Geochronology and geochemistry of volcanic rocks in Manketou'ebo Formation of Tulihe area, northern Da Hinggan Mountains

In this paper, the authors studied the chronology and geochemistry of volcanic rocks in Manketou'ebo Formation of Tulihe area within Da Hinggan Mountains to restrict the petrogenesis and the tectonic setting. Zircon U-Pb dating reveals that the volcanic rocks formed in (157±1) Ma, suggesting late Jurassic. The geochemical characteristics reveal that these rocks fall into the high-K calc-alkaline, metaluminous to slightly peraluminous rhyolite series, characterized by high SiO₂ content (69.09%-75.92%), high alkali content (8.04%-9.23%) but low MgO, CaO and Fe₂O₃ content. The REE patterns reveal that the rocks are enriched in light rare earth elements with significant fractionation of HREE and LREE ((La/Yb)_N=5.85-13.53), with no or lightly negative Eu anomaly. Rocks are enriched in LILE such as Rb, Th, U and K, relatively depleted in HFSE such as Nb, Ta and Ti. Mg^# ratios vary from 12.14 to 31.01, 22 on average; Nb/Ta ratios vary from 6.67 to 27.17, 12.23 on average; Rb/Sr ratios vary from 0.35 to 3.36, 1.58 on average, implying that the magmatic source was the lower crust. According to the geochemical features, discrimination diagrams of tectonic setting and regional tectonic evolution, the authors hold that the volcanic rocks formed in the post-orogenic extension setting after the closure of Mongol-Okhotsk Ocean.