河南鲁山地区早前寒武纪变质岩系的锆石SHRIMP U-Pb年龄、地球化学特征及环境演化

Zircon SHRIMP U-Pb ages, geochemical characteristics and environmental evolution of the Early Precambrian metamorphic series in the Lushan area, Henan, China

河南鲁山地区早前寒武系划分为新太古代荡泽河岩组、TTG岩系与古元古代太华岩群铁山岭岩组、水底沟岩组、雪花沟岩组。在水底沟岩组石墨矽线片麻岩中获得最年轻的碎屑锆石SHRIMPU-Pb年龄为2.250～2.310Ga,变质锆石年龄为1.84Ga±0.07Ga;在侵入于雪花沟岩组的石榴钾长花岗片麻岩中获得岩浆锆石SHRIMPU-Pb年龄为2.146Ga±0.02Ga,变质锆石年龄为1.87Ga±0.01Ga,从而确定太华岩群的形成时代为古元古代。地球化学特征分析表明,荡泽河岩组显示岛弧环境,铁山岭岩组具板内裂谷向浅海演化的特点,水底沟岩组形成于封闭的浅海,雪花沟岩组具初始洋盆的特征。该地区经历了新太古代古陆核俯冲与拼贴,古元古代地壳裂解、拉张成初始洋盆,到地体拼贴、洋盆闭合形成克拉通的漫长演化历程。

The Early Precambrian in the Lushan area, Henan, is divided into the Neoarchean Dangzehe Formation-complex and TTG series and the Paleoproterozoic Taihua Group-complex including the Tieshanling, Shuidigou and Xuehuagou formation-complexes. The author obtained the youngest detrital zircon SHRIMP U-Pb ages of 2.250-2.310 Ga and a metamorphic zircon age of 1.84±0.07 Ga for graphite-sillimanite gneiss of the Shuidigou Formation-complex, and a magmatic zircon SHRIMP U-Pb age of 2.146±0,02 Ga and a metamorphic zircon age of 1,87±0.01 Ga for garnet-bearing gneissic granite intruded into the Xuehuagou Formation-complex; thus the age of the Taihua Group-complex can be determined to be Paleoproterozoic. The analysis of the geochemical characteristics indicates that the Dangzehe Formation-complex indicates an island arc environmeng the Tieshanling Formation-complex has the characteristics of evolution from the intraplate rift to shallow sea; the Shuidigou Formation-complex was formed in an enclosed shallow sea; and the Xue-huagou Formation-complex has the features of an initial ocean basin. The area experienced a lengthy evolutionary process from the subduction and amalgamation of paleocontinental nuclei in the Neoarchean through the crustal breakup and extension into an initial ocean basin to the amalgamation ofterranes and oceanic basin closing to form a craton during the Paleoproterozoic.