GEOCHEMISTRY AND FORMATION ENVIRONMENT OF THE LATE TRIASSIC-MIDDLE JURASSIC SILICEOUS ROCKS IN EASTERN HEILONGJIANG PROVINCE

The Nadanhada accretionary complex in eastern Heilongjiang Province is mainly composed of the Late Triassic-Middle Jurassic radiolarian siliceous rocks intercalated with the mafic-ultramafic complex and Late Paleozoic shallow sea sedimentary rocks. The analysis results of siliceous rocks from Shichang, Qindeli and Shengli Farm areas in eastern Heilongjiang Province show that the samples, characterized by generally low Al₂O₃, TiO₂, CaO and ΣREE contents and low Al₂O₃/(Al₂O₃+TFe₂O₃) ratio and high SiO₂ content, are pure siliceous rocks. Combined with the Al-Fe-Mn triangle diagram and K₂O/Na₂O ratio, it is indicated that the formation of siliceous rocks has nothing to do with seafloor hydrothermal process. The element discrimination diagram and geochemical characteristics reveal the siliceous rocks in the above three areas were formed in continental slope and marginal sea environment.