Lithosphere thinning beneath west North China Craton: Evidence from geochemical and Sr–Nd–Hf isotope compositions of Jining basalts

•The lithosphere under the west North China Craton has been thinning since the early Cretaceous.•The lithosphere under the west North China Craton is thinning now.•The Jining 119.6-108.6 Ma basalts were the products of partial melting of ancient metasomatized lithospheric mantle.•The Jining Cenozoic basalts resulted from upwelling and decompression melting of eastward flowing asthenosphere.

This study shows lithosphere evolution history in the west North China Craton (NCC) from the early Cretaceous to Quaternary by studying the major element, trace element and Sr–Nd–Hf isotope compositions in Jining basalts of 119.6–108.6 Ma, 23.5–21.9 Ma and 1.3–0.11 Ma.The early Cretaceous basalts (119.6–108.6 Ma) display enriched characteristics with high contents of incompatible elements, high 87Sr/86Sri, low εNd(t) and low εHf(t). These basalts resulted from partial melting of ancient metasomatized lithospheric mantle, and we consider the 119.6–108.6 Ma magmatism as indicating lithosphere thinning in the west NCC. Although the Pacific slab seen seismically in the mantle transition zone beneath eastern China is no older than 60 Ma, there exists convincing evidence for the presence of the Paleo-Pacific slab in the transition-zone in the Mesozoic. Thus we propose that the water released from the transition-zone slab hydrated the overlying lithosphere and further converted the base of the lithosphere into asthenosphere. This is the most likely mechanism responsible for the lithosphere thinning in the west NCC and the petrogenesis of the Jining 119.6–108.6 Ma basalts.The Jining 23.5–21.9 Ma basalts also have high contents of incompatible elements, but they display high εNd(t), high εHf(t) and variably low 87Sr/86Sri. We propose that these Miocene basalts were derived from the asthenosphere with contributions from ancient metasomatized lithospheric mantle during melt ascent. The Jining Quaternary basalts (1.3–0.11 Ma) represent the melt of upwelling asthenosphere with low 87Sr/86Sri, high εNd(t) and high εHf(t). Upwelling and decompression melting of the eastward flowing asthenosphere from beneath western plateaus to beneath eastern hilly plains in the Cenozoic is the most plausible mechanism for the petrogenesis of Jining Cenozoic basalts (both of 23.5–21.9 Ma and 1.3–0.11 Ma), but the Jining 1.3–0.11 Ma basalts must have been produced beneath even thinner lithosphere.Taken together geophysical studies and our petrological and geochemical studies of all these three episodes of the Jining basalts, we propose that the lithosphere in the west NCC has been thinning since the early Cretaceous and the thinning continues to the present.