The Late Carboniferous–Permian magmatic and sedimentary records in the Alxa area are crucial to understanding the tectonic evolution of the Paleo-Asian Ocean. We present petrological, whole-rock geochemical, zircon U-Pb geochronological and Hf isotopic data for magmatic and siliciclastic rocks from northern Alxa. Rhyolite and granite porphyry related to the Amushan Formation crystallized at ca. 309–304 Ma, derived from juvenile to moderately evolved lower crust reworked by oceanic subduction. Sandstones from the Quagan Qulu and Engger Us tectonic belts display contrasting detrital-zircon age spectra. Quagan Qulu samples, characterized by an early Paleozoic peak at ca. 430 Ma, record mixed input from early Paleozoic arc rocks, Precambrian basement and recycled cover strata, whereas Engger Us samples are dominated by a Devonian peak at ca. 381 Ma and were supplied by a nearby Devonian arc source. Together with published data, our results support a segmented Late Carboniferous– Permian forearc–arc–retroarc system along the northern margin of Alxa. Continued southward subduction of the Quagan Qulu oceanic lithosphere beneath the Nuru–Langshan continental arc is the preferred interpretation, whereas Late Carboniferous to early Permian slab rollback is a plausible mechanism for the ensuing magmatic flare-up, arc uplift and provenance shift.