The Earliest Cretaceous Intra‐Oceanic Subduction Zone in the Neo‐Tethys: Evidence From an <scp>OIB</scp> ‐Like Intrusion in the Western Indus‐Tsangpo Suture Zone, Southwestern Tibet

ABSTRACT The Indus‐Tsangpo Suture Zone (ITSZ), a remnant of the Neo‐Tethys in southern Tibet, has been extensively investigated. OIB‐like (Ocean Island Basalt) rocks are widespread in the ITSZ, yet their origin and geodynamic implications remain controversial. This study identified a mafic intrusion in the western ITSZ. Zircon U–Pb dating yielded ages from 142 to 134 Ma, with ε Hf (t) values (−0.7 to +4.5 and −1.9 to +4.3). The alkaline diabases are light rare earth element (LREE)‐enriched, with low ε Nd (t), high initial 87 Sr/ 86 Sr and radiogenic Pb isotopic ratios, consistent with OIB‐like affinity. These features indicate that such short‐lived magmatism originated from two mantle sources: (1) partial melting of the metasomatized mantle wedge induced by slab‐derived melts, and (2) subsequent asthenosphere upwelling resulting from slab breakoff. Together with the intrusion ages and tectonic setting, these data demonstrate that an intra‐oceanic subduction zone existed within the Neo‐Tethys since at least the earliest Cretaceous.