<p>Contrasted subduction histories have been proposed for the northeast Asian margin since mid-Cretaceous times due to extensive subduction, which has recycled the Izanagi-Pacific mid-ocean ridge, the entire Izanagi rift flank, and part of the western Pacific plate into the mantle.&#160; Here we reconstruct northwest Pacific-Izanagi plate tectonics since Cretaceous times from imaged and predicted mantle structure.&#160; We compare our tomography-led NW Pacific-Panthalassa plate reconstruction against a relatively independent, large (n>1000) magmatic and isotopic geochemical database from East Asia.&#160; Our reconstruction reveals the ancient boundaries between the western Kula plate, the Izanagi plate, and the &#8216;Junction&#8217; realm, which divided Pacific-Panthalassa from Tethys during Cretaceous times, providing a new NW Pacific-Panthalassa plate tectonic framework during late Mesozoic times.</p><p>We reconstructed the western Pacific plate by structurally-restoring (i.e. unfolding) imaged slabs from tomography using area conservation of cross-sectional slab areas, following Wu et al (2016).&#160; The vanished Izanagi plate was then modeled as a conjugate rift flank. &#160;Western Pacific slab areas were assessed from global tomography models MITP08, GAPP4, UUP07, and from the full-waveform regional tomography FWEA18 (Tao et al., 2018). &#160;To mitigate image blurring, we introduced a new &#8216;tomographic smearing&#8217; correction based on computing input and output slab volumes from synthetic slab resolution tests.&#160;</p><p>Our tomography-led plate model indicates: (1) that the stagnant Pacific slabs have subducted along Eurasia since ~50 &#177; 10 Ma; (2) that the Izanagi-Pacific ridge intersected Korea to Kamchatka at a low angle ~50 &#177; 10 Ma, consistent with an observed 56 to 46 Ma magmatic gap between Japan and Sikhote-Alin, Russia, and with geodynamic models that assimilate low-angle 50 Ma ridge-trench intersection; &#160;and (3) that subduction of the Izanagi plate during the mid- to late Cretaceous was limited between Bohai Bay, China, and westernmost Alaska.&#160; During the late Cretaceous, the SW margin of the Izanagi plate was bounded by an extensive NW-SE transform that we call the &#8216;Qingdao line&#8217;.&#160; The newly-proposed Qingdao line explains the well-recognized, but poorly-understood contrasts in Cretaceous magmatism between southeast and northeast China.&#160; Subduction initiated along the Qingdao line during the Pacific plate motion change at ~50 Ma, forming the Izu-Bonin-Marianas subduction system.&#160;</p>
