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Identifying the petrogenesis and geodynamic mechanism of the Early Permian igneous rocks widely distributed in the Inner Mongolia–Daxing'an Orogenic Belt (IMDOB) is crucial for understanding the tectonic evolution of the southeastern Central Asian Orogenic Belt. In this study, a combined study of petrology, geochronology, and geochemistry of Early Permian volcanic–plutonic rocks from the Uliastai continental margin, northern IMDOB, was conducted aiming to constrain their petrogenesis and tectonic setting. The U Pb zircon data for the magmatic zircons indicate that the Baoligaomiao Formation (BG Fm.) volcanic rocks, including felsic and mafic rocks, erupted at approximately 298–285 Ma, and quartz monzonite porphyries that intruded the BG Fm. were emplaced at approximately 292 Ma. The mafic volcanic rocks exhibit intraplate nature with basaltic compositions transitional between the calc-alkaline and shoshonite series. The geochemical behavior and isotopic data of these volcanic rocks reflect a depleted lithospheric mantle source metasomatized by fluids released from the stagnant slab. Felsic volcanics and quartz monzonite porphyries show affinities with A-type granites and are derived from the partial melting of juvenile crustal materials. Moreover, we suggest that the Early Permian magmatism formed in a post-collisional extensional setting, which is the continuation of the Late Carboniferous extension and was induced by the lithospheric collapse after the slab break-off of the Hegenshan Ocean. Notably, the felsic rocks formed after 290 Ma, with affinity changing from A 2 -type to A 1 -type granite, and approximately 288 Ma mafic volcanic rocks exhibited intraplate characteristics. These changes, combined with the development of coeval bimodal volcanic rocks and dike swarms, suggest that the tectonic setting at the end of the Early Permian in the northern IMDOB may have gradually transferred to an intraplate environment. • Mafic rocks were derived by melting of depleted lithospheric mantle. • Felsic rocks with depleted Hf isotopes record the reworking of juvenile crust. • They formed in a post-collisional setting after the closure of Hegenshan Ocean. • Tectonic setting transferred to an intraplate extension in the late Early Permian. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive analysis of zircon U–Pb–Hf isotopic and whole-rock geochemical data of Carboniferous–Early Permian felsic igneous rocks from the Uliastai continental margin (UCM), southeastern Central Asian Orogenic Belt, to constrain the amalgamation of the Inner Mongolia–Daxing'an Orogenic Belt (IMDOB) in the late Paleozoic. Zircon laser ablation inductively coupled plasma mass spectrometry U Pb ages of monzogranite, granite porphyry, felsic volcanic rock, and alkali feldspar granite reveal three stages of magmatism in the Early Carboniferous (ca. 336–320 Ma), Late Carboniferous (ca. 311–307 Ma), and Early Permian (ca. 298 Ma). The Early Carboniferous igneous rocks, including monzogranites and later granite porphyries, exhibit affinity with the high-K calc-alkaline highly fractionated I-type granite, and are depleted in high-field-strength elements and enriched in large-ion lithophile elements. Their zircon ε Hf (t) values of the Early Carboniferous rocks range from +4.6 to +9.1, indicating that they were generated by partial melting of the juvenile crustal materials in a north-dipping subduction-related environment along with the opening of the Hegenshan Ocean. The Late Carboniferous felsic volcanic rocks are highly fractionated high-K calc-alkaline to alkali-calcic I- and A-type granitoids, with relatively strong peraluminous affinities. Considering the zircon ε Hf (t) values (+6.2 to +10.6) and relatively low Rb/Ba (0.71–3.57) and Rb/Sr (4.18–8.12) ratios, they were likely derived from a juvenile crust and are comparable to partial melts of clay-poor but plagioclase-rich metaigneous rocks. Notably, the A-type granitoids are gradually increasing in the UCM after 311 Ma, and these magmatic rocks have markedly increased zircon saturation temperatures and (K 2 O + Na 2 O)/CaO ratios. These changes may result from the slab break-off of the Hegenshan Ocean, and the Late Carboniferous felsic volcanic rocks were formed in a post-collisional setting. The Early Permian alkali feldspar granites are characterized by typical A-type granite geochemistry, with high Ga/Al ratios; low MgO, Cr, Co, and Ni contents; and high zircon saturation temperatures. These rocks have positive ε Hf (t) values of +10.2 to +12.7 and record an intracontinental extension setting. In combination with the regional geology, the Late Carboniferous post-collisional magmatic rocks suggest that a change from a subduction-related continental margin to a post-collisional tectonic regime might have occurred in the UCM before 311 Ma. • Late Paleozoic magmatism can be subdivided into three stages. • Magmatic rocks after 336 Ma formed in a subduction-related environment. • A tectonic setting transformed into post-collision occurred before 311 Ma. • Early Permian rocks formed in a regional-scale lithospheric extension setting. [ABSTRACT FROM AUTHOR]