Grossular-bearing jadeite omphacite rock in the Myanmar jadeite area: a kind of jadeitized rodingite?
Wang, Xia; Shi, Guang Hai; Qiu, Deng Feng; Wang, Jing; Cui, Wen Yuan
European Journal of Mineralogy Volume 24 Number 2 (2012), p. 237 - 246
published: Mar 1, 2012
ArtNo. ESP147052402004, Price: 29.00 €
A new rock type in the Hpakant jadeitite area, Myanmar is identified as jadeitized rodingite. The rock consists of omphacite, garnet and jadeite, with minor allanite-(La), phlogopite, zeolite, chlorite, and a barian mineral. The garnet contains more than 80 mol% of the grossular end-member. Omphacite has variable composition and is Mg-rich (XMg-aver = 90), while jadeite contains 82-92 mol% of jadeite end-member. Petrography shows that the garnet formed before omphacite, and many omphacite grains have jadeite rims or occur as island surrounded by replacement jadeite, indicating that a jadeitization event occurred subsequent to grossular and omphacite formation. Considering the geochemical interpretation that the protolith of rodingite (gabbro, plagiogranite or pyroxenite) has considerable Na2O (mostly >2.0 wt% bulk), whereas rodingite has low Na2O (mostly <1.0 wt% bulk), serpentinization-related rodingitization could locally yield Na-rich fluids, which could be an additional source for the fluids for jadeitite formation, and may play an important role in fluid-rock interactions in subduction zones.