JURASSIC TO CRETACEOUS INTRACONTINENTAL SHORTENING AND MAGMATISM IN NORTH CHINA: EVIDENCE FOR FLAT-SLAB SUBDUCTION OF THE IZANAGI PLATE

We attribute Middle-Late Jurassic to Early Cretaceous intracontinental deformation and magmatism in North China to changes in the dip of the westward-subducting Izanagi (i.e., paleo-Pacific) oceanic plate. The Middle-Late Jurassic to Early Cretaceous Taihang-Luliangshan fold belt, exposed in the central Shanxi Rift, represents an example of basement-involved shortening that occurred >~1000 km inboard from the Izanagi plate subduction trench. It is characterized by northeast-southwest trending folds, with wavelengths of ~50-100 km and amplitudes of ~3-5 km, and thrust faults involving Archean and paleo-Proterozoic metamorphic and igneous basement rocks. Shortening in the Taihang-Luliangshan fold belt, and coeval fold belts throughout North China, commenced shortly after or coincident with a shutoff in arc magmatism along the Korean Peninsula ca. 165 Ma, and can be explained by a unified kinematic model involving regional northwest-southeast shortening. A compilation of Jurassic–Cretaceous crystallization ages of igneous rocks from the Korean Peninsula, North China, and Inner Mongolia is presented along a ~2200 km transect orthogonal to the trend of the Eurasian-Izanagi paleo-trench. It shows that a magmatic arc was present in the Korean Peninsula until ca. 165 Ma, at which time the locus of magmatism began to systematically migrate into the interior of Asia. We attribute this inboard sweep in magmatism, and concurrent intracontinental, basement-involved shortening to flat-slab subduction of the Izanagi plate. Shortening continued to ca. 135–130 Ma, at which time magmatism began to retreat southeast towards the paleo-trench. Regional high-flux magmatism in the Early Cretaceous, followed by widespread extension and lithospheric thinning of the North China craton, are attributed to Izanagi slab rollback/foundering. We conclude that the Middle Jurassic to Cretaceous eastern margin of North China represents a Cordilleran-style orogen with analogous characteristics to other ancient and modern Cordilleran systems.