Abstract The history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zircon U–Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160–150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.

Abstract A compilation of 290 zircon U–Pb ages of intrusive rocks indicates that the Gangdese Batholith in southern Tibet was emplaced from c. 210 Ma to c. 10 Ma. Two intense magmatic pulses within the batholith occur at: (1) 90 ± 5 Ma, which is restricted to 89–94° E in the eastern segment of the southern Lhasa subterrane; and (2) 50 ± 3 Ma, which is widespread across the entire southern Lhasa subterrane. The latter pulse was followed by a phase of widespread but volumetrically small, dominantly felsic adakitic intrusive rocks at 16 ± 2 Ma. The Linzizong volcanism in the Linzhou Basin was active from 60.2 to 52.3 Ma, rather than 69–44 Ma as previously estimated. During 120–75 Ma, Gangdese Batholith magmatism migrated from south to north, arguing against rollback of the downgoing, north-dipping Neo-Tethyan oceanic lithosphere for the generation of the 90 ± 5 Ma magmatic pulse. Petrological, geochemical and metamorphic data indicate that this pulse was likely to have been generated through subduction of the Neo-Tethyan oceanic ridge lithosphere. Subsequent Gangdese Batholith magmatism propagated both south and north during 70–45 Ma, and finally concentrated at the southern margin of the Lhasa Terrane at 45–30 Ma. The enhanced mafic magmatism since c. 70 Ma, magmatic flare-up with compositional diversity at c. 51 Ma and increased magmatic temperature at 52–50 Ma are interpreted as the consequences of slab rollback from c. 70 Ma and slab breakoff of the Neo-Tethyan oceanic lithosphere that began at c. 53 Ma. The India–Asia convergence was driven by Neo-Tethyan subduction with a normal rate of convergence at 120–95 Ma, ridge subduction at 95–85 Ma, then subduction of a young and buoyant oceanic lithosphere after ridge subduction with rate deceleration at 84–67 Ma, Deccan plume activity and slab rollback with rate acceleration at 67–51 Ma, slab breakoff for sudden drop of the convergence rate at c. 51 Ma, and finally the descent of the high-density Indian continental lithosphere beneath Asia since c. 50 Ma.

Abstract The subduction of Indian plate lithosphere during its collision with Asian plate in the Eocene resulted in a regional metamorphic belt along the strike of the Himalayan orogen. High-/ultrahigh-pressure (HP/UHP) metamorphic rocks (eclogites and host gneisses) confirm the metamorphic event in western Himalaya (Kaghan c. 46 Ma and Tso Morari at c. 47 Ma) at mantle depths (>90 km: coesite-stable). In contrast, HP/UHP rocks have not been reported from central and eastern Himalaya and only highly retrogressed eclogites and granulites ( c. 25 to 13 Ma) occur. The presence of UHP rocks in western Himalaya and highly retrogressed eclogites and granulites in central and eastern Himalaya was regarded as evidence for a diachronous India–Asia collision. Despite the along-strike regional homogeneity in major lithotectonic units of the Himalayan orogen, metamorphic diachroneity is enigmatic. It is unlikely to have a subduction-related prolonged progressive metamorphic event. In contrast, the age difference and preservation of UHP phases in the west and their transformation into granulites in central and eastern Himalaya could be associated with their prolonged residence times at crustal levels in the central and eastern Himalaya whereas the rocks exhumed rapidly in the west. The higher thermal events relating to melting of the subducting Indian lithosphere in central and eastern Himalaya evidenced from ultra-potasic volcanics in southern Tibet probably decompressed the early metabasites into granulitized eclogites, even resetting their geological clock, which is why eclogites and granulites in the east show younger ages compared with their UHP counterparts in the west.