The Early Cretaceous tectonic evolution of the Neo-Tethys: constraints from zircon U–Pb geochronology and geochemistry of the Liuqiong adakite, Gongga, Tibet

• Published in: Geological magazine 2022-10, Vol.159 (10), p.1647-1662
• Main Authors: Zhong, Yao, Yang, Wen-Guang, Zhu, Li-Dong, Xie, Long, Mai, Yuan-Jun, Li, Nan, Zhou, Yu, Zhang, Hong-Liang, Tong, Xia, Feng, Wei-Na
• Format: Article
• Language: English
• Subjects: absolute age; adakites; Aluminum oxide; Asia; Basalt; Batholiths; cathodoluminescence; chemical composition; China; Cretaceous; Diorite; diorites; Earth mantle; Far East; framework silicates; Gangdese Belt; Geochemistry; Geochronology; Geochronometry; Geology; Gongga Mountain; hafnium; ICP mass spectra; igneous and metamorphic rocks; igneous rocks; intrusions; isotope ratios; Isotopes; laser ablation; laser methods; Lava; Lead; Lhasa China; lithophile elements; Liuqiong China; Lower Cretaceous; Lu/Hf; Magma; mantle; mantle wedges; mass spectra; Mesozoic; metals; Mid-ocean ridges; Nd/Nd; neodymium; Neotethys; nesosilicates; Oceanic crust; Original Article; orthosilicates; Paleoceanography; Peridotite; peridotites; Petrology; plate tectonics; plutonic rocks; Quartz; Radiometric dating; Rare earth elements; rare earths; Rock; Rocks; Sichuan China; Silica; silica minerals; silicates; Silicon dioxide; spectra; Sr/Sr; Strontium 87; Strontium isotopes; Subduction; Subduction (geology); Tectonics; thin sections; Tibetan Plateau; U/Pb; ultramafics; volcanic rocks; Xizang China; Zircon; zircon group
• ISSN: 0016-7568; 1469-5081
• DOI: 10.1017/S0016756822000401

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 ϵ Hf(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.