The origin and geochemistry of the Late Triassic siliceous rocks in Luchun, Yunnan

The Luchun Late Triassic volcano-sedimentary basin in Yunnan is a post-collisional strike-slip extensional basin grounded upon the Jomda-Weixi volcanic arc. The basin is conspicuous by bimodal volcanic rocks composed of basalts and rhyrolites and by associated siliceous rocks. The siliceous rocks in the basin may fall into two categories:tuffaceous and laminated. The former is characterized by high ΣREE, enriched LREE, minor negative Ce anomaly and marked negative Eu anomaly, whereas the latter is typical of low ΣREE, slightly enriched LREE, minor negative Eu anomaly and marked negative Ce anomaly. The study of the geochemistry of the above-mentioned two siliceous rocks shows that the tuffaceous siliceous rocks have a volcano-sedimentary origin, while the laminated siliceous rocks are of submarine-exhalative or hydrothermal (hot-spring)sedimentary origin.