ACTIVE SUCCESSION ESTABLISHMENT FOR VOLCANIC-INTRUSIVE COMPLEX IN MIDDLE-LATE LOWER CRETA-CEOUS IN GUANGFENG,JIANGXI AND ITS GEOLOGICAL IMPLICATION

The Lower Cretaceous Guangfeng in Jiangxi lies above the Shixi Formation of volcanic rock system with its Rb -Sr isochron a ge 124.51±11.9Ma,and it is a lake basin with a complete second grade stratigraphic sequence from prograding to degrading.Basinal sedimentary rocks are intercalated porphyry vein rock gro ups involving syenite porphyry and g ranite porphyry in the pro-grading time,the porphyries have 110.83±3.16Ma age of Rb -Sr isochron an d 105.4±1.3Ma age of U -Pb discordant chart lower ac ross.Eruption of alkalic basalt and subalkalic basalt re-spectively took place when the lake h ad the largest surface and had cut dow n the surface.the K -Ar age of the basalt is 100～104Ma and 98～103Ma.They hardly can be distinguis hed sequently by isotopic age,but by their overlying and the succession of sedimentary ro cks.So,a active succession of volcanic-intrusive complex was c onstituted by them,namely,from int ermediate-acid vein rock to alkalic basalt,then to subalkalic b asalt.This succession has an instru ctive significance to explore the genesis of extensional basic in middle-late Lower Cretaceous period.