Abstract
Ion microprobe study of rare-earth and trace element composition of zircons from miaskite lamproites of the Panozero sanukitoid complex in Central Karelia made it possible to divide them into weakly altered and metasomatically altered zircons. The latter differ in elevated contents of LREE, Ca, Al, Fe, Ti, Sr, Ba, and Th, a flat REE distribution pattern, and a reduced Ce anomaly. Zircons show moderate to strong degrees of alteration, which are recorded in their geochemical features. The metasomatic alteration was caused by fluid related to the mantle alkaline magmatism. At the final stage, this fluid caused the crystallization of zircon domain with extremely high contents of REE (55000 ppm), Ti, Ba, Sr, and Th. The use of a Ti thermometer for unaltered zircons from the miaskite lamproites yields strongly underestimated temperatures, which require additional explanation or revision of the thermometer. For strongly altered zircons with sharply elevated Ti content, the use of this thermometer seems to be impossible.
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