Composition and sources of clastic material in conglomerates from Precambrian metamorphic rocks of Kola Peninsula

Precambrian conglomerates, generally metamorphosed with concomitant loss of form, orientation, structure, and texture, are often regarded as fault breccias, mylonites, and even porphyroblastic formations. Study of the Precambrian of the Kola Peninsula has revealed that Proterozoic conglomerates are common, and although many original rock features have been obliterated by metamorphism, detailed study has led to the conclusion that valuable stratigraphic and petrologic data are discernible. The distribution of various metamorphosed conglomerates, their stratigraphic position and relationship to the enclosing rocks, their structure, the nature and location of source rocks, and the probable modes of transportation and environments of deposition were determined for many metamorphosed Proterozoic conglomerates of the eastern Kola Peninsula. This study shows that valuable information on the pre-metamorphic history of Precambrian areas can be obtained by careful analysis of metasedimentary rocks.—R. D. DeRudder