Seismic Reflection Profiling Reveals New Accretionary Structure in the Solonker Zone of the Central Asian Orogenic Belt

The Central Asian Orogenic Belt (CAOB) was formed by the aggregation and collage of numerous Paleozoic subduction-accretion assemblages and Precambrian microcontinental blocks. However, the tectonic nature of the southeastern CAOB remains controversial, which complicates the reconstruction of the Paleo-Asian Ocean. To address this issue, a deep seismic reflection survey was initiated across the southeastern CAOB and reveals broad gentle sub-horizontal reflectors in the middle-lower crust and a relatively transparent zone in the upper crust. Combining with the Precambrian geological outcrops and other geophysical features, we support a microcontinental block, the Xilinhot Block, existed in the Paleo-Asian domain. Thus, the Paleo-Asian Ocean was separated into two branches that underwent north-dipping and double-dipping oceanic plate subduction, respectively, to form the Hegenshan-Heihe and Solonker sutures. Multiple relics beneath Hegenshan-Heihe Suture indicate that multiple sets of unidirectional oceanic subduction-accretion and magmatism were important mechanisms of continental growth. During the consumption of the Paleo-Asian Ocean, a great number of Paleozoic subduction-related accretionary complexes were developed and combined with pre-existing Precambrian continental fragments to form the Central Asian Orogenic Belt (CAOB). However, research on the tectonic evolution of this area has been limited, and the tectonic nature of the southeastern CAOB remains controversial. A deep seismic reflection survey along the southeastern CAOB shows the crustal architecture in detail. The broad gentle sub-horizontal reflectors and a relatively transparent zone in the profile reveal a Precambrian continental fragment existed in the North Orogenic Belt of CAOB. The Paleo-Asian Ocean was further separated into two parts, the fossil subduction zones of which show northward and bidirectional dipping characteristics beneath the Hegenshan-Heihe and Solonker sutures, respectively. Several relics of the unidirectional subduction beneath the Hegenshan-Heihe Suture indicate that multiple sets of unidirectional oceanic subduction-accretion and magmatism were important mechanisms of continental growth. A preserved microcontinental block has been revealed in the North Orogenic Belt of Central Asian Orogenic Belt The Paleo-Asian Ocean was separated into two branches, which were closed respectively by north-dipping and double-dipping subduction Multiple unidirectional subduction-accretion and oceanic magmatism may contribute to continental growth