Compositional characteristics of tourmaline formed by the syn-metamorphic fluid infiltration in the footwall of the MCT, Dhankuta area, Nepal Himalaya

Abstract

In the footwall of the MCT at Dhankuta, Nepal, rim composition of tourmaline in ‘normal’ metapelites becomes higher in XMg and Ca/(Ca+Na), and lower in X-site vacancy (X[ ]) as the metamorphic grade increases.
Tourmaline in the tourmaline veins shows high X[ ] and constant XMg, and that at several cm away from the vein shows low X[ ] and varied XMg. This probably reflects the difference in water/rock ratio, where tourmaline formed under high water/rock ratio shows high X[ ]. Some of the abnormally tourmaline-rich metapelite show similar tourmaline composition, suggesting its formation through the fluid infiltration.