MAIN FEATURES IN THE DEVELOPMENT IN TIME OF METAMORPHIC ROCKS IN THE U.S.S.R.

Abstract

Intensive geological and petrological study of the territory of the U. S. S. R., especially notable, after 1945, has supplied an enormous amount of new published data on various metamorphic rocks that formed during different geological periods. Analyses (including those of the present writer) of abundant materials collected from various petrographic regions permit us to make a general sketch (in first approximation) of the principal particulars of distribution in time (geological eras) for metamorphic and metasomatic rock types that differ in chemical composition and in conditions of formation. It is necessary to indicate that elucidation of the main features of development of different metamorphic-rock types during definite intervals of geological time is not only of theoretical interest, but is of practical importance, in that different ore and mineral deposits are associated with metamorphic-rock zones. In this paper, metamorphic rocks of various types, which formed during different periods of time are considered briefly. Primarily considered are rocks that formed under regional conditions (dynamothermal metamorphism), and rocks of different age that formed as a result of contact-metasomatic and other metasomatic processes. The latter part of the paper discusses particulars of metamorphic rock development during different geological eras (Archean, Proterozoic, Paleozoic, Mesozoic, and Cenozoic). Genetic relationship is examined between various metamorphic and metasomatic formations with magmatic bodies that differ in composition and depth of formation. Finally, an attempt is made to establish some probable cuases of irregularities of metamorphic-rock development in the earth's crust. In addition, this paper deals with some possible causes of the irregular development of various metamorphic rocks in the earth's crust. Author