Lithospheric structures of the northern Hegenshan-Heihe suture: Implications for the Paleozoic metallogenic setting at the eastern segment of the central Asian orogenic belt

Abstract

The Hegenshan-Heihe Suture (HHS) is regarded as the collision boundary between the Erguna-Xing’an and Songnen Blocks at the eastern segment of the Central Asian Orogenic Belt (CAOB). However, the convergent processes associated with these two blocks are still controversial due to the lack of definitive geological evidence (i.e., ophiolites, accretionary prisms), which leads to a poor understanding of the relevant metallogenic setting. This paper provides new geophysical constraints on the lithospheric structures of the northern HHS from Dashizhai to Heihe. By the comprehensive interpretation of two parallel deep seismic profiles, the Qiqihaer-Chaihe profile and the newly acquired Duobaoshan profile, the configuration of the subduction-trench-arc-back-arc systems are studied. The subducted continental margin of the Songnen Block is recognized by a set of westward dipping reflections with an apparent dip angle of 20 to 25°, while the accretion complex with a lateral extension of more than 70 km is inferred as an area of short reflections with a westward tendency. The magmatic arc belts and the back-arc area have a quite different seismic reflection patterns. The former are recognized by inverted triangular-shaped transparent reflections, while the latter is featured by arched reflections as clusters. They are bounded by a set of remarkable inclined reflections from the topmost crust to the bottom of the middle crust. It is inferred that the final subduction relict of the northern HHS went through Qiqihaer to the west of Sunwu. Magmatic arc belts forming over two stages are recognized to be located to the west of the subduction relict, and they have a consistent distribution with the magnetic anomaly. A detailed model of the formation of the northern HHS is proposed, which includes two stages of westward oceanic subduction and the final collision.