Triassic volcanism on the North argin of the North China Craton: Insights for lithospheric modification during closure of Paleo-Asian Ocean

As a key tectonic region linking the northern margin of the North China craton (NCC) and eastern Central Asian Orogenic Belt (CAOB), western Liaoning, with extensively distributed magmatic activity, provides natural samples to investigate the evolutionary history of the Paleo-Asian Ocean plate subduction to closure. The Middle Triassic (ca. 241 Ma) trachyandesites and Late Triassic (ca. 223 Ma) basaltic andesites were first identified from the Tiaojishan Formation, western Liaoning. They have variable SiO2 contents (52.48-60.31 wt%) and alkaline or high-K calc-alkaline to shoshonite compositions, and belong to the metaluminous series. Middle Triassic trachyandesites are enriched in large ion lithophile elements (LILEs), high field strength elements (HFSEs), and light rare earth elements (LREEs) with high Nb/La ratios (0.63-0.76). They have homogeneous whole-rock Sr-Nd (87Sr/86Sri = 0.704684-0.704808, epsilon Nd(t) =-4.6 to-4.0) and variable zircon Hf isotopic signatures (epsilon Hf(t) =-10.3 to 8.2), indicating that they probably originated from the partial melting of the subcontinental lithospheric mantle with the addition of asthenosphere materials. In contrast, the Late Triassic basaltic andesites show arc-related geochemical affinities, such as LILEs and LREEs enrichment and HFSEs depletion. They have more enriched whole-rock 87Sr/86Sri (0.704895-0.705394), epsilon Nd(t) (-16.1 to -14.0), and zircon epsilon Hf(t) (-13.1 to-8.8) than the Middle Triassic trachyandesites, suggesting that they probably represent partial melts of the subduction-related fluids-modified lithospheric mantle. The modification of the northern margin of the NCC lithospheric mantle is closely related to the final subduction of the Palaeo-Asian oceanic plate and the subsequent post-orogenic extension.