Geochemical Patterns of Epidotes in Rocks of the Junction Zone between the Aldan Shield and the Dzhugdzur-Stanovoi Folded Area

摘要

Previously we demonstrated that the processes of ultrametamorphism in the junction zone between the Aldan Shield and the Dzhugdzhur- Stanovoi folded area include granitization reflected in extensive replacement of gneiss with trondhjemite-gneiss Lc1 and subsequent migmatization with the formation of several generations of leucosomes Lc2, Lc3, Lc4, and Lc5, which is consistent with the data of U-Pb dating of zircons [1-3]. Metamorphism and ultrametamorphism occurred under the conditions of the amphibo-lite facies of moderate pressures (＜6-7 kbar) at temperatures of ＜650-700℃. The mineral associations observed in all rock varieties are very uniform and include Bt + Ep + Pl + Qtz ± Hbl ± Ms. The high degree of secondary foliation is a peculiar feature of all rocks of the considered section, except for Lc5. This includes rock recrystallization and transformation into fine-granular gneiss in the zones of superposed deformations. Foliated migmatite and trondhjemite-gneiss contain areas of granite composition with gra-nophyric and prismatic-granular textures, which may provide evidence for the beginning partial melting after foliation.