Zircon U-Pb age and geochemistry of volcanic rocks in Manketouebo Formation from Jalaid Banner, central Da Hinggan Mountains

Chronologic and geochemical studies of volcanic rocks in Manketouebo Formation from Jalaid Banner area are presented in this paper. The zircon U-Pb dating results show that the ages of rhyolitic breccia (TW6) and rhyolite (TW14) are 157.2±1.2Ma (MSWD=0.33, n=22) and 154.8±1.1Ma (MSWD=0.34, n=28) respectively, indicating that the volcanic rocks were formed in Late Jurassic. Geochemical characteristics indicate that the volcanic rocks are rich in silicon and alkali but poor in calcium and magnesium, and belong to peraluminous calc-alkali series. The chondrite-normalized REE patterns indicate that the volcanic rocks are enriched in light rare earth elements with significant fractionation of HREE and LREE ((La/Yb)_N=20.24-22.68), and Eu has a positive anomaly. The primitive mantle-normalized trace element spidergram shows that the volcanic rocks contain high LILE(Rb, K) and low HFSE (Nb, Ti, P), suggesting crust magma source. In combination with all the characteristics of the volcanic rocks and other research results, the authors hold that the volcanic rocks in Manketouebo Formation were closely related to the lithosphere extension after the closure of Mongol-Okhotsk Ocean.