Element and isotope geochemistry of basaltic rocks in the Yakeshi area in the northern segment of the Da Hinggan Mountains, China and geological significance

A set of Early Cretaceous basaltic rocks is exposed in the Yakeshi area. They are basaltic trachyandesite in lithology, with the SiO2 content ranging between 52.81 and 53.39% and K2O ranging between 1.86 and 2.87%. They are enriched in the large ion lithophile elements Rb and Ba and strongly depleted in the high field strength elements Nb and Ta, with no pronounced Zr and Hf anomalies and δEu=0.77 to 0.82. In terms of the isotopic characteristics, the (87Sr/86Sr)i values have a variation of 0.704762-0.704941 and εNd(t) is 2.00-2.54. In the εNd(t)-(87Sr/86Sr)i diagram, all the samples fall in the field of oceanic island basalts (OIB) and the basin-range province of the United States. 206Pb/204Pb is 18.3288-18.4225, 207Pb/204Pb is 15.4566-15.4893, and 208Pb/204Pb is 37.9401-38.0523; in the diagrams of 207Pb/204Pb-206Pb/204Pb and 208Pb/204Pb-206Pb/204Pb, all samples plot near the depleted mid-ocean ridge basalt mantle (DMM). Judging from the geological and geochemical features of the volcanic rocks in the area, the authors conclude that they were derived from the lithosphere mantle metasomatized by subducted oceanic crust.