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The Abaga basalts, which erupted within an intraplate background in the late Cenozoic, are situated in eastern central Inner Mongolia. Previous studies have explored the genesis of these basalts, which were influenced by the subduction of slab. Although trace element ratios demonstrate that altered oceanic crust (AOC) and sediments have contributed to the genesis of the basalts, limited information about the detailed percentages of mixing among sediments, AOC, and depleted mantle (DM) based on Sr‒Nd‒Pb isotopic values has been reported. In this study, we modelled the possible mixing percentages among AOC, DM, and sediments. The calculated results illustrate that a proportion of 80% DM, 16% AOC, and 4% sediments is appropriate for interpreting the Sr‒Nd‒Pb isotopic variation of the basalts. In addition, the associated major and trace elements of olivine and the partition coefficient of V between olivine and melt are used to estimate the crystallization temperatures of the olivine phenocrysts and oxygen fugacity of the basalts. The calculated results display that the olivine mainly crystallized between 1248 and 1293°C (standard error estimate: 51°C), and the fO2 values of the Abaga basalts range from FMQ + 0.14 to FMQ + 1.46 (FMQ, fayalite–magnetite–quartz buffer). The estimated oxygen fugacity values plot in the range of island arc basalts (from FMQ to FMQ + 2) but are higher than those of both mid-ocean ridge basalt (MORB) (from FMQ-0.4 to FMQ + 0.5) and Abaga xenoliths (from FMQ-1.55 to FMQ + 0.53), which indicates that the basaltic melts were more oxidized than those of MORB and the Abaga lithospheric mantle. Furthermore, the primary magma and the corresponding mantle source were more oxidized than MORB. The Ba/Th and Ce/Pb ratios of the basalt present positive correlations with fO2 values, demonstrating that the addition of sediments and oceanic crust into the mantle source may have contributed to increasing the fO2 values of the basalts. [ABSTRACT FROM AUTHOR]

The Abaga volcanic rocks are intraplate basalts that formed in the late Cenozoic period and are located in eastern central Inner Mongolia. Previous studies have discussed the genesis of the studied basalts. However, limited information about subducted recycled materials (the water content, sediments, and melts of the subducted plate), which control the generation of basalts, in the studied basalts has been reported. In this study, the major element abundances and crystallization temperatures and pressures of clinopyroxenes have been reported to estimate the water content of the studied magma, which has been applied to the Wulanhada volcanic field. The calculated result displays that the water content in the Abaga melts are between 0.5% and 1.7% (standard error estimate: 0.45%; average value: 1.3%). These estimated values are in range of the Aershan–Chaihe basalts (0.19–2.7%), while it is higher than those of the mid-ocean ridge basalts (MORBs: 0.16–0.47%). The high-water content of the studied basalts may have a close relationship with the mantle transition zone, which has also been reported to contain high concentrations of H 2 O. Subduction related sediments and slab may contribute to high-water content of magma. In addition, the clinopyroxene-melt thermobarometer shows that clinopyroxenes generally crystallized at 1113–1246 °C at the crustal level (3.8–12.4 kbar), while olivines formed at 1243–1392 °C (assuming pressure is 13 kbar, H 2 O = 1.3%). We also studied whole-rock major and trace elements and Sr–Nd–Hf–O isotope compositions of the Abaga basalts. High (Ta/U) N and (Nb/Th) N values that are higher than 1, Nd Hf isotopic values that plot between sediments and oceanic crust, and low δ18O values (4.51–5.59‰) of the alkali basalts illustrate that a subducted oceanic slab may have been added to the studied mantle source. In addition, we decipher that sediments may also exist in the source with Ba/Th, Nb/La, Ce/Pb and Ba/La ratios and Nd Hf isotopic values locating between sediments and altered oceanic crust. We use sediments, depleted MORB mantle (DMM), and recycled oceanic crust to simulate mixing features among these endmembers, which demonstrates that 80% of depleted MORB mantle, 15% of altered oceanic crust, and 5% of global subducting sediment (GLOSS), with 4–5% partial melting of peridotite or pyroxenite is a proper result with which to interpret the genesis of the studied alkali basalts. • Clinopyroxene crystallized at 1113–1246 °C (3.8–12.4 kbar), while olivines formed at 1243 to 1392 °C. • δ18O values (4.51–5.59 ‰) of the basalts illustrate that subducted oceanic slab has been added to the mantle source. • The water content in the Abaga melts is about 0.5–1.7%, which may attribute to mantle transition zone. [ABSTRACT FROM AUTHOR]