冀西北尚义黄土窑地区尚义杂岩和红旗营子群的锆石S HRIMP U-Pb定年及地质意义

摘要

The Shangyi Complex is a representative metamorphic block in northwestern Hebei and is composed of supracrustal and intrusive rocks.The metamorphic supracrustal rocks were once considered to be late Neoarchean ophiolite oceanic relic.The Hongqiyingzi Group also occurs in the area.We carried out SHRIMP U-Pb zircon dating on different types of rocks of Shangyi Complex and Hongqiyingzi Group from a geological section in Huangtuyao,east of Shangyi.Garnet-bearing biotite plagioclase gneiss (HB1410)has 310~2500 Ma zircon cores and ~255 Ma metamorphic rims.All detrital zircons from biotite plagioclase gneiss (HB141 1 )and quartzite (HB1415)are ~2.5 Ga in age but no metamorphic zircon age have been obtained for them.Gabbro (HB1518) and quartz diorite (HB1519)have magmatic zircons with ages of 278~279 Ma.Based on these data and previous work,it is concluded that the majority of the Hongqiyingzi Group and Shangyi Complex are not late Neoarchean in age,and they are a tectonic complex being composed of geological units of different ages,such as Paleozoic metasediments,metavolcanic rocks and intrusive rocks as well as some early Paleoproterozoic to Neoarchean relics. It is evident that the Central Asian Orogen strongly influenced the northern margin of the North China Craton during the late Paleozoic.%尚义杂岩是冀西北地区有代表性的变质地质体，由变质表壳岩和侵入岩组成。其中的变质表壳岩曾认为是新太古代晚期蛇绿岩洋壳残片。该区也有红旗营子群存在。我们对尚义黄土窑地区尚义杂岩和红旗营子群不同类型岩石进行了锆石SHRIMP U-Pb定年。含石榴黑云斜长片麻岩（HB1410）核部锆石年龄为310～2500Ma，边部变质锆石年龄为255Ma左右。黑云片麻岩（HB1411）和石英岩（HB1415）碎屑锆石年龄都为2.5Ga左右。辉长岩（HB1518）和石英闪长岩（HB1519）岩浆锆石年龄为278～279Ma。根据这些资料和前人研究，该地区的原红旗营子群和尚义杂岩变质表壳岩主体可能不是新太古代地质作用产物，而是形成于晚古生代，由不同时代地质体组成的构造杂岩。不存在所谓的太古宙蛇绿岩残片。晚古生代时期，中亚造山带对华北克拉通北缘的影响十分强烈。