Petrological and Geochemical Constraints on the Origin of Early Cretaceous Volcanic Rocks in the Central‐East Asia: Implications for Crustal Growth and Evolution

Abstract

AbstractNew petrological and geochemical data for Early Cretaceous volcanic rocks in the North China Craton (NCC) combined with published data of cotemporaneous volcanic rocks in the NCC and eastern Central Asian Orogenic Belt (ECAOB) are used to understand their petrogenesis and crustal growth and evolution. Early Cretaceous volcanic rocks in the NCC show characteristics typical of continental crust, with negative Nb and Ta anomalies, and enrichment of K and Pb. The εNd of Early Cretaceous volcanic rocks in the NCC correlate with indices of differentiation (e.g., Mg#), implying that mantle‐derived magmas were modified by open‐system processes. The high‐Mg clinopyroxene and melt inclusions hosted by high‐Fo olivine in Early Cretaceous volcanic rocks in the NCC have lower 207Pb/206Pb and 208Pb/206Pb ratios than low‐Mg clinopyroxene and melt inclusions hosted by low‐Fo olivine, which can be explained by the interaction between lower crust and basaltic magmas (magma mixing or assimilation). Unlike contemporaneous counterparts in the NCC, Early Cretaceous volcanic rocks in the ECAOB have high εNd values. Such features can also be produced by crustal assimilation and/or magma mixing, given the juvenile lower crust beneath the ECAOB. The “adakitic” signature of Early Cretaceous volcanic rocks is most likely inherited from the lower continental crust. Large‐scale partial melting of the lower crust may have been related to continuous magmatic underplating in an extensional environment. This work suggests that Early Cretaceous volcanic rocks in the Central‐East Asia represent a nonnegligible contribution to crustal growth, despite having “crust‐like” trace element and isotopic characteristics.