EVIDENCE FOR MANTLE METASOMATISM FROM MICAS IN THE ALKALI BASALTS OF THE SOUTHERN TIEN-SHUN, TAJIKISTAN

Mantle micas are widespread among deep-seated xenoliths and xenocrysts from alkali basalts (P-J) of the southern Tien Shan and range from ma gnesium-sich, barium, and chrome phlogopite to titanium phlogopite and titanium biotite. Mantle micas from the basalts of heterogeneous geol ogic structures (alkali basalt provinces) differ in their chemical com position and major and trace element distribution, which are related t o the variations in fluid and geochemical conditions and P-T parameter s of the processes of mantle metasomatism. Within an individual lithos pheric block (alkali basalt area), micas from metasomatized mantle roc ks and alkali basalt melts (phenocrysts, cumulates) show similar conce ntrations of volatile (F, Cl), trace (Rb, Cs, Ba, Nb, Zr), and major e lements (K, Na, Ti).