GENESIS OF POSITIVE EU ANOMALIES IN ACID ROCKS FROM THE EASTERN BALTIC SHIELD

Abstract

The eastern part of the Baltic Shield contains an abundance of acid rocks with positive Eu anomalies. These rocks are vein granites and blastomylonites of similar chemical composition but with variable K2O concentrations. The rocks are depleted in Ti, Fe, Mg, Ca, Rb, Zr, and REE, but are enriched in Ba and Sr, a fact suggesting a deep-seated nature of the fluids that participated in the genesis of these rocks. A zone favorable for the derivation of these rocks was transitional from brittle to ductile deformations. The rocks were produced during the tectonic exhumation of lower and middle crustal material a horizontal extension. Shock decompression facilitated the inflow of reduced fluids, which, in turn, ensured the partial melting of the host rocks along open fractures and controlled REE fractionation with the development of Eu maxima. © Pleiades Publishing, Inc. 2006.