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The subduction model of the Neo-Tethys during the Early Cretaceous has always been a controversial topic, and the scarcity of Early Cretaceous magmatic rocks in the southern part of the Gangdese batholith is the main cause of this debate. To address this issue, this article presents new zircon U–Pb chronology, zircon Hf isotope, whole-rock geochemistry and Sr–Nd isotope data for the Early Cretaceous quartz diorite dykes with adakite affinity in Liuqiong, Gongga. Zircon U–Pb dating of three samples yielded ages of c. 141–137 Ma, indicating that the Liuqiong quartz diorite was emplaced in the Early Cretaceous. The whole-rock geochemical analysis shows that the Liuqiong quartz diorite is enriched in large-ion lithophile elements (LILEs) and light rare-earth elements (LREEs) and is depleted in high-field-strength elements (HFSEs), which are related to slab subduction. Additionally, the Liuqiong quartz diorite has high SiO2, Al2O3 and Sr contents, high Sr/Y ratios and low heavy rare-earth element (HREE) and Y contents, which are compatible with typical adakite signatures. The initial 87Sr/86Sr values of the Liuqiong adakite range from 0.705617 to 0.705853, and the whole-rock ϵNd(t) values vary between +5.78 and +6.24. The zircon ϵHf(t) values vary from +11.5 to +16.4. Our results show that the Liuqiong adakite magma was derived from partial melting of the Neo-Tethyan oceanic plate (mid-ocean ridge basalt (MORB) + sediment + fluid), with some degree of subsequent peridotite interaction within the overlying mantle wedge. Combining regional data, we favour the interpretation that the Neo-Tethyan oceanic crust was subducted at a low angle beneath the Gangdese during the Early Cretaceous. [ABSTRACT FROM AUTHOR]

Numerous research data have been obtained about the Sumdo Palaeo‐Tethys, but the reports on the occurrence of Permian Ocean islands are relatively scarce. Here, we present the zircon U–Pb geochronology, geochemistry, and in situ zircon Hf isotopic characteristics of the ocean island basalt (OIB)‐type gabbros from Ewulang in Nianqing‐Sumdo, Tibet. The zircon U–Pb age obtained from Ewulang OIB‐type gabbros is 263 Ma (the Middle Permian), representing the formation age of the gabbros. The geochemical characteristics of the samples show no contamination by crustal material. Meanwhile, all samples are enriched in light rare earths (LREEs) and large‐ionic lithophile elements (LILEs), which are similar to the typical OIB. In various geochemical discriminant diagrams, all samples fall into the fields of OIB and related tectonic settings, indicating that the rocks were formed in the oceanic island environment within the oceanic plate. Various geochemical indicators imply that the OIB‐type gabbros may originate from mantle plume and the in situ zircon εHf(t) values of Ewulang gabbros range from −0.34 to +4.30, suggesting that the magmas derived from an enriched mantle source. Combined with regional data and previous studies, this article further confirms that Sumdo Palaeo‐Tethys extends west to Nianqing‐Sumdo area and the Tangjia (Zhikong)‐Sumdo Palaeo‐Tethys was still an ocean basin with a certain scale during the Middle Permian. [ABSTRACT FROM AUTHOR]

Crustal material recycling in a subduction factory increases the diversity and complexity of arc magma. However, the exact origin and mechanism of its contribution to arc magma are not fully understood. Here, we present new data on the Molang basaltic rocks from the southern Lhasa terrane to gain an in-depth-understanding of the mechanisms of crustal recycling. The zircon U Pb ages indicate that these rocks were emplaced at 128 Ma. They display characteristics ranging from forearc basalts to tholeiitic arc basalts with depleted mantle isotope compositions (ε Nd (t) = +4.58 to +4.86) and zircon ɛ Hf (t) values (+7.3 to +8.7). The uniform isotopic composition (Sr Nd) and fractionation of trace elements show that crustal materials could have been added to the magma source in the form of bulk sediment. Therefore, we have proposed an argument supporting the mélange diapirs model. The age spectra of the inherited zircons are consistent with those of the detrital zircons from the subduction hanging wall. This implies that the inherited zircons may be unmolten residues of eroded forearc crust that survived erosion and subduction from the slab in well-mixed mélange diapirs that passed through a comparatively hot mantle wedge and occur as key evidence for crustal recycling in the arc magma. Based on a synthesis of earlier research, we suggest that the Molang basaltic rocks were derived from the partial melting of the mélange diapirs in a steep subduction setting during a new subduction initiation event involving the Neo-Tethyan oceanic slab. • Molang basaltic rocks were formed in a short-term slower subdction erosion rate by steep subdcution. • Inherited zircons may have come from subduction erosion crustal recycling. • Eroded crust can contribute arc magma through diapirs. [ABSTRACT FROM AUTHOR]