Although much evidence points to a Late Mesozoic large silicic igneous province in SE South China (SESC), diverse Andean-type and non-Andean-type models have been proposed to explain its origins. New age, isotope, and trace element data on zircon from wells in East China Sea (ECS) and offshore-onshore tectonomagmatic comparisons allow reassessment of the geodynamic interactions (ca. 200–86 Ma) between the Cathaysia-based arc and intraplate activity from a large mantle wedge framework. In region, remnants of the West ECS arc, Ryukyu-Taiwan mélange, and SESC intraplate define a trench–arc–intraplate architecture. Changes in arc magmatic states (flare-ups and lulls; high U/Yb, low T, variable εHf_(t)) permit identification of a cycle of arc initiation, thickening, decline, arc-root removal, and arc migration, highly correlating with changes of Izanagi subduction beneath East Asia. Voluminous intraplate silicic magmatism operated in response to the slab stagnation dynamics: slab dehydration, lithospheric delamination, fluid-fluxed crustal anataxis, and crustal–mantle melt hybridization in crustal hot zones. Such geodynamic scenarios, unlike an Andean-type continental margin, instead result in the construction of a Late Mesozoic Cathaysian-type active continental margin.