Si- and alkali-rich melt inclusions in minerals of mantle peridotites from eastern China: Implication for lithospheric evolution

CO2 fluid inclusions in mantle minerals are an im-portant source for us to get the information of mantle fluids. Fluid inclusions are mainly composed of CO2, with minor CO, H2O, CH4, N2, H2S, SO2, F, etc., which were demonstrated by lots of Raman spec-trometer analyses in recent years. In contrast, there are very few researches on CO2-bearing melt inclusions since it is more difficult to do so. The available studies have found that the primary CO2-bearing melt inclu-sions are basaltic …

Si-and alkali-rich melt inclusions in minerals of mantle peridotites from eastern China: Implication for lithospheric evolution

Minerals of spinel-and garnet-facies mantle xenoliths entrained in Cenozoic basalts from eastern China (North China, Northeastern China and Southeastern China coastal area) contains lots of melt inclusions. Studies on these melt inclusions show that the glass inclusions are rich in SiO₂ (60%-68%) and alkalis (K₂O+Na₂O=5%-11%, especially for K₂O) as well as volatiles such as H₂O and CO₂ (2%-7%), which belong to dacites and andesites of the high-K calcic alkali series rocks with few shoshonites. High Al and Ca diopside in melt inclusion is the product of melt crystallization at high temperature and pressure, rather than the product of devitrification. Results show that these K-rich (in general K₂O>3%) intermediate-acidic silicate melt inclusions have characteristics of continent without a genetical link to host basalts and their phenocrystic minerals. Thus, these trapped melt inclusions represent melts of Mesozoic lithospheric mantle-crust interaction and imply that the continental lithospheric mantle beneath eastern China had undergone fragmentation and recreation processes during the Mesozoic and Cenozoic periods. This result undoubtly provides important implication for the evolution of sub-continental lithosphere beneath eastern China. We propose that these Si-and alkalis-rich melts should be responsible for the mantle chemical heterogeneity underneath eastern China.