Geochemistry of Dabeigou Basalt in Chengde Basin, Hebei Province and Constraints on Lithospheric Mantle Thinning of North China Craton

Basalts of age between 120–100 Ma are rare in the North China Craton. The Dabeigou Group consists of olivine basalt in the lower part and andesite in the middle and upper parts. Zircons from the andesite are dated by LA-ICPMS and yielded a late Early Cretaceous age of 113.6 ± 0.87 Ma. Geochemical analyses of three basalt samples show depletion in high field-strength elements (Nb, Ta, Zr, Hf). Their 87Sr/86Sr ratio and ɛNd value are 0.7059 and-11.04 at 114 Ma. These values are consistent with a source from enriched lithospheric mantle. The source of the Dabeigou basalts is intermediate between those of <120 Ma basalts with ancient enriched lithospheric mantle character and < 100 Ma basalts with depleted asthenospheric mantle character. The data suggest that the ancient enriched lithospheric mantle might have been thinned and converted to the depleted asthenospheric mantle under the North China Craton in chemical composition at 114 Ma.