Geochronological and geochemical constraints on the granitic gneiss in the Huozhou Complex: implications for the tectonic evolution of the Trans-North China Orogen

The Trans-North China Orogen is a major Neoarchean Paleoproterozoic collisional orogenic belt above the North China Craton, formed due to prolonged and complex processes. Even though many Neoarchean-Paleoproterozoic magmatic and metamorphic activities have been reported, due to the Huozhou Complex's small outcropping range, little attention has been paid to the origin of various igneous rocks of the Huozhou Complex in the center of the Trans-North China Orogen. The Huozhou Complex, located south of the Luliang, Wutai, and Hengshan complexes, is an important window into the Early Precambrian structure and evolution of the North China Craton. Its magma and metamorphism are crucial to understanding the development of the structural evolution of the Trans-North China Orogen. The Huozhou metamorphic complex area exposes a range of Precambrian metamorphic rocks, among which the most extensively dispersed is felsic biotite plagioclase gneiss. In this study comprehensive geological field survey, micropetrology, chronology, geochemistry, and Hf isotope analysis were carried out for the Qinggangping and Anziping gneiss in the north of the Huozhou Complex. The results show that the magmatic zircon age of the Qinggangping gneiss is 2196 +/- 14 Ma, and its protolith is I-type granite, formed by partial melting of igneous rocks in the absence of weathering. Its source is mainly the juvenile crust from depleted mantle dating 2431-2719 Ma, with a small amount of mantle-derived material. The Anziping gneiss has a metamorphic zircon age of 1931 +/- 13 Ma with an S-type granite protolith belonging to peraluminous granite. The Anziping gneiss is formed by recycling pre-existing crustal components at 2613-2848 Ma. A minor quantity of mantle-derived magma is also introduced to the crust simultaneously. The samples of Qinggangping gneiss and Anziping gneiss show the characteristics of obvious negative Nb, Ti, and P elements in the spider diagram of primitive mantle standardization. This implies that the rocks have the characteristics of magmatic rocks in an island arc or subduction environment, which could have formed in the tectonic environment of the continental margin arc.