华北板块南部豫西褶皱冲断带构造地球化学研究

A STUDY ON TECTONO-GEOCHEMISTRY OF THE YUXI (WEST HENAN) FOLD-AND-THRUST BELT IN SOUTHERN PART OF THE NORTH CHINA PLATE

豫西褶皱冲断带是华北板块南部具有特色的北西向延展的巨型褶皱冲断带的一部分。构造地球化学研究揭示了该带具如下规律性。1)各种化学成份(SiO2、Al2O3、Fe2O3、MgO、CaO、FeO、灼失量以及TiO2、K2O和Na2O等)呈现有规律的递增、递减或峰值变化,说明南、北支冲断带均是在挤压应力作用下形成的压性断裂,而且处于演化阶段的晚期。2)从外围原岩到断裂带中心,Fe2O3的含量逐渐增高,FeO的含量逐渐降低,说明南、北支冲断带经历了封闭性还原环境系统到相对开放性氧化环境系统的过程。3)动热变质强度在南、北支冲断带存在差异:南支强烈,导致新生应力矿物的形成,为断裂的远距离相对逆冲运动增添了塑性润滑层;北支相对较弱,新生应力矿物稀少,反应了逆冲强度较弱。

The Yuxi （ West Henan） fold-and-thrust belt was one segment of the giant fold-and-thrust system in NW-striking in southern part of the North China plate. Based on the field investiga-ion, a study on tectono-geochemistry was carried out, and some laws along the belt were discovered. The contents of SiO2, Al2O3, Fe2O3, MgO, CaO, FeO, TiO2, H2O and CO2 increased/decrease gradually from the outside to the center part of the fault zone, and the contents of Na2O, K2O changed wavelike. All of these confirmed that both of the south and north branches of the fault zones were compressive ones during the Indosinian orogeny and in later tectono-thermal events. In the meantime, the facts of the contents of Fe2O3 increasing and FeO decreasing gradually from the outside to the center part of the fault zone, respectively, revealed an evolutional process that both of the south and north branches of the fault zone experienced from enclosed reduction to relatively open oxidation system. Moreover, a different intensity of dynamothermal metamorphism occurred in the south and north branches, the south one was more intense, so as to result in creation of neogenic stress minerals which provided plastic lubricating layer for long-distance thrusting gliding, and the thrusting of the north branch was relatively gentle and only a few neogenic stress minerals appeared.