Reconstructing oceanic plateau sequences and kinmatic analysis during the accretion process:insight from the Nuomuhongguole early Paleozoic accretionary complex in East Kunlun orogenic belt

The oceanic plateau is an area characterized by abnormal thickness of ocean crust formed by a mantle plume. It not only constitutes a distinct section of the oceanic crust but also plays a crucial role in reconstructing the stratigraphy of ancient orogenic belts. The Nuomuhongguole area, situated in the southern part of the East Kunlun orogenic belt, contains rich records of early Paleozoic accretionary complexes. It is distinguished by extensive outcrops of pillow basalt and interbedded limestone, likely remnants of a seamount or oceanic plateau. To ascertain its tectonic setting, reconstruct the oceanic plate stratigraphy, and elucidate the subduction and accretion processes of Proto-Tethys in this region, comprehensive field geological work, along with studies in petrology, geochemistry, and geochronology, were conducted. A relatively well-preserved remnant of an oceanic plateau was identified. Moving from north to south, distinct rock units, such as the pillow lava-limestone unit, the pillow lava-breccia-limestone unit, and the sandstone-siltstone-chert unit, represent the top, slope, and foothill facies of the oceanic plateau, respectively. The majority of the pillow lavas are basaltic, displaying flat chondrite-normalized rare earth element (REE) patterns similar to those observed in the Java oceanic plateau. Zircons extracted from the pillow lava and dacite-porphyry yielded a U-Pb age of 430±3.4Ma and 427.5±3.0Ma, indicating that the oceanic plateau formed approximately 427-430 million years ago. Melanges with a "block-in-matrix" structure are preserved on both the north and south sides of the oceanic plateau. Detrital zircon ages from sandstones in these melanges suggest a provenance from the Central Kunlun Arc. Consequently, we propose that there was a northward subduction-accretion process of the oceanic plateau in Proto-Tethys along the Central Kunlun Arc belt during the Early Paleozoic.