Metapseudotachylyte from central alcaline band of Ilmeny-Visnevogorsky polymetamorphic complex (South Urals)

For the first time, among Centeral Alkaline Band (CAB) mylonitic rocks of the Ilmeny-Vishnevogorsky polymetamorphic complex (IVPC) we foundа lenticular body of quarz-biotite- feldspar composition (2 ´ 3 m) with complicated network of thin intersecting recrystallizing veins of metapseudotachylytes. Microscopic research of textural and structural features revealed the presence of two types of metapseudotachylyte veins: early mylonitized metapseudotachylytes and late metapseudotachylytes. In the metapseudotachylyte body discovered Th-U-Y-REE-mineralisation are represented by rare minerals of solid-solution series thorogummite-coffinite and fergusonite-(Y) (REMMA-202 LZ Link systems with Si-Li detector). The composition of the metapseudotachylyte corresponds to normal alkaline granite and has high concentrations of LREE and Th, U, Y (AAS and ICP-MS). The presence of heterochronous metapseudotachylytes indicates a multistage transformation of CAB host rocks, and records the process of partial frictional melting of the rock under stress, in the final stages of formation of the complex.