Petrogenesis of the early Cretaceous Funiushan granites on the southern margin of the North China Craton: Implications for the Mesozoic geological evolution

Abstract

Late Mesozoic granitoids are ubiquitous in the southern margin of the North China Craton and are keys to the understanding of the Mesozoic geological evolution. The early Cretaceous Funiushan granitic pluton in the southern margin of the North China Craton is composed of porphyritic biotite monzogranites. Rocks from the Funiushan pluton have high SiO2 (64.45–73.98wt.%), Na2O (3.19–4.67wt.%) and K2O (3.76–7.95wt.%) and low MgO (0.11–1.34wt.%). They are enriched in Rb, Ba, Th, U and LREE ((La/Yb)N=9.63–45.0), and depleted in Nb, Ta, Ti and P, and have negative Eu anomalies (Eu/Eu*=0.29–0.72). This geochemical feature is similar to those of typical I-type granites. Zircons from the granites were dated using LA-ICP-MS and SIMS, and yielded 206Pb/238U ages of 115–131Ma. They have εHf(t) values mainly vary from −17.7 to +0.9 and TDMC ages mainly from 2301 to 1118Ma. Whole rock εNd(t) values range from −20.3 to −9.6 and TDM ages from 1.49 to 2.29Ga, indicating that the magma was produced by partial melting of the Neoarchean to Paleoproterozoic crustal rocks, as represented by the Taihua Group basement rocks, with minor involvement of mantle-derived melts. The Funiushan pluton is considered to have been formed through a strong crust-mantle interaction process under a low pressure condition in an extensional setting, due to the lithospheric thinning caused by westward subduction of the Paleo-Pacific oceanic crust.