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Radiogenic isotopes serve as a crucial tool for investigating crustal evolution, playing a pivotal role in revealing magma sources and petrogenesis. However, they can be ineffective in distinguishing between distinct magmatic sources with similar radiogenic isotopic compositions, a common occurrence in nature. Here we addresse this challenge in the Ordovician igneous rocks from the West Kunlun orogenic belt (WKOB), aiming to distinguish between two potential magmatic sources (i.e. the Tarim Craton and the Tianshuihai terrane) with similar isotopic compositions using appropriate thermodynamic and geochemical modeling based on mineral and whole-rock geochemistry. Zircon U–Pb dating yields ages of 483 ± 3 Ma for the Pushou gabbros and 469 ± 2 Ma and 461 ± 2 Ma for the Datong monzogranites and syenites, respectively. The Pushou gabbros exhibit low SiO2 (47.4–49.1 wt %), high MgO (5.5–6.9 wt %), high large-ion lithophile elements (LILEs, e.g. Rb, Ba, Th, and K), and low high field-strength elements (HFSEs, e.g. Nb, Ta, Zr, Hf, P, and Ti), suggesting an origin in subduction-modified mantle. They display high whole-rock (87Sr/86Sr)i ratios (0.7156 to 0.7192), negative whole-rock εNd(t) values (−7.1 to −7.8), as well as high zircon δ18O values (7.6–7.9‰) and enriched zircon Hf isotopic compositions (εHf(t) = −5.3 to −7.7), which are consistent with 1–5% subducted sediments in an enriched mantle source. Trace element models further confirm that the gabbros are most likely derived from low-degree (~15%) partial melting of subduction-modified Tarim mantle in the spinel–garnet facies rather than from the Tianshuihai mantle. The Datong syenites belong to the shoshonitic series and are characterized by medium SiO2 (59.5–61.4 wt %), relatively low MgO (0.9–1.2 wt %) and Mg# (37–42), enrichment in LILEs and depletion in HFSEs. They have high whole-rock (87Sr/86Sr)i ratios (0.7103 to 0.7105) and negative whole-rock εNd(t) values (−3.8 to −4.3), along with negative to slightly positive zircon εHf(t) values (−3.8 to +2.6), similar to coeval mafic rocks. Thermodynamic and geochemical modeling suggest that the Datong shoshonitic rocks likely originated via crystal fractionation of shoshonitic basaltic magmas in the SW Tarim Craton. The Datong monzogranites have high SiO2 (69.7–72.6 wt %), low MgO (0.6–0.7 wt %), and a typical enrichment in alkalis, Zr, and Nb, with depletion in Sr, P, and Ti, consistent with A-type granites. They are characterized by high whole-rock (87Sr/86Sr)i ratios (0.7321 to 0.7323), negative whole-rock εNd(t) values (−11.3 to −11.8), negative zircon εHf(t) values (−11.0 to −16.5), and high zircon δ18O values (7.2–8.0‰), indicating derivation from the remelting of an ancient crustal source. Thermodynamic, major, and trace element modeling indicate that their parent magma may have been generated by water-deficient (~2 wt %) partial melting of ancient crustal material beneath the SW Tarim Craton rather than that of the Tianshuihai terrane, under high-temperature (T  > ~950°C) and low-pressure (P  = 5–8 kbar) conditions. Based on the tectonic framework of the WKOB, we propose that the original mantle and crust beneath the southern Kunlun terrane may have been modified or partially replaced by that beneath the SW Tarim Craton during the Ordovician. Therefore, this evidence for Tarim-derived magmatism, when combined with regional sedimentary and structural records, indicates that Ordovician magmatism in the southern Kunlun terrane is most consistent with episodic northward subduction of the Proto-Tethys Ocean, commencing at ~485 Ma. Middle Ordovician slab break-off can explain the formation of the A-type granites, but reinstated northward subduction is required for the generation of late Ordovician Datong syenites. [ABSTRACT FROM AUTHOR]

The Erqis tectonic belt, situated at the junction of the Chinese Altai‐East Junggar, originated through the subduction of the Ob‐Zaisan Ocean, playing a pivotal role in unraveling the tectonic evolution of the southern Altaids. Tectonic and provenance analyses discern three distinct arcs: the Chinese Altai in the north exhibits a protracted history from the late Cambrian to early Permian with a slender accretionary complex (AC) termed the Supute AC; the Kuerti intra‐oceanic arc in the middle emerged during the Silurian to Devonian coevally with a minor AC known as the Tesibahan AC; and the Dulate arc in the south predominantly evolved from the Middle Devonian to Permian, giving rise to the Fuyun AC that independently developed on its northern margin at least until ∼273 Ma. Our findings indicate the existence of multiple arcs within the Ob‐Zaisan Ocean, forming an archipelago paleogeography in the Paleo‐Asian Ocean. Provenance studies lead us to propose that cryptic sutures demarcating the Chinese Altai, Kuerti, and Dulate lie approximately along the Kuerti and Tesibahan faults, respectively, and that the oceanic branches between these arcs subducted northward beneath the Chinese Altai and Kuerti arcs and southward beneath the Dulate arc. Additionally, our work demonstrates the closure of the Ob‐Zaisan Ocean most probably postdates ∼273 Ma. Combining our data with previous research, we present a novel tectonic evolution model, elucidating several arc amalgamations with multiple subduction polarities between Chinese Altai and East Junggar throughout the late Cambrian to Permian. Key Points: The Erqis tectonic belt predominantly comprises accretionary complex and slices of arcsThe cryptic suture between Chinese Altai and East Junggar extends along the Tesibahan‐Mayine'bo faults rather than the Erqis faultThe Ob‐Zaisan Ocean had subducted southward beneath the East Junggar and closed later than the Permian [ABSTRACT FROM AUTHOR]