THE VOLCANIC ROCKS IN MANKETOUEBO FORMATION FROM TAERQI AREA, SOUTH-CENTRAL DAXINGANLING MOUNTAINS: Geochemical Characteristics and Geological Implication

The volcanic rocks in Manketouebo Formation from Taerqi area are mainly rhyolite, rhyolitic tufflava and rhyolitic crystal tuff. The analysis results of major elements indicate that the volcanic rocks are characterized by quasi aluminum-weak peraluminum, with Al₂O₃=11.55%-14.76% and A/CNK=1.01-1.35, rich alkali (Na₂O+K₂O=4.56%-8.79%) and poor calcium and magnesium. The average content of REEs in the volcanic rocks is 168.69×10⁶. The distribution patterns show right-dipping curves with slight enrichment of LREEs and relatively flat distribution of HREEs, with distinctive negative Eu anomaly (δEu=0.29-0.72) and Rb/Sr=0.3-11.4. The trace elements are obviously enriched in LILEs such as Rb, Ba and K, but depleted in HFSEs like Nb, Ta and Ti. Combined with the geochemical characteristics and previous research data, it is thought that the volcanic rocks in Manketouebo Formation, bearing the typical characteristics of crust-derived magma, with residual plagioclase or fractional crystallization of plagioclase in the magma source area, belong to A-type, which is possibly the product of lithosphere extension tectonic system after the closure of Mongolia-Okhotsk Ocean.