Late Cretaceous Tectonic–Thermal Events Recorded in Qiangtang Terrane, Central Tibet

ABSTRACT Integrated with new field and analytical data, this study investigates the tectonic evolution of the central Qiangtang Terrane through multi‐chronological analysis of the Ejiumai Complex, a key outcrop in the northern Central Qiangtang Metamorphic Belt (CQMB). The complex, situated in the high‐altitude (> 4800 m) interior of the Tibetan Plateau, comprises granitic gneisses, paragneisses, and marbles intruded by tourmaline‐bearing leucogranite veins, preserving critical records of pre‐Cenozoic orogenic processes. Data from previous studies and our investigation reveal that the protoliths of the Ejiumai Complex originated during the Early Palaeozoic and experienced peak metamorphism in the Late Triassic. Hydrothermal zircons extracted from leucogranite veins display distinctive spongy textures with abundant inclusions and weak cathodoluminescence response. LA‐ICP‐MS U–Pb dating of these zircons yields Cretaceous ages ranging from 89 to 69 Ma, characterised by significant Th‐U content variations (Th = 8–1274 ppm, U = 96–2997 ppm). Complementary 40 Ar/ 39 Ar thermochronology of biotite (69.7 ± 0.5 Ma) and muscovite (70.4 ± 0.5 Ma and 70.7 ± 0.4 Ma) from host rocks indicates rapid Late Cretaceous cooling following thermal resetting. Synthesis of these results with regional geology suggests a two‐phase Cretaceous tectonic evolution: (1) 89–69 Ma crustal shortening manifested through thrusting and folding accompanied by intense hydrothermal activity, and (2) subsequent rapid exhumation and cooling prior to Cenozoic India‐Asia collision. This revised chronology demonstrates that major crustal thickening in central Qiangtang initiated during the Late Cretaceous as part of the broader Mesozoic Tethyan orogenic system related to Lhasha‐Qiangtang collision.