THE GEOLOGICAL EFFECT OF RIDGE SUBDUCTION IN ARC AREA

Ridge subduction is an important stage of Wilson cycle.If the spreading rate of the active ridge is smaller than the rate of subduction,the subducting oceanic plate will decrease in size,and the ridge itself will be eventually subducted.There are four possible kinematic scenarios of ridge subduction,we investigate one of the possibility:both the leading and the trailing plates are subducted.Subduction of a hot active ridge will significantly affect the thermal state of the subduction zone,and leave tectonic and petrologic signatures.In this study,we use twodimensional finite element method to calculate the thermal consequence of an active ridge subduction.Upwind technique is adopted to secure a stable and accurate solution for advective heat transfer.Frictional/shear heating is included in our modeling.The shear stress is limited by the friction law in the brittle regime and by the flow law in the ductile regime.Sequential changes of temperature created by ridge subduction are calculated,and the resulting geological consequences at arc areas are discussed.The results of computation can well explain cessation of arc volcanism,low-temperature metamorphism,uplift and subsidence of arc-trench margin.