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It was recognized that two magmatic belts in the Lhasa‐Tengchong terrane formed due to the Mesozoic‐Cenozoic Tethyan evolution. Still, their spatiotemporal variations of magmatic flare‐ups/lulls are rarely discussed. Here we use the new U‐Pb and Lu‐Hf isotopic data of captured zircons and a comprehensive data set to show that the flare‐up of northern magmatic belt has peak ages of 110 Ma in central and northern Lhasa and 120 Ma in eastern Tengchong, possibly related to the tectonic transition from Meso‐ and Neo‐Tethyan double subduction to Neo‐Tethyan single subduction. For the southern magmatic belt, the flare‐ups at 100–85 Ma and 65–45 Ma in eastern southern Lhasa indicate obvious juvenile crustal growth, while flare‐ups at 75–45 Ma in western southern Lhasa and Tengchong record ancient crustal reworking. Such flare‐up variations in the southern magmatic belt possibly resulted from asynchronous changes in the Neo‐Tethyan slab dip. Plain Language Summary: The Tethyan slab subduction and following collision of India and Asia produced two magmatic belts in the Lhasa‐Tengchong terrane. How did the magmatic flare‐ups or high‐flux episodes and sources spatiotemporally vary? We combine the new U‐Pb and Lu‐Hf isotopic data of captured zircons (xenocrystic zircons caught by volcanics from country rocks) and a comprehensive data set to show that the peak ages of early Cretaceous flare‐up of the northern magmatic belt are ca.10 Ma younger in central and northern Lhasa than in eastern Tengchong, possibly related to the diachronous closure of the Meso‐Tethys and flat subduction of the Neo‐Tethys. The southern magmatic belt in Tengchong and western southern Lhasa exhibit 75–45 Ma flare‐ups featured by the reworking of ancient crust, different from the eastern southern Lhasa with the flare‐ups at 100–85 Ma and 65–45 Ma which are dominated by the juvenile crustal growth. Such flare‐up variations may be related to changes of the Neo‐Tethyan slab dip. Key Points: The Neo‐Tethyan arc has asynchronous magmatic flare‐ups and diverse magmatic sourcesThe spatiotemporal changes of slab dip triggered the asynchronous flare‐ups of the Neo‐Tethyan arc [ABSTRACT FROM AUTHOR]

Early Cretaceous granitoids are widespread on the Tibetan Plateau and record the tectonic evolution of several Tethyan oceans. We describe Early Cretaceous high-Mg (Mg# > 50) and low-Mg (Mg# < 50) granitoids, minor diorites, and mafic enclaves from the Bomi–Chayu Fold Belt, SE Tibet. Zircon U-Pb dating reveals two episodes of granitoid emplacement at ~122 and ~117 Ma. High-Mg series rocks have higher Mg# and compatible element concentrations (e.g., Cr and Ni) than low-Mg series samples. Their Mg# and compatible element abundances are also elevated relative to an experimental melt generated under the conditions of a thickened lower crustal. Enriched whole-rock Nd and zircon Hf isotopic signatures, coupled with low Y (<18 ppm) and Yb (<1.9 ppm) concentrations in some samples, indicate that the high-Mg series was derived from thickened lower crust and underwent minor mixing with cumulate pyroxenite in the lower crust. In contrast, low-Mg series rocks record a purely crustal origin, although differences are noted between Na-rich (subgroup 1) and K-rich (subgroup 2) compositions. Mafic enclaves hosted in the granitoids yield identical formation ages and isotopic compositions to their host rocks, suggesting a common origin. The spatial–temporal distribution of Early Cretaceous granitoids in the Bomi–Chayu Fold Belt indicates that magmatism occurred in an analogous tectonic regime to that of similar rocks in the Tengchong Terrane. The Bomi–Chayu granitoids are therefore distinct from those in the northern and central Lhasa subterranes and are related to the evolution of the Myitkyina Tethys Ocean in eastern Myanmar. • Early Cretaceous high- and low-Mg series rocks in Bomi-Chayu Fold Belt. • High-Mg series rocks originated from the crust but modified by minor pyroxenite. • Cretaceous granitoids in the BCF are of predominant I-type granites. • Slab breakoff of the Myitkyina Ocean resulted in Early Cretaceous magmatism. [ABSTRACT FROM AUTHOR]