Subduction polarity reversal along the Hegenshan-Nenjiang suture in the eastern Central Asian Orogenic Belt: Evidence from two deep seismic reflection profiles

Subduction polarity reversal, one of the key mechanisms for subduction initiation, plays a pivotal role in lithospheric material recycling and convergent margin transformation. Despite its tectonic significance, related processes have rarely been documented in the tectonic traces and deep seismic exploration results in the eastern Central Asian Orogenic Belt (CAOB). Based on two deep seismic reflection profiles across the Hegenshan-Nenjiang Suture, this study reveals distinct fossil subduction zone structures within the crust-mantle transition zone beneath the suture. The eastern profile displays relics of southeast-dipping paleo-plate subduction, while the western profile shows a northwest-dipping fossil subduction zone that truncates the southeast-dipping tectonic traces. Integrating regional geological and geochemical evidence, we propose that subduction polarity reversal may have occurred prior to the formation of the Hegenshan-Nenjiang Suture. This study further highlights the striking parallels between the CAOB and the present-day Southwest Pacific as archipelagic accretionary orogenic systems, offering valuable insights for comparative tectonic studies and advancing our understanding of orogenic belt evolution.