Petrogenesis of the Shuicaoba monzonitic granite porphyry in Ninglang, Yunnan: constraints from zircon U-Pb geochronology and geochemistry

The Shuicaoba monzonitic granite porphyry is located north segment of the Xiangyun-ninglang Cu-Au metallogenic belt, and it is also an important part of the Jinshajiang-Red River enozoic alkali-rich porphyry belt.Based on petrography, zircon U-Pb geochronology and petrogeochemical analysis of the Shuicaoba Monzogranite porphyry, new constraints have be provided for the Cenozoic tectonic magmatic evolution in this area.LA-ICP-MS zircon U-Pb dating indicates that Shuicaoba monzonitic granite porphyry is of Early Oligocene (33.1±0.3 Ma).The pluton is rich in SiO₂ and alkali, with the ratio of A/CNK > 1, belonging to the peraluminaceous alkali rich monzonite porphyry.The rock has a total high amount of REE elements(ΣREE=114.68×10^-6~384.79×10^-6), right-leaning REE distribution pattern, and obvious fractionation of LREE((La/Yb)_N = 440.37~114.09), showing no significant Eu anomaly(0.84~1.14).The adakite is enriching in LILE(such as Rb, Sr and Ba) and HFSE (such as Th, U, K and La), depleting in HREE, high field strength elements (Nb, Ta, Ti, etc.), with a high amount of Sr and low amount of Y and Yb, which is typical C-type Adakite.Comprehensive analysis shows that the magmatic source area of the Shuicaoba monzogranite porphyry is mainly partial melting of the thickened lower crust, and a small amount of mantle-derived components may be involved.Combined with the regional tectonic evolution, it is considered that the Shuicaoba monzogranite porphyry was formed under the dynamic background of the tectonic stress transition from compression to extension during the late Indian-Eurasian plate collision strike slip period.