Chronology, geochemical characteristics and its geological significance of Mesozoic volcanic rocks in Ganzhuyinaobao area, Abag Banner, Inner Mongolia

LA-ICP-MS zircon U-Pb dating results and geochemical data for the Mesozoic volcanic rocks from the Ganzhuyinaobao area of Inner Mongolia were presented in order to constrain their chronology, petrogenesis and the regional tectonic evolution. Manketouebo Formation persilicic volcanic rocks and Meiletu Formation intermediate volcanic rocks are extensively distributed in the study area. LA-ICP-MS zircon U-Pb dating results show that rocks of the two formations were formed at 163.6±0.6Ma and 139.6±0.7Ma, respectively. Geochemical researches indicate that the volcanic rocks in Manketouebo Formation are characterized by rich silica and alkali but poor TFeO, Al₂O₃, TiO₂, MgO, CaO and Na₂O, belonging to the alkaline series. The rocks with characteristics of A-type granite are enriched in LREE and LILE (Rb, Ba, Th, U and K) and depleted in HREE, some(Ba, Sr) and HFSE, especially Nb, Ta, P and Ti, with highly negative Eu anomalies, suggesting that they originated from the melting of the crust rocks. The Meiletu Formation intermediate rocks belong to the alkaline series, with enrichment of alkali, K, Al₂O₃, TiO₂, MgO and (LILEs) Rb, Ba, Th, U, K and depletion of HREE as well as Nb, Ta, Ti, Y, Yb and Lu and weak negative Eu anomalies. They were derived from the melting of mafic iron in the lower crust. Combined with characteristics of petrology and tectonic setting of the area, it is held that Manketouebo Formation persilicic volcanic rocks and Meiletu Formation intermediate volcanic rocks occurred in an intense lithopheric extension tectonic setting that was caused by the collapse or delamination of thickening crust resulting from the subduction of Mongolo-Okhotsk heading to the west slope of Da Hinggan Mountains-northern Hebei-western Liaoning region.