Magma Source,Formation Mechanism And Tectonic Significance Of The Dalianhuashan And Zhuopan Plutons,Yunan Province

In this paper,we will aim at the alkali-rich rocks porphyries in Dalianhuashan and Zhoupan.Based on the petrology,petrography,geochemistry,zircon U-Pb geochronology and Hf isotope research methods,we focus on the material source of alkaline intrusive,formation process and tectonic environment.(1)The Dalianhuashan and Zhoupan plutons are characterized by high potassium and alkali and enrich LILE and LREE,deplete in Nb,Ta,Ti,P and weak negative Eu anomalies.Both of plutons belong to shoshonitic series.Two plutons are depleted in Nb,Ta,Ti,indicating that the magma source are related to subduction dehydration metasomatism enriched lithospheric mantle.(2)Zircon U–Pb dating of the amphibole quartz porphyry and biotite monzonite from the Dalianhuashan yield the weighted mean ages of 34 ± 0.4 Ma and 33 ± 0.3Ma,and syenite and gabbro from the Zhuopan yield the weighted mean ages of33±0.4Ma and 34±0.3Ma.We suggest that the Cenozoic magmatic activities of the Lanping basin are between 37 Ma tand 33 Ma.(3)The Hf isotope values of Dalianhuashan range from-1.1 to 8.9,indicating magma from the mantle and minor crustal material.The zircon Hf isotopic values from the Zhuopan are between-4.3 and-10.6,indicating the source material from the lower crust.(4)Analyze the forming process and geological setting of magma: the bisubduction of oceanic plate formed metasomatic enriched mantle in Mesoproterozoic,in the meantime,the crust has thickened and formed juvenile lower crust.In the end of the Eocene,the stress state of Jinshajiang-Honghe strike-slip fault changed from compressional shearing to extensional shearing because of the decompression of delamination,and formed Dalianhuashan alkali-rich porphyry and Zhuopan alkaline complex.