Chronology, geochemical characteristics and geological significance of two types of amphibolites within the Liaohe Group in the eastern block of the North China Craton
Abstract:Petrology, geochemistry and zircon U-pb chronology were studied on the amphibolite in Gaojiayu Formation of Liaohe Group in Huanren area, eastern Liaoning Province. The results show that the original rock of amphibolite is basalt and can be divided into two types: low Ti and high Ti. The original rock of the low-Ti sample belongs to tholeiite series, with slight loss of Nb, Ta and Zr, obvious loss of P, and weak enrichment of light rare earth and heavy enrichment of rare earth, showing the geochemical characteristics of E-MORB. The original rock of the high Ti sample belongs to alkaline basalt series, with enrichment of large ionic lithophile elements such as Rb, Th and U, and enrichment of rare earth and loss of heavy rare earth, showing the geochemical characteristics of OIB. The two types of amphibolites have low contents of MgO, Cr, Ni and Mg# values, indicating that their protoliths are not primitive magma, but formed by separate crystallization of different mineral phases. The U-Pb dating of zircon indicates that the diagenetic ages of the low Ti type and the high Ti type are 2158±15 Ma and 2173±12 Ma, and the metamorphic ages are 1870±6 Ma and 1861±7 Ma. There are obvious differences in the geochemical characteristics of the two types of amphibolite, which indicates that there is no transitional relationship between them. The regional geological characteristics and petrogenetic studies jointly indicate that the two types of plagioclase were formed in the back-arc basin environment. Based on the available petrology, geochemistry and isotopic characteristics, the Liaoji area may have been in the tectonic environment of the back-arc basin of the active continental margin in the early Paleoproterozoic, and the formation of the Liaoji orogenic belt is related to the arc-land collision.
