Structural Geochemical Study of the Yuxi Fold-Thrust Belt in the Southern North China Plate

The Yuxi （豫西） fold-thrust fracture belt is part of the gigantic fold-thrust fracture belt that extends NW in the southern North China plate. The contents of major elements of tectonites were analyzed by ICP-AES. The analysis of chemical compositions and new stress minerals indicates： extending from the surrounding country rocks to the center of the fracture belt, the Fe2O3 content gradually increases while the FeO content gradually decreases; regular increase, decrease or peak changes are shown for chemical compositions like SiO2, Al2O3, Fe2O3, MgO, CaO, FeO, loss on ignition, TIO：, K2O, Na2 O, etc.. New stress minerals are developed for the south branch and few for the north branch. The characteristics of chemical compositions and new stress minerals of the thrust fracture demonstrate that the fracture belt has undergone a process from a closed reducing environmental system to a relatively open. oxidizing environmental system, andcompressive fractures have resulted from compression in the late stages of evolution, and the dynamothermal metamorphism and thrusting intensities are different between the south and north branches of the belt, which is strong for the south branch but relatively weak for the north branch.