Archean magmatism and metamorphism in the Huangbaiyu-Yangyashan area, eastern Hebei Province: Evidence from SHRIMP zircon U-Pb dating

This paper reports SHRIMP zircon U-Pb ages of eight samples for different types of Archean meta-magmatic rocks in the Huangbaiyu-Yangyashan area, eastern Hebei Province, which include meta-gabbro, biotite plagioclase gneiss, gneissic monzo-granite and gneissic K-rich granite. 3.1Ga monzogranite(sample J1111) was identified for the first time in the area. Biotite plagioclase gneiss(sample J1116) also probably formed at~3.0Ga. In metagabbros(samples J1109 and J1110), which are considered to form at the end of the Neoarchean although no~2.5Ga magmatic zircon age has been determined, there are a few trapped zircons of 3.2~3.6Ga. Almost all samples record~2.5Ga metamorphic zircon ages. Combined with early studies, the authors have arrived at following conclusions:(1) Tectono-thermal events of the Late Neoarchean were well developed, ~2.5Ga metamorphism, mantle magmatism and crust-derived granite formation were all caused by magma underplating resulting from upwelling of asthenosphere; (2) > 2.8Ga con-tinental materials widely occur in eastern Hebei Province, and there might exist an ancient continental nucleus in the Huangbaiyu-Yangyashan area.