Wagnerite in high-MgAl granulites of Anakapalle, Eastern Ghats Belt, India
Simmat, Ralf; Rickers, Karen
European Journal of Mineralogy Volume 12 Number 3 (2000), p. 661 - 666
published: May 31, 2000
manuscript accepted: Jan 4, 2000
manuscript received: Jun 28, 1999
ArtNo. ESP147051203012, Price: 29.00 €
Abstract Wagnerite (Mg,Fe,Ca,Mn)2[PO4(F,OH)] was found in high-MgAl granulite near Anakapalle, ca. 40 km W of Vishakhapatnam, East-India. This is the first reported occurrence of this mineral in the granulite-facies Eastern Ghats Belt (EGB). The high-MgAl granulite occurs as xenoliths of several meters in diameter within basic granulite. The rocks experienced Grenvillian ultra-high-temperature (UHT) metamoiphism (8 kbar: T > 900°C). Still at high- grade conditions, the rock assemblage was intruded by large volumes of felsic melt (chamockite). Hence, the MgAl granulite became partially metasomatised. resulting in microdomains with variable Ca/(Ca+Mg) - ratios and different assemblages. Three principal wagnerite-bearing petrographic domains are distinguished. Within domains 1 & 2 (Ca/(Ca+Mg) ~ 0.02) wagnerite occurs as a stable phase of the UHT-assemblage and is the major phosphorus-bearing phase, while apatite is absent. In domain 3 (Ca/(Ca+Mg) ~ 0.25), wagnerite reacted with the intruding felsic melt and is now rimmed by apatite. Isokite, CaMg[PO4F], was not observed and seems not to be stable at UHT-conditions. Wagnerite from Anakapalle is characterised by unusually high OH content (F/(F+OH) = 0.47-0.60) and low Ca content (0-0.5 wt% CaO). The Fe content in domain 3 is slightly higher (3-3.5 wt% FeO) compared| to domains 1 & 2 (1.5-2.5 wt%).