40Ar-39Ar geochronology and geochemistry of mafic rocks from Qingshan Group, Jiaodong area: Implications for the destruction of the North China Craton
胶东青山群基性火山岩的Ar-Ar年代学和地球化学特征: 对华北克拉通破坏过程的启示

The volcanic rocks of the Qingshan Group formed during the destruction of the North China Craton, therefore retaining important information as to the deep processes in this region. 40Ar/39Ar dating and geochemical analyses have been carried out on mafic volcanic rocks of the Qingshan Group collected from Jiaodong Peninsula. In combination with previously published data on the silicic rocks of the Qingshan Group, the newly acquired data show that, (1) the mafic volcanic rocks erupted during 122~113Ma, predating the silicic volcanism (110~98Ma); (2) the mafic and silicic rocks display distinct elemental and isotopic compositions. Based on these data, it is shown that the mafic rocks may have resulted from melting of metasomatically enriched lithosphere, whereas the silicic magmas represent partial melts of ancient lower crust and late Mesozoic magmas underplated at the crust-mantle boundary (Ling et al., 2009). The volcanic rocks of the Qingshan Group in Jiaodong Peninsula therefore records a shift in magma source from the upper mantle to the lower crust. Such a temporal transition in magmatic composition mirrors the thermal transfer from mantle to crust during the protracted lithospheric thinning processes, but is at odds with the magmatic evolution trends predicted by the crustal delamination model.