Geochemical characteristics and petrogenesis of Mesozoic basalts from the North China Craton: A cast study in Fuxin, Liaoning Province

摘要

Occurrence of Cretaceous basalts in Fuxin County, Liaoning Province provides us an opportunity to understand Mesozoic mantle processes beneath the northern margin of the North China Craton (NNCC). Fuxin Jianguo basalts occur as volcanic channel phases with well-developed columnar jointings and contain few spinel lherzolite and pyroxenite xenoliths. They are poor in silica and rich in alkalis, Ti and Al, belonging to alkaline basalts. In trace element compositions, Jianguo basalts are moderately enriched in LREE and LILE, but not depleted in HFSE. They have low Sr and high Nd and Pb isotopic ratios. These geochemical characteristics suggest that Jianguo basalts originated from the depleted asthenosphere, representing an undifferentiated and uncontaminated primitive magma. Presence of these basalts indicates that the lithosphere beneath the region had thickness less than 65 km at the time of basalt eruption and was mainly composed of fertile pargasite-bearing spinel lherzolite and plagioclase pyroxenite. The voluminous basaltic-andesitic magmatism during the early Jurassic-late Cretaceous time indicates that the commencement and accomplishment of lithosphere thinning in the NNCC was much earlier than that in the southern margin, since the mafic-intermediate volcanism only occurred at the Cretaceous time in the southern margin and the basalts with an asthenosphere isotopic signature at the Tertiary. This shows that highly spatial and temporal heterogeneity existed in the Mesozoic lithosphere evolution.