Magma source and formation mechanism of the Zhuopan alkaline complex in Yongping, Southwest China: Constraints from geochemistry, zircon U-Pb geochronology and Hf isotopes

The Zhuopan alkaline complex in the western margin of the Lanping Basin, is an important part of the Cenozoic potassic magmatic belt in Sanjiang Tethys. The Zhuopan alkaline complex mainly consists of syenite-pyroxenolite, gabbro-syenite, syenite and nepheline. Those rocks are characterized by high alkaline, high K2O/Na2O, low TiO2 and high Al2O3. Primitive mantle-normalized incompatible trace element patterns exhibit strong enrichments in large ion lithophile elements, relatively high field strength elements and strong negative Ta, Nb, Ti anomalies content, which are typical characteristics of subduction-related magma. Chondrite-normalized rare earth element (REE) patterns show enrichment in light rare earth elements (LREE) , flat heavy rare earth elements (HREE) patterns and no or weak negative Eu anomalies and high (La/Yb)(N) value ranging from 38. 2 to 80. 3. The LA-ICP-MS zircon U-Pb ages from the syenite and syenite-pyroxencterite are 33. 40 +/- 0. 38Ma and 34. 22 +/- 0. 33Ma. Zircon epsilon(Hf)(t) values range from -10.6 to - 4. 3, corresponding Hf crust model ages (t(DM)(c)) rang from 1. 36Ga to 1. 76Ga. All of the rocks in the Zhuopan alkaline complex have similar chondrite-normalized REE patterns and primitive mantle-normalized trace element patterns, suggesting that they were derived from similar parental magmas. Mean Nb/U values 2. 95 between the subduction zone fluid and the global subduction sediments, exhibits strong negative high field strength elements (HESE) such as Ta, Nb, Ti, and shows enrichment in LREE and no or weak negative Ce and Eu anomalies. Those characteristics suggest that the fluid of the subducted oceanic or continental crust deposits in the magmatism source area or shows the metasomatic enrichment in molten rock and lithosphere mantle. The double-sided subduction of Changning-Menglian Paleo-Tethyan oceanic and Jinshajing-Ailaoshan Paleo-Tethyan oceanic resulted in the formation of metasomatic enriched mantle magma during, Late Carboniferous-Late Permian (305 similar to 205Ma) and K-rich metasomatic lithosphere mantle has been formed. During the Cenozoic, the Neo-Tethys Ocean lithosphere broke off from the Indian continental lithosphere and enrichment metasomatic continental lithosphere mantle delaminates, and residual K-rich mafic magmas were generated by partial melting of enrich lithospheric mantle by hot upwelling asthenosphere. Finally, the magmatism emplaced in the extensional environment and formed the Zhuopan intrusion.