The potassic intrusive belt, distributing along the southern margin of the Luzong volcanic basin, comprises syenite, quartz syenite, and syenogranite, and quartz syenite constitutes the greatest part of the belt. They formed from about 123 to 130 Ma, with a peak about 126 Ma, the emplacement of the syenite and quartz syenite were a litter earlier than the syenogranite. The emplacement of the potassic intrusive belt were later than the volcanism in the Luzong basin by about 4~7 Ma as a whole, and it was also one of latest products of the Mesozoic magmatism in the Middle and Lower Yangtze River reaches except the easternmost part (Ningzhen district). This potassic intrusive rocks are characterized by high K and alkali, indicateing enrichment in strong incompatible elements (LILE) such as Rb, Th, U and K as well as light rare earth elements (LREE), depletion in highfieldstrongelements (HFSE) such as Nb, Ta and Ti in geochemistry. Their parental magma mainly came from partial melting of the enriched subcontinental lithospheric mantle, and evolution from syenite to quartz syenite to syenogranite was mainly controlled by fractional crystallization, but the assimilation of crustal material only played a minor role even if existing. Compared with the volcanic complex developed in the Luzong basin, their parental magma also came from partial melting of the enriched mantle, the parental magma of the potassic intrusive belt may come from deeper or containing more material from asthenospheric mantle. The evolutional processes between the parental magma of the potassic intrusive belt and the volcanic complex in the Luzong basin are of great difference, the former not only had undergone highpressure fractional crystallization, but also had undergone lowpressure fractional crystallization, dominant feldspar, possible biotite, as well as minor contamination of upper crust. But lowpressure fractional crystallization and upper crustal contamination process are unconspicuous for the latter. Geochemical features of the potassic intrusive belt and the volcanic complex in the Luzong basin all indicate continental arc setting, implying that subduction had happened previously (infer it happened in the late stang of Paleoproterozoic) along the northern margin of the Yangtze Craton. The metasomatism of upper mantle may be related with the subduction.