THE GEOLOGIC STRUCTURE OF THE AKKERMANOVKA FRAGMENT OF THE KHABARNY MASSIF OPHIOLITE ASSOCIATION (SOUTH URAL)

Abstract

Using the results of geological mapping, including the petrostructural and petrochemical data, available, as well as the results of the previous researchers, a composite characteristic is offered for the geologic structure of the Akkermanovka fragment of the ophiolite sequence of the Khabarny Massif (South Ural). The position of this fragment in the enclosing structure is shown, and the structure of its paleooceanic crust rocks is discussed. The plutonic rock complex is distinguished by the unified layering from the olivine pyroxenite-wehrlite to olivine gabbro - gabbronorite. The linear banding folds show the NW strike and predominant gentle and intermediate dip angles of their limbs. The general bedding is violated by late gabbronorite and pyroxenite veins. The composition of the gabbro-"pegmatites" (the latest rocks) correlates with the composition of the enclosing rocks. The root zone of the dike complex is almost completely absent. The screen distribution shows the discrete distribution of the layered rock complex in the mantle tectonites. The sheeted dike complex is characterized by acid magmatism, expressed in the presence of veins and stocks of different sizes and also by the granitoid material filling the matrix of the magmatic breccias. These rock complexes seem to have been formed under the conditions of a supra-subduction marginal-sea basin. Spreading took place under the conditions of a deficient magma budget and was marked by the existence of numerous totally or partly synchronous extension axes, both differing in the direction of the spreading block vector. The upper age limit of this process is assumed to be Famennian (366±2 million years). At the post-oceanic stage of their development the rock complexes discussed were included into the structure of the accretion prism and thrust over the margin of the East European Continent (Late Devonian to Early Carboniferous). The active phase of the collision deformation terminated at the end of the Early Carboniferous by the disintegration of the nappe slabs by left shears. The final structural separation of the Akkermanovka fragment is believed to have been associated with post-Cretaceous faults.