Linking lithospheric thinning and magmatic evolution of late Jurassic to early cretaceous granitoids in the Jiaobei Terrane, southeastern North China Craton

Abstract

Late Mesozoic granitoids are widely distributed in the Jiaobei Terrane, southeastern North China Craton (NCC) and crucial to understanding the processes and mechanisms of the lithospheric thinning. Here we present petro-geochemical, zircon UPb, LuHf and O isotopic constrains on three stages of granitoids, building an integrated model of lithospheric thinning from beginning through peak to waning stages. The early stage Linglong granite (166–158 Ma) is geochemically comparable to adakitic rocks with negative ɛNd(t) (−21.3 to −19.2), zircon ɛHf(t) (−26.8 to −18.7), and high zircon δ18O (6.7–8.3‰). It was originated from the subduction-thickened lower crust of the eastern NCC, with minor contribution from the subducted Yangtze Block, in an extensional setting, representing the beginning of lithospheric thinning. The middle stage Guojialing granodiorite (130–128 Ma), characterized by higher Sr/Y, Ba (898–5075 ppm), Sr (657–2256 ppm), ɛNd(t) (−19.1 to −11.5), zircon ɛHf(t) (−19.0 to −11.6) and δ18O (7.5–8.7‰) than the Linglong granite, addressing a fluid-metasomatized lithospheric mantle and extensive crust-mantle interaction in the Paleoproterozoic crustal source, is coeval with peak lithospheric thinning due to roll-back of the subducted Pacific plate. The late stage Aishan complex (118–115 Ma), which is composed of granodiorite, syenogranite, porphyritic quartz syenogranite, alkali granite and monzodiorite, exhibits slightly lower ɛNd(t) (−17.9 to −16.2), zircon ɛHf(t) (−21.4 to −15.3) and δ18O (6.6–7.9‰) than the Guojialing granodiorite. It was derived from the melting of Neoarchean- Paleoproterozoic crust with limited crust-mantle interaction and experienced crustal assimilation and fractional crystallization, indicating an extended process associated with the waning stage of lithospheric thinning. We document the magmatic responses to the lithospheric thinning at different stages which account for the genesis and evolution of the continental adakitic rocks and decratonization of the NCC.