Study on the compositional zoning and evolution of symplectitic coronal in jadeitite

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Abstract Based on the fact that multi-stage fluid activities play an important role in the interaction between jadeitite and symplectitic coronas, the author focuses on the study of the compositional zoning and evolution of the representative in Myanmar jadeitite, as the symplectitic coronas with multi-layer concentric ring metasomatic structure (chromite + uvarovite + kosmochlor) and chromite malcrystalline crystals in the core. The results show that: with the participation of multi-stage Ca, Na and Si rich fluid activities, some minerals in Myanmar jadeitite form symplectitic coronas with concentric rings and multi-layer metasomatic reaction edge structure, and the concentration of Cr and Fe decreases from the core to the peripheral jadeite minerals, the concentration of Si increases obviously. There is almost no Si and Ca in the core of chromite, and the concentration of Si and Ca increases sharply at the rim of the uvarovite reaction mineral. Due to the diffusion of Cr, the edge of jadeite adjacent to the kosmochlor is rich in Cr and poor in Al. The variation of element concentration reveals that the ouvarovite is formed by the interaction between the chromite and the jadeite or the Si of the kosmochlor after the metasomatism, or the external Ca-rich fluid. One possibility of the formation of kosmochlor is the interaction between the chromite and the fluid rich in Na and Si. Another is that the Ca-rich fluid first interacted with the chromite and forms the ouvarovite, leading to the decrease of Ca and increase of Fe and AL, later the Na-rich fluid enters and saturates the kosmochlor, leading to the formation of kosmochlor surrounding the ouvarovite.

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