Zonal metamorphism and petrology of metapelites in the Tim-Yastrebovskaya structure, Voronezh crystalline massif

Our detailed petrographic study of the Early Proterozoic metapelites of the Tim-Yastrebovskaya structure resulted in distinguishing the following four metamorphic zones: garnet-chlorite, staurolite-andalusite. staurolite-sill imanite, and sillimanite-muscovite. The zoning mapped in the area is noted for the fact that its Mn-rich metapelites contain the assemblage of Fe-Mn g arnet with andalusite in place of staurolite. Based on its morphology, comp osition, and zoning, the garnet of the rocks can be subdivided into two typ es: early kinematic with prograde zoning and late kinematic with retrograde zoning or unzoned. The results of microthermometry and mineralogical therm obarometry led us to conclude that the metapelites of the Tim-Yas-trebovska ya structure were affected by two metamorphic events. During the early epis ode, which was related to folding at 2250 Ma, the metasediments were region ally metamorphosed to the garnet-chlorite grade (zone). The intrusion of la rge granodiorite bodies at 2086 Ma induced the second metamorphic episode, during which the metapelites were metamorphosed at 520-620 degreesC and 3-4 kbar.