Position of Rocks of Riftogenic and Collisional Sedimentary Sequences on Different Paleogeodynamic Diagrams

The distribution of composition fields of syn-rift and syncollisional sandstones and fine-grained clastic/clayey rocks of various structures and different ages are compared on the SiO 2 –K 2 O/Na 2 O, F1–F2, and DF1–DF2 diagrams. Syn-rift sedimentary sequences fill intraplate rifts, rifts at divergent, conservative and convergent plate boundaries, as well as their triple junctions. Syncollisional sediments are referred to rocks of foredeep and intermontane troughs, which are made up of molasses proper, flysch and schliers, and volcanogenic and nonfolded (distal) molasses. Fields of syn-rift and syncollisional sandstones in the SiO 2 –K 2 O/Na 2 O diagram show significant overlap. In the F1–F2 and DF1–DF2 diagrams, the distribution of the fields of syn-rift and syncollisional fine-grained clastic/clayey rocks is also substantially similar. Hence, the above mentioned diagrams cannot be used for reliable discrimination between syn-rift and syncollisional terrigenous associations. Correspondingly, it is hardly possible to use these diagrams alone for determination of geodynamic nature of sediments.