Petrogenesis and tectonic implications of the Early Cretaceous Dagushan adakitic porphyries in the Anshan area,North China Craton

The eastern part of the North China Craton suffered significant lithospheric thinning since the Mesozoic,and petrogenesis of the Dagushan adakitic diorite porphyries provides an excellent opportunity to investigate the lithospheric thinning mechanism and geodynamic setting.The zircon LA-ICP-MS U–Pb geochronology reveals that the representative Dagushan adakitic porphyry was formed at 120.5±0.5 Ma.The Dagushan diorite porphyries are characterized by the relatively high contents of SiO_(2)(64.25–65.70 wt%),Al_(2) O_(3)(15.00–15.38 wt%),Sr(333–491 ppm),low contents of Y(6.50–10.3 ppm),and Yb(0.57–0.85 ppm),and resultant high Sr/Y(47–57)and La/Yb(37–55)ratios,exhibiting geochemical characteristics of typical adakites.Moreover,the relatively high Mg O contents(MgO=2.23–2.29 wt%)and Mg numbers(Mg^(#)-=54–56)of the Dagushan adakitic rocks imply that the pristine adakitic magma interacted with mantle peridotite.However,the zircon Hf isotopic signatures(εHf(t)=-19.0 to-28.0;TDM2=2378–2944 Ma)suggest an ancient lower crustal source.Therefore,it is proposed that the Dagushan adakitic rock was probably generated by partial melting of delaminated lower crust which was triggered by the Tan-Lu Fault Zone,and the interaction of pristine adakitic magma with mantle peridotite during the ascent finally generated the Dagushan high Mg^(#)adakitic rocks.It is suggested that delamination was an important mechanism for lithospheric thinning of the NCC.