Decoupling of U-Pb and Lu-Hf isotopes and trace elements in zircon from the UHP North Qaidam orogen, NE Tibet (China): Tracing the deep subduction of continental blocks

► Decoupled isotopic and elemental behavior of zircon in eclogite-facies metamorphism ► Magmas from the depleted mantle intruded the Qaidam block at 2.0 and 1.1-0.8 Ga. ► These mafic magmas transformed the block into a mafic overall composition. ► 440 Ma UHP metamorphism created a dense “sinker,” to expedite the deep subduction.