The Central Asian Orogenic Belt, the largest accretionary orogen on Earth, grew from the progressive closure of the Paleo-Asian Ocean (PAO), and its terminal event was the amalgamation of the NE China block collage with the North China Craton along the Solonker–Xar Moron–Changchun–Yanji suture. When the easternmost, Changchun–Yanji segment of this suture finally closed — and whether closure proceeded diachronously in a scissor-like manner from west to east, was contemporaneous along strike, or was overprinted by Paleo-Pacific subduction — remains unresolved. Yin et al. (2024) showed from detrital zircon U–Pb ages and geochemistry of the Miaoling Formation and Kedao Group at Wangqing that a reduced remnant ocean still existed there at ca. 243 Ma (early Middle Triassic), and proposed that final closure occurred between the latest Middle Triassic and early Late Triassic in a scissor-like manner. Work published through 2026 still disagrees at the tens-of-millions-of-years level: a 2025 study of adakitic rocks (silica-rich intrusive rocks generated by melting of a subducted oceanic slab or thickened continental crust) proposes Permian scissor closure, a 2026 provenance study argues Late Permian closure at Changchun, and a 2024 Earth-Science Reviews synthesis argues near-contemporaneous Middle–Late Triassic closure of all PAO segments. The open problem is to establish a regionally consistent chronology and along-strike pattern of final suturing along the Changchun–Yanji suture.

Background

The Central Asian Orogenic Belt (CAOB) is a giant, roughly 5000 km long collage of magmatic arcs, accretionary complexes, and microcontinental blocks that formed over much of the Paleozoic through the subduction and progressive closure of the Paleo-Asian Ocean (PAO), the ocean that once separated the Siberian Craton from the North China and Tarim Cratons. In northeastern (NE) China the eastern CAOB (also called the Xing'an–Mongolian Orogenic Belt) consists of several displaced terranes — Erguna, Xing'an, Songnen–Zhangguangcai Range, and Jiamusi–Khanka — that were finally welded to the northern margin of the North China Craton (NCC) along the Solonker–Xar Moron–Changchun–Yanji suture (SXCYS). This terminal collision is generally regarded as the final closure of the PAO and a key step in the assembly of northeast Pangaea. A widely used dating tool in this debate is the uranium–lead (U–Pb) age of detrital zircon grains eroded from surrounding magmatic arcs and deposited in sedimentary basins: because the youngest dated zircon population in a sediment must be older than (or contemporaneous with) the sediment itself, the youngest coherent zircon age cluster provides a maximum depositional age (MDA) for the stratum. An MDA from a marine succession that still receives ocean-margin detritus can therefore testify that a remnant ocean basin existed at that time. On this basis, the Wangqing area of eastern Jilin Province, which lies directly on the Changchun–Yanji (eastern) segment of the suture, hosts the Late Permian Miaoling Formation (dated at ca. 253 Ma) and the overlying Triassic Kedao Group — a lithostratigraphic unit whose internal subdivision and regional definition have long been considered unclear — both of which are marine to paralic (coastal, mixed marine and terrestrial) successions that should bracket the last oceanic stage. Published estimates of the final PAO closure time span the range from before the Late Devonian, through the Late Permian and Late Permian–Early Triassic (probably the most common position), to the Middle–Late Triassic. Several distinct lines of evidence conflict: (i) paleomagnetic data (e.g., Zhao et al. 2013) indicating that the paleolatitudes of the North China Craton and the Mongolian blocks have been mutually consistent since the Late Devonian, implying the PAO between them had already closed before the late Paleozoic; (ii) provenance and sedimentological work on Permian–Triassic strata across the suture (Wang et al. 2016 on the Triassic Dajianggang Formation; Zhou et al. 2017; Du et al. 2019, which brackets final closure between 242 and 227 Ma; Shen et al. 2019, which proposed a west-to-east 'scissor-like' closure from Late Permian–Middle Triassic flora-bearing strata), a view echoed in the review of Liu et al. (2017); and (iii) an alternative reading (Cao et al. 2020; cf. Chen et al. 2023) in which the Changchun–Yanji zone is not simply the eastern continuation of the Solonker suture but partly records Late Triassic eastward subduction of the Paleo-Pacific Plate, the successor tectonic regime in NE Asia. Yin et al. (2024) added new petrology, whole-rock geochemistry, detrital-zircon U–Pb ages, and zircon hafmium (Hf) isotope data (a tracer of whether the zircon's parent magma came from juvenile versus old crustal sources) for the Miaoling Formation and Kedao Group at Wangqing, constraining their maximum depositional ages to ca. 253 Ma and ca. 243 Ma, respectively, with provenance from NE China continental-margin arcs on both occasions. Their central inference is that a reduced remnant ocean basin persisted along the Changchun–Yanji suture until at least the early Middle Triassic (ca. 243 Ma), so that the final closure of the easternmost PAO — the latest Middle Triassic (Ladinian) to early Late Triassic (Carnian) — postdates the commonly invoked end-Permian closure of the main Solonker ocean further west, implying a scissor-like, west-to-east diachronous suturing. Here 'scissor-like closure' means that suturing did not happen simultaneously along the suture's length but migrated in time along strike, like scissor blades closing from pivot to tip.

Problem Statement

Determine when and how the eastern segment of the Paleo-Asian Ocean finally closed along the Changchun–Yanji suture zone, NE China — that is, establish a regionally consistent chronology of terminal suturing and its along-strike pattern, replacing the currently competing, tens-of-millions-of-years-apart proposals (Late Permian; Late Permian–Early Triassic; 242–227 Ma; latest Middle Triassic to early Late Triassic) with a single framework that reconciles the sedimentary, magmatic, metamorphic, paleontological, and paleomagnetic evidence. A defensible resolution must adjudicate among the scissor-like (west-to-east diachronous) closure hypothesis, the contemporaneous-closure alternative, and the possibility that the Changchun–Yanji zone records a later Paleo-Pacific architecture rather than Paleo-Asian closure, and must confront the evidence underpinning the Middle-Triassic remnant-ocean inference — in particular the still-unclear stratigraphic definition and regional correlation of the Kedao Group, the remnant-basin fill whose maximum depositional age (ca. 243 Ma at Wangqing) underpins the inference that an ocean still existed there in the early Middle Triassic, and the reliability of the detrital-zircon U–Pb ages used for depositional-age constraints, including the possibility of post-depositional thermal or hydrothermal resetting. Determine at what time(s), and in what along-strike order, the easternmost Paleo-Asian Ocean closed along the Changchun–Yanji suture zone, and determine whether that zone instead records a later Paleo-Pacific architecture rather than Paleo-Asian closure.

References

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