Petrology and geochemistry of the Zhuopan alkaline complex in Yongping, Yunnan Province: Constraints on petrogenesis and tectonic setting

Located in Yongping region in the middle area of the Jinsa River-Ailaoshan tectonic zone and emplaced in Jurassic sandstone in the northern segment of strike-slip extensional basin of Lanping, Zhuopari alkaline complex is the important part of the Sanjiang alkali-rich intrusive rocks and is composed of alkali gabbro, pyroxene syenite and nepheline syenite. The major element of the alkaline complex is characterized by rich potassium, high alkaline(K2O + Na2O =6. 92% similar to 13.43%) and low titanium(TiO2 =0. 31% similar to 1. 20%). The research showed that all samples are potassic alkaline series rocks. All samples are enriched in large ion lithophile elements (Rb, Sr, Ba, Th), and depleted in high field strength elements (Nb, Ta, Ti) and exhibits LREE-enriched with right-inclined REE distribution patterns. The Sr-Nd-Pb isotopes characterized by high Sr-87/Sr-86, (206)pb/(204)pb, (207)pb/(204)pb and (208)pb/(204)pb and low Nd-143/Nd-144 and showed the source area have obvious characteristics of contamination by crustal materials and the crust-mantle transitional zone between EM II enriched mantle and lower crust. The Zhuopan alkaline complex formed in shear-extensional tectonic setting post India-Eurasia collision associated with the crustal shortening and thickening, the westward subduction of Yangtze paleo-plate, and the upwelling of asthenosphere mixed with the subducted Yangtze paleo-plate materials. Due to the shear-extensional in the Jinsa River-Ailaoshan fault zone, the magma rapidly erupted into the strike-slip extensional basin of Lanping with primary magma characteristics.