Intracontinental Mesozoic Composite Magmatism in Central North China Craton-A Tectonic Response to the Westward Subduction of the Paleo-Pacific Plate

The influence, extent, intensity, and spatiotemporal evolution of the subduction of the Paleo-Pacific Plate on West-Central North China Craton during the middle-late Mesozoic remains unknown. Detailed petrological investigations, systematic zircon U-Pb dating, whole-rock geochemistry, and in situ zircon Lu-Hf isotopic analysis were conducted on various lithologies of the composite pluton in the central part of the North China Craton. The composite pluton can be divided into four distinct periods: quartz-porphyry (162 +/- 1 Ma), porphyritic biotitic granite (152 +/- 1 Ma), quartz diorite (142 +/- 1 Ma), granite (136 +/- 2 Ma). These rocks are belonged to high silica, potassium-calcareous alkalinity, aluminium content and enriched in large-ion lithophile elements such as Rb and K, and depleted in high-field-strength elements such as Nb and Ta. The epsilon Hf(t) values and the TDMC ages of the quartz-porphyry, porphyritic biotitic granite indicated these igneous rocks originated from the lower crust to the mid-lower crust which exhibit a lithospheric evolution process consistent with that of the North China Craton. The epsilon Hf(t) values of quartz diorite and granite indicate that the igneous rocks originated from the ancient lower crust with contributions of mantle-derived material, and from a mixture of the ancient mid-lower crust and the Late Palaeozoic younger lower crust. Considering the regional geological background, it is believed that this magmatism indicates a transition in the central North China Craton from compression to extension from the Late Jurassic to the Early Cretaceous. This transition is associated with the subduction of the Paleo-Pacific Plate, which began subducting under eastern Asia in the Early Jurassic and led to an extensional state in the Cretaceous due to the retreat of the Pacific subduction slab.