Abstract:
The North China craton preserves the history of crustal growth and craton formation during the early Precambrian, followed by extensive lithospheric thinning in the Mesozoic associated with large-scale magmatism and metallogeny. The timing and petrogenesis of the voluminous Mesozoic magmatic rocks are important in understanding the mechanism of craton destruction. Here, we investigate a suite of volcanic rocks including basalt and trachybasalt, basaltic andesite and andesite, dacite and trachydacite, and rhyolite from the Yanshan belt in the northern part of the North China craton and provide evidence for intraplate magmatism along a paleosuture. We present bulk chemistry, zircon U-Pb geochronology and rare earth element data, and Lu-Hf isotopes from the volcanic suite and attempt to constrain the timing of magmatism and source characteristics. The zircon U-Pb data show two age peaks at 175-165 Ma and 155-145 Ma. Geochemically, the rocks are calc-alkaline with arc-related features. The andesites show adakitic affinities with high Sr contents (up to 1140 ppm), high Sr/Y (up to 76.2) and LaN/YbN ratios (up to 21.7), lack of a negative Eu anomaly, extreme depletion in Y and Yb, and relatively low MgO contents (1.3-4.4 wt percent), indicating that they were likely derived from the partial melting of thickened lower continental crust. The Zr/Ba ratios indicate interaction between lower crust and primitive magma, possibly through magma underplating at the crust-mantle boundary. However, there was no arc-related tectonic setting in the study area during the Jurassic, which indicates that the elemental and isotopic compositions are possibly inherited from the basement rocks generated during the Paleoproterozoic subduction-accretion-collision process in the North China craton, subsequent to the 2.5 Ga cratonization event. Our zircon Hf isotope data also confirm the incorporation of Paleoproterozoic reworked material. The magmatism and craton destruction along a paleosuture were induced by mantle upwelling through far-field tectonics of the Pacific plate subduction. Our study presents a case where source components have strongly influenced the geochemical imprint of the magmas, with intraplate volcanics preserving a continental arc magmatic signature.
