From mountains to basin: A Tibetan model for the post-collisional magmatic and tectonic evolution in North China

Sun-Lin Chung1, Ching-Hua Lo1, Xianhua Li2, W.L. Griffin3,4, S.Y. O'Reilly3 and Chen-Hong Chen5 1. Dept. Geol., Natl. Taiwan Univ., Taipei, Taiwan, 2. Guangzhou Inst. Geochem., Chinese Acad. Sci., 3. GEMOC, Macquarie, 4. CSIRO EM, 5. Inst. Earth Sci., Acad. Sinica, Taipei, Taiwan

The North and South China blocks are generally believed to have collided in Triassic time as manifested by the exhumation of ultrahigh-pressure metamorphic rocks in between. The eastern part of North China, underlain by the Sino-Korean Craton, has been therefore tectonically active and underwent a Jurassic regional uplift followed by basement subsidence and basin formation. Two main stages of magmatic activity occurred in the Late Jurassic-Early Cretaceous (ca. 165-100 Ma) and the latest Cretaceous-Cenozoic (since ca. 70 Ma), respectively. Whereas the early stage activity produced shoshonitic and high-K calc-alkaline rocks around the Tanlu fault, magmas formed by the latter after 30-Ma. igneous quiescence consist exclusively of intraplate basalts. Mantle xenolith and geophysical data available from this area indicate that the lithosphere was ~200 km thick in the Ordovician but is now as thin as ~60-120 km, suggesting removal of ~100 km of Archean lithospheric root. All these observations imply a causative link, which, in comparison with the Tibetan example related to the India-Asia collision, we suggest to have been extensional orogenic collapse in eastern North China starting from the Late Jurassic as a result of delamination of thickened lithosphere. Geotherm thus raised triggered partial melting of certain enriched sources in remnant lithospheric mantle and caused the early stage magmatism. The ascended asthenosphere, however, became significantly involved in magma generation only in the Cenozoic when a substantial amount of lithospheric extension has been achieved. Geophysical data further show that Archean crust of this area has been thinned to ~25-35 km. North China eventually records a whole spectrum of tectonomagmatic scenario which evolves from mountain ranges to rift basin postdating continental collision.

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