Lithology, Source Areas, and Formation Settings of the Upper Triassic Deposits of Southwestern Primorye

Abstract

The paper considers the composition of sandy rocks from the Upper Triassic deposits of the Mongugai Formation of southwestern Primorye and presents the results of its paleogeodynamic interpretation. It has been established that, according to their mineralogical and geochemical parameters, sandstones are petrogenic, correspond to graywackes and, only partially, to lithite arenites, are characterized by a significant degree of geochemical maturity of the clastic material, and their formation occurred due to the erosion of significantly weathered parent rocks of the source areas. Generalization and paleogeodynamic interpretation of the data obtained indicate that sedimentation in the southwestern Primorye in the Late Triassic occurred in basins related to the active continental margin settings probably complicated by strike-slip dislocations along transform faults. The dominant source of detrital material was continental land: cratons and crystalline basement inliers surrounding the rift zones or along transform faults. Felsic granite-metamorphic complexes were eroded with the participation of sedimentary rocks enriched with ancient components. A secondary source was a deeply dissected continental-margin igneous arc, which supplied an additional amount of sialic material, as well as a small amount of the basic–intermediate volcaniclastic rocks into the basin. The U–Pb geochronological studies of detrital zircons from sandy rocks of the formation made it possible to establish the age and the possible position of igneous complexes, destruction of which formed the sediments.