Early Mesozoic alkaline complexes in the northern North China Craton: Implications for cratonic lithospheric destruction

Abstract

Early Mesozoic alkaline intrusive complexes are widespread in the northern North China Craton (NCC) and constitute an E–W trending alkaline magmatic belt that is more than 1500km long along the northern Sino–Korean Craton. Our new zircon and baddeleyite U–Pb dating results of the Yongfucun, Yaojiazhuang and Sungezhuang alkaline complexes combined with previous geochronological data indicate emplacement of the E–W trending alkaline belt in the northern NCC during the Middle–Late Triassic at around 235–220Ma. Geochemical and Sr–Nd–Hf isotopic data suggest a common source region for the syenites, pyroxene syenites and mafic rocks within the complexes. They were mainly derived from a metasomatized enriched lithospheric mantle; however some materials from depleted asthenospheric mantle have been involved during formation of these alkaline complexes. Involvement of depleted asthenospheric mantle materials indicates upwelling of the asthenospheric mantle and asthenosphere–lithospheric mantle interaction in northern NCC during the Early Mesozoic. Initiation of lithospheric thinning and destruction of the northern NCC occurred in the Middle–Late Triassic, which is much earlier than in other parts of the NCC during the Late Mesozoic. Delamination at the root of the subduction-induced thick lithospheric mantle is likely main mechanism for the Early Mesozoic lithospheric thinning and destruction of the northern NCC. Multiple subduction of oceanic plates beneath the northern, southern and eastern parts of the NCC and interactions of the surrounding orogenesis during the Late Paleozoic to Mesozoic may play important roles on the Late Mesozoic lithospheric destruction of the NCC.