THE CHANGE IN PROVENANCE AND RECYCLING OF MESOPROTEROZOIC SEDIMENTARY ROCKS WITH TIME, SIBERIA

The mineralogy and elemental compositions of sedimentary rocks of Riphean age were determined. The sandstones are quartz-rich and range from wackes to arenites. Plots in A-CN-K diagrams suggest that samples of the Kerpyl Group have undergone K-metasomatism from a source with a high ratio of plagioclase to K-feldspar, but the other groups show no evidence of K-metasomatism. The ICV's of most samples are less than one so most samples are likely composed of recycled material; some samples have ICV's greater than one so some first cycle input may have occurred. The Eu/Eu* and (La/Lu)cn ratios of the shales decrease and the Th/Sc ratios increase with decreasing age. These results suggest that the average source for the shales changed from an initially more tonalite-rich source to gradually increasing amounts of granodiorite-granite. These chemical changes with time are similar to those in Proterozoic shales such as those exposed in the southeastern USA due to recycling of original tonalite-rich sources with periodic input of first cycle input of granites with time.