Zircon U-Pb Ages and Geochemical Characteristics of the Plagioclase Amphibolite in the Aohan Banner, Inner Mongolia

A series of intermediate metamorphic rocks,discovered in Aohan Banner, Chifeng City, Inner Mongolia, was characterized by plagioclase amphibolite, marble and granulite. The LA-ICP-MS zircon U-Pb dating and petrographic tests on the plagioclase amphibolites have been completed in this paper. According to petrological and geochemical characteristics, the metamorphic rock series has been classified as a set of basic calc-alkaline volcanic rocks and sedimentary rocks.The source rock of plagioclase amphibolite is similar to intraplate basalt, which was formed by the crustal or lithospheric contaminationin extensional environment. LA-ICP-MS zircon U-Pb dating of the plagioclase amphibolites yielded four groups of weighted mean ²⁰⁶Pb/²³⁸U ages. In which, the ages of (498±13)Ma, (434±16)Ma and (390.4±6.8)Ma stand for the age of trapped zircon, while the age of (351.2±5.2)Ma for magmatic zircon represents the crystallization time of the volcanic rocks, belonging to early stage of Early Carboniferous Epoch.