Deciphering of the Tectonic Elements and Internal Structure of the Paleoproterozoic Losevo Terrane (Volga–Don Orogen) Using Density Modeling Data

Many conceptions relating to the structure of terranes that compose orogens remain controversial. This article focuses on the widest part of the Losevo Terrane of the Paleoproterozoic Volga–Don Orogen in the southeastern part of the East European Craton. The subjects of discussion are the tectonic origin of the terrane, its relationship with neighboring blocks, the kinematics and depth of the limiting faults, the shape and depth of occurrence of paleovolcanoes and intrusions, and the thickness and subdivision of stratified formations. A three-dimensional model of the distribution of the absolute values of density of the Earth’s crust to a depth of 10 km was obtained as a result of the inversion of local anomalies of the gravity field. The results of the density modeling were interpreted in three ways: (1) identification of lineaments as a reflection of major dislocations, (2) tracing the structural features of stratified or similar geological units, and (3) characteristics of local, contrasting objects, mainly plutons and paleovolcanoes of different compositions. The studied area is a large paleosynform, the base of which is composed of undivided gneisses and the Terrigene (lower) Formation of the Losevo Series. The kinematics of major faults limiting the Losevo Terrane has been established. Greenstone structures of the Strelitsa and Podgornoye formations of the Losevo Series have been identified and traced to depth. The contours of the Voronezh Suite, the thickness of which is about 4 km, have been clarified. The vertical dip of batholiths and stocks of the Usman complex, the Olkhovka pluton, and other intrusions indicates their injection in a post-collisional setting.