Ningwu Basin is one of the Mesozoic continental volcanic basins in the middle and lower reaches of the Yangtze River.The volcanic rocks of the Longwangshan,dawangshan,Gushan and Niangniangshan forma-tions,as well as the homologous subvolcanic rocks or small intrusions,are developed from old to new in the Ningwu Basin.Zircon U-Pb dating results show the latialite phonolite of Niangniangshan Formation was erupted at 128 ±1 Ma (i.e.,Early Cretaceous).The latialite phonolite contains moderate SiO2 contents (57.28％-60.96％)with high Na2 O +K2 O contents,belonging to shoshonite series.The samples have high REE con-tents,and display right-inclined REE distribution patt.They are characterized by enrichment in some large ion lithophile elements (e.g.,LILEs,Rb,K),and depletion in some high field strength elements (e.g.,HF-SEs,Nb,Ta,Ti).All volcanic samples have relatively depleted Nd isotopic compositions (ISr =0.707197--0.707878;εNd(t)=-0.5--0.9),indicating no genetic relationship with the lower crust of Yangtze plate, but a drift trend towards the EMII.The geochemical data suggest that the Early Cretaceous latialite phonolite was derived from the partial melting of an enriched lithospheric mantle metasomatized by subduction-related flu-ids in an arc-related setting.Based on the temporal and spatial distribution and geochemical variation character-istics of the regional volcanic rocks,it is suggested that the tectonic system within the study area changed from a subduction-related compression to an extensional environment in the early Early Cretaceous,which was caused by the ridge subduction of the Paleo-Pacific Ocean.