Geologic structure of Western Primorye: Structuring dynamics

Abstract

The first data are reported on the structuring dynamics of Western Primorye. The analysis of the structural parageneses of the least studied macro- and mesolevels of the arrangement of the geologic space allowed us to distinguish three sequentially superposed structural patterns (parageneses), each of which was formed by its own stress field during separate geodynamic periods: the Late Proterozoic-Early Paleozoic, the Middle-Late Paleozoic, and the Mesozoic-Cenozoic. During the first two episodes of geodynamic activation (Late Proterozoic-Early Paleozoic), the main compression axis was oriented longitudinally. The first episode was characterized by the formation of a thrust-fold structural pattern. The second episode resulted in the superposition of the meridional riftogenic structures and, respectively, in the pull-apart normal-fault segmentation of the crystalline basement into mainly longitudinal blocks, which partially coincide with the previously distinguished terranes. During the latitudinal compression and oblate deformation that predominanted during the Middle-Late Paleozoic geodynamic period, the down-thrown and uplifted blocks were transformed into depressions and arches, respectively. The depressions were filled with Paleozoic sediments, while the primary rocks in the arches experienced granitization with the formation of two granitic complexes that joined terranes. The granites are characterized by shadow and shear-type fold and pseudofolded forms. The Mesozoic-Cenozoic period governed by NNW compression is divided into the Triassic-Jurassic, Early Cretaceous, and Tertiary tectonic episodes. During the Triassic-Jurassic period, the ENE-trending narrow arches and depressions were formed by warping. The arches accumulated granitized rocks, while the depressions were compensated for by the Early-Late Triassic sedimentary-volcanogenic sediments. All these processes led to the formation of structural complexes that joined and overlapped older complexes of meridional blocks (terranes) across the strike. Two subsequent Mesozoic-Cenozoic episodes manifested themselves in the discrete formation of coal-bearing depressions due to the NNW compression and ENE extension of the warping products.