The First Discovery of Abnormal (Y+REE)-Enriched Zircons in Rocks of the Baltic Shield

摘要

Zircons with an anomalously high content of Y and REEs in rims were first found in rocks of the Baltic shield (in a pegmatite vein in the Gridino eclogite-bearing melange and in quartz syenites of the NorthKarelian greenstone belt); the total content reaching 17 wt %. The presence of such an amount of nonformula elements is caused by the isomorphic occurrence of them in zircon and is not associated with microinclusions of accessory minerals. The age of formation of these rims was determined as the Svecofennian, although the direct dating yields underestimated values of the age, which are void of geological sense.