Abstract: As the most significant geological units in Northeast China, the tectonic nature and evolutionary history of the Jilin-Heilongjiang high-pressure belt remain controversial. To reveal the crust-mantle-scale structure of this belt and constrain the subduction-accretion processes of the Heilongjiang Ocean, this paper constructs a deep geophysical model based on magnetotelluric  and deep seismic reflection data. The model reveals pronounced lateral heterogeneity in both electrical conductivity and seismic reflectivity across different tectonic units. A key finding is a west-dipping zone of high resistivity and strong seismic reflectivity, which extends from the crust into the lithospheric mantle within the tectonic convergence zone. We interpret this feature as a fossil subduction zone associated with the closure of the Heilongjiang Ocean. In the upper crust, both the Heilongjiang and the Zhangguangcai Range complexes exhibit consistent high resistivity and short, arcuate reflection packages. In contrast, the middle to lower crust of the Zhangguangcai Range is characterized by a pronounced high-conductivity anomaly and a distinctive reversed U-shaped reflection pattern. Integrating these geophysical observations with existing geological understanding, we propose that the Zhangguangcai Range complex is not an integral part of the Songliao block. Instead, our data support a model of westward subduction of the Heilongjiang Ocean, with successive accretion of the Zhangguangcai Range and the Heilongjiang complexes as major components of the accretionary wedge. The Zhangguangcai Range complex thus records the early stage of the subduction-accretion process.

Key words: Central Asian orogenic belt, Jilin-Heilongjiang high-pressure belt, lithospheric structure, tectonic transition zone, integrated geophysical study