Late Paleozoic architecture, deformation, and geodynamics of the Xing’an–Mongolia intracontinental orogenic belt

The architecture and geodynamics of intracontinental orogens remain a fundamental geological challenge. The Xing’an-Mongolia intracontinental orogenic belt (XMIOB), superimposed on the eastern Central Asian Orogenic Belt (CAOB), provides key insights into intracontinental orogenic belt dynamics. However, its architecture, deformation patterns, and geodynamic processes are poorly understood. This study integrates geological mapping, structural analysis, EBSD quartz c-axis fabrics, seismic reflection interpretation, and zircon U-Pb geochronology to unravel the XMIOB’s tectonic evolution and compare it with global intracontinental orogenic belts. Our findings reveal that the XMIOB is shaped by alternating fold-thrust belts and metamorphic zones, dominantly controlled by the inversion of pre-existing extensional structures. EBSD analysis indicates mid-temperature (400 °C – 500 °C) ductile deformation in the deep crust, while seismic profiles highlight structural decoupling driven by a décollement zone. Integrated crustal thickness reconstructions from zircon Eu/Eu* ratios delineate three tectonic stages: Late Carboniferous-Permian asthenospheric upwelling induced crustal thinning from ∼50 km to ∼35 km, forming lithospheric weak zones with Buchan-type metamorphism and bimodal magmatism; Late Permian-Middle Triassic mantle subduction triggered compressional thickening (∼55 km), fold-thrust belt formation, and tectonic inversion of early extensional faults, exposing metamorphic zones; from the Middle Triassic continued mantle subduction and deep-crustal decoupling drove large-scale lateral extrusion and dextral shear, reshaping the XMIOB architecture. Comparisons with global intracontinental orogenic belts highlight two key traits of intracontinental orogenic belt evolution: pre-orogenic lithospheric thinning generates inherited weak zones that localize subsequent deformation; inherited extensional features dictate the final architecture, producing the systematic alternation of metamorphic zones and fold–thrust belts.