Crustal‐Scale Seismic Reflection Profiling Constrains How the Paleo‐Asian Ocean Was Closed.

The Central Asian Orogenic Belt (CAOB) is the most significant accretionary orogenic belt since the Phanerozoic and the most ideal site for studying continental growth evolution processes. A 460‐km‐long high‐resolution crustal‐scale seismic reflection study was conducted across the eastern CAOB in North‐Central China to constrain the closure mode and location of the Paleo‐Asian Ocean, that is, the previous ocean of the CAOB. The resultant seismic reflection profile revealed opposite‐dipping reflectors in the northern and southern parts of the profile, which converge at the profile center to form an inverted U‐shaped reflector pattern near the crust–mantle transition zone beneath the Solonker Suture. The dipping reflectors represent bidirectional fossil subduction zones sloping to the north and south, and the convergence reflector pattern represents the ocean closure location. Integration of these results with available geological data facilitated model construction whereby Paleo‐Asian Ocean closure was accomplished by divergent subduction of the Paleo‐Asian oceanic plate, with northward subduction beneath the southern margin of the Mongolian Block and southward subduction beneath the northern margin of the North China Craton. The oceanic lithosphere contracted and deformed, yielding the observed inverted U‐shaped reflector pattern, representing Paleo‐Asian Ocean closure. This subsurface location lies beneath the Solonker Suture surface exposure, suggesting that this suture marks the ocean closure location, rather than the previously proposed Hegenshan–Heihe Suture to the north or Xar Moron Suture to the south. Our study suggests that divergently dipping subduction and associated accretion and magmatism may constitute the primary continental growth mode for accretionary‐type orogens. Plain Language Summary: The Central Asian Orogenic Belt (CAOB) is Earth's largest Phanerozoic accretionary orogenic belt, but its tectonic history remains uncertain, including the Paleo‐Asian Ocean closure location and mode. Here, we present a 460‐km‐long crustal‐scale seismic reflection survey across the eastern CAOB. According to the generated seismic profile, near‐symmetrical north‐ and south‐dipping reflectors occur in the crust–mantle transition zone, which are interpreted combined with published geological data to reveal that the Paleo‐Asian oceanic plate underwent divergent subduction beneath the South Mongolian Block and North China Craton. The inferred Paleo‐Asian Ocean closure location, the Solonker Suture, is identified by converging seismic reflectors in the central part of the profile. During oceanic subduction, newly formed accretionary complexes experienced soft collision with preexisting continental fragments. Therefore, we suggest that the eastern CAOB mainly comprises Paleozoic accretionary complexes with incorporated Precambrian fragments. We consider that divergently dipping oceanic subduction and associated accretion and magmatism constitute the main mode of CAOB continental growth and possibly of accretionary orogenic belts in general. Key Points: A crustal‐scale seismic profile reveals that the Paleo‐Asian Ocean was closed by double‐dipping subduction in the eastern Central Asian Orogenic BeltThe closure location of the ocean occurs between the Xar Moron and Hegenshan–Heihe sutures and extends eastward to central SongliaoOceanic double‐dipping subduction–accretion and magmatism are important mechanisms for accretionary orogens [ABSTRACT FROM AUTHOR]