Udurchukan formation and ayakit complex (Bureya massif, Sikhote-Alin): location, age and geochemistry

Abstract

Neogene basalts in the eastern of the Bureya massif and the adjacent Kursk-Komsomolskaya zone of the Sikhote-Alin fold system occur in the seismically and tectonically active area along the Khingan, Amgun and Tanlu-Kharpi deep faults. Analysis of age constraints on the timing of basaltoid magmatism in the Miocene suggests three phases of magmatism in the study areas: Early Miocene (Udurchukan Formation: 22,6–18,6 Ma); Middle Miocene (Ayakit Complex: 14,8–13,0 Ma), and Late Miocene (Ayakit Complex: 10,0–9,3 Ma). Rock studies have found that basalts (Ayakit plateau), basaltic andesites (Udurchukan plateau), and leucitites (Yadasen Island) are enriched in sodium oxides, potassium, titanium, iron, magnesium, and phosphorus. Two samples of alkaline olivine basalts from the Ayakit plateau yielded high KkTe (578,0) and Ag (172,7); elevated Kk in high field-strength Nb (6,2), Ta (3,4) and radioactive Th (2,7), U (2,4). The contents of Co, Ni, Zr, Mo, W, Zn, Sr, Ba, Hg, light and middle REE are 1,1–1,5 times or even higher than the clarke values for mafic rocks. There is a slight deficit of Sb, Cs, Bi, Cu, Li, Sc, Rb, Tm, Yb, Lu (Kk < 0,7). A similar chemical composition of the SASS basalts (Solnechny settlement and Yadasen Island) suggests that they have a common magma source.