Tektono-Stratigraphy as a Reflection of Accretion Tectonics Processes (on an Example of the Nadankhada-Bikin Terrane of the Sikhote-Alin Jurassic Accretionary Prism, Russia Far East)

Abstract

The Sikhote-Alin folded belt is one of the Asia eastern margin regions, where terranes of ancient accretionary prisms are widely distributed. Within this region there are fragments, as a minimum, of three such different-aged prisms Jurassic, Early Cretaceous and Middle Cretaceous (fig. 1). Accretionary prisms are complicate-dislocated sedimentary complexes that are formed at the basis of continental or island-arc slopes as a result of accretion of fragments of the sedimentary cover and morphologically positive structures of an oceanic plate during its subduction. The subduction of an oceanic plate under a continent or an island arc is commonly accompanied by intense deformation of the sedimentary cover deposits. At first, in the frontal part of the slope basis the upper part of a sedimentary cover (trench turbidite) under the action of “bulldozer effect” (off-scraping) repeatedly imbricate, forming a series of tectonic slices of terrigenous composition (fig. 2). Secondly, pelagic and hemipeladic sediments located below of an imbrication zone, plunging into a subduction zone rumple under the action of simple shear (effect of drag folding) into the differentamplitude and disharmonious overturned folds, which axial planes are inclined towards a trench. Crumpling of sediments continues until ultimate strength limit of rocks is reached and the ruptures are appearing. Further along these ruptures numerous underplating and doubling of a primary cut-section of an oceanic plate cover occur that results in formation of imbricate-underthrusted structure of the accreated rocks (Hashimoto & Kimura, 1999; Kimura, 1997; Kimura & Mukai, 1991; Moore & Byrne, 1987; Seely et al., 1974; Sokolov, 1992, 1997; Sokolov et al., 2001; etc.). For this reason the accretionary prisms are a tectonic package of repeatedly alternating tectonic slices consisting of marine (pelagic and hemipelagic deposits and also fragments of seamountns), oceanic-margin (turbidites), and chaotic (melange and olistostromes) formations. Structure of ancient accretionary prisms is even more complex because of a numerous post-accretion deformations such as thrusts and strike-slip faults.