Petrogenesis And Tectonic Implications Of The Longwangmiao And The Shangzhuang Intrusions In The Central-Northern Margin Of The North China Craton

The sub-continental lithospheric mantle(SCLM)in the central-northern margin of the North China Craton(NCC)has undergone significant modification during Ordovician to Triassic through multiple stages of subduction of the Mongolian oceanic slab.This study focuses on the Middle Devonian Longwangmiao intrusion(~399 Ma)and the Early Cretaceous Shangzhuang intrusion(~123? 128 Ma)to constrain their petrogenesis and tectonic setting.A combination of new data and a compilation of published works are used to gain important insights on the evolution of the SCLM beneath the central-northern margin of the NCC.The Longwangmiao intrusion shows dual IAB and CRB signature and is constrained as a transitional phase between arc-related compression and back-arc extension,which is correlated with the Late Silurian arc-continent collision between the Bainaimiao arc and the NCC.By comparison with the coeval Hongshila and Erdaogou-Xiahabaqin complexes,it is concluded that the SCLM was slightly affected by the Mongolian slab subduction with heterogeneous enrichment during the first pulse.The age of ~123–128 Ma for the Shangzhuang gabbro is well correlated to the regional extensional tectonics between ca.135 and 115 Ma in the eastern and central NCC.The Dy/Yb(3.48–3.55)and La/Yb(50.83–53.22)values of the equivalent fine grained gabbros indicate that the parent magma was derived from low(less than ~ 5%)degree of partial melting of the spinel lherzolite source in the lithospheric mantle.Besides,their Zr/Nb(8.03–9.09),Zr/Y(13.0–15.1)and Nb/Y(1.62–1.66)values also suggest a source that was locally mixed with limited asthenospheric or deeper-mantle materials by mantle upwelling.Heat input from the mantle upwelling and water derived from the ongoing subducted Pacific plate aided in the formation of the parent magma.However,the subducted Pacific did not cause marked enrichment to the SCLM in this region.Information from the mantle-derived rocks belonging to the three pulses of magmatism along the central-northern margin,leads to the conclusion that the SCLMbeneath the central-northern margin of the NCC was gradually enriched during the different stages of subduction of the Mongolian oceanic slab.After the final collision between the Mongolian composite terranes and the NCC in Late Permian,the central-northern margin underwent lithospheric delamination accompanied by the emplacement of mafic-ultramafic rocks characterized by the dual signature of lithospheric mantle and asthenospheric mantle.Thereafter,the lithospheric delamination spread to the interior domain of the NCC,as evidenced by the voluminous Late Jurassic(~160 Ma)high-Mg andesites,dacites and adakites.The Shangzhuang gabbro indicates that the mechanism for lithospheric thinning of the NCC in Early Cretaceous is thermal and/or chemical erosion,at least in the central-northern margin.