Early Cretaceous−Oligocene tectonic evolution of the Tengchong terrane in the southeastern Tibetan Plateau: Insights into the Tethyan orogenic system

Deciphering the tectonic architecture of the southeastern Tibetan Plateau is essential for understanding the transition from Neo-Tethyan subduction to India−Asia collision. The Tengchong terrane occupies a key position within this orogenic collage, yet its magmatic evolution and links with adjacent terranes remain debated. Resolving these issues requires evaluating along-strike variations in magmatism across the southern Asian margin. Here we integrate new zircon U-Pb geochronology, in situ zircon Hf isotopes, and whole-rock geochemical data to reconstruct the Early Cretaceous−Oligocene magmatic history of the Tengchong terrane and clarify the tectonic significance of three major suture zones in the region. Our results reveal four phases of magmatism at 130−110 Ma, 77−62 Ma, 55−47 Ma, and ca. 33 Ma, each linked to changes in subduction style and plate coupling. Magmatism at 130−122 Ma involved significant crustal input reflecting a transition from collisional to post-collisional conditions following Meso-Tethys closure. After ca. 122 Ma, Neo-Tethyan slab rollback followed a period of flat subduction. The mid-Cretaceous (110−77 Ma) magmatic lull reflects tectonic shielding of the Tengchong mantle wedge by the Western Myanmar arc, which intercepted slab-derived fluids and focused magmatism away from Tengchong. This mechanism accounts for along-strike contrasts in magmatism and the distinct history relative to the adjacent Gangdese arc of the Lhasa terrane. Magmatism resumed in the Late Cretaceous (77−62 Ma), reflecting accelerated rollback of the eastern Neo-Tethyan slab segment. After a brief magmatic hiatus at ca. 62−55 Ma, coincident with the initial stages of India−Asia collision, magmatism peaked in the Eocene (55−47 Ma) in response to Neo-Tethyan slab breakoff. Evolved Oligocene (ca. 33 Ma) leucogranitic magmatism marks a transition to post-collisional extension along the southeastern Tibetan Plateau margin, driven by differential subduction and slab tearing. Comparison with the Kohistan−Ladakh arc to the west further suggests that the southern Asian margin experienced multi-stage accretion of arc-derived crustal fragments prior to terminal India−Asia collision, supporting a segmented Trans-Tethyan arc system. These results offer a framework for understanding geodynamic links between multi-basin closure, segmented subduction, and arc-scale magmatic episodicity along convergent plate margins.