Petrogenesis and Geological Significance of the Taihua Group TTG Gneisses in the Xiong'ershan Area, Southern Margin of the North China Craton

The North China Craton underwent a prolonged and complex geological evolution during the Archean to Paleoproterozoic, with the magmatic and metamorphic processes remain as the research questions. This study focuses on the TTG (tonalite-trondhjemite-granodiorite) gneisses of the Taihua Group in the Xiong’ershan area along the southern margin of the North China Craton. The integrated field investigations, petrographic analysis under the microscope, geochemistry, zircon U-Pb dating and Hf isotopic studies are conducted to elucidate the Paleoproterozoic magmatic mechanisms and the tectonic evolution of this region. Zircon U-Pb dating constrains the magmatic crystallization age of the Taihua Group TTG gneisses in the Xiong’ershan area to approximately 2300 Ma, while the metamorphic ages range from 1984 Ma to 1940 Ma. The Taihua Group TTG gneisses exhibit a wide compositional range, with SiO ₂ (59.35%～70.78%), Al ₂O ₃ (12.41%～17.93%), and relatively high CaO (1.40%～5.52%) and MgO (0.95%～2.56%) contents. It is enriched in light rare earth elements (LREE) and depleted in heavy rare earth elements (HREE), displaying strong fractionation between LREE and HREE. In composition, it resembles high-Al TTG gneisses. The samples are enriched in large-ion lithophile elements (LILEs) such as Rb, Ba, and Sr, but depleted in high-field-strength elements (HFSEs) like Nb, Ta, and Ti, which are similar to the features of island arc granites. Additionally, magmatic zircons display relatively high ( ¹⁷⁶Hf/ ¹⁷⁷Hf)ᵢ ratios ( 0.281282～ 0.281332), εHf(t) values (−2.98 ～ +0.20), and two-stage model ages ( 2844～ 2994 Ma), indicating that the magmatic source originated from the partial melting of Mesoarchean ancient crust. These findings suggest that the TTG gneisses in the Xiong’ershan area formed during the Paleoproterozoic subduction process between the eastern and western blocks of the North China Craton. The metamorphic age of 1984～ 1940 Ma records the collisional process along the Trans-North China Orogeny. This further constrains the timing of collision between the eastern and western continental blocks.