Lanthanide kinked shape, similar to Tetrad effect, observed in sub-volcanic rocks from Qiaga, southern Tibet, China

Qiaga sub-volcanic rocks intruded into the southern-eastern Tethys Himalaya, between the Yardoi gneiss dome to the north and South Tibetan Detachment System to the south. Based on the study by thin-section and whole-rock geochemical analysis, it is classified as rhyolitic sub-volcanic rock. Geochemical analysis results indicate that these rhyolitic sub-volcanic rocks are rich in silicon, aluminum, alkalis, poor in calcium, magnesium and total iron. The Rittmann index(σ) varies from 1.07 to 2.37, which shows the rhyolitic sub-volcanic rocks belong to calc-alkaline series. The trace elements data show that they are enrichment of LILE and depletion of HFSE, low total REE concentration (∑REE). Rare earth elements Chondrite-normalized distribution pattern is like a kinked shape, similar to tetrad effect; the ratio of K/Rb and Rb/Cs are below the average ratio of acid igneous rocks, and the ratio of Y/Ho, Nb/Ta and Zr/Hf are contrasting difference from those in chondrite. Thus, combine with former tetrad effect researchs, we concluded that after magmatic-hydrothermal alteration, the REE distribution pattern in high-silica peraluminous magma can be a "kinked" shape, similar to tetrad effect, which has positive Gd anomaly.