establishment of an island arc along the eastern margin of the Jiamusi Block. Our findings suggest that the suture zone between the Paleo-Pacific and Central Asian Orogenic Belt should be positioned west of Tongjiang, near the HTD-1 borehole, rather than along the Yuejinshan–Fuyuan fault as previously thought.