Atypical magmatism and strike-slip faulting as markers of Meso-Cenozoic tectonic inversion within the East Asia continental margin

The Pacific margin of East Asia attracts researchers as a potential source of various geological information used to construct geodynamic evolution models of the Palaeo-Asian continental margin. The WNW-ward motion of the Izanagi oceanic plate in the Turonian–Maastrichtian caused frontal subduction. Spatiotemporal distribution of А-type igneous rocks in the Sikhote-Alin (Russian Far East) was controlled by sinistral strike-slip displacements during the Palaeocene. However, it remains unclear how and when the subduction ceded to transform motion at the East Asia margin. The first discovery of the Latest Maastrichtian granite in southern Sikhote-Alin uncovers the Mesozoic-Cenozoic geodynamic evolution of the Pacific margin of Asia. In this paper, we report detailed petrology, zircon and apatite U-Pb ages, whole rock geochemistry, and isotopic (Sr – Nd – Pb) values obtained by studying the late Maastrichtian granitoid units in the Russian Far East. The observed variations in the geochemical and isotopic characteristics of calc-alkaline granitoids formed at the early stages (ca. 71–69 Ma) were caused by underplating of large volumes of hot basic magmas that served as a heat source for partial melting of heterogeneous crustal protoliths and FG-A-type peraluminous granite crystallization. Considering the petrogenesis of peralkaline A₁-type granite (ca. 67 Ma), we propose a model of magmatic transition from calc- to peralkaline magmas during the culmination of the magmatic event. The formation of the Latest Maastrichtian granitoid suites was defined by the structural and dynamic character of deformations in terrigenous strata developed under the NW-oriented stress at the initial stages (~71–69 Ма), and under the NNW-oriented stress reaching the final stage (ca. 67 Ma). The time of the anomalous A₁-type occurrence (ca. 67 Ma), possibly caused by the opening of the proto-Izu-Bonin fracture zone, should be regarded as the period when tectonic inversion from subduction to episodic transform environment was initiated.