Compositional zoning and evolution of symplectite coronas in jadeitite

Abstract

Multistage fluid activities play an important role in the interaction between jadeitite and symplectite coronas; therefore, we studied the compositional zoning and evolution of representative Myanmar jadeitite. Under the influence of multistage Ca-, Na-, and Si-rich fluid activity, some minerals in Myanmar jadeitite formed symplectite coronas with concentric rings and multilayer metasomatic reaction rim structures. Additionally, the concentrations of Cr and Fe decrease from the core to the peripheral jadeite minerals, whereas the concentration of Si markedly increases. There is almost no Si or Ca in the chromite core, and the concentrations of Si and Ca increase sharply in rims composed of uvarovite. Due to Cr diffusion, the edge of the jadeite adjacent to kosmochlor is Cr-rich and Al-poor. The different element concentrations indicate that the uvarovite formed from the presence of a chromite and jadeite interaction, Si in the kosmochlor after metasomatism or an external Ca-rich fluid. One possible explanation for the formation of kosmochlor is the interaction between chromite and a Na- and Si-rich fluid. Also, Ca-rich fluid could have first interacted with chromite and formed uvarovite; subsequently, a Na-rich fluid could have entered and become saturated with kosmochlor, leading to the formation of kosmochlor surrounding the uvarovite.