Structure Composition and Formation Process of Cenozoic High-K Calc-Alkaline Volcanic Rocks in Tengchong Area
Jiang Tao
Zheng Jianping
Su Yuping
Yang Zhiguo
Li Xin
Abstract：Since the Cenozoic,a large amount of high-potassium calc-alkaline volcanic rocks(basaltic trachyandesite and trachyandesite)have developed in the Tengchong area,but the specific formation process remains unclear.Based on petrographic analysis,in this paper it conducts whole-rock major element and mineral major and trace element analyses of these volcanic rocks,and discusses their formation and evolution process in combination with the published data.The rocks commonly exhibit porphyritic textures,with phenocrysts predominantly consisting of olivine,pyroxene,and plagioclase,and the development of glomerocrysts.Clinopyroxene phenocrysts commonly show normal zoning,reverse zoning,and oscillatory zoning,with oscillatory zoning indicating multi-stage mafic magma replenishment and possible local contamination during magma evolution.Whole-rock major element analysis reveals that these rocks belong to the high-potassium calc-alkaline rock series.Clinopyroxene,orthopyroxene,and plagioclase phenocrysts and glomerocrysts show similar REE and trace element distribution patterns,with clinopyroxene being the most enriched in trace elements,followed by plagioclase,and orthopyroxene showing the lowest concentrations.The geochemical characteristics of olivine phenocrysts suggest that the magma source region may have originated from partial melting of peridotite,while the trace element compositions of the whole rocks and clinopyroxene phenocrysts record geochemical signatures characteristic of an arc-related tectonic setting.The mineral equilibrium temperature-pressure calculations reveal the existence of two intermediate to felsic magma reservoirs beneath the study area:a shallow dacitic magma reservoir(depth 8.3-13.6 km)and a deep andesitic magma reservoir(depth 18.4-30.2 km).The studied samples are derived from the deeper reservoir.Their formation involves mafic magma recharge,triggering mixing between crystal mush and melt;when newly generated melts become dominant within the reservoir,eruption is triggered,carrying semi-consolidated magmatic clots to the surface and forming the typical(glomerocrystic)textures.
Keywords：Cenozoichigh-K calc-alkaline volcanic rocksphenocrystmagma reservoirTengchong arearare earth elementspetrology
Publication Date：2025-11-30
Online Publishing Date：2025-12-15(First online date of this platform, not the publication date of the document)
Pages：18( 4387-4404 )